Arsenic Table analytical techniques

The accuracy of the analytical method was established hy independent analysis of the three additional filters from each of the 5 10 and 20 yg/m3 generation runs using both NAA and XRF analyses. Because NAA and XRF analysis techniques provide only a total arsenic measurement, the IC-AAS speciation results obtained for MMA, DMA and p-APA were used to estimate the total amount of arsenic. Table X presents the total arsenic obtained by the three techniques. The accuracy ranged from 90-120 of the values obtained by NAA and XRF. 

As a branch of chemistry, the activities of nuclear chemists frequentiy span several traditional areas of chemistry such as organic, analytical, inorganic, and physical chemistry. Nuclear chemistry has ties to all branches of chemistry. For example, nuclear chemists are frequently involved with the synthesis and preparation of radiolabeled molecules for use in research or medicine. Nuclear analytical techniques are an important part of the arsenal of the modem analytical chemist. The study of the actinide and transactinide elements has involved the joint efforts of nuclear and inorganic chemists in extending knowledge of the periodic table. Certainly, the physical concepts and reasoning at the heart of modem nuclear chemistry are familiar to physical chemists. In this book we will touch on many of these interdisciplinary topics and attempt to bring in familiar chemical concepts. 

The hydrides ASH3 and SbH3 resemble those of PH3 (Table 15.4), but they are less stable with respect to decomposition into their elements. The thermal instability of ASH3 and SbH3 was the basis for the Marsh test. This is a classic analytical technique used in forensic science in which arsenic- or antimony-containing materials were first converted to AsHs or SbH3, and the latter were then thermally decomposed (equation 15.30). Treatment of the brown-black residue with aqueous NaOCl was used to distinguish between As (which reacted, equation 15.31) and Sb (which did not react). 

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. 

Schramel [103] discusses the conditions for multi-element analysis of over 50 trace elements, giving detection limits. Wolnik [104] described a sample introduction system that extends the analytical capability of the inductively coupled argon plasma/polychromator to include the simultaneous determination of six elemental hydrides along with a variety of other elements in plant materials. Detection limits for arsenic, bismuth, selenium and tellurium range from 0.5 to 3 ng/ml and are better by at least an order of magnitude than those obtained with conventional pneumatic nebulisers, whereas detection limits for the other elements investigated remain the same. Results from the analysis of freeze-dried crop samples and NBS standard reference materials demonstrated the applicability of the technique. Results obtained by the analysis of a variety of plant materials are presented in Table 7.10. 

In thermospray interfaces, the column effluent is rapidly heated in a narrow bore capillary to allow partial evaporation of the solvent. Ionisation occurs by ion-evaporation or solvent-mediated chemical ionisation initiated by electrons from a heated filament or discharge electrode. In the particle beam interface the column effluent is pneumatically nebulised in an atmospheric pressure desolvation chamber this is connected to a momentum separator where the analyte is transferred to the MS ion source and solvent molecules are pumped away. Magi and Ianni (1998) used LC-MS with a particle beam interface for the determination of tributyl tin in the marine environment. Florencio et al. (1997) compared a wide range of mass spectrometry techniques including ICP-MS for the identification of arsenic species in estuarine waters. Applications of HPLC-MS for speciation studies are given in Table 4.3. 

Arsenic, chromium, mercury, selenium, and tin have been the object of numerous investigations. Because some of them are classified as probable human carcinogens23-25 (strictly speaking, some of their species), the accurate assessment of concentration and speciation in environmental matrices is enormously important. Unfortunately, such factors as chemical reactions between species, low concentration, microbial activity, redox conditions, as well as the presence of other dissolved metal ions, may cause the amounts and distributions of chemical species in a sample to vary. In response to these problems, analytical research efforts have focused on developing techniques enabling the original valence state of the metals to be preserved. Table 2.3 lists some of these stabilization methods. 

The first requirement can be easily fulfilled by the preconcentration of the analyte before the analysis. Preconcentration has been applied to sample preparation for flame atomic absorption (25) and, more recently, for ICP (79,80) spectroscopy. However, preconcentration is not completely satisfactory, because of the increased analysis time (which may be critical in clinical analysis) and the increased chance of contamination or sample loss. Most important, however, a larger initial sample size is necessary. The apparent solution is a more sensitive technique. Table 2 lists concentrations of various metals in whole blood or serum (81,82) in comparison to limits of detection for the various atomic spectroscopy techniques. In many cases, especially for the toxic heavy metals, only flameless atomic absorption using a graphite furnace can provide the necessary sensitivity and accommodate a sample of only a few microliters (Table 1). The determination of therapeutic gold in urine and serum (83,84), chromium in serum (85), skin (86) and liver (87), copper in semen (88), arsenic in urine (89), manganese in animal tissues (90), and lead in blood (91) are but a few examples in analyses which have utilized the flameless atomic absorption technique. 

The Trace Metals Project conducted a study to identify the type of container which would provide minimum losses of arsenic and mercury by precipitation, volatilization, adsorption, or diffusion. Solutions of organomercury and organoarsenic compounds added to petroleum feedstock were used. Because of the relative ease with which mercury and arsenic can be determined at sub-parts-per-million levels in a hydrocarbon matrix by instrumental neutron activation analysis (INAA), this technique was used for the analytical measurements. The solutions were stored in five different types of glass and/or plastic containers and sampled periodically over eight months (12). The results of the study are summarized in Tables 2.III and 2.IV. 

---