Milk lactate determination with a rotating bioreactor based on an electron transfer mediated by osmium complexes incorporating a continuous-flow/stopped-flow system

Abstract The high sensitivity that can be attained using a bienzymatic system and mediated by the redox polymer [Os(bpy) 2 ClPyCH 2 NHpoly(allylamine)] (Os-PAA), has been verified by on-line interfacing of a rotating bioreactor and continuous-flow/stopped-flow/continuous-flow processing. When the hydrogen peroxide formed by LO x layer reaches the inner layer, the electronic flow between the immobilized peroxidase and the electrode surface produces a current, proportional to lactate concentration. The determination of lactate was possible with a limit of detection of 5 nmol l −1 in the processing of as many as 30 samples per hour. This arrangement allows working in undiluted milk samples with a good stability and reproducibility. Horseradish peroxidase [EC 1.11.1.7] and Os-PAA were covalently immobilized on the glassy carbon electrode surface (upper cell body), lactate oxidase [EC 1.1.3. x ] was immobilized on a disk that can be rotated.