On-line preconcentration of chromium(III) and speciation of chromium in waters by flame atomic absorption spectrometry

The chemistry of complexation has been investigated and conditions optimized for on-line preconcentration of Cr-III by resins with immobilized quinolin-8-ol or iminodiacetate functional groups. When solutions were buffered to 0.1 mol l(-1) acetate at pH 9, the detection limit of Cr-III was 6 ng ml(-1) for preconcentration on the quinolin-8-ol resin at 6 ml min(-1) for 3 min. With the iminodiacetate resin (Muromac A-1), the optimum buffer conditions were 0.1 mol l(-1) acetate at pH 4, which gave a Cr-III detection limit of 2 ng ml(-1) (3 min preconcentration at 6 ml min(-1)). The major ions in sea-water did not interfere with preconcentration of 100 ng ml(-1) Cr-III by Muromac A-1. However, suppressive interferences were caused by 100 mu g ml(-1) of Ca2+ or Fe2+ with the quinolin-8-ol resin. Despite having similar log stability constants of complexation with either resin, the interference caused by Ca2+ was much greater than that by Mg2+. Muromac A-1 was used for preconcentration of Cr-III in estuarine- and sea-waters, prior to determination by flame atomic absorption spectrometry (FAAS). By reduction of Cr-VI to Cr-III, it was also possible to determine the total concentration of ionic Cr in the waters, which allowed calculation of the Cr-VI concentration by difference. The Cr-III concentration in the samples from the Clyde estuary were 3-8 ng ml(-1), with the Cr-VI concentration about 0.7 ng ml(-1). Only Cr-III (3 ng ml(-1)) was found in the sea-water samples from the Cumbrian Coast