Bioanalytical system for control of hemodialysis treatment based on potentiometric biosensors for urea and creatinine

Highly stable, sensitive and fast responding urea and creatinine biosensors have been successfully used for development of new flow injection analysis (FIA) system dedicated for biomedical bloodless control of hemodialysis. The biosensors are based on ammonium ion-selective electrodes with covalently bound monomolecular layer of enzymes. To improve the selectivity of the biosensing the FIA system contains cation exchange column for separation of endogenous ammonia and alkaline cations, that interfere in the course of urea and creatinine determination. In the developed analytical procedure the steps of separation and regeneration of the ion exchanger are fully automated. Other metabolites, commonly used drugs, as well as anionic components of dialysate fluids did not interfere. Under optimized conditions the determination ranges offered by this bioanalytical system completely cover levels of urea and creatinine present in real samples of postdialysate fluid. The results of analysis are fully comparable with those obtained using reference methods (bienzymatic spectrophotometric for urea, and kinetic spectrophotometric Jaffe and electrophoretic/UV methods for creatinine). The available frequency of this biparametric analysis is 8–9 samples of postdialysate per hour without any additional sample pretreatment. The operational stability of the developed FIA system exceeds one month. Storage stability determined by storage lifetimes of the biosensors was found to be longer than six months without any loss of sensitivity. The demonstrated bioanalytical system could be used as discrete on-line monitor of urea and creatinine profiles in spent dialysate. Such profiles are useful for evaluation of biomedical parameters important for quantitative description of hemodialysis therapy.