A Specific Micromethod for the Colorimetric Determination of Glycine in Blood and Urine*

Recently we described a method for the determination of alanine based upon its conversion into acetaldehyde by the action of ninhydrin (1). A method for the measurement of glycine has been devised which involves its conversion by ninhydrin to formaldehyde; the latter is then measured by its reaction with chromotropic acid. Earlier methods for the measurement of glycine are less sensitive and specific than the one here proposed. In 1902 Fischer (2) described a procedure for the gravimetric determination of glycine by isolating it from protein hydrolysates. Other gravimetric methods were devised by Town (3) and Bergmann and Fox (4). The former added nitranilic acid to a protein hydrolysate containing glycine and weighed the insoluble glycoco11 nitranilate thus obtained. The hydrolysate had to be freed of many inorganic salts which interfered with the precipitation. Bergmann and Fox (4) used trioxalatochromiate to produce an insoluble compound with glycine. All of these methods are too insensitive to be applicable to biologic materials in which the amounts of glycine are very small. Zimmermann (5) reported a calorimetric method for glycine based upon its reaction with o-phthalic dialdehyde. The method was subsequently improved by Klein and Linser (6) and Patton (7). Many substances other than glycine, such as histidine, histamine, arginine, cysteine, tryptophane, and ammonia, gave similar reactions and consequently had to be removed before the addition of the dialdehyde. The sensitivity of the method was limited to a minimum of about 1 mg. of glycine. The reaction between a-amino acids and ninhydrin has been clearly