The Leather Research Laboratory is able to determine the percentage of leather fiber (hide or collagen fiber) in bonded leather (or genuine leather) according to ASTM D 2868, Standard Test Method for Nitrogen Content (Kjeldahl) and Hide Substance Content of Leather.

The sample is digested with acid in the presence of a catalyst to convert the nitrogen to the ammonium ion, which is non-volatile under the highly acidic conditions. The acid mixture is then made alkaline, and the liberated ammonia distilled into boric acid solution, which absorbs the ammonia. Finally, the amount of ammonia in the boric acid is determined by back titration, giving the nitrogen and hide substance (protein fiber) content.