CR(III) AND CR(VI) ONLINE PRECONCENTRATION AND HIGH-PERFORMANCE FLOW FLAME EMISSION SPECTROMETRIC DETERMINATION IN WATER SAMPLES

The concentration of chromium in environmental and biological samples (ground, sea, and drinking water, blood serum, urine) is too low (0.1- 1 ng/ml) to be determined directly from the sample with either flame a tomic absorption, ICP/AES, or even ICP/MS methods. To determine the Cr (III) and Cr(VI) content of these samples is even more difficult. To s olve this problem we combined a high-pressure liquid chromatographic s eparation method with atomic spectrometric detection. In addition to t he Cr(VI) preconcentration, a new on-line preconcentration/elution met hod with a C18 HPLC column was developed to determine the Cr(III) conc entration. For the preconcentration, in the case of Cr(VI), 0.05 M tet rabutylammonium bromide was used as an ion pair forming agent while 0. 075 M potassium hydrogen phthalate was used to preconcentrate Cr(III). The eluent was a methanol-water mixture of 60% or 80%, respectively. One of the most effective methods of atomic spectrometry, hydraulic hi gh-pressure nebulization, was used for sample introduction. In a compr ehensive study, flame emission spectrometry with a stoichiometric nitr ous oxide/acetylene flame proved to be the most effective detector to analyze Cr(IU) and Cr(VI). Samples of 5 ml were preconcentrated and el uted with 1 ml of methanol; the lambda=425.43 nm emission line of chro mium was used for detection. Under these conditions the detection limi t (3 sigma) was 25 pg/ml for Cr(III) and 20 pg/ml for Cr(VI). The rela tive standard deviations (N=10) are 5.6 and 2.1% for 1 mu g/l Cr(III) and Cr(VI), respectively. These achievements allowed the determination of the toxic Cr(VI) content of surface and drinking water samples. (C ) 1996 Academic Press, Inc.