MEASUREMENT IN-VITRO OF HUMAN PLASMA GLYCEROL WITH A HYDROGEN-PEROXIDE DETECTING MICRODIALYSIS ENZYME ELECTRODE

Human plasma glycerol was determined with a microdialysis electrode, c ontaining the enzymes glycerol kinase and glycerol phosphate oxidase h eld stationary within the electrode. A microdialysis electrode is esse ntially a conventional microdialysis probe, with a platinum working el ectrode inserted into the tip of the dialysis fiber and reference and counter electrodes contained in the upper compartment. The linear rang e of response to glycerol was directly dependent on the concentration of ATP. At 4 mM ATP, the linear range was 0.5-500 mu M. A fast respons e time of 20 s was obtained. Two types of interferences were observed when plasma glycerol was measured: direct oxidation of interferents at the electrode and attenuation of response to glycerol by reaction wit h hydrogen peroxide and/or poisoning of the platinum electrode. Ascorb ate, mate, and acetaminophen were removed from plasma samples by a pre treatment step involving peroxidase and catalase. Any remaining interf erent current was reduced by electropolymerizing o-phenylenediamine on to the platinum electrode. Adsorption of plasma proteins on the dialys is fiber was minimal and was not reduced by the preadsorption of human serum albumin. Very good correlation was obtained between the electro de and the standard spectrophotometric technique for the variation in glycerol concentration with time.