19] Flow enthalpimetric determination of glucose

Abstract

The most important thermal condition for the flow enthalpimetric determination is not high precision thermostatting of the detection unit, but the thermal equilibration of the sample solution. In principle, flow enthalpimetry requires a relatively large sample volume, because the sample pulse broadening caused by the thermal equilibration coil influences the signal change with concomitant decrease in the analytical sensitivity. Therefore, the sample volume giving the most sensitive analytical signal is mainly set by the volume of the heat exchanger. An optimum flow rate is determined mainly by a combination of column adiabaticity or column length and the activity of the immobilized enzyme provided a sufficient sample volume is supplied. A limiting factor of this and other flow enthalpimetry methods is the nonspecific heat effect seen as peak height changes caused by slight differences in sample composition. Thus, the reproducibility (coefficient of variation) of this method is slightly poorer than those of other immobilized enzyme columns with end-point detection. By considering the analytical sensitivity based on the heat of reaction and the magnitude of nonspecific heat, the lower limit of determination is estimated to be 0.1 m M glucose. Therefore, on application of the method to various practical samples satisfactory results are obtained with samples above 1 m M (18 mg/dl) in glucose. The important feature of the method is its practicability and its ease of adaptability for routine analysis.