Determination of selenite, selenate and selenomethionine by ion chromatography, microwave digestion and HGAAS

An on-line system for the simultaneous determination of Se(IV), Se(VI) and selenomethionine (Se-Met) in aqueous samples was developed, consisting of separation by ion chromatography, microwave digestion and detection by hydride generation atomic absorption spectrometry. 8.3 mmol/l Na2HPO4 (pH 9.2) was used as mobile phase for the ion siloxane phases (C18, SE 52, SE 54, OV 1701) normally used for the separation of these compounds. Varying the cyclodextrin- and sugar-derivative content in the investigated procentual range allows a simple way of tuning a capillary for a specific application. As shown in Figs. 1 and 2, a 10% content of permethylated beta-cyclodextrin in OV 1701 increases particularly the retention of the 3.3'4,4'-substituted PCB congeners 77, 105, 126 and 128. Similar results have been achieved by using 16 m of the commercially available Cyclodex B from J & W. The changed selectivity by adding 5% dodecyl-beta-D-maltoside to SE 52 is demonstrated in Figs. 3 and 4 (the other PCB-compounds of the standard mixture show no significant difference).