HOMOGENEOUS AMPEROMETRIC IMMUNOASSAY FOR THEOPHYLLINE IN WHOLE-BLOOD

A homogeneous spectrophotometric EMIT immunoassay kit for the quantita tion of theophylline in serum or plasma has been modified to produce a rapid, amperometric immunoassay requiring a 50 mu l whole blood sampl e. The basis of the detection system for the assay is the electrochemi cal oxidation of NADH produced by G6PDH-labelled theophylline at a pot ential of +150 mV vs Ag/AgCl using platinised activated carbon (PACE) electrodes. Comparison of the amperometric whole blood method with the conventional spectrophotometric plasma assay produced a reasonable co rrelation: y = 0.90x - 1.01, (r = 0.98, n = 12). The advantage of the new method is that simple and robust instrumentation can rapidly deter mine theophylline in whole blood with no sample pre-treatment or separ ation steps.