To measure cross-linking amino acids in a collagen hydrolyzate using a conventional amino acid analyzer with ninhydrin detection, the bulk amino acids must be largely removed to avoid plugging the reaction coil. Tissue is thoroughly reacted with sodium borohydride to convert all intermediate cross-linking residues to their reduced, acid-stable forms. More vigorous reduction conditions may be used than when preparing profiles of tritium-labeled cross-links using NaB3H4 and direct amino acid analysis.
