INDIRECT ATOMIC-ABSORPTION SPECTROMETRIC DETERMINATION OF SULFATE IN HUMAN BLOOD-SERUM

An indirect method for the determination of sulfate by atomic absorption spectrometry (AAS) is described. Sulfate forms a stable ion-association complex, [Cu(neocuproine)2]2+ (SO42-, in neutral medium, which can be extracted into isobutly methyl ketone in the presence of a polar medium (methanol) with an efficiency higher than 98.0% and the extract can be analysed directly for copper (and hence indirectly for sulfate) by AAS. Measurement of the copper atomic absorption signal from the organic phase allows the indirect determination of 0.14-1.12-mu-g ml-1 of sulfate, giving a 450-fold increase in sensitivity over the conventional method of precipitation with barium. The limit of detection (3-sigma) is 3.2 ng ml-1 which is better than that of ion chromatography (0.15-mu-g ml-1). Indirect AAS allows the accurate assay of inorganic sulfate anion in biological fluids and tissues. The sulfate concentration determined by the proposed method in human blood serum (n = 6 in each instance) was 35.4-43.3-mu-g ml-1 in normal persons, 50.3-62.5-mu-g ml-1 in jaundice patients and 83.3-155.6-mu-g ml-1 in diabetic patients. A good correlation between measured sulfate and the sulfate added to blood serum was obtained.