A Flow-Through Enzyme Reactor System for Urea Determination in Blood Serum Using Conductimetric Measurement

A flow-through enzyme reactor system for the determination of urea using conductimetric measurement is described. Samples are introduced as pulses in a continuous flow of buffer which is passed through a dialyser. The dialysis solution on the other side of the dialysis membrane collects urea molecules from the samples which diffuse through the membrane and is pumped through an enzyme reactor containing urease immobilized to porous glass. Conductivity electrodes are used to measure the increase in conductivity of the dialysis solution resulting from the hydrolysis of urea into charged products. The effects of the flow rate and the possible interferences of cells or NaCl in the sample solutions to the response of the enzyme sensor system have been investigated. The system is used for the determination of urea in standard solutions as well as in human blood serum samples. The enzyme sensor is operated in a linear mode in the concentration range 5-70 mmol/L (correlation coefficient, r = 0.998). Good agreement is obtained when the urea concentrations of human blood serum samples are determined using the enzyme sensor system compared to the diacetyl monoxime colorimetric method (r = 0.997) and to the results obtained by a commercial automated analysis system (r = 0.998).

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