Simple fluorometric ultramicroassay for urea in tubular fluid of the kidney.

Sensitive fluorometric method for the determination of picomole amount of urea in tubular fluid of the kidney is presented. It is a modification and simplification of the macromethod by McCleskey (6) for the urea determination in blood. Assay is based on the reaction of urea with diacetylmonoxime and sulphuric acid in boiling water within 20 minutes. The reaction is highly specific for urea. The simple procedure requires only one micropipetting step. The fluorometric determination of urea can be made in 20 nanoliters of proximal and in 5 nanoliters of distal tubular fluid with the reproducibility of +/- 4.44% and of +/- 5.38%, respectively. The minimum detection limit is 20 picomoles of urea.