On-line calibration of a computerized biosensor system for continuous measurements of glucose and lactate

An on-line calibration procedure for application in continuous monitoring systems has been developed. Control of the calibration value and recalibration on-line during monitoring is possible without having to disrupt the sample withdrawal. The calibration procedure has been applied and evaluated in a continuous biosensor system based on the detection of oxygen depletion during enzymatic substrate conversion by immobilized oxidases. Evaluation included on-line calibration during continuous measurements of glucose and lactate in bovine blood samples. Calibration of the complete system consisting of a sampling device, a sample handling step, a biocatalytic step, a detection step, and a data processing unit is performed by the on-line addition of a calibration solution to a blank sample which is fed through the system. The calibration cycle is completed within 5.5 min. When recalibration is carried out during monitoring, the calibration solution is added to the sample, instead of to a blank sample, and the increase in outlet signal is registered. The major advantage of this internal standard principle is that the calibration solution is fed through the whole system according to the same path as the sample solution and thus takes into account all parameters influence the sample