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CONTENT… Introduction Need for automation Objective of automation Advantages automatic analyses Unit operations in chemical analysis Types of automated analysis Flow-injection analysis Discrete automatic systems Reference2
INTRODUCTION … Automation is the performance of operations without human intervention. Automation may involve operation like the preparation of samples, the measurements of responses, and the calculation of results.3
NEED FOR AUTOMATION… The partial or complete replacement of human participation in laboratory process. Increasingly stricter control of growing number of samples in which a large number of analytes are to be determined at increasingly low concentration. Cost reduction.4
OBJECTIVE OF AUTOMATION… Automation is used for : Facilitating an analytical method or technique Processing of large number samples Determination of several components in the same sample Reduction of human participation To avoid error Process ( industrial or otherwise ) control Lowering consumption of sample and/or reagents5
Analytes , which are sometimes present in very low concentration in sample Reagents , some of which are rare or expensive, even unstable Rapidity Economy , in personnel and material expenditure Precision, closely related to the elimination of both definite and indefinite errors arising from human factors Data generation6
ADVANTAGES OF AUTOMATIC ANALYSES… Automated instruments offer a major economic advantage because of their savings in labor costs. Their speed, which is frequently significantly greater than that of manual devices. So, the number of determination per day can be much higher than with manual methods. A well-designed analyzer can usually produce more reproducible results over a long period of time than can an operator employing a manual instrument. The ability to process samples in situation that7 would be dangerous for humans.
UNIT OPERATIONS IN CHEMICALANALYSIS... All analytical methods can be broken down into a series of eight steps, or unit operations, any one of or more can be automated. The next table lists the steps in the order in which they occur in a typical analysis.8
TYPES OF AUTOMATED ANALYSIS… Automatic analytical systems are of two general types: 1) Discrete analyzers 2) Continuous-flow analyzers9
1) Discrete analyzers… In this , individual samples are maintained as separate entities and kept in separate vessels throughout each unit operation. The system has many moving parts. Ex. Discrete automatic analyzer Advantage: Cross contamination among samples is totally eliminated. Inexpensive and reliable10
2) Continuous-flow analyzers.. In this , the sample becomes a part of a flowing stream where several of the steps take place. Ex. Flow injection analysis Here, interaction among samples are always concern. So, special precaution are required to minimize sample contamination.11
FLOW-INJECTION ANALYSIS... Flow-injection methods are an outgrowth of segmented-flow procedures, which were widely used in clinical laboratories in the 1960s and 1970s for automatic routine determination of a variety of species in blood and urine samples for medical diagnostic purposes. In segmented-flow system , samples were carried through the system to a detector by flowing aqueous solution.12
Instrumentation... In this, a peristaltic pump moves colorimetric reagent directly into a valve that permits injection of samples into the flowing stream. The sample and reagent then pass through a 50 cm reactor coil where the reagent diffuses into the sample plug and produces a colored product by sequence of reactions. From the reactor coil, the solution passes into a flow- through photometer and the signal output from this13 system for a series of standards .
Sample and reagent transport system... Ordinarily, the solution in a flow-injection analysis is moved through the system by a peristaltic pump, a device in which a fluid (liquid or gas) is squeezed through plastic tubing by rollers.14
Sample injectors and detectors... The injectors and detectors employed in flow- injection analysis are similar in kind and performance requirements to those used in HPLC. Sample size for flow injection procedure ranges from 1μL to 200 μL. For successful analysis, injectors must not disturb the flow of the carrier system. The most common detectors in flow injection are spectrophotometer, photometer and fluorometer.15
Separations in FIA... Separations by dialysis, by liquid/liquid extraction, and by gaseous diffusion are readily carried out automatically with flow-injection systems. 1. Dialysis and gas diffusion 2. Extraction16
1) Dialysis and gas diffusion... Dialysis is often used in continuous-flow methods to separate inorganic ions, such as chloride or sodium or small organic molecules, such as glucose, from high-molecular-weight species such as proteins. It is used for determination of ions and small molecules in whole blood stream or serum. Gas diffusion from a donor stream containing a gaseous analyte to an acceptor stream containing reagent that permits its determination.17
2)Extraction... Another common separation technique readily adapted to continuous-flow methods is extraction. Ex. A system for the colorimetric determination of an inorganic cation by extracting an aqueous solution of the sample with chloroform containing a complexing agent such as 8-hydroxyquinoline. It is important to reiterate that none of the separation procedures in FIA methods are complete.18
analysis... After injection with a sampling valve, it moves through tubing, so band broadening or dispersion takes place. In this, convection arising from laminar flow and creating a parabolic front and skewed zone profile. Diffusion also causes band broadening. Two types of diffusion occur: radial (perpendicular the flow direction) and longitudinal(parallel to the flow direction). At low flow rate, radial diffusion is the major source of dispersion. So, dispersion by both convection and radial19 diffusion occur.
Dispersion... Dispersion D is defined by the equation D = co/c where , co = analyte concentration of the injected sample and c = peak concentration at the detector. Dispersion is influenced by three interrelated and controllable variables: sample volume, tube length, and pumping rate.20
Applications of flow-injection analysis… In the flow-injection literature, the terms limited dispersion, medium dispersion, and large dispersion are frequently encountered where they refer to dispersions of 1 to 3, 3 to 10, and greater than 10, respectively.21
1) Limited-dispersion applications: Limited-dispersion flow-injection techniques have found considerable application for high-speed feeding of such detector systems as flame atomic absorption and emission as well as inductively coupled plasma . 2)stopped flow methods: It is used for kinetic measurement. 3)flow injection titration: Titration can also be performed continuously in a flow injection apparatus.22
DISCRETE AUTOMATIC SYSTEMS... A wide variety of discrete automatic systems are offered by numerous instrument manufacturers. Some of these devices are designed to perform one or more unit operation. For ex. Determination of nitrogen in organic compounds or determination of glucose in blood.23
Automatic sampling and sampledefinition of liquids and gases... This device consists of a movable probe, which is a syringe needle or a piece of fine plastic tubing supported by an arm that periodically lifts the tip of the needle or tube form the sample container and positions it over a second container in which the analysis is performed.24
Robotics... The robotic system is controlled by a microprocessor that can be instructed to bring samples to the master laboratory station where they can be diluted, filtered, partitioned, ground, centrifuged, extracted, and treated with reagents. For general purpose laboratory robots, robotics units are designed for specific tasks such as loading and unloading of microtiter.25
REFERENCE Skoog D.A. , “Instrumental Analysis” , second edition, New Delhi, 1015 Gary D. Christian, “Analytical Chemistry”, 6th edn, page no 660. Hobart H. Willard, Lynne L. Merrit, “Instrumental Methods of Analysis”, 7th edn, page no- 786. N. Gray, M. Calvin, S C Bhatia, “Instrumental Methods of Analysis”, page no-2726