Colorimetric method for estimating polylysine and polyarginine

A rapid and sensitive method is described for estimating polylysine and polyarginine. The method involves the stoichiometric precipitation of these polyamino acids by excess of the anionic dye methyl orange, followed by spectrophotometric determination of unbound dye. 10 μg or less of polylysine or polyarginine can thus be estimated. The effects of various salts on the estimation are described.