Amperometric probe for 3-hydroxybutyrate with immobilized 3-hydroxybutyrate dehydrogenase

The enzyme 3-hydroxybutyrate dehydrogenase is immobilized on a graphite electrode suitable for determination of NADH. Of the several procedures tested for the immobilization, direct adsorption on the electrode surface was most satisfactory, with useful lifetimes of up to 3 days. The best calibration graphs for the NADH, and for 3-hydroxybutyrate were obtained at pH 7.5 (phosphate buffer). 3-Hydroxybutyrate was determined in the range 5–100 μmol l^?1 at pH 7.5 with good precision. Interferences are discussed.