Reduction of matrix interferences in the determination of lead in aqueous samples by atomic-absorption spectrophotometry with electrothermal atomisation with lanthanum pre-treatment

Abstract

A previous paper described a lanthanum pre-treatment procedure for overcoming matrix interferences in the determination of lead in drinking water. In this paper, the amounts of lanthanum and nitric acid employed have been optimised such that the technique is now applicable to a wide range of aqueous samples, for example river waters, borehole waters, sewage effluents and trade effluents. The technique has been tested and found to be satisfactory for samples containing up to 1150 mg l^–1 of chloride, 1420 mg l^–1 of sulphate, 760 mg l^–1 of sodium and 1530 mg l^–1 total hardness (as calcium carbonate). The optimum pre-treatment conditions for samples was 1%V/V nitric acid and 0.05%m/V of lanthanum (as lanthanum chloride), which completely overcame suppressive interferences in the determination of lead, and gave a furnace tube lifetime of approximately 600 firings. This investigation enabled a close study to be made of the processes by which interferences are overcome by nitric acid-lanthanum matrix modification, and some possible mechanisms are presented and discussed.