Material and Methods

We describe a simple procedure for estimating amino acids, based on the formation of charge-transfer com-plexes with p-benzoquinone. The reaction is insensitive to ammonia, urea, purifles, creatinine, and other nitrog-enous compounds present in serum or urine, except amines, peptides, and proteins. The reagent is cheap, stable, and does not require prior treatment of urine be-fore determination. Specifity, precision, and normal values of this method are reported and compared with those obtained by a colorimetric ninhydrin technique. Additional Keyphrases: glycine equivalents #{149} normal values #{149}p-benzoquinone reagent #{149}liver disease Several methods have been proposed for measur-ing an increase in free amino acids in blood and urine, deemed an indicator of liver cell destruction. Though the gasometric ninhydrin method is unques-tionably the most specific one, it takes too long, and colorimetric techniques in which ninhydrin (1, 2), 1-fluoro-2,4-dinitrobenzene (3, 4), 2,4,6-trinitroben-zenesulfonic acid (5), or 2-naphthoquinone-4-sul-fonic acid (6) is used have some disadvantages: inter-ference by ammOnia, urea, or uric acid; poor or no reaction of proline; instability of the reagent against oxygen; or required heating. Use of formol titration (7) is confined to urine because of its low sensitivity, and the formation of amino acid-copper complexes, followed by iodometric titration (8), colorimetric de-termination (9), or atomic absorption spectropho-tometry (10), yields too-high values by reaction of copper with many organic acids. This communication describes a simple colorimet-nc method based on the formation of red charge-transfer complexes of p-benzoquinone with amino acids (11)