Immunoassay by graphite furnace atomic absorption spectrometry using a metal chelate as a label

A new immunoassay method was developed by using graphite furnace atomic abs orption spectrometry and EDTA-Cd2+ chelate as a label. The new approach com bined the use of EDTA-Cd2+ chelate labeled streptavidin (SA), biotinylated antibody or antigen, and graphite furnace atomic absorption detection for b oth sandwich-type immunoassay and competitive-type immunoassay. The measure ments of alpha -fetoprotein (AFP) in human sera and bensulfuron-methyl (BSM ) in water were used as the models to evaluate the usefulness of the method . The assays were carried out with 96-well microtiter plate as solid-phase carrier. After the immune reaction and biotin-streptavidin binding reaction , a solution of 0.2 M HNO3 was added to each well to dissociate Cd2+ in the immune complex on the solid-phase into the solution. The antigen concentra tion, was thus, determined by measuring the Cd2+ absorbance of the solution with graphite furnace atomic absorption spectrometry. The present method g ives detection limits of 0.12 ng ml(-1) for AFP and 0.95 ng ml(-1) for BSM, respectively. The coefficient variations (CVs) of the method are less than 8.0%, and the recoveries are in the range of 90-110%. The concentrations o f AFP in 23 human serum samples were determined, and the results were compa red with those of the independently determined by time-resolved fluoroimmun oassay method. A good correlation was obtained with a correlation coefficie nt of 0.993. (C) 2001 Elsevier Science B.V. All rights reserved.