A colorimetric assay for amino nitrogen in small volumes of blood: reaction with beta-naphthoquinone sulfonate.

An assay has been developed for the colorimetric estimation of total amino acids in small volumes (100 microliters) of whole blood. The procedure utilizes the reaction of amino nitrogen with beta-naphthoquinone sulfonate. It represents a substantial improvement on previously published methods by decreasing reagent volumes and accurately specifying and maintaining pH conditions for the reaction itself (9.2-9.4) and for removal of excess reagent prior to measurement of the resulting complex (2.2-2.4). Ammonia is the only compound shown to significantly interfere with the assay but this is not a problem at physiological concentrations.