Direct determination of chromium in estuarine and coastal waters by electrothermal atomic absorption spectrometry

Abstract

The determination of chromium in sea-water by electrothermal atomic absorption spectrometry suffers from large variations in sensitivity that are a function of the salinity, the batch and age of the graphite tube, and the analytical instrument used. To avoid the need for lengthy standard additions calibration, work was undertaken to discover a chemical modifier permitting direct analysis over a range of salinities. Two such modifiers were identified as suitable for use in the determination of total dissolved chromium. Magnesium nitrate (100 µg) gave good recoveries (with respect to de-ionized water) for low to medium salinities, with a limit of detection of 0.05 µg l^–1. At high salinities however (about 34 parts per thousand), about 15% suppression was measured, making the method unsuitable for sea-water samples. Sodium tungstate (2.5 µg) although slightly less sensitive (detection limit of 0.1 µg l^–1), produced excellent recoveries over all salinities. Thus the method allows the direct determination of dissolved chromium in estuarine and polluted coastal waters.