SELENITE AND SELENATE QUANTIFICATION BY HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY, ION CHROMATOGRAPHY, AND COLORIMETRY

The need for a routine, inexpensive method with nanomolar detection li mits for soluble SeO32- and SeO42- is increasing as Se research on soi l-plant-water systems intensifies and speciation of Se valence states is required. This study was undertaken to compare hydride generation-a tomic absorption spectrometry (HGAAS), colorimetry using 2,3-diaminona phthalene (DAN), and ion chromatography (IC) as suitable methods for a nalysis of SeO32- and SeO42- in soil extracts and water samples. Selen ium standards in solutions of either 1.0 mM KH2PO4, CaSO4, and KNO3, o r in distilled water were analyzed to determine detection limits (DL), limits of quantitation (LOQ), and practicality for routine use of the above methods. A 0.1 mM K2HPO4/KH2PO4 soil extract spiked with 2.0 or 20 muM SeO32- and SeO42- was also used to compare the precision of th e three methods. The HGAAS method was the most sensitive (0.212 absorb ance units/muM) and had the lowest DL for SeO32- (0.03 mumol Se/L) of the three methods employed. Detection limits for the DAN and IC method s were significantly higher (18 and 0.24 mumol Se/L, respectively). Po or reproducibility between methods was obtained for SeO42- content of the soil extract containing 20 muM SeO42-, with concentrations ranging from 9.1 +/- 1.2 mumol/L determined by HGAAS to 24.6 +/- 0.05 mumol/L by IC. The variability and poor recovery of SeO42- was due to variabi lty in efficiency of the HCI reduction required to reduce SeO42- to Se O32- before analysis in the HGAAS and DAN procedures. Selenium determi nations in samples where low detection limits (<0.1 muM) are required are most effectively accomplished with HGAAS. Colorimetry requires gre ater effort and time from the analyst to obtain the low detection limi ts of HGAAS, but is useful in that only a visible light spectrometer i s required. Ion chromatography is capable of automated determinations of SeO32- and SeO42- directly in combination with other ions of intere st and may be appropriate for soil solution Se analysis where Se speci ation is required.