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

Abstract

The chemistry of complexation has been investigated and conditions optimized for on-line preconcentration of CrIII 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 CrIII 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 CrIII 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 CrIII by Muromac A-1. However, suppressive interferences were caused by 100 µg 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 CrIII in estuarine- and sea-waters, prior to determination by flame atomic absorption spectrometry (FAAS). By reduction of CrVI to CrIII, it was also possible to determine the total concentration of ionic Cr in the waters, which allowed calculation of the CrVI concentration by difference. The CrIII concentration in the samples from the Clyde estuary were 3–8 ng ml–1, with the CrVI concentration about 0.7 ng ml–1. Only CrIII(3 ng ml–1) was found in the sea-water samples from the Cumbrian Coast.