Application of L ‐(+)‐Lactate electrode for clinical analysis and monitoring of tissue culture medium

L ‐(+)‐Lactate oxidase (EC 1.1.3.2) was immobilized onto the porous side of a cellulose acetate membrane with asymmetric structure which has selective permeability to hydrogen peroxide. The lactate electrode was constructed by combination of a hydrogen peroxide electrode with the immobilized enzyme membrane. Properties of the enzyme membrane and characteristics of the lactate electrode were clarified for the determination of L ‐(+)‐lactic acid. The lactate electrode responded linearly to L ‐(+)‐lactic acid over the final concentration 0‐0.25 mmol/L within 30 s. When the enzyme electrode was applied to the determination of L ‐(+)‐lactic acid in control serum, within‐day precision (CV), analytical recovery, and correlation coefficient between the electrode method and the colorimetric method were 1.4% with a mean value of 4.54 mmol/L, 98.0%, and 0.986, respectively. The lactate electrode was sufficiently stable to perform 1040 assays over 13 days operation for the determination of L ‐(+)‐lactic acid. The dried immobilized enzyme membrane retained 84% of its initial activity after storage at 4°C for 12 months. Moreover, the enzyme electrode was applied to the monitoring of culture medium for human melanoma cells. L ‐(+)‐Lactate production and D‐glucose consumption were closely related to cell numbers.