SIMULTANEOUS DETERMINATION OF ARSENITE, ARSENATE, SELENITE AND SELENATE IN WATERS USING SUPPRESSED ION CHROMATOGRAPHY WITH ULTRAVIOLET ABSORBENCY DETECTION

Using Dionex AS4A anion-exchange column, with micromembrane supressor and UV detector at 195 nm, arsenite, arsenate, selenite and selenate can be determined simultaneously in water samples. The mole fraction of sodium carbonate in the eluent as well as eluent concentration affected the retention times especially for the divalent anions. An eluent of 2.25 mM Na2CO3 and 0.75 mM NaHCO3 was found to be the most suitable for sample analysis. The responses for all ions tested was linear in 0-5 mg 1(-1) range. The system can tolerate up to 1600 mg 1(-1) of SO4(2-), before affecting arsenate peaks. Selenate peak area was not affected due to SO4(2-) concentration up to 2000 mg 1(-1). The detection limits using 100-mu-l loop were 0.1 mg 1(-1) for AsO2- and SeO3(2-) and 0.25 mg 1(-1) AsO4(3-) and SeO4(2-).