Emission spectroscopy determination of 15N in ammonia and amino acids extracted from biological material

A method is described of the sample preparation for the emission spectroscopy determination of 15N in ammonia, glutamic acid, aspartic acid, leucine and alanine. It consists of the chromatographic separation of ammonia and amino acids from the components of biological material on ion-exchange resins, the release of ammonia from amino acids by the ninhydrin reaction, the microdiffusion extraction of ammonia from Li citrate buffers and the following catalytic conversion to nitrogen in vacuum. The method makes it possible to extract isotopically pure ammonia and amino acids from mixtures of 15N-amino acids and 15N-urea (C15N <= 50 at.%). The optimum concentration of ammonia and amino acids in the samples is 40 μg of N. (author)