DIRECT DETERMINATION OF TOTAL CHROMIUM IN SEA-WATER BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY WITH MULTIPLE INJECTIONS

The method of multiple injections coupled with graphite furnace and at omic absorption spectrometry is applied to direct determination of tot al chromium at extremely small concentrations in samples of open sea w ater. The method involves the in situ preconcentration of trace chromi um in sea water onto a pyrocoated graphite tube by multiple injections (up to 4 x 90 muL) prior to analysis. The selected ashing temperature is up to 1800-degrees-C, and the background signal caused by high sea -salt contents will be markedly reduced when the ashing time is prolon ged up to 200 s. A CASS-2 reference sea water has been used as a quali ty control sample in the analyses of samples of open sea water samples ; the results were found to agree with the certified value. Due to the use of a relatively large volume (up to 0.36 mL) of sample for direct determination of trace chromium in sea water, the detection limit for chromium is 0.057 ppb.