Measurement in vitro of human plasma glycerol with a hydrogen peroxide detecting microdialysis enzyme electrode

Human plasma glycerol was determined with a microdialysis electrode, containing the enzymes glycerol kinase and glycerol phosphate oxidase held stationary within the electrode. A microdialysis electrode is essentially a conventional microdialysis probe, with a platinum working electrode inserted into the tip of the dialysis fiber and reference and counter electrodes contained in the upper compartment. The linear range of response to glycerol was directly dependent on the concentration of ATP. At 4 mM ATP, the linear range was 0.5-500 microM. A fast response 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 with hydrogen peroxide and/or poisoning of the platinum electrode. Ascorbate, urate, and acetaminophen were removed from plasma samples by a pretreatment step involving peroxidase and catalase. Any remaining interferent current was reduced by electropolymerizing o-phenylenediamine onto the platinum electrode. Adsorption of plasma proteins on the dialysis fiber was minimal and was not reduced by the preadsorption of human serum albumin. Very good correlation was obtained between the electrode and the standard spectrophotometric technique for the variation in glycerol concentration with time.