DETERMINATION OF TRACE LEVELS OF SELENIUM IN BIOLOGICAL SAMPLES BY GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY WITH A SOLID SAMPLING TECHNIQUE - APPLICATION OF PRE-ASHING CONCENTRATION TECHNIQUE

A highly sensitive and convenient analytical method for the direct det ermination of selenium in biological samples by GF-AAS with a solid sa mpling technique using a graphite miniature cup was established by usi ng a Pd solution containing 3 mol/l sulfuric acid or a Pd solution con taining 0.1 mol/l nitric acid as a matrix modifier in order to prevent the volatilization of selenium. The determination of mu g/g levels of selenium in biological samples was performed using calibration curves prepared by a selenium standard solution containing 100 mu g/ml of Pd in 3 mol/l sulfuric acid as the matrix modifier. On the other hand, t he pre- ashing concentration technique, which was previously developed by us, was applied to the determination of 10 ng/g levels of selenium in biological samples. The analytes in biological samples were concen trated by decomposing the sample matrix with a conventional electrothe rmal muffle furnace at 600 degrees C for 30 min. At the pre-ashing sta ge, a Pd solution containing 0.1 mol/l nitric acid was added, because the addition of the Pd solution containing sulfuric acid caused charri ng and coagulation of the samples. The concentration factor for seleni um in biological samples was 10 to 40. The analytical results of sever al NIST biological certified reference materials obtained by the propo sed method were in good agreement with the certified values. The detec tion limit of GF-AAS was 0.13 ng of selenium; therefore, 3.3 ng/g leve ls of selenium in biological samples is detectable by the proposed met hod.