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Water test methods

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water testing

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Water test methods

  1. 1. COAGULATION FLOCCULATION JAR TEST SUMMARY OF METHOD The coagulation – flocculation jar test is carried out to determine chemicals and their dosages, and conditions required in order to reduce suspended, colloidal, and non-settleable matter from water by chemical coagulation – flocculation, followed by gravity settling. APPARATUS 1. Multiple Stirrers – with continuous speed variation from about 20 to 150 rpm. The stirring paddles should be of light gauge, corrosion resistant material, all of the same configuration and size. An illuminated base to observe the floc formation. 2. Beakers – glass beakers, 1000 to 1500 ml capacity. 3. Reagent Racks – for introducing each test solution to all beakers simultaneously. There should be at least one rack for each test solution or suspension. REAGENTS 1. Water – conforming to specifications Type III. 2. Prime Coagulants Concentration (10g/litre) : a. Alum [ Al2 (SO4)3. 18H2O]. b. Ferric Sulphate [Fe2 (SO4)3. XH2O]. c. Ferric Chloride [FeCl3. 6H2O]. d. Ferrous Sulphate [FeSO4. 7H2O]. e. Magnesium Carbonate [MgCO3. 3H2O]. f. Sodium Aluminate [NaAlO2]. 3. Coagulant Aids – activated silica, polyelectrolytes (anionic, cationic and neutral). 4. Oxidising Agents – Chlorine (Cl2), Chlorine dioxide (ClO2), Potassium permaganate (KMnO4), Calcium hypochlorite [CaO(ClO). 4H2O], Sodium hypochlorite (NaClO). 5. Alkalis – Calcium carbonate (CaCO3), Dolomitic lime (58% CaO, 40% MgO), Lime-hydrated [Ca(OH)2] Magnesium oxide (MgO), Sodium carbonate (Na2CO3), Sodium hydroxide (NaOH). 6. Weighting Agents – Bentonite, Kaolin, Fuller’s earth, other clays and minerals. PROCEDURE 1. Place equal volumes (1000 ml) of sample into each beaker (1500 ml capacity) and record the temperature of the sample. 2. Start the multiple stirrer at flash mix speed (approximately 120 rpm) for all beakers. Add the test solutions or suspensions at predetermined dosage levels and sequences. Flash mix for approximately 1 minute after the addition of chemicals. Record the flash mix time and mixer speed (rpm). 3. Reduce the speed to the minimum required, to keep floc particles uniformly suspended throughout the ‘slow mix’ period. Slow mix for 20 minutes. Record the mixer speed (rpm). 4. After the slow mix period, withdraw the paddles and observe settling of floc particles. Record the time required for the bulk of the particles to settle. 5. After 15 minutes of settling, record the sample temperature and by means of a pipet, withdraw supernatent liquor for conducting colour, turbidity, pH, non-reactive and/or colloidal silica and other required analysis. INTERFERENCES 1. Temperature changes during test – Thermal or convection currents may occur, interfering with the settling of coagulated particles. 2. Gas release during test – Floatation of coagulated floc may occur due to gas bubble formation, caused by mechanical agitator, temperature increase or chemical reaction. 3. Testing period – Biological activity or other factors may alter the coagulation characteristics of water upon prolonged standing. Therefore, the period between sampling and testing should be kept to a minimum. 1
  2. 2. NOTES 1. All polyelectrolytes are classified as anionic, cationic, or neutral, depending upon their composition. A small dosage, under 1 ppm, may permit a reduction in the dosage or complete elimination of the coagulant. 2. It is recognized that reproducibility of results is important. To demonstrate reproducibility, the so-called 3 and 3 procedure is suggested. In this procedure, duplicate sets of 3 breakers each, are treated simultaneously with the same chemical dosages in beakers 1 & 4, 2 & 5 and 3 & 6. 3. A suggested format for recording the results is given below: FORMAT FOR RESULTS RECORDING STATION - DATE - LOCATION - SAMPLE - pH - TURBIDITY - COLOUR - TEMPERATURE - SAMPLE SIZE (ml) - 2
  3. 3. S. No. Beaker No. 1 2 3 4 5 6 1. Chemicals, * mg/litre a. b. c. . . . 2. Flash mix speed, rpm 3. Flash mix time, minutes 4. Slow mix speed, rpm 5. Slow mix time, minutes 6. Temperature, o C. 7. Time first floc, minutes 8. Floc size, mm (approx.) 9. Settling rate 10. Supernatent Tests: a. Turbidity b. pH c. Colour d. Non-reactive/collidal Silica * Indicate order of addition of Chemicals. 3
  4. 4. COLOUR SUMMARY OF METHOD Sample colour is visually compared with a standard Chloroplatinate colour solution. The unit of colour (Hazen unit) is that produced by 1mg platinum/litre in the form of the chloroplatinate ion. APPARATUS 1. Nessler tubes – matched, 50 ml capacity, tall form. 2. pH meter. REAGENTS 1. Water – conforming to specifications Type II. 2. Standard Stock Solution (colour of 500 units) Dissolve 1.246 g Potassium chloroplatinate, K2PtCl6, (equivalent to 500 mg Pt) and 1.00g Cobaltous chloride, CoCl2.6H2O, (equivalent to about 250 mg Co) in water with 100 ml Hydrochloric acid (sp gr 1.19) and dilute to 1 litre with water. 3. Colour Standards Prepare standards having colours of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60 and 70 units by diluting suitable volumes of standard stock solution (3.2) to 50 ml with water in nessler tubes. PROCEDURE 1. Place 50 ml of sample in a Nessler tube. 2. Compare the colour of the sample with standard colour by looking vertically downwards against a white surface. 3. If the colour exceeds 70 units, dilute with water until the colour is within the range of the standards. 4. If the sample is turbid, report as ‘apparent colour’. 5. Measure the pH of the sample. CALCULATIONS 1. Calculate colour unit (Hazen Units) by the following equation: Colour unit = A x 50 B Where: A = estimated colour of the diluted sample. B = milliliters of sample. 2. Report colour results in whole numbers and record as follows: Colour Unit Record to Nearest 1-50 1 51-100 5 101-250 10 251-500 20 Report Sample pH. INTERFERENCES 1. Even a slight turbidity causes the apparent colour to be noticeably higher than the true colour, therefore turbidity should be removed before measurement of true colour. 2. The colour value of water is extremely pH dependent and invariably increases as the pH of the water is raised. When reporting a colour value, specify the pH at which colour is determined. 4
  5. 5. CONDUCTIVITY SUMMARY OF METHOD The conductivity cell is dipped in the sample contained in a beaker and the conductivity is read directly from the conductivity meter. APPARATUS 1. Conductivity meter. 2. Conductivity cells with cell constants from 0.01 to 10 cm-1 . 3. Thermometer, accurate to 0.5o C, when the instrument is not provided with manual or automatic temperature compensation. REAGENTS 1. Water – conforming to specifications Type I. 2. Potassium Chloride (KCl) – Dry at 105o C for 2 hours. Reference Solution A (Conductivity of 97838 microsiemens/cm at 18o C and 111342 microsiemens/cm at 25o C) – Dissolve 74.2460 g of potassium chloride in water and dilute to 1 litre at 20o ± 2o C. Reference Solution B (Conductivity of 11167 microsiemens/cm at 18o C and 12856 microsiemens/cm at 25o C) – Dissolve 7.4365g of potassium chloride in water and dilute to 1 litre at 20 ± 2o C. Reference Solution C (Conductivity of 1220.5 microsiemens/cm at 18o C and 1408.8 microsiemens/cm at 25o C) – Dissolve 0.7440g of potassium chloride in water and dilute to 1 litre at 20 ± 2o C. Reference Solution D (Conductivity of 146.93 microsiemens/cm at 25o C) – Dilute 100 ml of reference solution C to 1 litre with water at 20 ± 2o C shortly before using. PROCEDURE 1. Determination of Cell Constant 1.1 Rinse the conductivity cell with at least three portions of standard potassium chloride solution. 1.2 Thermostat the reference standard at 18 or 25o C and measure conductivity in accordance with the instrument manufacturer instruments. K1 + K2 Cell constant (A) = ---------- Kx Where: K1 = Conductivity of the reference standard potassium chloride solution (microsiemens/cm) at the temperature of measurement. K2 = Conductivity of water (microsiemens/cm), used to prepare the reference solution, at the temperature of measurement. Kx = Measured conductance (microsiemens/cm). 2. Measurement of Conductivity 2.1 Conductivity Below 10 microsiemens/cm. 2.1.1 Use a flow type conductivity cell. Adjust the sample stream to a proper flow rate and bring the temperature to a steady value as near 25o C as possible. Read the temperature to the nearest 0.5o C. 2.1.2 If the conductivity meter is provided with a manual temperature compensator, adjust this to the sample temperature value. 2.1.3 If an automatic temperature compensator is provided, no adjustment is necessary but sufficient time must be allowed to permit equalization of temperature. 2.1.4 Read the conductivity. 2.1.5 If the instrument has no means of temperature compensation, determine a temperature correction to convert readings to 25o C (see notes). 2.2 Conductivity Above 10 microsiemens/cm. 2.2.1 Either a flow-type, dip-type, or piped-type cell may be used. If a flow- type cell is used, proceed in accordance with 4.2.1. 2.2.2 If another type of cell is used, rinse the cell thoroughly several times with water and then two or more times with the sample. Measure the conductivity and the temperature (to the nearest 0.5o C) on successive portions of the sample until a constant value is obtained. 5
  6. 6. 2.2.3 Proceed in accordance with 4.2.1.2, 4.2.1.3 and 4.2.1.5. CALCULATIONS 1. Calculate the conductivity of the sample as follows: Conductivity (K), microsiemens/cm = A x Kx Where: A = cell constant. Kx = measured conductance of the sample, in microsiemens/cm. PRECISION 1. Results obtained should not differ by more than 1% of the conductivity. INTERFERENCES 1. Exposure of a sample to the atmosphere may cause changes in conductivity due to loss or gain of dissolved gases. 2. The carbondioxide, normally present in the air, can drastically change the conductivity of pure water. Contact with air should be avoided by using flow through or inline cells. NOTES 1. The unit of conductivity is siemens per centimeter. The conductance is directly proportional to the cross-sectional area, A (cm2 ) and inversely proportional to the length of the path, L (cm) K x A Conductance = --------- L The conductance measured between opposite faces of a centimeter cube, K, is called specific conductivity. 2. Recommended cell constants for various conductivity ranges are given below: Range of conductivity, Cell constant, Microsiemens/cm Cm-1 0.05 to 20 0.01 1 to 200 0.1 10 to 2000 1 100 to 20000 10 1000 to 2000000 50 3. The conductivity of water and aqueous solutions depends strongly upon the temperature. To avoid making a correction, it is necessary to hold the temperature of the sample to 25 ± 0.5o C. If this cannot be done, the temperature coefficient is determined by conductivity and temperature measurements on the sample over the required temperature range. The conductivity is plotted against temperature and from this curve a table of temperature correction factors may be prepared, or the ratio of conductivity at temperature, T, to conductivity at 25o C may be plotted against temperature and this ratio taken from the curve. 4. When using an instrument provided with a manual or automatic temperature compensator, follow the manufacturers instructions to calibrate the compensator or check its accuracy and applicability to the sample being tested. 6
  7. 7. pH SUMMARY OF METHOD The pH meter and associated electrodes are standardized against two reference buffer solutions, which are close to the anticipated sample pH. The sample measurement is made under specified conditions and prescribed techniques. Apparatus 1. Laboratory pH meter together with its associated glass and reference electrodes. Reagents 1. Water – conforming to specifications Type I. 2. Reference Buffer Solution a. Borax (pH = 9.18 at 25o C) – Dissolve 3.80 g of sodium tetraborate decahydrate (Na2B4O7. 10H2O) in water and dilute to 1-litre. b. Phosphate (pH = 6.86 at 25o C) – Dissolve 3.39g of potassium dihydrogen phosphate (dried at 130o C for 2 hours) (KH2PO4) and 3.53g of anhydrous disodium hydrogen phosphate (dried at 130o C for 2 hours) (Na2HPO4) in water and dilute to 1-litre. c. Phthalate (pH = 4.00 at 25o C) – Dissolve 10.12g of potassium hydrogen phthalate (dried at 110o C for 2 hours) (KHC8H4O4) in water and dilute to 1-litre. d. Tetroxalate (pH = 1.68 at 25o C) – Dissolve 12.61g of potassium tetroxalate dihydrate (KHC2H4H2C2O4. 2H2O) in water and dilute to 1-litre. e. Sodium Bicarbonate – Sodium Carbonate (pH = 10.01 at 25o C) – Dissolve 2.092g of sodium bicarbonate (NaHCO3) and 2.640g of sodium carbonate (dried at 275o C for 2 hours) (Na2Co3) in water and dilute to 1-litre. PROCEDURE 1. Switch on the pH meter, allow it to warm up thoroughly, and bring it to electrical balance with the manufacturer’s instructions. 2. Select two reference buffer solutions, the pH values of which are close to the anticipated sample pH and if possible bracket the sample pH. 3. Standardize the pH meter with the above two (4.2) reference buffer solutions in accordance with the manufacturer’s instructions. 4. Wash the electrodes with water and fill the beaker (provided with a thermometer) with water sample. Insert the electrodes into the beaker and record the pH of the water sample when the drift is less than 0.02 units in 1-minute. CALCULATIONS 1. Most pH meters are calibrated in pH units and the pH of the sample is obtained directly by reading the meter scale. 2. Report the temperature of measurement to the nearest 1o C. 3. Report the pH of the test solution to the nearest 0.01pH units when the pH measurement lies between 1.0 and 12.0. 4. Report the pH of the test solution to the nearest 0.1 pH units when the pH measurement is less than 1.0 and greater than 12.0. PRECISION 1. The precision of this method is 0.05 pH units for pH measurements between 1.0 and 12.0. 2. When the pH is less than 1.0 and greater than 12.0, the precision is 0.1 pH units. 3. In order to attain this precision the condition of the instrumentation and the technique for standardization and operation is extremely important. 7
  8. 8. INTERFERENCES 1. The true pH of an aqueous solution is affected by the temperature, which can be compensated automatically in many instruments or can be manually compensated in most other instruments. The temperature compensation corrects for the effect of the water temperature on the instrument, including the electrodes, but does not correct for temperature effects on the chemical system being monitored. It does not adjust the measured pH to a common temperature; therefore, the temperature should be reported for each pH measurement. 2. The glass electrode reliably measures pH is nearly all aqueous solutions and in general, is not subject to solution interference from colour, turbidity, colloidal matter, oxidants or reductants. 3. The pH response of most glass electrodes is imperfect at both ends of the pH scale. The indicated pH value of highly alkaline solutions will be too low. This is minimized by the selection of proper glass electrode. 4. The indicated pH value of strong aqueous solutions of salts and strong acids having a pH less than 1, will often be higher than the true pH value. This is termed the negative error and the pH indicated is somewhat greater than the true pH. 5. The pH response of the glass electrode may be impaired by a few coating substances such as oily materials and particulates. The electrodes can be restored to normal by an appropriate cleaning procedure recommended by the manufacturer. NOTES 1. The pH is the negative logarithm to the base ten of the conventional hydrogen ion activity. It is derived from the electromotive force (emf) of the cell, reference electrode solution glass electrode (E – Er) F pH = pHr = -------------- 2.3026 RT Where: pHr = pH of the reference buffer. E = emf obtained when the electrodes are immersed in the sample. Er = emf obtained when the electrodes are immersed in a reference buffer solution. F = Faraday constant = 96485.3415 sA/mol or 96500 C mol-1 R = Gas constant = 8.314 (J)(K-1 )(mol-1 ) T = absolute temperature. 2. New glass electrodes and those which have been stored dry, shall be conditioned and maintained as recommended by the manufacturer. If is necessary to keep the immersible ends of the electrodes in water between measurements. For prolonged storage, glass electrodes may be allowed to become dry, but the junction and filling openings of reference electrodes should be caped to decrease evaporation. Glass electrodes should be stored as recommended by the manufacturer and reference electrodes in saturated potassium chloride solution. 3. Both the saturated Calomel electrode and silver-silver chlorine electrode are satisfactory for measurement at room temperature. The silver-silver chloride electrode is recommended for measurement at elevated temperatures where its potential is more stable than that of the saturated calomel electrode. 4. Where emulsions of free oil and water are to be measured for pH, it is necessary to clean the glass electrodes thoroughly after each measurement. The cleaning is done by washing with soap or detergent and water, followed by several rinse with water, after which, the lower third of the electrode is immersed in hydrochloric acid (1+9) and finally washed thoroughly with water. 8
  9. 9. 5. If the sample contains sticky soaps or suspended particles, the cleaning is done with a suitable solvent or by chemical treatment, to dissolve the deposited coating. After cleaning with solvent the lower third is immersed in hydrochloric acid (1+9) followed by thorough washing with water. 6. If glass electrode has failed to respond the treatment as described in 8.4, it is immersed in chromic acid cleaning solution for several minutes. This drastic treatment, limits the life of electrode and is used only as an alternative to discarding it. After chromic acid treatment, the electrode is allowed to stand in water overnight. 7. If the electrode fails to respond to chromic acid cleaning, it is immersed in a 20% solution of ammonium bifluoride (NH4HF2) for about 1-minute. This treatment removes a portion of the bulb glass and should be used only as a last resort. After the fluoride treatment the electrode is thoroughly rinsed with water and conditioned, as is recommended for a new glass electrode. 9
  10. 10. TURBIDITY(Nephelometric) SUMMARY OF METHOD The intensity of light scattered by the sample under given conditions is compared with the intensity of light scattered by a standard reference suspension under the same conditions. APPARATUS 1. Nephelometer – covering the range 0 to 1000 NTU. 2. Sample tubes. REAGENTS 1. Turbidity free water – water conforming to specifications Type I. 2. Stock Turbidity Suspension Solution A – Dissolve 1.000 g of Hydrazine Sulphate [(NH2)2 H2SO4] in turbidity free water and dilute to 100 ml in a volumetric flask. Solution B – Dissolve 10.00 g of Hexamethylene Tetramine [(CH2)6 N4] in turbidity free water and dilute to 100 ml in a volumetric flask. 2.1 In a 100 ml volumetric flask, mix 5.0 ml solution A with 5.0 ml Solution B. Allow to stand for 24 hours at room temperature. Make up to the mark with turbidity free water and mix well. The turbidity of this suspension is 400 NTU. 3. Standard Turbidity Suspension. 3.1 Dilute 10.0 ml of stock turbidity suspension (3.2.3) to 100 ml with turbidity free water. The turbidity of this suspension is 40 NTU. Prepare weekly this suspension. 4. Dilute Turbidity Standard 4.1 Dilute portions of the standard turbidity suspension (3.3.1) with turbidity free water, as required. Prepare weekly. PROCEDURE 1. Calibrate the Nephelometer with standard turbidity suspension for each range, in accordance with the manufacturer’s instructions. 2. Replace the standard by the sample in the same tube after thoroughly washing the tube with turbidity – free water or in an optically identical tube and record the reading. CALCULATIONS 1. Report the result as nephelos turbidity units (NTU). 10
  11. 11. SUSPENDED AND TOTAL DISSOLVED SOLIDS (25 mg/litre or Less of Total Solids) SUMMARY OF METHOD Total solids are determined by evaporation, or the suspended and dissolved solids are separated by filtration and individually determined. The suspended solids are dried and weighed. The solution of dissolved solids is evaporated to dryness using a dish provided with a constant level control. The residue is dried and weighed. APPARATUS 1. Sample Reservoir – A covered 20-litre container of corrosion resistant metal, TFE fluorocarbon, polyethylene, or chemical resistant glass with necessary tubular connections. 2. Automatic Evaporation Assembly - A dust shield, constant level device, heater and evaporation dish. 3. Sampling Device – A cooling coil with overflow pipe and solenoid valve suitable for sampling from a water source to a continuous sample evaporator. (The cooling coil is necessary, only when, sample is above room temperature). 4. Membrane Filter Assembly - A borosilicate glass or stainless steel funnel with a flat, fritted base of the same material, and membrane filters (0.45 micron pore size) to fit. 5. Glass Petri Dish, 150 mm diameter. 6. Evaporating Dish – A straight walled or round bottom platinum dish of 80 to 100 mm diameter and approximately 200 ml capacity. REAGENTS 1. Purified, Chloroform or Benzene. PROCEDURE 1. Select a volume of sample sufficient to yield on evaporation a residue of approximately 25 mg. 2. Suspended Solids (W2) 2.1 Place the membrane filter in a petri dish and dry in an oven at 103o C for 15 minutes or in a vacuum desiccator for 30 minutes. Weigh the filter to the nearest 0.1 mg. 2.2 Filter the sample through membrane filter (4.2.1) using the filtration assembly and the vacuum pump or water aspirator. Wash the residue with chloroform or benzene. Place the filter in the petri dish. 2.3 Place the petri dish in the oven at 103o C for 30 minutes. Reweigh the filter and record the weight of the residue on the filter. (W2) 3. Total Solids and Dissolved Solids. 3.1 Weigh a platinum dish that has been dried at 103o C for 1 hour and cooled in a desiccator. Using evaporation assembly start the evaporation of the selected volume of the sample for total solids (4.1) (W1) or the filtrate from the suspended solids determination (4.2) for dissolved solids (W3). 3.2 When the evaporation is almost complete remove the dish from the assembly and dry at 103o C for 1 hour in an oven. Cool in a desiccator and weigh. Record the weight of the residue. CALCULATIONS Calculate the result of each specific determination as follows: W1 x 1000 Total Solids, mg/litre = ------------ V W2 x 1000 Suspended solids, mg/litre = ------------ V W3 x 1000 Total dissolved solids, mg/litre = ------------ V Where: 11
  12. 12. W1 = grams of total solids. W2 = grams of suspended solids. W3 = grams of dissolved solids. V = litres of sample used. NOTES 1. Some evaporation residues readily absorb moisture, therefore rapid weighing should be done. 2. Samples containing 25 mg/litre or less of total solids on which only the total solids content is to be determined shall be immediately acidified with 0.2 ml of hydrochloric acid (sp gr 1.19) per litre of water. If suspended solids is to be separately determined, the sample, regardless of total solids content, shall be filtered, as soon as possible and then acidified. 12
  13. 13. SUSPENDED AND TOTAL DISSOLVED SOLIDS (More than 25 mg/litre of Total Solids) SUMMARY OF METHOD Total solids are determined by evaporation of an appropriate portion of the sample and weighing the residue obtained. The suspended and dissolved solids can be separated by filtration and then determined individually. The suspended solids are dried and weighed and dissolved solids are determined by weighing the residue, obtained by evaporating the filtered sample. APPARATUS 1. Sample Reservoir – A chemical resistant container of 1 to 4-litre capacity, having a valve controlled outlet. 2. Membrane Filter Assembly - A borosilicate glass or stainless steel funnel with a flat, fritted base of the same material, and membrane filters (0.45 micron pore size) to fit. 3. Glass Petri Dish, 150 mm diameter. 4. Evaporating Dish – A straight wall or round bottomed platinum dish of 80 to 100 mm diameter and approximately 200 ml capacity. A porcelain dish may be substituted for the platinum dish. 5. Heater – Hot plate or steam bath for maintaining the temperature of the evaporating sample near the boiling point. REAGENTS 1. Purified, Chloroform or Benzene. PROCEDURE 1. Measure a quantity of sample sufficient to yield, on evaporation, approximately 25 mg of residue. 2. Suspended Solids 2.1 Place the membrane filter in a petri dish and dry in an oven at 103o C for 15 minutes or in a vacuum desiccator for 30 minutes. Weigh the filter to the nearest 0.1 mg. 2.2 Filter the sample through membrane filter (4.2.1) using the filtration assembly and the vacuum pump or water aspirator. Place the filter in the petri dish. 2.3 Place the petri dish in the oven at 103o C for 30 minutes. Reweigh the filter and record the weight of the residue on the filter. 3. Total Solids and Dissolved Solids. 3.1 Transfer the sample for total solids determination (4.1) or the filtrate from suspended solid determination (4.2) to a sample reservoir. 3.2 Fill an evaporating dish (previously dried at 103o C for 1 hour and weighed) to within 6.3 mm of the top, with sample. 3.3 Evaporate the sample on a hot plate or steam bath. Periodically, add sample from the reservoir to the dish until the reservoir is empty. 3.4 Dry the dist at 103o C for 1 hour. Cool in a desiccator and weigh. Record the weight of the residue in the dish. CALCULATIONS 1. Calculate the result of each specific determination as follows: W1 x 1000 Total Solids, mg/litre = -------------- V W2 x 1000 Suspended solids, mg/litre = -------------- V W3 x 1000 Total dissolved solids, mg/litre = -------------- V Where: W1 = grams of total solids. W2 = grams of suspended solids. W3 = grams of dissolved solids. 13
  14. 14. V = litres of sample used. NOTES 1. Some evaporation residues readily absorb moisture, therefore rapid weighing should be done. 2. Suspended solids are defined as those solids, exclusive of gases and in non-liquid state, which are dispersed in water to give a heterogeneous mixture. Dissolved solids (exclusive of gases) are dispersed in water to give a homogenous liquid and total solids is the sum of suspended and dissolved solids. 14
  15. 15. ALKALINITY (Titration Method, 10 to 500 mg/litre) SUMMARY OF METHOD The sample is titrated with acid solution to a designated pH and the end point is determined using internal indicator. RANGE 10 to 500 mg/litre as CaCO3. REAGENTS 1. Water – conforming to specifications Type I. 2. Phenolphthalein Indicator Solution (5.0 g/litre) – Dissolve 0.5g of phenolphthalein in 50 ml of ethyl alcohol (95%) and dilute to 100 ml with water. 3. Standard Hydrochloric Acid (0.02 N) – Dilute 1.66 ml of hydrochloric acid (sp gr 1.19) to 1 litre with water. For standardization - see notes. 4. Mixed Bromocresol Green – Methyl Red Indicator Solution – Dissolve 20 mg of methyl red and 100 mg of bromocresol green (sodium salt) in either 100 ml of water or 100ml of ethyl alcohol (95%). 5. Methyl Orange Indicator Solution (0.5 g/litre) – Dissolve 0.05g of methyl orange in water and dilute to 100 ml. 6. Sodium Thiosulphate Solution (0.1 N) – Dissolve 2.5g of sodium thiosulphate (Na2S2O3. 5H2O) in 50 ml of water, add 0.011g of sodium carbonate. Dilute to 100 ml and allow to stand for 24 hours. PROCEDURE 1. Phenolphthalein Alkalinity (P-Alkalinity) 1.1 Place 50 ml sample in a titration flask and add 2 drops of phenolphthalein indicator. 1.2 Titrate over a white surface 0.02 N standard hydrochloric acid from a pink colour to a colourless end point (A). 2. Total Alkalinity by Mixed Indicator 2.1 Add 3 drops of the mixed indicator to the solution in which the phenolphthalein alkalinity has been determined. 2.2 Titrate over a white surface with 0.02 N standard hydrochloric acid to the required end point. Above pH 5.2 - Greenish blue At pH 5.0 - Light blue pH 4.8 - Pink grey with bluish tinge pH 4.6 - Light Pink 3. Total Alkalinity (M-Alkalinity) by Methyl Orange 3.1 Add 2 drops of methyl orange indicator to the solution in which the phenolphthalein alkalinity has been determined. 3.2 Titrate over a white surface with 0.02 N standard hydrochloric acid to the required end point. (At pH 4.6 the colour changes to orange and at pH 4.0 to pink) (B). CALCULATIONS A x N x 50,000 1. Phenolphthalein Alkalinity, mg/litre as CaCO3 = --------------------- V B x N x 50,000 2. M-Alkalinity (Total Alkalinity), mg/litre as CaCO3 = ---------------------- V Where: A = millilitres of standard hydrochloric acid to reach the phenolphthalein end point B = total milliliters of standard hydrochloric acid to reach the mixed indictor or methyl orange end point. N = normality of hydrochloric acid. V = milliliters of sample. 3. Alkalinity Relationship. 15
  16. 16. The following table gives the stoichiometric classification of the three principal forms of alkalinity present in water. Results of Titration Hydroxide Alkalinity (as CaCO3) Carbonate Alkalinity (as CaCO3) Bicarbonate Alkalinity (as CaCO3) P = 0 0 0 M P < ½ M 0 2 P M – 2P P = ½ M 0 2 P 0 P > ½ M 2 P – M 2 ( M – P) 0 P = M M 0 0 Where: P = Phenolphthalein Alkalinity. M = M-Alkalinity (or total alkalinity). PRECISION 1. The precision of this method is ± 1 mg/litre as CaCO3. INTERFERENCES 1. Free residual chlorine markedly affects the indicator colour response in some water samples through its bleaching action. It can be removed by the addition of sodium thiosulphate. 2. Natural colour or the formation of a precipitate during titration may mask the colour change. 3. Salts of weak organic and inorganic acids also affect the titration. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. Phenolphthalein indicator is used for alkalinity determination contributed by hydroxide and half the carbonate. Indicators responding in the pH range 4-5 are used to measure the alkalinity contributed by hydroxide, carbonate and bicarbonate. The stoichiometric relationship between hydroxide, carbonate and bicarbonate are valid only in the absence of significant concentration of weak acid radicals other than hydroxide, carbonate or bicarbonate. 3. The following pH values are suggested as the equivalence points for the corresponding alkalinity concentration as calcium carbonate: pH of 5.1 for total Alkalinities of about 30 mg/litre, pH of 4.8 for 150 mg/litre, and pH of 4.5 for 500 mg/litre. 3.1 Indicators effective in these ranges which give the most reliable results are mixed indicator for higher pH values and methyl orange for pH values below 4.6. 4. To standardize 0.2 N hydrochloric acid, Weigh accurately 0.088 ± 0.001 g of sodium carbonate (previously dried in a platinum crucible at 250o C for 4 hours) and transfer to a 500 ml conical flask. Add 50 ml of water to dissolve the carbonate and add 2 drops of 0.1% solution of methyl red in alcohol. Titrate with hydrochloric acid to the first appearance of a red colour, and boil the solution carefully until the colour is discharged. Cool to room temperature and continue the titration. Repeat the process of boiling and titration until a faint red colour is obtained that is not discharged on further heating. 5. Sulphuric acid can also be used in place of hydrochloric acid for titration. 16
  17. 17. ALKALINITY DUE TO HYDROXIDE SUMMARY OF METHOD The sample is treated with a solution of strontium chloride to precipitate dissolved carbonates and phosphates and the hydroxide ion is titrated with a standard hydrochloric acid solution using phenolphthalein indicator. REAGENTS 1. Water – conforming to specifications type III. 2. Hydrochloric acid (0.02 N) – Dilute 1.66 ml of hydrochloric acid (sp gr. 1.19) to 1 litre with water. For standardization – see notes. 3. Phenolphthalein Indicator Solution (5.0 g/litre) – Dissolve 0.5 g of phenolphthalein in 50 ml of ethyl alcohol (95%) and dilute to 100 ml with water. 4. Strontium Chloride Solution (4.5 g/litre) – Dissolve 4.5 g of strontium chloride (SrCl2. 6H2O) in water and dilute to 1 litre. PROCEDURE 1. Transfer 100 ml of the sample to a 500 ml conical flask. 2. Add quickly, while swirling the flash, 1 ml of strontium chloride solution for each milligram of carbonate or phosphate ion in the sample aliquot, plus a 4 ml excess. 3. Stopper the flask loosely, boil the contents for a few seconds, and then cool to room temperature. 4. Add 4 drops of phenolphthalein indicator solution and quickly titrate with standard hydrochloric acid to a colourless end-point. CALCULATIONS 1. Calculate the concentration of hydroxide ion, in mg/litre, as follows: N x V1 x 17000 Hydroxide ion, mg/litre as OH =- ------------------- V Where: N = normality of standard hydrochloric acid. V1 = millimetres of standard hydrochloric acid. V = millimetres of sample. 2. Calculate the concentration of hydroxide ion, in mg/litre as CaCO3, as follows: Hydroxide ion, mg/litre as CaCO3 = B x 2.94 Where: B = hydroxide ion, mg/litre as OH. PRECISION 1. The single operator precision of the method can be expressed as follows: S = 0.05 mg/litre. Where: S = single operator precision. INTEREFENCES 1. Aluminium, carbonates, chromates, phosphates, silicates, and some organic matter affect the sample titration. 2. The effects of carbonates and phosphates are eliminated by the addition of strontium chloride in excess. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. To standardize 0.02 N hydrochloric acid, weigh accurately 0.088 ± 0.001 g of sodium carbonate (previously dried in a platinum crucible at 250o C for 4 hours) and transfer to a 500 ml conical flask. Add 50 ml of water to dissolve the carbonate the add 2 drops 0.1% solution of methyl red in alcohol. Titrate with hydrochloric acid to the first appearance of a red colour, and boil the solution carefully until the colour is discharged. Cool to room temperature and continue the titration. Repeat the process of boiling and titration until a faint red colour is obtained that is not discharged on further heating. 17
  18. 18. AMMONIA (Indophenol Method, 10 to 500 micrograms/litre) SUMMARY OF The sample is reacted with hypochlorite and phenol in the presence METHOD of a manganous salt to produce an intense blue compound, the intensity of which is measured spectrophotometrically at a wavelength of 630 nm. RANGE 10 to 500 micrograms/litre as N. APPARATUS 1. Spectrophotometer for use at 630 nm. 2. Matched pair of 10 mm and 50 mm cells. REAGENTS 1. Water – conforming to specifications Type I. 2. Phenate Reagent Solution – Dissolve 2.5g of sodium hydroxide and 10g of phenol in 100 ml of water. Prepare every week. 3. Hypochlorous Acid Solution – Add 10 ml of a 5% commercial bleaching powder solution to 4ml of water. Adjust the pH to 6.5 to 7.0 with hydrochloric acid (check with a narrow range pH paper). Prepare every week. 4. Manganous Sulphate Solution – Dissolve 0.050g of manganous sulphate (MnSO4.H2O) in 100 ml of water. 5. Ammonia Nitrogen Standard Solution (1ml = 0.5 microgram N) – Dissolve 0.3819g of anhydrous ammonium chloride (NH4Cl), previously dried at 105o C for 1 hour, in water and dilute to 1 litre. Dilute 5.0 ml of this solution to 1 litre. CALIBRATION 1. Transfer 0.0, 1.0, 5.0, 10.0, 15.0 and 20.0 ml of the standard ammonia nitrogen solution (1ml = 0.5 microgram N) to 25ml of volumetric flasks. 2. Add 0.05 ml of manganous sulphate solution and mix. 3. Add 0.5 ml of hypochlorous acid solution and add immediately but slowly 0.6 ml of the phenate solution. Dilute to 25ml with water. 4. Measure the absorbance of each standard at 630nm against the zero standard (blank). 5. Prepare a calibration curve by plotting absorbance versus micrograms of ammonia nitrogen. PROCEDURE 1. Place 10 ml (or other suitable volume containing not more than 10 micrograms ammonia nitrogen) of the sample in a 25 ml volumetric flask. 2. Proceed in accordance with section 5.0 (5.2 to 5.4). CALCULATIONS 1. Calculate the ammonia concentration in microgram/litre of nitrogen in the sample, as follows: A x 1000 Ammonia, micrograms/litre as N = ------------- V Where: A = micrograms of ammonia nitrogen observed from the calibration curve. V = millilitres of sample. 2. Calculate the ammonia concentration, in micrograms/litre of ammonia in the sample, as follows: Ammonia, microgram/litre as NH3 = B x 1.22 Where: B = ammonia nitrogen, micrograms/litre. INTERFERENCES 1. More than 500 mg/litre of alkalinity, more than 100 mg/litre of acidity, colour and turbidity interfere. These interferences can be removed by distillation prior to analysis. 18
  19. 19. AMMONIA (Nessler’s Method 0.1 to 2 mg/litre) SUMMARY OF METHOD The same is reacted with Nessler’s reagent (K2HgI4) to produce a reddish brown colloidal compound, the intensity of which is measured spectrophotometrically at a wavelength of 425 nm. RANGE 0.1 to 2 mg/litre as N. APPARATUS 1. Spectrophotometer for use at 425 nm. 2. Matched pair of 10mm cells. REAGENTS 1. Water – conforming to specifications Type I. 2. Ammonia Nitrogen, Standard solution (1ml = 0.01 mgN) – Dissolve 4.718g of ammonium sulphate [(NH4)2 SO4] (previously dried at 100o C for 1 hour) in water and dilute to 1 litre. Dilute 10 ml of this solution to 1 litre. 3. Nessler Reagent – Dissolve 100 g of anhydrous mercuric iodide (HgI2) and 70g of anhydrous potassium iodide (KI) in a small volume of water; add this mixture slowly, with stirring, to a cooled solution of 160g of sodium hydroxide in 500 ml of water. Dilute the mixture to 1 litre. Store the solution in dark for 5 days and filter twice through a fritted glass crucible before using. This reagent has a shelf life of 1 year, if stored in dark. 4. Reagents for Sample Turbidity/Cloudiness Removal. 4.1 Sodium Hydroxide Solution (250g/litre) – Dissolve 250g of sodium hydroxide in water and dilute to 1 litre. 4.2 Zinc Sulphate Solution (100 g/litre) – Dissolve 100g of zinc sulphate (ZnSO4.7H2O) in water and dilute to 1 litre. 4.3 Sodium Potassium Tartrate Solution (300 g/litre) – Dissolve 30g of sodium potassium tartrate tetrahydrate in 100ml of water. 4.4 Disodium Dihydrogen Ethylenediamine tetraacetate solution (500 g/litre) – Dissolve 50g of disodium dihydrogen ethylenediamine tetraacetate – dihydrate in water containing 10g of sodium hydroxide. Gently heat to complete dissolution. Cool and dilute to 100 ml. INTERFERENCES 1. Glycerine, hydrazine, and some amines will react with Nessler’s reagent to give the characteristic yellow colour in the time required for the test. 2. Residual chlorine must be removed prior to ammonia determination with sodium arsenite (NaAsO2) solution (lg/litre). One millilitre of this solution will remove 1mg/litre of residual chlorine from the 500 ml sample. 3. Turbidity in the sample can be removed as follows: Add 1 ml of Zinc sulphate solution to 100 ml sample and mix. Add sodium hydroxide solution to raise the pH to about 10.5 (check with a pH paper). Allow to settle and filter through whatman No. 40 filter paper. To prevent cloudiness add 2 drops of sodium potassium tartrate solution or disodium dihydrogen ethylenediamine tetraacetate. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. The Nessler reagent should give the characteristic colour with ammonia within 10 minutes after addition, and should not produce a precipitate with small amounts of ammonia (0.04 mg in 50 ml volume). The solution may be used without 5 day storage if it is filtered through a 0.45 – micron membrane filter shortly before use. 19
  20. 20. CARBON DIOXIDE (Bicarbonate Titration Method) SUMMARY OF METHOD Carbon dioxide concentration is determined from measured values of pH and bicarbonate ion. APPARATUS 1. pH meter. REAGENTS 1. Water – conforming to specifications Type.I. 2. Hydrochloric Acid, Standard (0.04N) – Dilute 3.42 ml of hydrochloric acid (sp gr 1.19) to 1 litre with water and standardize with sodium carbonate (dried at 250o C for 4 hours) using methyl red indicator. 3. Methyl Red Indicator Solution (5g/litre) – Dissolve 0.5 g of methyl red in 100 ml of 95% ethanol. PROCEDURE 1. Determine the pH of the sample. 2. Place 50 ml or less of sample water containing no more than 80 mg of bicarbonate ion into a 200 ml beaker. 3. If the pH of the sample is above 8.3, titrate with 0.04N hydrochloric acid to this pH value using the pH meter for end-point detection. 4. Continue to titrate to pH 4.5 5. Record the millilitres of hydrochloric acid required to titrate to pH 8.3 as V1 and millilitres required to titrate from pH 8.3 to pH 4.5 as V2. CALCULATIONS 1. Calculate the bicarbonate ion concentration using the following equation: 2440 x (V2 – V1) Bicarbonate (HCO3), mg/litre = ---------------------- V Where: V = volume of sample is millilitres. V1 = millilitres of hydrochloric acid required for titration to pH 8.3. V2 = millilitres of hydrochloric acid required for titrating from pH 8.3 to 4.5 2. Calculate the free carbon dioxide concentration in mg/litre by using the following equation for waters with pH values from 6 to 9: Free CO2, mg/litre as CO2 = 1.60 x 10(6.0-pH) x mg HCO3/litre. 3. Calculate free CO2 concentration in mg/litre as CaCO3 as follows: Free CO2, mg/litre as CaCO3 = A x 1.14 Where: A = concentration of CO2, mg/litre as CO2. PRECISION 1. Precision of the bicarbonate determination is approximately 1mg/litre for bicarbonate ion concentrations below 100mg/litre and 2 mg/litre in the 100 to 200 mg/litre bicarbonate ion range. Precision of carbon dioxide measurement will be proportional to the fractional relationship between bicarbonate ion and carbon dioxide values determined. 20
  21. 21. CARBON DIOXIDE (Direct Titration of Free Carbon Dioxide) SUMMARY OF METHOD Free carbon dioxide is reacted with sodium hydroxide to form sodium bicarbonate. The end point of the reaction is detected electrometrically or by means of a pH colour indicator. APPARATUS 1. pH meter. REAGENTS 1. Water – conforming to specifications Type I. 2. Phenolphthalein Indicator Solution (5g/litre) – Dissolve 0.5g of phenolphthalein in 100 ml of a 50% solution of ethyl alcohol in water. 3. Sodium Hydroxide solution, Standard (0.04N) – Dissolve 1.6 g of sodium hydroxide in approximately 100 ml of water, add 0.1 g of barium hydroxide and dilute to 1 litre with water. Allow the carbonate to settle and standardize against the 0.04N hydrochloric acid. 4. Sodium Bicarbonate Solution (1g/litre) – Dissolve 0.1g of anhydrous sodium bicarbonate in 50 ml of water and dilute to 1 litre. Prepare just before use. 5. Hydrochloric Acid, standard (0.04 N) – Dilute 3.42 ml of hydrochloric acid (sp. gr. 1.19) to 1 litre with water and standardize with sodium carbonate (dried at 250o C for 4 hours) using methyl red indicator. 6. Methyl Red Indicator solution (5g/litre) – Dissolve 0.5g of methyl red in 100 ml of 95% ethanol. PROCEDURE 1. Place 100 ml of sample in a 250 ml breaker and add 5 drops of phenolphthalein indicator solution. 2. If the sample remains colourless, titrate rapidly with standard sodium hydroxide solution until the first faint pink colour is detectable in the solution. 2.1 Alternatively, titrate the sample to pH 8.3 using a pH meter to detect the end point. CALCULATIONS 1. Calculate the free carbon dioxide content of the water in mg/litre using the following equation: Free CO2, mg/litre as CO2 = V x N x 440 Where: V = millilitres of sodium hydroxide required to titrate 100 ml of sample N = normality of sodium hydroxide solution. 2. Calculate free CO2 concentration in mg/litre as CaCO3 as follows: Free CO2, mg/litre as CaCO3 = A x 1.14 Where: A = concentration of CO2, mg/litre as CO2. PRECISION 1. Under the most favourable conditions, precision is approximately 10% of the indicated carbon dioxide content. INTERFERENCES 1. Cations or anions which affect the carbonate equilibrium or precipitate or consume the reactant preferentially affect the accuracy. Aluminium, iron, chromium and copper are examples of metal ions that may yield erroneous results. 2. Abnormal results also may be obtained in the presence of ammonia, amines, phosphate, borate, sulphide and nitrate. 3. Excessive dissolved solids also, will introduce error. 21
  22. 22. CHLORIDE (Mercuric Thiocyanate Method, 0.05 to 1.4 mg/litre) SUMMARY OF METHOD The sample is treated with ferric ammonium sulphate and mercuric thiocyanate solutions. The chloride ion reacts with mercuric thiocyanate to release the thiocyanate ion which combines with ferric ion to form red ferric thiocyanate. The intensity of the colour is measured at a wavelength of 463 nm. RANGE 0.05 to 1.4 mg/litre as Cl. APPARATUS 1. Spectrophotometer for use at 463 nm. 2. Matched pair of 50 mm cells. REAGENTS 1. Water – conforming to specifications Type II. 2. Ferric Alum Solution – Dissolve 5.0 g of ferrous ammonium sulphate [Fe (NH4)2 (SO4)2. 6H2O] in 20 ml of water. Add 38 ml of nitric acid (sp gr 1.42) and boil to oxidize the iron and remove the oxides of nitrogen. Dilute to 100 ml with water. 3. Mercuric Thiocyanate Solution – Dissolve 0.30 g of mercuric thiocyanate [Hg(CNS)2] in 100 ml of absolute methanol in an amber bottle. Allow to stand for 24 hours before using. This solution has a shelf life of 4 weeks. 4. Standard Sodium Chloride Solution (1 ml = 0.01 mg chloride) – Dissolve 1.649 g of sodium chloride (dried at 600o C for 1 hour) in water and dilute to 1 litre (solution A). Dilute 10.0 ml of solution A to 1 litre with water. CALIBRATION 1. Prepare a series of standards by diluting 0, 0.5, 2.5, 5.0, 7.5, 10 and 14 ml of the standard sodium chloride solution (1 ml = 0.01 mg chloride) to 100 ml with water in volumetric flasks. 2. Proceed in accordance with section 6.0. 3. Prepare a calibration curve by plotting absorbance versus the concentration of chloride in mg/litre. PROCEDURE 1. Place 25 ml of sample in a 50 ml glass stoppered cylinder. 2. Add 5.0 ml of ferric alum solution and 2.5 ml of mercuric thiocyanate solution. Mix thoroughly and allow to stand for 10 minutes. 3. Measure the intensity of colour at 463 m, against the reagent blank, prepared by using 25 ml of water and following step 6.2, using 50 mm matched absorption cells. CALCULATIONS 1. Read the concentration of chloride ion in mg/litre directly from the calibration curve prepared in accordance with section 5.0. 2. Calculate the chloride concentration in mg/litre as CaCO3 as follows: Chloride, mg/litre as CaCO3 – A x 1.41 Where: A = chloride concentration, mg/litre as Cl. PRECISION 1. The precision of this method may be expressed as follows: Sr = 0.054 X So = 0.013 X Where: Sr = overall precision, mg/litre. So = single operator precision, mg/litre. X = concentration of chloride ion determined, mg/litre. INTERFERENCES 1. Bromides, iodides, cyanides, thiosulphate, hydrazine and nitrites interfere. 2. Morpholine concentrations greater than 6mg/litre may interfere. 3. Colour may also interfere depending upon its spectral absorbance. 4. Boric acid upto 13000 mg/litre does not interfere. 22
  23. 23. NOTES 1. Reagent grade chemicals should be used for preparing all the reagents. 2. Mercuric salts are very poisonous. Due precautions should be observed when using these salts. 3. In the preparation of mercuric thiocyanate solution, a slight precipitate may form and settle out after 24 hours. Only the clear, supernatent liquid must be used. 4. Soak all new glassware in hot nitric acid (1+19) for several hours and in water (halide free) between tests. Discard all glassware that appear etched or scratched. 5. For best results, the temperatures of the standard solutions should be within 1.0o C of the reagent blank, and the samples. 23
  24. 24. CHLORIDE (Mercuric Thiocyanate Method, Modified, 2 to 100 micrograms/litre) SUMMARY OF METHOD A solution of lead nitrate is added to the sample followed by addition of phosphate buffer. The resulting precipitation of lead phosphate coprecipitates the Chloride in the sample. The sample is centrifuged and the supernatent liquid discarded. The precipitate is dissolved in a ferric iron-mercuric thiocyanate reaction medium and the Chloride is determined Spectrophotometrically at 463 nm. RANGE 2 to 100 micrograms/litre as Cl. APPARATUS 1. Spectrophotometer for use at 463 nm. 2. Matched pair of 50 mm Cells. REAGENTS 1. Water – conforming to specifications Type II. 2. Ferric Nitrate Solution – Dissolve 8.0g of ferric nitrate [Fe(NO3)3. 9H2O] in about 400 ml of water and add 58.5 ml of nitric acid (sp gr 1.42). Dilute to 1 litre with water. 3. Lead Nitrate Solution – Dissolve 20g of lead nitrate [Pb(NO3)2] in water and dilute to 1 litre. 4. Mercuric Thiocyanate Solution – Dissolve 0.30 g of mercuric thiocyanate [Hg(SCN)2] in 100 ml of methanol. Store in amber bottle. Allow to stand for 24 hours before using. 5. Standard Sodium Chloride Solution (1ml = 1 microgram of Chloride) – Dissolve 1.649g of sodium chloride (dried at 600o C for 1 hour) in water and dilute to 1-litre (Solution A). Dilute 100 ml of Solution A to 1 litre (Solution B). Finally dilute 10.0 ml of Solution B to 1 litre. This solution should be prepared fresh before use. 6. Sodium Phosphate Solution – Dissolve 16.7 g of sodium dihydrogen phosphate (NaH2PO4.7H2O) and 16.2 g of disodium hydrogen phosphate (Na2HPO4.7H2O) in water and dilute to 1 litre. CALIBRATION 1. Prepare a series of standards by diluting 0, 1.0, 5.0, 10.0, 15.0, and 25.0 ml of Standard Sodium Chloride Solution (1ml = 1 microgram of chloride) to 250 ml in 250 ml glass stoppered bottles. 2. Proceed in accordance with Section 6.0 (6.2 to 6.7). 3. Prepare a calibration curve by plotting absorbance versus concentration of Chloride in mg/litre. PROCEDURE 1. Place 250 ml sample in a clean 250 ml glass stoppered bottle. 2. Add 5.0 ml of the lead nitrate solution to the bottle. Cap the bottle and mix. Allow to stand for 2 minutes. 3. Add 5.0 ml of sodium phosphate solution and mix. Allow to stand for 5 minutes. 4. Centrifuge the capped bottle solution at 1500 rpm for 6 minutes. Decant the supernatent liquid immediately after centrifuging. 5. Add 15.0 ml of ferric nitrate solution and mix to dissolve the precipitate. 6. Add 1.0 ml of mercuric thiocyanate solution and mix. Dilute to 25 ml with water. Allow to stand for 10 minutes. 7. Measure the absorbance, against reagent blank prepared by taking 250 ml instead of sample and repeating the steps 6.2 to 6.6, at 463 nm using 50 mm matched cells. CALCULATIONS 1. Read the concentration of chloride in micrograms/litre directly from the calibration curve prepared in accordance with Section 5.0. 2. Calculate the chloride concentration in microgram/litre as CaCO3 as follows: Chloride, micrograms/litre as CaCO3 = A x 1.41 Where: 24
  25. 25. A = chloride concentration, micrograms/litre as Cl. INTERFERENCES 1. See mercuric thiocyanate method (Section 9.0) for the determination of Chloride. NOTES 1. See mercuric thiocyanate method (Section 10.0) for the determination of Chloride. 2. Lead nitrate is very toxic. Due precautions should be observed when using this chemical. 3. 2 microgram/litre chloride represents 0.006 absorbance with respect to a reagent blank when using 50 mm matched cells. 25
  26. 26. CHLORIDE (Silver Nitrate Method, 5 mg/litre or more) SUMMARY OF METHOD The sample is adjusted to a pH of 8.3 and titrated with silver nitrate solution using potassium chromate indicator to a brick red colour. RANGE 5 mg/litre or more as Cl. REAGENTS 1. Water – conforming to specifications Type II. 2. Standard Silver Nitrate Solution (0.025N) – Dissolve 4.247g of silver nitrate (dried to constant weight at 40o C) in water and dilute to 1 litre. Standardize against standard sodium chloride solution. 3. Standard Sodium Chloride Solution (0.025N) – Dissolve 1.461g of sodium chloride (dried at 600o C for 1 hour) in water and dilute to 1 litre. 4. Hydrogen Peroxide (30%). 5. Phenolphthalein Indicator Solution (10g/litre) – Dissolve 1g of phenolphthalein in 100 ml of ethanol (95%), methanol or isopropyl alcohol. 6. Potassium Chromate Indicator Solution (5%) – Dissolve 50g of potassium chromate (K2CrO4) in 100 ml of water, and add silver nitrate until a slight red precipitate is produced. Allow to stand for 24 hours in dark. Filter and dilute to 1 litre. 7. Sodium Hydroxide Solution (10g/litre) – Dissolve 10g of sodium hydroxide in water and dilute to 1 litre. 8. Sulphuric Acid Solution (1+19) – Mix 1 volume of Sulphuric acid (sp gr 1.84) with 19 volumes of water. PROCEDURE 1. Place 50 ml of sample into a 125 ml conical flask. 2. If Sulphite is present, add 0.5 ml of hydrogen peroxide solution and mix for 1 minute. 3. Adjust the pH to the phenolphthalein endpoint (pH 8.3), using Sulphuric acid solution, or sodium hydroxide solution. 4. Add 1 ml of potassium chromate indicator and mix. 5. Titrate with standard silver nitrate solution to a brick red colour. 6. Repeat 4.1 to 4.5 using 25 ml of sample diluted to 50 ml with water. CALCULATIONS 1. Calculate the chloride ion concentration in the sample, in milligrams per litre, as follows: (V1 – V2) x N x 71000 Chloride, mg/litre as Cl = ------------------------------ V Where: V1 = millilitres of standard silver nitrate solution for the sample (4.1). V2 = millilitres of standard silver nitrate solution for the sample (4.6). N = normality of standard silver nitrate solution. V = millilitres of sample (4.1). 2. Calculate the chloride concentration in mg/litre as CaCO3 as follows: Chloride, mg/litre as CaCO3 = A x 1.41 Where: A = Chloride concentration, mg/litre as Cl. PRECISION The precision of this method may be expressed as follows: ST = 0.013X + 0.70 So = 0.007X + 0.53 Where: ST = overall precision, mg/litre So = Single operator precision, mg/litre. X = Concentration of Chloride ion determined, mg/litre. INTERFERENCES 1. Bromide, iodide, and sulphide are titrated along-with the chloride. 2. Orthophosphate and polyphosphate interfere, if present, in concentrations greater than 250 and 25 mg/litre, respectively. 26
  27. 27. 3. Sulphite and objectionable colour or turbidity must be eliminated. 4. Compounds which precipitate at pH 8.3 may interfere. NOTES 1. Reagent grade chemicals should be used for preparing all the reagents. 2. If the titration required more than 25ml of silver nitrate in 4.5, use a smaller sample size. 27
  28. 28. CHLORINE DEMAND SUMMARY OF METHOD A chlorinating solution of known concentration is applied in increasing increments of chlorine concentration to a series of portions of the individual sample of water to be tested. The residual chlorine is determined at succeeding intervals of time. APPARATUS 1. pH meter. REAGENTS 1. Water – conforming to specifications Type III. 2. Calcium Hydroxide Solution (10.7g/litre) – Weigh 10.7g of 100% hydrated lime [Ca(OH)2] and suspend in water. Dilute to 1 litre. 3. Calcium Hypochlorite Solution (1ml = 0.5 to 100mg available Chlorine) – Dissolve 145g of calcium hypochlorite (70% available chlorine, by weight) in water and make up to 1 litre. Allow to settle and decant the supernatent solution containing approximately 100 mg available chlorine per ml. Dilute with water to give 0.5 to 100 mg of available chlorine per ml. Standardize prior to use in accordance with 3.4. 4. Chlorine Water (1ml = 0.5 to 3mg available chlorine) – Pass gaseous chlorine through water until the solution contains 0.5 to 3.0 mg available chlorine per ml. For standardization add 10 ml of chlorine water to a flask containing 10 ml of acetic acid (1+1) and 10 ml of potassium iodide solution (5%). Titrate with 0.10N sodium thiosulphate solution using starch indicator. V1 x 3.546 Available Chlorine, mg/litre = --------------- V (V1 is millilitres of 0.10 N sodium thiosulphate solution used in the titration and V is millilitres chlorine water taken for titration.) 5. Hydrochloric Acid (1+1) – Mix equal volumes hydrochloric acid (sp gr 1.19) and water. PROCEDURE 1. Establishing Test Conditions 1.1 Ascertain the range of pH, time of chlorine contact, and the chlorine application concentration to achieve the objective of Chlorination from past experience, from literature survey, by experimentation, or from plant conditions. 1.2 Determine the pH of each test and additions of chlorinating solutions such that there is not less than five equal increments of the chlorine application concentrations. 1.3 In each of a series of clean 1 litre glass containers, place a 500 ml portions of the sample. 2. Trial Chlorination 2.1 To the first of the series of 500 ml portions of the samples, add the maximum anticipated amount of chlorinating solution. Determine the pH of the solution. 2.2 Adjust the pH (see notes). 2.3 Allow the chlorinated sample to stand for a minimum predetermined time. Determine total and free available residual chlorine. Withdraw successive samples at selected time intervals to cover the estimated range of minimum to maximum contact times. 3. Chlorination 3.1 On the basis of information obtained by the trial chlorination, add desired increments of chlorinating solution to separate 500 ml portions of the sample. Determine the pH of each portion. 3.2 Adjust the pH (see notes) 3.3 Allow each portion of chlorinated sample to stand for a predetermined time. Withdraw a portion of the sample and determine the total residual chlorine. 28
  29. 29. CALCULATIONS Calculate the chlorine dosage, in mg/litre, for each increment of chlorinating solution as follows: Chlorine dosage, mg/litre = 2AB Where: A = millilitres of chlorinating solution added to 500 ml of sample. B = milligrams of available chlorine per millilitre of the chlorinating solution. Determine the chlorine consumed, mg/litre, for each increment of chlorine application as follows: On log-log graph paper, plot, for a given chlorine application, temperature, and pH, the chlorine consumed versus the contact time in hours. Determine the value of the chlorine consumed at the intercept of the line with the co-ordinate corresponding to a contact time of 1 hour. Designate the value of this intercept as K. Determine the slop of the line and designate as n. The straight lines for each chlorine application at each temperature and pH are of the general form: DT = K T t n Where: DT = Chlorine consumed at a given temperature . t = contact time in hours. KT = Chlorine consumed after 1 hour, mg/litre at a given temperature. n = Slope of curve. The chlorine consumed can be interpolated between test values by use of the above expression. NOTES 1. Chlorine requirement is the amount of chlorine required to achieve under specified conditions the objectives of chlorination. Chlorine consumed is the amount of chlorine expressed in mg/litre, determined as the difference between the calculated concentration of chlorine applied at zero time and the residual concentration measured at any selected interval of time thereafter. 2. When the anticipated chlorine requirement is less than 600 mg/litre, use the chlorinating solution which is to be used in ultimate plant treatment. When the anticipated chlorine requirement is 600 mg/litre or more, use the appropriate hypochlorite solution. 3. pH Adjustment 3.1 If the pH of the chlorinated sample is higher than the desired range, add hydrochloric acid (1+1) to the chlorinated sample until the pH of sample reaches the upper limit of the desired range. 3.2 If the pH of the chlorinated sample is lower than the desired range, discard the sample and proceed with another series of sample portions, as follows: add sufficient calcium hydroxide solution to bring the pH of the unchlorinated sample portion to the midpoint of the desired pH range. 3.3 If the chlorinating solution is chlorine water, add an additional 0.1 ml of calcium hydroxide solution for each milligram of available chlorine to be applied to the sample. 29
  30. 30. CHLORINE, RESIDUAL (DPD Method, 0.02 to 4.0 mg/litre) SUMMARY OF METHOD In the absence of iodide ion, free chlorine reacts with para-amino diethylaniline (NN-Diethyl-p-Phenylene Diamine abbreviated as DPD) to produce a red colour. Stepwise colour change is carried out to identify monochloramine, dichloramine, and nitrogen trichloride. The individual fractions are determined by titration with ferrous ammonium sulphate. RANGE Upto 4mg/litre with minimum detection limit of 18 micrograms/litre. REAGENTS 1. Water – conforming to specifications Type III, further treated to be free of chlorine demand (see notes). 2. DPD Reagent – Dissolve 0.115g DPD sulphate, [NH2C6H4 N(C2H5)2]. H2SO4. 5H2O], in 50 ml of water containing 8 ml of sulphuric acid (1+3) and 0.2g of EDTA disodium salt. Dilute to 100 ml and store in a brown coloured glass bottle. Prepare fresh after every two weeks or discard it when discoloured. 3. Phosphate Buffer Solution – Dissolve 2.4 g disodium-hydrogen phosphate (Na2HPO4) and 4.6g of potassium-dihydrogen phosphate (KH2PO4) in 50 ml of water. Add 10 ml of EDTA disodium salt (8g/litre) and make up to 100 ml. Add 1 drop of mercuric chloride (20 mg/litre). 4. Sodium Arsenite Solution – Dissolve 0.5g sodium, arsenite (NaAsO2) in 100 ml of water. 5. Potassium Iodide, crystalline. 6. Potassium Iodide solution (5g/litre) – Dissolve 0.5g of potassium iodide in water and dilute to 100 ml. Store in a brown coloured glass bottle. Discard when yellow colour developes. 7. Ferrous Ammonium Sulphate Solution (1ml = 1mg chlorine) – Dissolve 1.106 g of ferrous ammonium sulphate [FeSO4(NH4)2SO4. 6H2O] in water containing 1 ml of Sulphuric acid (1+3) and make up to 1 litre. Standardize against potassium dichromate (for standardization see notes). 8. Potassium Dichromate Standard Solution (0.003N) – Dissolve 0.147 g of potassium dichromate (K2Cr2O7), previously dried at 103o C for 2 hours, in water and dilute to 1 litre. 9. Phenanthroline – Ferrous Sulphate Indicator Solution – Dissolve 1.48 g of 1, 10 – phenanthroline monohydrate, and 0.70 g of ferrous sulphate (FeSO4. 7H2O) in 100 ml of water. PROCEDURE 1. Free Chlorine 1.1 Place 5.0 ml of DPD solution and 5.0 ml of phosphate buffer in a 250 ml titration flask. 1.2 Add 100 ml of sample and mix. 1.3 Titrate with ferrous ammonium sulphate solution until the red colour is discharged. 1.4 Record the volume of ferrous ammonium sulphate in ml used in the titration as A. 2. Monochloramine (NH2Cl) 2.1 To the solution after titration for free chlorine (4.1) add 2 drops of potassium iodide solution (5g/litre) and continue the titration. 2.2 Record the total volume of ferrous ammonium sulphate in ml as B. For free chlorine + monochloramine) 3. Dichloramine (NHCl2) 3.1 To the solution after titration for monochloramine (4.2) add about 1 g of potassium iodide and mix rapidly to dissolve, and allow to stand for 2 minutes. 3.2 Continue titration with ferrous ammonium sulphate. 3.3 Record the total volume of ferrous ammonium sulphate in ml as C (for free chlorine + monochloramine + dichloramine). 4. Nitrogen Trichloride (NCl3) 30
  31. 31. 4.1 Place a small crystal of potassium iodide in a 250 ml titration flask, add 100 ml of sample and mix. 4.2 Transfer the contents (4.4.1) to another flask containing 5 ml each of buffer solution and DPD solution. 4.3 Titrate rapidly with ferrous ammonium sulphate solution. 4.4 Record the volume of ferrous ammonium sulphate in ml as D. 5. Total Available Chlorine 5.1 Place 1 g of potassium iodide in a 250 ml titration flask, add 100ml of sample and mix. 5.2 Transfer the contents (4.5.1) to another flask containing 5 ml each of buffer solution and DPD solution and allow to stand for 2 minutes. 5.3 Titrate with ferrous ammonium sulphate solution and record the volume in ml as V1. CALCULATIONS V1 x 100 1. Total available chlorine, mg/litre as Cl = ------------- V Where: V1 = millilitres of ferrous ammonium sulphate used for total available chlorine. V = millilitres of sample. 2. The following table may be used to determine various constituents: TITRATE VALUE NCl3 – ABSENT NCl3 – PRESENT A Free Chlorine Free Chlorine B – A NH2Cl NH2Cl C – B NHCl2 NHCl2 + ½ NCl3 D - Free chlorine + ½ NCl3 2 (D – A) - NCl3 C – D - NHCl2 INTERFERENCES 1. Copper and dissolved oxygen interfere in measurement, however, this is suppressed by using ETDA in phosphate buffer. 2. Nitrite nitrogen up to 5 mg/litre does not interfere. 3. For accurate results, careful pH control is essential. At the proper pH of 6.2 of 6.5, the red colour produced may be titrated to sharp colourless endpoints. 3.1 The titration should be carried out as soon as the red colour is formed in each step. 3.2 Too low a pH in the first step will tend to make the monochloramine show in the free-chlorine step and the dichloramine in the monochloramine step. 3.3 Too high a pH may cause dissolved oxygen to give colour. 4. Oxidising manganese gives a colour leading erroneous measurement. To correct for this, 5.0 ml buffer solution, one small crystal of potassium iodide and 0.5 ml sodium arsenite solution in titration flask. Add 100 ml of sample and mix. 5.0 ml of DPD solution, mix and titrate with standard ferrous ammonium sulphate until red colour discharged. Subtract the reading ‘A’ as given the procedure or from 4.5 as the case may be. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. For preparing chlorine demand free water, approximately 20 mg/litre of available chlorine to III reagent grade water. Allow the chlorinated to stand about 1 week in the absence of sunlight no residual chlorine remains. 3. For standardizing ferrous ammonium sulphate (1 litre), place 25 ml of 0.003 N potassium dichromate 500 ml titration flask and dilute to about 250 ml and 20 ml of sulphuric acid (sp gr 1.84) and allow solution to 31
  32. 32. cool. Titrate with ferrous ammonia sulphate, using phenanthroline- ferrous sulphate indicator. Calculate the strength of ferrous ammonium sulphate solution as follows: Strength of ferrous ammonium sulphate solution g/litre V1 x N1 x 392 = ------------------- V Where: V1 = millilitres of potassium dichromate solution N1 = normality of potassium dichromate solution V = millilitres of ferrous ammonium sulphate soluion. 32
  33. 33. COPPER (Neocuproine Method, 2 to 1000 micrograms/litre Cu) SUMMARY OF METHOD The copper is reduced with hydroxylamine-hydrochloride. The pH of the aqueous phase is adjusted to 4.0-6.0 with sodium acetate buffer. The cuprous ion is then reacted with neocuproine (2,9 – dimethyl –1, 10 – phenanthroline) and the yellow complex extracted either with chloroform or isoamyl alcohol. The intensity of colour, when extracted with chloroform, is measured at 457 nm and at 454 nm when extracted with isoamyl alcohol. RANGE 20 to 1,000 micrograms/litre Cu (10 mm cell). 2 to 150 micrograms/litre Cu (50 mm cell). 2 to 100 micrograms/litre Cu (100 mm cell). APPARATUS 1. Spectrophotometer for use at 454 and 457 nm. 2. Matched pairs of 10 mm, 50 mm & 100 mm cells. REAGENTS 1. Water – conforming to specifications Type-I. 2. Copper Stock Solution (200 mg/litre) – Place 0.200 g electrolytic grade copper in a 250 ml beaker, add 3 ml of water and 3 ml of nitric acid (sp gr 1.42). After the metal has completely dissolved, add 1 ml sulphuric acid (sp gr 1.84) and evaporate on a hot plate to nearly dryness. Dissolve the residue in water and dilute to 1 litre. 3. Copper Standard Solution (2mg/litre) – Dilute 100 ml of copper stock solution (4.2) to 1 – litre. Again dilute 100 ml of this diluted solution to 1 litre. 4. Hydrochloric Acid (sp gr 1.19). 5. Hydroxylamine Hydrochloride Solution (20%) – Dissolve 40g of hydroxylamine hydrochloride (NH2OH.HCl) in water and dilute to 200 ml. Remove traces of copper from this solution by treating with neocuproine solution and extracting with chloroform or isoamyl alcohol. 6. Neocuproine Solution (1g/litre) – Dissolve 0.1 g of neocuproine in 50 ml of isopropyl alcohol. Dilute to 100 ml with water. 7. Sodium Acetate Solution (275 g/litre) – Dissolve 55g of sodium acetate trihydrate (NaC2H3O2.3H2O) in water and dilute to 200 ml. Remove traces of copper from this solution by treating with hydroxylamine hydrochloride, neocuproine and extracting with chloroform or isoamyl alcohol. 8. Chloroform Solvent – Mix 9 volumes of chloroform (CHCl3) with one volume of isopropyl alcohol. 9. Isoamyl Alcohol, copper free. 10. Isopropyl Alcohol, copper free. CALIBRATION 1. Prepare a series of standards (at least five concentrations) to cover the expected range of copper concentrations by diluting appropriate volumes of copper standard solution (4.3, 1 ml = 2 micrograms Cu) as follows: 1.1 Place the required volumes of copper standard solution (4.3) in 250 ml separatory funnels. 1.2 Add 0.4 ml hydrochloric acid (sp gr 1.19) to each funnel and add water to make 200 ml. 1.3 Prepare a blank (zero standard) by diluting 0.4 ml hydrochloric acid (sp gr 1.19) to 200 ml with water. 1.4 Proceed in accordance with section 6.0 (6.2 to 6.7) and measure the absorbance of each individual standard. 1.5 Use the organic liquid from the bland as a reference solution for the initial spectrophotometer setting. 1.6 Prepare a calibration curve by plotting the absorbance of the standards against the copper content in micrograms. 33
  34. 34. PROCEDURE 1. Transfer 200 ml of acidified (with 0.4 ml hydrochloric acid, sp gr 1.19) and unfiltered sample (for total copper) or 200 ml of filtered (through 0.45 micron filter) and acidified sample (for dissolved copper) into a 250 ml separatory funnel. 2. Add 1 ml of hydroxylamine hydrochloride solution and mix. 3. Add 10 ml of sodium acetate solution and mix. 4. Add 2 to 4 ml of neocuproine solution and shake the funnel and contents for 1 minute. 5. Add 25 ml of chloroform solvent or isoamyl alcohol, shake vigorously for at least 1 minute and allow to stand for 5 minutes. 6. Transfer the organic layer into a dry 50 ml Erlenmeyer flask and add 10 ml of isopropyl alcohol to clear the solution. Make upto 35 ml with chloroform solvent or isoamyl alcohol depending on the extractant used. 7. Measure the absorbance of the organic solution (6.6) at 457 nm (when chloroform solvent is the extractant) using a mixture of 25 ml of chloroform solvent and 10 ml of isopropyl alcohol as a reference solution for initial spectrophotometer setting or at 454 nm (when isoamyl alcohol is the extractant) using a mixture of 25 ml of isoamyl alcohol and 10 ml of isopropyl alcohol as a reference solution. 8. Carry out a blank determination on 200 ml of water with all reagents and extracting in the same manner as for the sample. CALCULATIONS 1. Calculate the concentration of copper in micrograms per litre in the sample, as follows: W x 1000 Copper, micrograms/litre, as Cu = -------------- V Where: W = micrograms of copper determined in accordance with sections 5.0 and 6.0. V = millilitres of sample used. PRECISION 1. The overall precision of this method may be expressed as follows: ST = 0.008 X + 0.9 Where: ST = overall precision. X = determined concentration of copper, micrograms/litre. INTERFERENCES 1. None of the ions commonly found in low solids water interfere with the test. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. A polythene bottle must be used for sample collection. Hydrochloric acid (sp gr 1.19) should be added to the filtered sample for total recoverable copper immediately at the time of collection. The volume of acid should be sufficient to neutralize the sample to pH 4 (using narrow range pH paper) and then add 2.0 ml for each litre of sample. 3. Soak all new glassware in hot nitric acid (1+9) for several hours. To ensure the conditioning of glassware, rinse it with water and run a copper determination (blank) on copper free water. Repeat until the copper value is less than 4 micrograms per litre. After carrying out the test, always rinse the glassware with organic solvent, followed by water. Always keep the glassware soaked in nitric acid (1+9) until used again. Discard any glassware that appears etched or scratched. 4. If the sample contains more than maximum concentration of copper specified in the range, a smaller size sample should be diluted to 200 ml with copper free water containing 0.4 ml of hydrochloric acid (sp gr 1.19) per 200 ml of solution. 34
  35. 35. 5. Normally, 2 ml of neocuproine solution is sufficient in a test. 4 ml of the reagent should be used when the sample contains more than 100 micrograms of copper or when it is high in heavy metal ions. 6. The blank determination made for calibration in section 5.0 compensates for copper in both the reagents and 200 ml of water. When the test water contains less than 10 micrograms/litre of copper, it is important (in 6.7) to compensate only for the copper in the reagents and not to include the few micrograms per litre of copper found in copper free water. The reagent blank is found, by extracting the copper from two 200 ml aliquots of copper free water. In aliquot the normal values of reagents in hydrochloric acid, hydroxylamine hydrochloride, sodium acetate and neocuproine solution are used and in the other aliquot twice the normal values of reagents are used. The organic extract from the normal blank used as reference solution for initial spectrophotometer setting and the blank obtained from double reagents is measured against the normal blank. The correct value for copper is found in the unknown sample (6.7) by subtracting from it the value for the reagent blank. 35
  36. 36. HARDNESS – TOTAL, CALCIUM AND MAGNESIUM SUMMARY OF METHOD For the determination of total hardness the sample pH is adjusted to 10 with ammonium chloride – ammonium hydroxide buffer solution and then titrated with EDTA (ethylene diamine tetraacetic acid or its sodium salt) using Erichrome Black-T as indicator. For calcium hardness determination the sample pH is adjusted to 12 to 13 with Sodium Hydroxide and then titrated with EDTA using ammonium purpurate as indicator. Magnesium is determined by difference. RANGE 1 to 1000 mg/litre of Ca plus Mg expressed as Ca. REAGENTS 1. Water – conforming to specifications Type II. 2. Buffer Solution – Dissolve 67.6 g of ammonium chloride in 200 ml of water. Add 570 ml of ammonium hydroxide (sp gr 0.90) and mix. Add 5.0 g of magnesium salt of EDTA and dilute to 1 litre with water. 3. Sodium Hydroxide Solution (8% w/v). 4. Ammonium Purpurate – Mix thoroughly 1.0g of ammonium purpurate with 200 g of sucrose. 5. Eriochrome Black-T – Dissolve 0.4 g of Eriochrome Black-T in 100 ml of water. This solution has a self life of 1 week. Alternatively a dry powder mixture of 0.5g of Eriochrome Black-T and 100 g of sodium chloride can be used. This mixture has a shelf life of 1 year. 6. Calcium Standard Solution (1ml = 0.4 mg Ca) – Suspend 1.000g of calcium carbonate (dried at 180o C for 1 hour) in 600 ml of water and dissolve with a minimum of dilute hydrochloric acid. Dilute to 1 litre with water. 7. EDTA standard Solution (0.01M, 1ml = 0.4mg Ca or 0.243mg Mg) – Dissolve 3.72 g of Na2EDTA dihydrate [dried overnight over Sulphuric acid (sp gr 1.84) in a desiccator] in water and dilute to 1 litre. Standardize against standard calcium solution (3.6). PROCEDURE 1. Total Hardness (Ca plus Mg) 1.1 Pipet 50.0 ml of sample into a titration flask and adjust the pH to 7-10 by the dropwise addition of ammonium hydroxide (sp gr 0.90). 1.2 Add 1 ml of buffer solution. 1.3 Add 4 to 5 drops of Eriochrome Black T indicator or approximately 0.2g of powdered indicator. 1.4 Titrate with EDTA standard solution. The end point will be indicted by colour change from pink to clear blue. 1.5 Record the volume of EDTA solution required in the titration. 1.6 Determine a reagent blank correction by similarly titrating 50.0 ml of water including all added reagents. 2. Calcium Hardness 2.1 Pipet 50.0 ml of sample into a titration flask and add 1 ml of sodium hydroxide solution. 2.2 Add 0.2 g ammonium purpurate indicator and mix. 2.3 Titrate with EDTA standard solution. The endpoint will be indicated by colour change from pink to purple. 2.4 Record the volume of EDTA solution required to titrate the calcium. 2.5 Determine a reagent blank correction by similarly titrating 50.0 ml of water including all added reagents. CALCULATIONS V1 x M x 10,000 1. Total hardness, mg/litre as CaCO3 = ----------------------- V V2 x M x 10,000 36
  37. 37. 2. Calcium hardness, mg.litre as CaCO3 = ----------------------- V 3. Magnesium hardness, mg/litre as CaCO3 = Total hardness, mg/litre as CaCO3 minus calcium hardness, mg/litre as CaCO3. Where: V1 = millilitres of standard EDTA solution required for magnesium plus calcium (4.1.5) minus the blank determination (4.1.6). V2 = millilitres of standard EDTA solution required for calcium (4.2.4) minus the blank determination (4.2.5). V = millilitres of sample taken. M = molarity of standard EDTA solution. PRECISION 1. The precision of this method for calcium (13 to 88 mg/ litre as Ca) may be expressed as follows: Sr = 0.006 X + 0.62 So = 0.006 X + 0.51 Where: Sr = overall precision. So = single operator precision. X = determined concentration of calcium, mg/litre as Ca. 2. The precision of this method for magnesium (2.5 to 36 mg/litre, as Mg) may be expressed as follows: ST = 0.017 X + 0.85 SO = 0.002 X + 0.70 Where: ST = overall precision. SO = single operator precision. X = determined concentration of magnesium, mg/litre as Mg. INTERFERENCES 1. EDTA reacts with several metallic ions. The interference due to these ions can be minimized by addition of hydroxylamine and cyanide. Metal concentrations as high as 5 mg/litre Fe, 10 mg/litre Mn, 10 mg/litre Cu, 10 mg/litre Zn and 10 mg/litre Pb can be tolerated when hydroxylamine and cyanide are added. 2. In the titration of total hardness the higher oxidation states of manganese above 2 reacts rapidly with the indicator to form discoloured oxidation products. Hydroxylamine hydrochloride reagent is used to reduce manganese to divalent state. The divalent manganese interference can be eliminated by addition of one or two small crystals of potassium ferrocyanide. 3. In the presence of aluminium concentrations in excess of 10 mg/litre, the blue colour which indicates that the end point has been reached will appear and then on short standing will revert to red. 4. In the titration of calcium, ammonium purpurate reacts with strontium but not with magnesium or barium. In the presence of strontium, the endpoint is slow and the titration is not strictly stoichiometric. Barium does not titrate as calcium, but affects the indicator in some unknown way so that no endpoint or a poor endpoint is obtained. Barium can be removed by precipitation with Sulphuric acid. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. If total recoverable calcium and magnesium concentration are being determined, acidify the sample with nitric acid (sp gr 1.42) to a pH of 2 or less (check with the help of narrow range pH paper) immediately at the time of collection; normally about 2 ml/litre is required. 3. If dissolved calcium and magnesium concentrations are being determined, filter the samples through a 0.45 micron membrane filter and acidify the filtrate with nitric acid (sp gr 1.42), 2 ml/litre. 4. The upper and lower limits of concentration given in range (3.0) may be extended either by dilution or use of micro apparatus. 37
  38. 38. 5. The titration of the sample with EDTA should be completed within 5 minutes of the buffer addition. If more than 15 ml titrant is required, take a smaller sample aliquot and repeat the test. 6. Fluorescein methylene iminodiacetic acid indicator can be used in place of ammonium purpurate used in the titration of calcium. The end point will be indicated by a colour change from deep green to purple. This indicator is prepared by grinding 0.2g of fluorescein methylene iminodiacetic acid and 0.12g of thymol-phthalein with 20 g of potassium chloride to 300 to 425 micron size. 38
  39. 39. HYDRAZINE (p-Dimethylamino Benaldehyde Method, 4 to 100 micrograms/litre). SUMMARY OF METHOD The sample is reacted with a solution of para-dimethyl aminobenzaldehyde to produce a yellow colour. The intensity of the colour is measured colorimetrically at a wavelength of 458 nm. RANGE 4 to 100 micrograms/litre N2H4. APPARATUS 1. Spectrophotometer suitable for measurement at 458 nm. 2. Matched pairs of 10 mm and 50 mm cells. REAGENTS 1. Water – conforming to specifications Type II. 2. Hydrazine standard solution (1 ml = 100 microgram N2H4) – Dissolve 0.328 g of hydrazine dihydro chloride (N2H4.2HCl) in 100 ml of water and 10 ml of hydrochloric acid (sp gr 1.19). Dilute to 1 litre with water. 3. Hydrochloric Acid (sp gr 1.19). 4. Hydrochloric Acid (1+9) – Mix 1 volume of hydrochloric acid (sp gr 1.19) with 9 volumes of water. 5. Hydrochloric Acid (1+99) – Mix 1 volume of hydrochloric acid (sp gr 1.19) with 99 volumes of water. 6. Para Dimethylaminobenzaldehyde Solution – Dissolve 4.0 g of p- dimethylaminobenzaldehyde in 200 ml of methyl alcohol and 20 ml of hydrochloric acid (sp gr 1.19). Store in a dark bottle, out of direct sunlight. CALIBRATION 1. Prepare a series of hydrazine standards by making appropriate dilutions of the hydrazine solution (1ml = 100 micrograms N2H4) with hydrochloric acid (1+99), so that a 50 ml aliquot of each dilution will contain the desired quantity of hydrazine (0.2 to 5.0 micrograms). 2. Pipet 50 ml portions of the hydrazine standard solutions as prepared in section 5.1 into 100 ml cylinders and proceed in accordance with section 6.0 (6.3 – 6.4). 3. Prepare a calibration curve by plotting transmittance against micrograms of hydrazine. PROCEDURE 1. Place 5.0 ml of hydrochloric acid (1+9) into a 100 ml measuring flask. Collect that sample upto the mark. 2. Transfer the sample, to the cylinder that will contain approximately 0.20 to 5.0 micrograms of hydrazine and make the final volume to 50 ml with water. 3. Add 10.0 ml of p-dimethylaminobenzaldehyde solution, mix and allow to stand for 10 minutes. 4. Measure the transmittance of the solution of 458 nm by adjusting the spectrophotometer at 100% transmittance with the blank, prepared by adding 10.0 ml of p-dimethylaminobenzaldehyde to 50 ml of water. CALCULATIONS 1. Calculate the hydrazine concentration in micrograms per litre as follows: W x 1000 2. Hydrazine, micrograms/litre = -------------- V Where: W = micrograms of hydrazine found in accordance with section 6.0. V = millilitres of sample. PRECISION The precision of this method may be expressed as follows: SO = (0.99 X + 0.041) / V St = (1.08 X + 0.081) / V Where: SO = single operator precision expressed in mg/litre of hydrazine. St = overall precision expressed in mg/litre. of hydrazine. X = concentration of hydrazine determined in mg/litre. 39
  40. 40. V = millilitres of sample taken for test. INTERFERENCES 1. The hydrazine content may be diminished by oxidizing agents collected with the sample or absorbed by it prior to testing. 2. Colours, that absorb in the prescribed wavelength, also, interfere. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. The purity of hydrazine dihydrochloride may be checked by iodimetric methods. 3. Para-dimethylaminobenzaldehyde reagent obtained from different manufacturers produce different intensities of colour in solution. It is necessary that each new supply of reagent be tested on standard solutions before using with previously determined calibration curves. 4. The sample should be analyzed as quickly as possible after collection since hydrazine undergoes auto-oxidation, as well as, oxidation by oxidizing agents. Such agents may be in the sample or may enter the sample from the atmosphere. If it is suspected that oxidation of the hydrazine in the sample is occurring in the interval between collection and analysis or if the sample is not to be analyzed immediately then the sample is to be collected under acid by placing 5.0 ml of hydrochloric acid (1+9) in a 50 ml volumetric flask, and collecting sufficient sample to make total volume to 50 ml. When the sample is collected under acid, the step 6.1 of section 6.0 should be deleted and in step 6.2 hydrochloric acid (1+99) to be used, instead of water for dilution. 40
  41. 41. IRON (Bathophenanthroline Method, 200 micrograms/litre and less) SUMMARY OF METHOD Iron is reduced with hydroxylamine hydrochloride and then reacted with bathophenanthroline (4, 7-diphenyl – 1, 10 phenanthroline). The red ferrous complex is extracted with n-hexyl or isoamyl alcohol and the intensity of the colour is measured at 533 nm. RANGE 4 to 80 micrograms/litre Fe with 100 mm cell. 10 to 160 micrograms/litre Fe with 50 mm cell. APPARATUS 1. Spectrophotometer for use at 533 nm. 2. Matched pair of 50 mm and 100 mm cells. REAGENTS 1. Water – conforming to specifications Type II. 2. Alcohol, n-Hexyl or Isoamyl. 3. Alcohol, Methyl, ethyl or Isopropyl. 4. Bathophenanthroline Solution (0.835 g/litre) – Dissolve 0.0835 g of bathophenanthroline in 100 ml of ethyl alcohol. 5. Hydrochloric Acid (1+1) – Mix equal volumes of hydrochloric acid (sp gr 1.19) and water. 6. Hydroxylamine Hydrochloride Solution (10%). 7. Iron Standard Solution (1ml = 1 microgram Fe) – Dissolve 0.1000 g of pure iron in 10 ml of hydrochloric acid (1+1) and 1 ml of bromine water. Boil to remove excess bromine. Add 200 ml of hydrochloric acid (1+1), cool, and dilute to 1 litre with water (solution A). To 10 ml of solution A add 12 ml of hydrochloric acid (1+1) and dilute to 1 litre with water. 8. Hydrochloric Acid (1+9) – Mix 1 volume of hydrochloric acid (sp gr 1.19) with 9 volumes of water. 9. Ammonium hydroxide (1+1) – Mix equal volumes of ammonium hydroxide (sp gr 0.90) and water. CALIBRATION 1. Prepare a series of standards (at least five concentrations) to cover the expected range of iron concentrations by diluting appropriate volumes of Iron standard solution (4.7, 1 ml = 1 microgram Fe) as follows: 1.1 Place the required volumes of Iron standard solution (4.7) in 125 ml separatory funnels. 1.2 Add water to make 50 ml. 1.3 Add 2.0 ml of hydroxylamine hydrochloride solution and mix. 1.4 Add 3.0 ml of bathophenanthroline solution and shake for 30 seconds. 1.5 Add ammonium hydroxide (1+1) dropwise with mixing until a distinct turbidity forms. Add hydrochloric acid (1+9) dropwise with mixing until 1 drop clears the solution. Allow to stand for 1 minute. 1.6 Proceed in accordance with section 6.0 (6.5 to 6.8). 1.7 Simultaneously carry out a blank determination containing no added iron using 50 ml of water and all reagents. PROCEDURE 1. Transfer a volume of sample (filtered through 0.45 micron membrane filter) containing not more than 8 micrograms of iron, to a 125 ml separatory funnel. 2. Add 1.0 ml of hydroxylamine hydrochloride solution and mix. 3. Add 3.0 ml of bathophenanthroline solution and shake for 30 seconds. 4. Add ammonium hydroxide (1+1) dropwise with mixing until a distinct turbidity forms. Add hydrochloric acid (1+9) dropwise with mixing until 1 drop clears the solution. Allow to stand for 1 minute. 5. Add 15.0 ml of n-hexyl or isoamyl alcohol and shake vigorously for 1 minute. Allow to stand for 15 minutes. 6. Discard the aqueous layer and transfer the alcohol layer into a 25 ml volumetric flask. 7. Add 10 ml of methyl, ethyl or isopropyl/alcohol to the funnel and wash the internal surfaces by rolling and tumbling the funnel. Transfer this 41
  42. 42. alcohol into the previous alcohol extract (6.6). Dilute to the 25 ml mark with the alcohol used for extraction (6.6). 8. Measure the colour of the alcohol solution at 533 nm, adjusting the spectrophotometer to zero absorbance reading with a reference solution of 15 ml of alcohol used in step 6.5 and 10 ml of alcohol used in step 6.7. 9. Carry out a blank determination on 50 ml of water, with all reagents and extracting in the same manner as for the sample. CALCULATIONS 1. Calculate the concentration of iron in micrograms per litre in the sample as follows: W x 1000 Iron, micrograms/litre = ------------- V Where: W = micrograms of iron, read from the calibration curve. V = millilitres of original sample used. PRECISION 1. The single operator and overall precision varies with the determined concentration and may be expressed as follows: SO = 0.008 X + 0.92 St = 0.039 X + 1.47 Where: SO = single operator precision, micrograms/litre. St = overall precision, micrograms/litre. X = determined concentration micrograms/litre. INTERFERENCES 1. If pH is between 3.3 and 3.7 a 1 mg/litre concentration of the following ions does not interfere with the test : copper, manganese, aluminium, zinc, magnesium, sodium, silica, nitrate and orthophosphate. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. If either dissolved or ferrous iron is to be determined, the sample must be analyzed as soon as possible after collection. If only total iron is to be determined, the sample should be immediately acidified with 2 ml of hydrochloric acid (sp gr 1.19) per 50 ml. 3. Soak all new glassware is hot hydrochloric acid (1+1) for 2 hours. Drain and rinse at least 3 times with iron free water. Before and after use, clean all glassware by making an iron extraction of each piece (without separating the alcohol – water layers). Drain and flush with iron free methyl alcohol, ethyl alcohol, or isopropyl alcohol. 4. If iron content is high in hydrochloric acid (4.5) causing a high blank, distil in an all glass apparatus, rejecting the first 50 ml and the last 100 ml of distillate. 5. Hydroxylamine hydrochloride solution (4.6) can be purified as follows: Adjust pH to 3.5 using a pH meter by dropwise addition of ammonium hydroxide (1+1) and hydrochloric acid (1+9). Transfer to a separatory funnel, add 6.0 ml of bathophenanthroline solution and shake. Allow to stand for 1 minute. Add 20 ml of n-hexyl or isoamyl alcohol and shake for 1 minute. Allow to stand for 15 minutes. Remove the aqueous layer and discard alcoholic layer. Repeat extraction by again adding 3 ml of bathophenanthroline solution and 20 ml of alcohol. Discard the alcohol. If no further extractions are indicated make an extraction with alcohol alone and allow to stand for a long time to remove all of the alcohol layer. Discard the alcohol layer. 6. For total iron determination, heat the sample for 1 hour at 60o C with 4 ml of hydrochloric acid (1+1) and 2 ml of hydroxylamine hydrochloride solution. Thioglycolic acid can also be used for solubilising unreactive iron. 42
  43. 43. ORGANIC MATTER (Potassium Permanganate Consumption Method) SUMMARY OF METHOD The sample is reached with a standard solution of potassium permanganate at 27o C for 4 hours and the residual permanganate is determined iodometrically. RECORDS 1. Water – conforming to specifications Type III. 2. Potassium Permanganate Stock Solution – Dissolve 3.951g of potassium permanganate (previously dried at 105o C) in water and dilute to 1 – litre. Standardize with sodium oxalate. (see notes). 3. Potassium Permanganate Standard Solution (N/80) (1ml = 0.1 mg oxygen) – Dilute 100 ml of potassium permanganate stock solution (2.2) to 1 litre. 4. Sulphuric Acid (1+3) – Mix 1 volume of Sulphuric acid (sp gr 1.84) with 3 volumes of water. Add standard permanganate solution until a very faint pink colour persists after 4 hours. 5. Potassium Iodide. 6. Sodium Thiosulphate Stock Solution – Dissolve 31.2 g of sodium thiosulphate and 6g of sodium bicarbonate in water and dilute to 1-litre. 7. Sodium Thiosulphate Standard Solution (N/80) – Dilute 100 ml of sodium thiosulphate stock solution (2.6) to 1-litre. Standardize with N/80 potassium permanganate solution. 8. Starch Indicator Solution – Make a paste of 1g of soluble starch and mix into 1 litre of boiling water. Add 20g of potassium hydroxide, mix, and allow to stand for 2 hours. Add 6ml of glacial acetic acid, mix, and add sufficient hydrochloric acid to adjust the pH to 4.0 (Check with a narrow range pH paper). This has a shelf life of 1 year. PROCEDURE 1. Place 100 ml of the sample into a clean, glass stoppered bottle of 250 ml capacity and place in a thermostat at 27o C. 2. When the temperature of the sample becomes 27o C, add 4ml of Sulphuric acid (1+3) and 10ml of potassium permanganate solution (N/80). Mix well and allow to stand for 4 hours at 27o C protected from sunlight. 3. Add few crystals of potassium iodide (0.2-0.3g) and titrate the librated iodine with standard sodium thiosulphate solution (N/80) using starch indicator. 4. Run a blank of 100ml of water under the same conditions. CALCULATIONS 1. Calculate the milligrams of oxygen consumed per litre of sample as follows: Oxygen consumed, mg/litre = V2 – V1 Where: V2 = millilitres of standard sodium thiosulphate used for blank titration. V1 = millilitres of standard sodium thiosulphate used for sample titration. 43
  44. 44. OXYGEN, DISSOLVED (Indigo Carmine Method, less than 60 micrograms/litre) SUMMARY OF METHOD Dissolved oxygen reacts, under alkaline conditions, with the indigo carmine solution to produce a progressive colour change from yellow- green through red to blue and blue-green. The colour developed in the sample is compared with colour standards representing different concentrations of dissolved oxygen. RANGE Less than 60 micrograms/litre. APPARATUS 1. Burette, 25 or 50 ml. 2. Sampling Bucket, with an overflow at least 20 mm above the top of the sampling vessel. 3. Sampling Vessels – Nessler type 60 ml tubes or 300 ml BOD bottles having a raised lip around the neck and glass stoppers ground to a conical lower tip. REAGENTS 1. Water – conforming to specifications Type II. 2. Colour standards, stock solutions. 2.1 Red Colour Standard-Dissolve 59.29g of cobaltous chloride (CoCl2.6H2O) in hydrochloric acid (1+99) and dilute to 1 litre. 2.2 Yellow Colour Standard-Dissolve 45.05g of ferric chloride (FeCl3.6H2O) in hydrochloric acid (1+99) and dilute to 1 litre. 2.3 Blue Colour Standard – Dissolve 62.45g of cupric sulphate (CuSO4. 5H2O) in hydrochloric acid (1+99) and dilute to 1-litre. 2.4 Hydrochloric Acid (sp gr 1.19) 2.5 Hydrochloric Acid (1+99)-Mix 1 volume of hydrochloric acid (sp gr 1.19) with 99 volumes of water. 2.6 Indigo Carmine Solution-Dissolve 0.18g of indigo carmine and 2.0g of dextrose (or glucose) in 50ml of water. Add 750 ml of glycerin and mix thoroughly. 2.7 Indigo Carmine-Potassium Hydroxide Reagent-In a small bottle mix 4 parts by volume of indigo carmine solution (4.2.6) with 1 part of potassium hydroxide solution (4.2.8). Allow to stand until the initial red colour changes to lemon yellow. Prepare fresh solution daily. 2.8 Potassium Hydroxide Solution (530g/litre)- Dissolve 530g of potassium hydroxide in water and dilute to 1 litre. CALIBRATION 1. Prepare a series of colour standards as listed below: EQUIVALENT DISSOLVED OXYGEN (micrograms/litre) MILLILITRES OF COLOUR STANDARDS RED YELLOW BLUE 0 0.75 35.0 - 5 5.0 20.0 - 10 6.25 12.5 - 15 9.4 10.0 - 20 13.0 6.4 - 25 14.4 3.8 - 30 14.6 3.3 0.2 35 15.1 2.9 1.1 40 15.5 2.4 2.2 45 16.1 2.0 2.8 50 18.3 1.7 8.1 55 21.7 1.4 13.1 60 25.0 1.0 15.0 44
  45. 45. 2. Place the amounts of stock solutions listed above in 300 ml borosilicate glass stoppered reagent bottles. Add 3.0 ml of hydrochloric acid (sp gr 1.19) to each. Dilute to neck of the bottle with water. Stopper and mix by inversion. Store in a dark place. PROCEDURE 1. Place a clean sampling vessel in the sampling bucket and collect the sample under water. Allow the sample to overflow for several minutes. 2. Fix a burette such that its tip dips into the overflowing sample to a depth of 10 to 15 mm. 3. Fill the burrette with indigo carmine-potassium hydroxide reagent. Drain about 1ml of reagent into the overflowing sample, and allow the sample to flush for 1 minute. 4. Remove the sample tubing from the sampling vessel. 5. Quickly introduce 0.8ml of the reagent if 60 ml tube is used or 4ml of reagent if a BOD bottle is used, stopper the vessel and mix by inversion. 6. Place the vessel on a white surface and match its colour with the standard by viewing at a 45o angle using a ‘Cool’ white fluorescent lamp for illumination. PRECISION 1. The single operator precision of this method may be expressed as follows: SO = 0.052 X + 0.7 Where: SO = single operator precision X = concentration of dissolved oxygen determined, micrograms/litre. INTERFERENCES 1. Tannin, hydrazine, and sulphate do not interfere up to 1 mg/litre. 2. Ferric iron, cyclohexylamine, and morpholine up to 4 mg/litre can be tolerated. 3. Ferrous iron will produce low results and copper will cause high results. 4. In samples, where ferrous iron and copper are present, their combined effect is frequently zero. 5. Nitrate is a possible interference. NOTES 1. Reagent grade chemicals should be used for preparing the reagents. 2. All colour stock solutions should be stock in coloured bottles to prevent fading. 3. Indigo carmine solution (4.2.6) is stable for 30 days if stored in a refrigerator. 4. In the procedure (6.1), the sample flow should be between 500 to 1000 ml/minute when using 300 ml bottle, or 100 to 200 ml/minute when using 60 ml sample tubes. 5. In the procedure (6.6), the colours should be matched as soon as possible after mixing the reagents and sample, since the colours are not stable for more than 30 minutes and air leakage may cause a change in colour. 6. The sample should be analysed as soon as possible after the collection. 45
  46. 46. OXYGEN DEMAND, BIOCHEMICAL (Dissolved Oxygen Loss Method) SUMMARY OF METHOD The sample is incubated at 20o C for 5 days. Dissolved oxygen is measured initially and after incubation. The BOD is computed from the difference between initial and final dissolved oxygen (DO). APPARATUS 1. Incubation Bottles - 250 to 300 ml capacity with ground glass stoppers. 2. Air Incubator – thermostatically controlled at 20+10 C. All light should be excluded to prevent possibility of photosynthetic production of DO. REAGENTS 1. Dilution Water – Add 0.3 g of sodium bicarbonate per litre of Type II water. PROCEDURE 1. Adjust the temperature of a suitable portion of the well mixed sample to 20o C. Remove the oxygen or excess air by maintaining the sample under vacuum for 10 minutes using laboratory vacuum pump. 2. Fill completely two incubation bottles (250 or 300 ml capacity) with the sample as treated above (4.1). Allow to stand for 15 minutes. 3. Determine the dissolved oxygen in one bottle by the Iodometric method and in the other after 5 days incubation in darkness in the stoppered bottle at 20o C. CALCULATIONS 1. Calculate the BOD of the sample as follows: Bichemical oxygen demand (BOD), mg/litre = D1 – D2 (5 days at 20o C). Where: D1 = initial dissolved oxygen content, mg/litre. D2 = dissolved oxygen content after 5 days incubation, mg/litre. INTERFERENCES 1. Samples for BOD analysis may degrade significantly during storage, resulting in low BOD values. This can be minimized by analyzing the sample promptly or cooling it to 4o C or below. Analysis should be done before 24 hours after grab sample collection. NOTES 1. The dissolved oxygen content of the sample before incubation shall be approximately 9 mg/litre or preferably less. 2. For samples of doubtful purity, the sample should be mixed with dilution water in the ratio 1:1 at 20o C. Further dilutions shall be used if necessary to ensure that not more than half the oxygen is consumed during the incubation. Determine the dissolved oxygen before and after incubation and calculate the result using the appropriate dilution factor. 46

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