Graphite furnace atomization behaviour of lead contained in clinical and environmental materials in the presence of palladium-induced isoformation and citric acid

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Abstract
The behaviour of Pb in electrothermal atomic absorption spectrometry with graphite furnace atomization undergoing Pb- or phosphate–magnesium-induced isoformation in conjunction with the carbon-reducing effect achieved by the addition of citric acid was studied. Analyte isoformation solutions contained 0.5 mg l–1 of Pd and 2% m/v citric acid, and 0.6% m/v NH4H2PO4, 0.3% m/v Mg(NO3)2 and 8% m/v citric acid. An appearance time of 1.56 s was obtained for atomic Pb in samples and aqueous standards when 200 µg (for Pd) and 800 µg (for phosphate–magnesium) of citric acid were used. Under a CO atmosphere, the Pb absorption signal was shifted late in time to 1.75 s for Pd and 1.69 s for phosphate–magnesium. These results suggested a carbon-dependent mechanism for the reduction of the atomic precursor (the same for both analytical isoformers employed) to form Pb atoms with production of CO. A simple method for the determination of Pb by stabilized temperature platform furnace electrothermal atomic absorption spectrometry in clinical and environmental samples was developed using Pd-induced isoformation and citric acid. The limit of detection (3σ) was 0.1 µg l–1 of Pb for a 10 µl injection of test solution and the characteristic mass was 13 pg. The method was validated using human serum, freezedried urine, whole blood, pond sediment, Chlorella, tea leaves, vehicle exhaust particulates and Sargasso reference materials. Recoveries ranged from 94 to 104%. An RSD of 2.2% was found for both the within and between-run precisions. The proposed method was used to establish the Pb levels of 40 healthy adults from Maracaibo City. The levels (mean ± SD, µg l–1 of Pb) were as follows: whole blood, 148 ± 27; red blood cells, 326 ± 60; urine, 10.2 ± 3.8; and bone, 7.8 ± 2.8 (µg g–1 of Pb). The Pb content of the drinking water supplied to the city was µg l–1. The method was free from interferences, reliable and reproducible.

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