The non-protein nitrogen composition of grass silages: I. The estimation of the basic amino acids and non-volatile amines by chromatography on a weak cation exchange resin

SUMMARYInvestigations into the non-protein nitrogen composition of grass silages using the 50 cm strong cation-exchange column of Spackman, Stein & Moore (1958) to determine the basic amino acids led to difficulties in the determination of ethanolamine in the presence of high concentrations of ammonia, and of histidine in the presence of δ amino-n-valeric acid. An alternative technique for the ion exchange chromatography and estimation of histidine, lysine, ornithine, ethanolamine, arginine and ammonia on a weak cation-exchange resin has been developed. This method enables small amounts of ethanolamine to be determined in the presence of large amounts of ammonia and values for the ethanolamine content of a number of silage samples are presented. When used in conjunction with the technique of Spackman et al. (1958) the δ-amino-n-valeric acid content of grass silages could also be determined in the presence of histidine.The estimation of amines produced by the microbial decomposition of herbage proteins during ensiling has previously involved their initial separation from the amino acids followed by quantitative partition chromatography. An alternative method for the estimation of these amines by ion-exchange chromatography on a weak cation-exchange resin is described. This method permits the colorimetric determination of β-phenylethylamine, tyramine, tryptamine, 5-hydroxytryptamine, putrescine, cadaverine and histamine without interference from the amino acids. The efficiency of this technique has been investigated using standard solutions of the naturally occurring amines and samples of good quality and of high pH spoilt silages.