GRAPHITE-FURNACE ATOMIZATION BEHAVIOR OF LEAD CONTAINED IN CLINICAL AND ENVIRONMENTAL MATERIALS IN THE PRESENCE OF PALLADIUM-INDUCED ISOFORMATION AND CITRIC-ACID

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 mug (for Pd) and 800 mug (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 (3sigma) was 0.1 mug l-1 of Pb for a 10 mul injection of test solution and the characteristic mass was 13 pg. The method was validated using human serum, freeze-dried 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, mug 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 (mug g-1 of Pb). The Pb content of the drinking water supplied to the city was < 0.1 mug l-1. The method was free from interferences, reliable and reproducible.