Electrothermal atomic absorption spectrometric determination of selenium in biological fluids with rhodium modifier compared with hydride generation atomic spectrometric techniques

Abstract

Analytical procedures for direct electrothermal atomic absorption spectrometric (ET-AAS) determination of selenium in urine, blood serum and solubilized hair, employing rhodium modifier (10–20 μg) in a transverse-heated graphite atomizer (THGA) with integrated pyrolytic graphite-coated platform and longitudinal Zeeman-effect background correction were developed. Results for urine were compared with flow-injection hydride generation with in-atomizer trapping of hydrogen selenide in Ir–Zr treated THGA (FI-HG–ET-AAS) and with continuous flow hydride generation coupled with a non-dispersive atomic fluorescence spectrometry (CF-HG–ND-AFS). Two different bomb decompositions proved useful: (i) urine sample (1 ml) soaked overnight with HNO 3, followed by pressurized digestion with HNO 3 in a microwave oven, then H 2O 2 added, and bomb decomposition completed with HNO 3–H 2O 2, then selenium pre-reduced to Se(IV) in 4.8 M HCl; and (ii) sample (1 ml) soaked overnight with HBr–BrO 3 −, then pressurized digestion in a microwave oven, followed by quantitation by FI-HG–ET-AAS or CF-HG–ND-AFS with standard addition calibration. Several certified reference materials (urine, blood serum and hair) as well as the NIES candidate CRM No. 18 ‘Human Urine’ from the National Institute of Environmental Studies (NIES) (Tsukuba, Japan) were analyzed and the results are in agreement between techniques and with certified values. Preference is given to the direct ET-AAS determination of Se in biological liquids after two- to threefold dilution in the presence of 10 μg of Rh. Pyrolysis and atomization temperatures are within 1100–1200°C and 2100–2200°C, respectively, and the ‘end-capped’ graphite tubes are preferred for better sensitivity and lower background absorbance. The limits of detection of the direct ETAAS are approximately 6 ng ml −1 Se in biological fluids. For 24 paired samples of blood serum and urine from non-exposed individuals (Sofia, Bulgaria), selenium levels are: serum 66.5±15.5 (45.5–116.4) ng ml −1 and urine 16.8±8.1 (6.0–41.9) ng ml −1.