Use of masking agents in the determination of lead in tap water by flame atomic absorption spectrometry with flow injection pre-concentration

The selectivity of immobilised 8-hydroxyquinoline for lead is shown to be improved by the use of masking agents during pre-concentration, prior to determination by flame atomic absorption spectrometry. Interference by iron, copper, aluminium and zinc is suppressed by including triethanolamine, thiourea, fluoride, acetylacetone or cyanide in the buffer as masking agents. Species such as iron or copper can completely prevent the pre-concentration of lead. This is shown to be overcome by using a buffer consisting of 0.2 M boric acid, 2% triethanolamine, 2% thiourea and 2% acetylacetone, even when the interfering species is in a 200-fold excess over lead. Recoveries from tap water samples, to which various amounts of lead had been added, ranged from 94 to 108%. Results of analyses of tap water samples using this method were in good agreement with those obtained by electrothermal atomic absorption spectrometry.