Arsenate, arsenite, selenate and selenite

Ion chromatography can readily determine arsenate, selenite, and selenate species in water in the absence of interferences. However, they will usually be completely obscured by the major anions. Arsenic and selenium are ordinarily at their highest oxidation state in surface waters but that is not necessarily the case in groiond waters. 

An eluent composition of 2.0m mol L sodium bicarbonate and 1.5m mol L sodium carbonate was found to elute arsenate about midway 

Suppressed eluent retained in the concentrator columns produced a large carbonate peak on direct reinjection. This peak obscured or interfered with everything eluting before nitrate, hi the determination of selenite, the concentrator was washed witti deionised water for 5min after collection and before injection. The wash step was omitted in the determinations of arsenate and selenate where the carbonate did not interfere. 

15 show representative chromatograms for each of the trace anions at close to the statistical detection limit. The initial injection is shown on a logarithmic scale of conductance to include complete peaks of the major constituents. The recycle portion of the chromatogram was obtained at the linear scale, usually Ips cm full scale sensitivity. Fig. 2.14 shows a second collection and recycling of selenite. The process can be repeated indefinitely but there is evidence (below) of 10-15% loss of material each time. 

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