SIMULTANEOUS DETERMINATION OF CHROMIUM(III) AND CHROMIUM(VI) BY REVERSED-PHASE ION-PAIR HPLC WITH CHROMIUM-SPECIFIC DETECTION

A method for the simultaneous determination of Cr(III) and Cr(VI) with reversed-phase ion-pair HPLC employing chromium-specific detection by flame atomic absorption spectrometry (FAAS) and inductively-coupled p lasma mass spectrometry (ICP-MS) is presented. Experimental parameters of the chromatographic separation, such as concentration of the ion-p airing reagent, pH and polarity of the mobile phase have been optimize d for two different ion-pairing reagents, tetrabutylammonium phosphate (TBA) and tetraethylammonium nitrate (TEA). Best chromatographic cond itions have been obtained with a polymer-based reversed-phase column ( Hamilton PRP1) and mobile phases containing either TBA (1 mmol/l) in m ethanol-water (60:40, v/v) or TEA (2 mmol/l) in water at a pH between 3 and 4. With FAAS the detection limits (3 sigma) have been found to b e 24 mu g/l for Cr(III) and 40 mu g/l for Cr(VI). A detection limit of 0.3 mu g/1 Cr(3 sigma) for both chromium species has been obtained wh en ICP-MS has been used for detection. The method has been applied to analyze tap- and groundwater and to investigate the behaviour of Cr(II I) and Cr(VI) in spiked tap-water, as well as to analyze aqueous extra cts of coal fly ash (NIST SRM 1633a) and of an ash from a wood treatme nt company.