Minimization of sulfate interference on lead atomization with palladium–strontium nitrate as chemical modifier in electrothermal atomic absorption spectrometry
Different chemical modifiers were employed to minimize sulfate interference on lead. The maximum tolerable pyrolysis temperatures for lead, obtained by adding modifiers, were 800, 1000, 1000 and 1300 °C for lanthanum, palladium alone, palladium–magnesium nitrate and palladium–strontium nitrate, respectively. Palladium–strontium nitrate, with which lead can withstand the highest pyrolysis temperature, eliminated the interference from 200 µg of sulfate (10 g l–1 of SO42–) on 0.5 ng of lead. The mode of action of Pd—Sr in eliminating the interference is probably due to the high melting-point (1605 °C) of the strontium sulfate, which occludes the lead until the temperature in the furnace is sufficiently high to release lead into the high temperature and reducing environment, which enhances the atomization of lead; hence the co-expulsion of lead with sodium sulfate (melting-point 884 °C) is prevented. The method was applied to sea-water analysis. The recoveries of spiked lead were 94–103%.