Determination of urea in serum based on the combination of an enzymatic reaction with immobilized urease and ion chromatographic analysis.

A quantitative method for the determination of urea in serum was studied. An ion chromatograph (IC) with a conductivity detector was used in this method, where the chromatograph was modified by placing an immobilized urease column between the injection loop and a guard column of the cation analysis column. Immobilized urease was prepared by the adsorption of urease on cedar sawdust with triethylenetetramine. The adsorption capacity of urease was 190 mg g(-1), and its activity was 3500 U g(-1). The conversion efficiency of urea to ammonium ion was 100%, and the half life of immobilized urease was 60 days. It was possible to use the immobilized urease in a pH range of 3.0 to 9.0, and at temperatures up to 60 degrees C. The determination of urea was attempted by IC attaching an immobilized urease column. The limit of detection of urea was 0.2 mg L(-1), and the calibration curves of urea were very linear over 0.8-25 mg L(-1). The urea concentration in the human serum could be determined with a standard deviation of 0.06-0.13 within 5 min after injecting the serum sample.