Anion exchange arsenic species

A. Woller, H. Garraud, J. Boisson, A. M. Dorthe, P. Fodor and O. F. X. Donard, Simultaneuous speciation of redox species of arsenic and selenium using an anion-exchange microbore column coupled with a micro-concentric nebuliser and an inductively coupled plasma mass spectrometer as detector, J. Anal. At. Spectrom., 13, 1998, 141-149. 

Six different fish samples were analyzed for As species by Branch et al. [76]. Five species were separated [AB, DMA, As(III), MMA and As(V)] using a Benson strong anion-exchange resin. The predominant arsenic compound was found to be AB which is non-toxic. Arsenic levels were in the range 1.0 mg kg-1 dry mass in mackerel to 187 mg kg-1 dry mass in plaice. Nitrogen addition was used to remove ArCl+ interference at m/z 75. 

Arsenic species were preconcentrated on Zipax, a pellicular anion exchange material and separated on a column packed with high performance liquid chromatography grade strong anion exchange resin, then continuously reduced with sodium tetrahydroborate and detected by atomic absorption spectrometiy. Detection limits were 2ng for arsenite, arsenate and monomethylarsinate and lng for dimethylarsonate. 

Grabinski [12] has described an ion exchange method for the complete separation of the above four arsenic species, on a single column containing both cation and anion exchange resins. Flameless atomic absorption spectrometry with a deuterium arc background correction is used as a detection system for this procedure. This detection system was chosen because of its linear response and lack of specificity for these compounds combined with its resistance to matrix bias in this type of analysis. 

Aggett and Kadwani [13] report the development and application of a relatively simple anion exchange method for the speciation of arsenate, arsenite, monomethylarsonic acid and dimethylarsinic acid. As these four arsenic species are weak acids the dissociation constants of which are quite different it seemed that separation by anion exchange chromatography was both logical and possible. 

The term speciation is used to describe any analytical procedure in which the amounts of an element in discrete chemical forms are determined, as opposed to the total amount of an element in the sample. For example, it may be of interest to determine the amounts of Cr3 + and Cr042 in environmental samples, if the two ionic species have different toxicities, rather than the total amount of chromium. In this instance ion exchange may be used to separate the cationic and anionic species.23 Sometimes all the species to be determined may be either cationic or anionic, as in the case of the determination of Fe2+ and Fe3+ or S2, S032-, and S042-. Sometimes inorganic and organically bound forms may be determined, as in the case of arsenic species in natural waters.24 Where flame spectrometric determination has been employed in speciation studies of this type, selected key references may be found in the element-by-element section of Chapter 6. 

Tye et al.56 used hydride generation coupled to AAS to quantify organic and inorganic arsenic species in soil pore waters, after pre-concentration on a pellicular anion-exchange column. They were able to detect down to 2 ng of arsenate, arsenite, and monomethyl arsenite and down to 1 ng of dimethyl arsonate. More recently, an argon-hydrogen-entrained air flame fitted with a... 

Wine is a very complex matrix and the accurate, selective determination of species constitutes a challenge for analytical chemists. Furthermore, the speciation analysis of metals bound to biological ligands is a subject of increasing interest since complexation may reduce their toxicity and bioavailability. There is a limited number of studies concerning the speciation analysis of metals or metalloids in wines. Arsenite, arsenate, MMA, and DMA were separated in less than 10 min by means of an anion-exchange column [88], Arsenic species detection was accomplished by the direct coupling of the column effluent to an HG system and AFS was used for detection. LoDs in white wine were 0.16, 0.33, 0.32, and 0.57 ng ml-1 for As(III), DMA, MMA, and As(V), respectively. In real samples... 

Oddly, IPC was also performed on a classical ion exchange colnmn to separate 17 anionic, neutral, and cationic arsenic species in a single chromatographic run, thanks to a multiplicity of retention modes on this packing material [39], Ion pairing proved also valuable in size exclusion chromatography of sulfonated lignins [40],... 

The separation of various arsenic species is a good example of the application of ICP-AES detection to anion chromatography [26]. A microbore colunm 10 cm X 1.7 mm I.D. was used with a low flow rate (<100 pL/min). The column was packed with a low-capacity anion-exchange material (0.05 mequiv/g and solution containing 5 mM ammonium carbonate and 5 mM ammonium bicarbonate at pH 8.6 served as the mobile phase. The column hardware was connected directly to the inlet of the DIN-ICP-AES via a short length of 0.3 mm I.D. PEEK tubing. 

Figure 3 Separation of multispecies standard of As lll), DMA(V), MA(V), and As V) on a short strong anion exchange column (150 mm PRP X-100, Hamilton, 30 mol 1 phosphate buffer adjusted with ammonia to pH 6.0). Concentration of each species 5,10, 15, and 30 ng arsenic per liter.

Recently, IC has also foimd increased application in the field of metal speciation. Short anion exchange columns have been used for the rapid separation of anionic species of arsenic, selenium, and chromium. 

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