Monitoring urea levels during haemodialysis with a pulsed-flow chemiluminescence analyser

We have developed a rapid and robust method for the determination of urea in spent haemodialysis fluid as a measure of the efficiency of haemodialysis treatments. A novel flow analysis instrument (which generates a pulsed solution flow) was coupled with a chemiluminescence detection system, based on the oxidation of urea with hypohromite. The 'pulsed-flow chemiluminescence analyser' exhibited high precision (1.6% relative standard deviation (R.S.D.) for a 1 x 10(-5) M urea standard, n = 10) and good limit of detection (9 x 10(-7) M, S/N = 3) as a result of the rapid and reproducible mixing of small volumes of reagent and sample at the point of detection. The proposed chemiluminescence technique and an established urease-based laboratory procedure were compared, and showed a very similar trend for the change in urea concentration during a typical haemodialysis treatment. The relative chemiluminescence response from the oxidation of species with similar structure has revealed the inherent selectivity of the light producing pathway, but a positive interference was obtained from protein when this technique was applied to the determination of urea in serum samples. Arginine was identified as the predominant source of this interference. (C) 2002 Elsevier Science B.V. All rights reserved.