Application of the phenol-hypochlorite reaction to measurement of ammonia concentrations in Kjeldahl digests of serum and various tissues.

Conditions have been defined that enable the use of nitroprusside as a catalyst for the phenol-hypochiorite reaction when the latter is applied to measurement of nitrogen in Kjeldahl digests containing mercury. This is accomplished by lowering the concentration of mercury to a range where it remains effective in accelerating the destruction of organic matter during digestion but no longer reacts with nitroprusside. In addition, the use of minimal concentrations of nitroprusside diminishes further the possibility of interference by mercury and has the added advantage of decreasing the pH dependence of indophenol blue formation. The sensitivity of the reaction makes possible measurement of nitrogen in very small samples with relatively short digestion times.