On the Determination of Creatinine and Creatine in Urine

Ever since the introduction of the calorimetric method for the determination of creatinine, potassium bichromate, in half normal solution, has been used as the standard for measuring the color obtained in the reaction of creatinine with picric acid and sodium hydroxide. That the bichromate has been serviceable for the purpose is evidenced by the fact that no other standard has ever been proposed. Potassium bichromate is, however, by no means ideal as a general standard of measure for the color comparisons involved in creatinine determinations. For determinations in ordinary urines containing 7-15 mgm. of creatinine in a volume of 5-15 cc. it may be regarded as satisfactory. For more dilute urines (or creatinine solutions) obtainable in unlimited quantities a fair degree of accuracy can be obtained with the bichromate standard by using the proportions of picric acid and alkali recommended by Shaffer. The use of the rigid bichromate standard imposes distinct and wholly unnecessary limitations on the applications of a remarkably flexible analytical method, and now that pure creatinine compounds can be prepared from urine with very little work it is, I think, a mistake to continue the use of the bichromate except perhaps for purely routine determinations in the course of ordinary urine analysis. The technique described in this paper is based on the use of 1 mgm. of creatinine as a standard in the making of the color comparisons.