Preconcentration of trace heavy metals in water by coprecipitation with magnesium oxinate for electrothermal atomic absorption spectrometry

Nanogram quantities of heavy metals in 200 mi of water were quantitatively preconcentrated by coprecipitation with magnesium oxinate at pH 9-9.5. The precipitate was collected on a 1-mu m Nuclepore membrane filter and then dissolved in 5 mi of 1 mol/l nitric acid. After diluting to 10 mi with water, a 10- or 20-mu l aliquot of the solution was directly analyzed by electrothermal atomic absorption spectrometry using deuterium background correction. The background absorption due to the collector magnesium oxinate was negligibly small. The optimized coprecipitation technique has been applied to the determination of cobalt, nickel, copper, cadmium and lead at the ppt level in river and seawater. The relative standard deviations were within 10% and the detection limits were 0.025 (for Co), 0.019 (for Ni), 0.006 (for Cu), 0.001 (for Cd) and 0.017 mu g/l (for Pb). Blanks through the whole procedure were not detectable.