Automatic estimation of urea using urease and alkaline phenol.

HE BLUE COLOR produced by the reaction of alkaline phenol with ammonia was first described by Berthelot (1), and Thomas (2) demonstrated that the reaction could be applied to the colorimetric determination of amnionium salts. \all Slvke and Hiller (3) estimated blood ammonia by means of this reaction, a11(l Borsook (4) applied the reaction to the estimation of urea after urease hydrolysis, by distilling tile ammonia so formed into dilute acid. Russell (5) speculated that urea might he estimated by direct reaction with biologic fluids before and after urease treatment, and Fleury and Eherhard (6), following this suggestion, estimated urea in serum. However, Russell, and later, Muftic (7) indicated that tile reaction may not be specific for ammonia, amId thley believed that interference by amino groups precluded the application of tile reaction directly to biologic fluids. Logsdon (8) adapted the method so that ammonia in fermentation mediums could he estimated with an AutoAnalyzer.* He tested a large group of amino acids and related substances and showed that these compounds did not interfere with his modification of the reaction. Since the modification involved dialysis of the sample before analysis, it is possible that interfering substances may have been removed.