Chloride Interference in Total Nitrogen Analysis by the Kjeldahl Method

Very low recovery of NH4+-N was observed in total N determination of (NH4)2SO4in KCl solutions by a semimicro Kjeldahl method using permanganate and reduced iron to recover NO3- and NO2-, whereas complete recovery was obtained in analysis of NH4+-N in water, and of NO3--N or NO2--N in either water or KCl solutions. The loss of NH4+-N observed with KCl was attributed to the formation of NCl3upon reaction of NH4+with Cl2generated during oxidation of Cl- by MnO4-. This difficulty is avoided by using K2SO4instead of KCl for extraction of inorganic N from soil. Complete recovery was obtained by adding 15N-labeled NH4+, NO3-, or NO2- to 0.5 M K2SO4 soil extracts, and total 15N analyses of the labeled extracts were in good agreement with values calculated from the additions of 15N and the total N contents of the soil extracts.