NEW APPLICATIONS OF CARBONYLMETALLOIMMUNOASSAY (CMIA) - A NONRADIOISOTOPIC APPROACH TO CORTISOL ASSAY

A non-isotopic heterogeneous competitive immunoassay procedure, carbon yimetalloimmunoassay (CMIA) has been applied to the assay of cortisol. The organometallic tracers employed were two stereoisomers (Z and E) of certain cobalt carbonyl complexes of cortisol which have strong, ch aracteristic v(CO) absorptions in the infrared, detectable by Fourier transform infrared (FT-IR) spectroscopy at the femtomole level. The se paration of the free and bound organometallic-labelled fractions was a chieved by solvent extraction with isopropyl ether. Complete character ization (i.e., dilution, competition and standard curves) of two diffe rent polyclonal anticortisol antibodies was possible using the CMIA me thod. Identical titre values were obtained for the two different stere oisomers used as tracers. In terms of the standard curves, however, th e isomers behaved differently depending on which batch of antibody was used. When the best antibody/tracer pair (30 pmol of E isomer; antico rtisol 1 antibody) was employed, we obtained a B/B-c value at 50% of 4 2 +/- 2.12 pmol and a coefficient of variation of 5%. Finally, prelimi nary results of a CMIA analysis of plasma cortisol from a patient indi cate that reliable and reproducible assays are possible for amounts as small as 50 mu l of serum.