A new adsorbent for creatinine.

Abstract

The use of kaolin in removing creatinine from dilute solution is disadvantageous in that the adsorbed creatinine cannot be released again for identification. An adsorbing agent which can be decomposed under conditions that will not destroy creatinine therefore appears desirable.

If one adds to 10 cc. of the strongest creatinine standard for blood determinations (1 mg. of creatinine in 100 cc. of saturated picric acid), 0.1 cc. of 9.5 per cent potassium chloride, and 1 cc. of 10 per cent phosphotungstic acid, a finely divided yellow precipitate forms, which settles out very slowly, but can be centrifuged out quickly. The supernatant liquid is decanted, and the precipitate suspended in 10 cc. of saturated picric acid. On adding 1 cc. of 10 per cent sodium hydroxide, the precipitate dissolves and the color developed matches that of 10 cc. of the same standard, made alkaline directly with the same amount of sodium hydroxide. Controls with the potassium precipitate in absence of creatinine are negative.

Complete adsorption of creatinine is practically coincident with appearance of the precipitate. Supersaturation is occasionally encountered. If the precipitate fails to appear, the difficulty is overcome, when working with larger amounts, by adding a drop of potassium chloride solution after the phosphotungstic acid. The precipitate is more difficult to centrifuge out if all of the potassium chloride is added after the phosphotungstic acid.

The precipitate obtained from a liter of saturated picric acid containing 10 mg. of creatinine, on adding 10 cc. of 9.5 per cent potassium chloride, and 100 cc. of 10 per cent phosphotungstic acid, can be suspended in the centrifuge tube in which it has been collected, in 30 cc. of normal sulfuric acid. On diluting the mixture to about 50 cc. and shaking with ether, an emulsion forms, which separates on a moment's centrifuging into three sharp layers, predominantly ether, sulfuric acid, and phosphotungstic acid solutions.