Determination of lead in biological samples by high-resolution continuum source graphite furnace atomic absorption spectrometry with direct solid sampling

Abstract

Direct solid sampling is an attractive alternative for the determination of lead in biological samples, since it requires almost no sample preparation and provides higher sensitivity as no dilution is employed. In addition, the time required for the analysis and the risk of analyte loss or contamination during sample pre-treatment are reduced, the latter being the main problem associated with the usual digestion and dissolution procedures. In the present work, treating the determination of Pb in biological samples at 217.001 nm with solid sampling graphite furnace atomic absorption spectrometry (GF AAS), it will be shown that high-resolution continuum source AAS (HR-CS AAS) provides a variety of new possibilities for method development that have been unavailable previously. The use of ruthenium as a permanent modifier allowed a pyrolysis temperature of 900 °C to be applied, which was sufficient to eliminate the continuous background that preceded the analyte signal due to incomplete elimination of the matrix when lower pyrolysis temperatures were used. At atomization temperatures higher than 1500 °C, background absorption with pronounced fine structure followed the atomic signal. This was due to the electron excitation spectrum of PO, as was demonstrated by applying a least-squares background correction algorithm using the spectrum obtained by vaporization of (NH₄)₂HPO₄ as a reference. Under optimum conditions, interference-free determination could be carried out by setting integration limits adjusted to integrate only the atomic signal; calibration against aqueous standards was performed and compared with calibration against a solid certified reference material (CRM). A total of seven biological CRM were analyzed (bovine muscle, pig kidney, lobster hepatopancreas, human hair, dogfish liver, oyster tissue and bovine blood), and the determined concentration of Pb was in agreement with the certified values using both calibration procedures, according to the t-test for a 95% confidence level. The detection limit (3s, n = 10) was 0.01 μg g⁻¹, and the precision was typically better than 10%. The method is therefore adequate because of its simplicity, high sensitivity, good accuracy and wide applicability.