The metabolism of creatine: A micro-method for the determination of creatine and creatinine.
The technique, which makes possible the estimation of creatinine in 5 ml.
Abstract
WE have been occupied with the problem of estimating accurately the creatinine present in samples of a Ringer-Locke perfusate in which the creatinine content is 1-16y/ml. Not more than 10 ml. of perfusate are usually available for duplicate estimation, so that each sample contains 5-80y of creatinine. Simple concentration of the perfusates, which contain relatively large amounts of calcium, makes direct estimation of creatinine impossible, owing to interference with the development of the colour in the Jaffe reaction by the formation of a precipitate of calcium hydroxide when the alkali is added. The observation of Gaebler & Kelch [1928] that creatinine is adsorbed selectively on to fuller's earth in solutions containing other chromogenic substances led us to think that an adsorption method might eliminate difficulties due to the presence of substances interfering with the Jaff6 reaction and might also be sensitive enough to make possible the accurate estimation of very small amounts of creatinine. We were encouraged by the brief description by Borsook [1935] of a method of this character to adopt his technique, which consists in adsorbing the creatinine on to fuller's earth in acid solution and eluting it with the alkaline picrate in which the colour is developed. The method as we first used it had considerable disadvantages, which are described below. We believe that we have succeeded in overcoming them, and we feel that it may be useful to other workers to describe our technique, which makes possible the estimation of creatinine in 5 ml. of solution containing 5-80y of creatinine with an error of the order of + ly.