Automatic determination of malate dehydrogenase activity with a flow-injection multidetection system

An automatic flow-injection method for the determination of malate dehydrogenase activity is proposed. The manifold used includes a selecting valve for closing the circuit along which the reacting plug is continuously circulated, and passed through the flow-cell of a conventional spectrophotometer, inserted into the closed circuit. A multipeak recording is obtained, each peak corresponding to one passage of the plug through the flow-cell. This recording allows the sensitivity to be modified, as required, using different types of measurements (for example, absorbance of the maxima or minima and absorbance differences between maxima or minima or their sums). The activity of the analyte can be determined in the range 0.02-2.00 U/l, with an r.s.d, of less than 0.90% at a sampling rate between 11 and 65 samples/h. The applicability of the method was checked by applying it to human serum samples. Analyte recoveries between 96 and 103% were obtained.