DIRECT DETERMINATION OF CADMIUM IN SEA-WATER BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY WITH SODIUM-HYDROXIDE AS A CHEMICAL MODIFIER

The use of sodium hydroxide as a chemical modifier for the direct determination of trace amounts of cadmium in sea-water by electrothermal atomic absorption spectrometry is described. It permits a selected ashing temperature up to 1400-degrees-C and markedly reduces the background signal caused by high sea-salt contents, while the ashing time is prolonged up to 100 s. Colloidal magnesium hydroxide precipitates were produced by the addition of NaOH modifier to sea-water, and trace amounts of cadmium were considered to be coprecipitated with magnesium hydroxide. The proposed method was used for the direct determination of cadmium in open ocean sea-water. The validity of the procedure was checked with two certified reference sea-waters (CASS-1 and CASS-2) and the results were found to be in good agreement with the certified values. A detection limit of 0.015 ng ml-1 was obtained for 80 mul injections.