ONLINE PRECONCENTRATION AND HIGH-PERFORMA NCE FLOW FLAME EMISSION SPECTROMETRIC DETERMINATION OF CR(III) AND CR(VI) IN NATURAL SAMPLES

The concentration of chromium in environmental and biological samples (ground or sea water, drinking water, blood serum, urine) is too low ( 0.1-1 ng/ml) to be determined directly from the sample either by means of flame atomic absorption (FAAS), ICP/AES or even by ICP/MS methods. It is even more difficult to determine the Cr(III) and Cr(VI) content of these samples. To solve this problem we combined high pressure liq uid chromatographic separation with atomic spectrometric detection. Be side the preconcentration of Cr(VI), a new on-line preconcentration/el ution method using a C18 HPLC column was developed to determine the co ncentration of Cr(UI). For preconcentration, in case of Cr(VI) 0.05 M tetrabutylammonium bromide (TBABr) was used as an ion pair forming age nt while 0.075 M potassium hydrogen phthalate was used to preconcentra te Cr(III). The eluent was methanal -water mixture of 60 and 80 %, res pectively. One of the most effective methods of atomic spectrometry, h ydraulic high pressure nebulization was used for sample introduction. In a comprehensive study, flame emission spectrometry with stoichiomet ric nitrous oxide/acetylene flame proved to be the most effective dete ctor to determine Cr(III) and Cr(VI). Samples of 5 ml volume were prec oncentrated and eluted with 1 ml of methanol, and the lambda = 425.43 nm emission line of chromium was used for detection. Under these condi tions the detection limit (3 sigma) was 25 pg/ml for Cr(III) and 20 pg /ml for Cr(VI). The relative standard deviations (N = 10) are 5.6 % an d 2.1 % for 1 mu g/l Cr(III) and Cr(VI), respectively. These results a llowed to determine the toxic Cr(VI) content of surface and drinking w ater samples.