DETERMINATION OF AMINO NITROGEN IN PLANT EXTRACTS

Abstract

In nitrogen partition studies it is customary to estimate the amount of nitrogen contained in the alpha-amino groups of amino acids by means of the Van Slyke gasometric or the Sorensen formol titration method. As is generally known, these methods were developed for the analysis of pure amino acids or products of protein hydrolysis as applied particularly to animal tissues. Since plant extracts usually contain water soluble pigments and buffering substances which interfere with the formol titration, the Van Slyke method is more frequently employed. While engaged in some nitrogen partition studies with alcoholic extracts of apple leaves (9), the writer observed that the yield of amino nitrogen by the standard Van Slyke procedure was in excess of the total soluble, non-protein nitrogen. This finding has repeatedly been confirmed and the same error noted in varying degrees in several other plant tissues extracted with water or 80 per cent, alcohol. The present investigation was undertaken to study the factors responsible for these anomalous results, and to develop, if possible, corrective measures.