Arsenic Table hydride generation

The manifold for hydride generation is shown in Fig. 12.7. The operating conditions are as follows forward power 1400W, reflected power less than 10W, cooling gas flow 12L nr1, plasma gas flow 0.12L nr1, injector flow, 0.34L m 1. The standard deviation of this procedure was 0.02pL 1 arsenic and the detection limit O.lpg L-1. Results obtained on a selection of standard reference sediment samples are quoted in Table 12.14. 

These methods were used to determine arsenic in certified sediments (Table 12.15). Conventional inductively coupled plasma atomic emission spectrometry is satisfactory for all types of samples, but its usefulness was limited to concentrations of arsenic greater than 5pg g-1 dry weight. Better detection limits were achieved using the flow-injection-hydride generation inductively coupled plasma technique in which a coefficient of variation of about 2% for concentrations of lOpg g 1 were achieved. 

Several methods have been developed for the determination of arsenic species, involving different extraction, derivatisation, separation and detection steps [13] these include hyphenated techniques based on liquid chromatography coupled to detectors such as ICP-MS or ICP-AES, and hydride generation in line with QFAAS and UV degradation followed by ICP-AES detection. The techniques that were selected in the certification campaign are listed in Table 7.8. 

Eight elements including germanium, tin, lead, arsenic, antimony, bismuth, selenium, and tellurium form volatile, covalent hydrides (Table 14). Hydride generation can be employed both to separate these elements from the main... 

Hydride generation in AAS became popular after 1970 in response to a study by Holak, which demonstrated the analytical potential of this approach for arsenic. Since then, elements of groups IVA, VA, and VIA of the periodic table have been shown to form volatile covalent hydrogen compounds with sufficient efficiency to be of practical analytical use. These include arsenic, bismuth, germanium, lead, antimony, selenium, tin, tellurium, and to some extent, indium and thallium. 

Microcomponents Inorganic microcomponents cover almost the entire periodic table. Here we discuss only those elements that are determined most frequently beryllium, vanadium, chromium, cobalt, nickel, copper, zinc, arsenic, selenium, silver, cadmium, antimony, barium, and lead. The techniques of choice are FAAS, graphite furnace-AAS (GF-AAS), ICP, and hydride generation-AAS (HG-AAS). An ultrasonic nebulizer has recently become commercially available for FAAS and ICP-AES, which decreases the lower determination limits. ICP-mass spectrometry (ICP-MS) is a recent development in which ionization is combined with sensitive mass discrimination. In a further development a graphite furnace is used in front of the ICP-MS. Selective evaporation of elements in the graphite furnace reduces the influence of highly interfering matrices. ICP-MS is expensive, which deters its widespread use. 

Arsenic species that have been identified in the terrestrial environment are listed in Table 3. Apart from the inorganic species, which predominate in all environmental compartments, they are mainly methylarsenicals and are presumably formed via the same biological process outlined above. The formulations given for the methylarsenic(III) species are probably not correct because compounds of this type are unknown. It is likely that the species are actually thiols CH3As(SR)2 and (CH3)2AsSR (19). The reason for the uncertainty is that the analytical technique commonly used to determine arsenic species is hydride generation (HG) followed by some form of separation and detection, e.g, gas chromatography (GC) and atomic absorption (AA) spectrometry hence HG/GC/AA. 

Recommended conditions for flame and approximate values for ETA (graphite rod, etc.) atomizers are given in Table 2 for a number of elements important with regard to air pollution studies. Conditions are included in the table for the flame system used when hydrides of arsenic, antimony and selenium are generated and passed through the flame. Burrel [16] discusses generation of metal hydrides and cold-vapor mercury evolution techniques in great detail. 

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