A new colorimetric method for the determination of urea nitrogen in blood with diacetyl monoxime-glucuronolactone-glucosaccharodilactone reagent.

In a previous paper,3) a colorimetric method for the determination of urea nitrogen in blood and urine was presented on the basis of a color reaction of urea with diacetyl monoxime (DAM) in phosphoric acid solution in the presence of D-glucuronolactone (GL), which served to produce a photo-stable color and eliminate the sigmoidal nature of calibration curve observed usually in the DAM method.4) The method was then modified for the microdetermination5) and the automated determination of urea nitrogen in blood.6) These methods, however, required a relatively long heating time (40 min) to obtain an appropriate and constant intensity. In the course of study on the determination of urea in biological fluids, D-gluco-1,4-3,6disaccharolactone (SL) was found to produce rapidly an intense color when added to the reaction mixture of urea with DAM in phosphoric acid solution. The developed color gradually faded in daylight, but the initial color became stable when GL was present in the reaction mixture. Then a simple, rapid and reliable method for the determination of urea nitrogen in blood was developed utilizing this finding.