Flow system for direct determination of enzyme substrate in undiluted whole blood

Enzyme sensors requiring reagent and controlled pH to detect substrate at non-steady-state conditions are described. Hematocrit dependence in sample transportation, in sample and reagent mixing, and in sample dialysis is minimized in the system by the use of segmented sample injection, membrane deposited reagent, and membranes of low permeability. The clinical features of the flow system are illustrated by a beta-D-glucose determination. Other aspects of the flow system are illustrated by L-lactate and creatinine determinations. All three assays end up with a NADH detection at a chemically modified electrode (CME).