4. Comparison of Techniques ICP-MS ICP-AES GFAAS FAAS Detection Limits Excellent Good Excellent Good Productivity Excellent Excellent Low Good Precision 1-3% 0.3 – 2 % 1 – 5 % 0.1 – 1 % Chemical Interferences Moderate Few Many Many Ionization Minimal Minimal Minimal Some Mass Effects High on low mass None None None Dissolved solids 0.1 – 0.4 % 2 – 25 % Up to 20 % 0.5 – 3 % # Elements 75 73 50 68 Sample Usage Low Medium Very Low High Isotope Analysis Yes No No No Method Development Skill required Skill required Skill required Easy Running Costs High High Medium Low Capital Costs Very high High Medium Low
5. ICP-MS Components • Sample Introduction • Plasma Generation • Interface • Ion Optics • Mass Analyzer • Vacuum System
13. The Plasma • A plasma is a cloud of ionized gas • Plasma temperature 6000 - 7000 K • Most elements >90% ionized • Singly charged positive ions predominate • Small molecular and doubly charged ion population • Complete elemental analysis in a single determination
25. Elements analysed by ICP-MS in ARD Element Name Element Symbol Element Symbol Element Symbol Arsenic As Lithium Li Barium Ba Manganese Mn Beryllium Be Mercury Hg Bismuth Bi Nickel Ni Cadmium Cd Rubidium Rb Cesium Cs Selenium Se Chromium Cr Silver Ag Cobalt Co Strontium Sr Copper Cu Thallium Tl Gallium Ga Uranium U Indium In Vanadium V Lead Pb Zinc Zn
11/21/11 This is a overview of the processes that take place for a metal ion (M) as it enters the torch and passes through the plasma.
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11/21/11 The interface assembly provides a means of sampling the atmospheric pressure gases created in the plasma into a vacuum chamber and separates most of the unwanted gas stream from the ion beam. All ICP-MS instruments have one. Assembly always consists of two metal cones with small orifices at their tips mounted one behind the other, usually known as the “sampler” and “skimmer” cones, respectively. These are mounted in a large metal block that is water-cooled to dissipate the heat absorbed from the plasma. The region between the cones is kept at 1- 5 torr using a mechanical rotary vacuum pump. Ion extraction is performed with very little opportunity for gas-phase reactions –the gas forms a supersonic jet as it accelerates into the vacuum and cools so quickly that there is very little chance for secondary reactions to occur. The skimmer cone is placed inside the supersonic jet; ions are extracted into the mass spectrometer, most of the gases are lost as they are deflected around the tip of the cone. This results in a collimated ion beam which then passes through the ion optics for further focusing and elimination of neutral species.
Plasma interface consists of two cones: a sampler cone and a skimmer cone. The skimmer cone is located downstream of the sampler cone in the instrument. The function of the cones is to enable sampling of ions from the plasma.
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11/21/11 There are many different types of mass spectrometers (used in many other instruments besides ICPMS). All of the types of mass spectrometers listed above have been used for ICPMS, but we will focus in this presentation on the quadrupole mass spectrometer, as this configuration is used in the vast majority of all ICPMS instruments.
11/21/11 For a given set of RF/DC conditions in the quadrupole, only one mass will have a stable trajectory through the mass analyzer, all other ions will be lost. The RF/DC settings can be altered very quickly (<1ms) and this is how the mass spectrometer scans across the entire mass range. Precision assembly of 4 electrically conducting rods to which RF and DC voltages are applied opposing rod pairs, opposite polarity resulting electric fields in the center of the assembly filters the ions by mass only one mass/charge ratio has stable trajectory, others are excluded RF/DC ratio determines resolution Rigid, stable geometry, no moving parts Compact size Accepts ions of a wide energy range Good resolution/mass range capabilities for atomic spectroscopy
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