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 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 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 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.