Atomization of lead from whole blood using novel tungsten filaments in electrothermal atomic absorption spectrometry

Abstract

Several novel W-filament designs are investigated and compared as atomization devices for blood Pb measurements by atomic absorption spectrometry. Two designs (short and long wire filaments) are based on rigidly-wound W-filaments from Osram, while a third (etched filament) is based on lithographic imaging and photoetching technology. The filaments are positioned in an aluminum atomization cell that is mounted in the optical path of a compact AAS instrument. This instrument is designed specifically for blood lead testing using W-filament technology with a Pb hollow cathode lamp and incorporates a self-reversal background correction system. Whole blood is diluted 1 + 4 with a phosphate modifier, Triton X-100 and nitric acid, and 15 µL are deposited on the filament using a micropipette. A simple heating program dries, pyrolyzes and atomizes the sample. Integrated absorbance measurements are used for improved precision and detection limits. Matrix-matched Pb standards are necessary for blood lead calibration. Of the three filaments studied, the long wire filament proved most suitable, with a characteristic mass (m0) of 200 pg, a method detection limit (3σ) of1–2 µg dL−1 (0.05–0.10 µmol L−1), and a lifetime of the order of 60–70 firings. Method accuracy is verified using blood lead reference materials from the National Institute of Standards and Technology (SRM 955a,b), the Centers for Disease Control (BLLRS) and the New York State Department of Health (RMs 028, 040, and 043). For the long wire filament, blood lead results below 40 µg dL−1 were mostly within ±1 µg dL−1 of certified values, and within ±10% above 40 µg dL−1; within-run precision was almost always better than ±10%. Additional validation is reported using proficiency test materials and human blood specimens. All blood lead results were within the acceptable limits established by regulatory authorities in the US.