Application of hydride generation atomic absorption spectrometry to the determination of lead collected on air filters and Sphagnum moss

Abstract

A commercial continuous-flow hydride generation system combined with atomic absorption spectrometry (HGAAS) was applied to the determination of lead in the urban atmosphere of Oporto. The procedure was used for both atmospheric aerosols collected on cellulose filters and extracellular aqueous extract of the moss Sphagnum auriculatum. Under optimized conditions, which were 0.75% HNO₃, 6%(NH₄)₂S₂O₈ and 2% sodium citrate for the sample solution (flow rate 6 ml min^–1), and 7% NaBH₄ for the reducing solution (flow rate 3 ml min^–1), the characteristic concentration (0.0044 absorbance) was 0.3 ng ml^–1 of lead and the response was linear up to 40 ng ml^–1. No interferences occur up to 60 ng ml^–1(Ni), 30 ng ml^–1(Cu) and 1.0 µg ml^–1(Fe, Mn and Zn), with these metals together in the sample. The ruggedness of the procedure towards either small uncontrolled fluctuations of the experimental parameters or the major interferent heavy metals was ascertained by Youden ruggedness tests. Direct comparison of HGAAS with AAS with electrothermal atomization (both type of samples) and differential-pulse anodic stripping voltammetry (moss extracts) was used for validation of the method. A precision study performed on real samples showed that the standard deviation associated with the over-all procedure (sample pre-treatment and subsequent determination) was mainly due to both lack of sample homogeneity and its treatment, the proposed analytical method having sufficient precision for the type of environmental applications under consideration.