Minimally-invasive filter paper test in combination with solid sampling-graphite furnace atomic absorption spectrometry for Pb determination in whole blood

This work describes a simple procedure for the determination of blood lead levels in dried-spot filter paper specimens. The method permits the minimally-invasive collection of blood on filter paper and the subsequent direct analysis of discs punched from these filters by solid sampling-graphite furnace atomic absorption spectrometry (SS-GFAAS). A systematic study on the possible effects of different factors (total volume of blood deposited onto the filter paper, potential chromatographic effects affecting the distribution of Pb over the surface, potential differences in the amount of blood deposited per surface area for samples with different haematocrit values) was carried out, leading to the conclusion that the variation of these parameters within the usual clinical range does not result in any significant effect on the amount of Pb deposited in each disc. Thus, a simple methodology was developed based on (i) the performance of Pt as a chemical modifier and (ii) the use of matrix-matched standards for calibration (Pb-free blood samples spiked with known amounts of Pb) treated in the same way as the samples. The method was validated by analysis of a reference material, as well as by comparison of the results obtained for 18 patients from which blood was also taken and analyzed following the standard procedure (venous sampling, blood dilution and GFAAS monitoring). The main analytical features of the method proposed are: a detection limit of 2.5 µg Pb L^–1, a working range up to 840 µg Pb L^–1, a sample throughput of approximately 10 min per sample (5 replicates) and precision values below 10% RSD. The ease of sample collection, transporting and storing, in combination with the expeditiousness and relative inexpensiveness of the analytical technique used, make the procedure investigated very attractive for the screening of children in order to detect those with blood lead levels above the present threshold of concern (100 µg L^–1), particularly in countries/areas were collecting sites might be far away from central laboratories.