Comparative study of first-, second- and third-generation amperometric glucose enzyme electrodes in continuous-flow analysis of undiluted whole blood

First-, second- and third-generation amperometric glucose enzyme electrodes were compared under flow-injection and steady-state conditions for the monitoring of undiluted whole blood. First-generation electrodes, based on the detection of hydrogen peroxide at a platinum electrode, are generally unsuitable because of the eventual poisoning of the electrode and because of their susceptibility to oxygen variation. Second-generation electrodes in which a mediator is used for the reoxidation of glucose oxidase are more suitable for the analysis of whole blood under both steady-state and flow-injection conditions. However, the choice of mediator is important. The best results with regard to linear range and stability were obtained with tetrathiafulvalene, whereas dimethylferrocene required considerable pretreatment before use. A third-generation electrode based on tetrathiafulvalene-tetracyanoquinodimethane where direct oxidation of glucose oxidase occurs also proved useful but showed lower stability and a smaller dynamic range compared with the second-generation devices. Flow-injection and steady-state studies were carried out using wall-jet cell geometry.