By addition of mercuric chloride to the reaction-mixture in the Van Slyke apparatus, practically the theoretical values for the amino-nitrogen content of glycine and peptides having a terminal glycyl-rest are obtained. If a considerable amount of lithium bromide is present at the same time, the effect of mercuric chloride is greatly lost. Using potassium iodide in that case the right value is found for glycine, but the values for diglycine and triglycine are 7% and 5% too high.
Sluyterman, L. A. A. E., & Kooistra, M. (1951). Volumetric amino-nitrogen determinations in glycine and glycyl-peptides. Recueil des Travaux Chimiques des Pays-Bas, 70(12), 1045-1048. https://doi.org/10.1002/recl.19510701204