Method for Determination of Volatile Fatty Acids in Stools.

Abstract

In a previous report it was shown that the volatile fatty acids, formic, acetid and butyric, could be steam distilled from a concentrated solution of magnesium sulphate at rates of 60 to 100% faster than from watery solutions. We wish to report here a method for the precipitation of stools and the application of the rapid method of steam distillation to the filtrates obtained. Stools were collected in a volume of 10% sodium hydrate equal to that of the stool. The alkali stops fermentation almost completely, deodorizing the stool, and favors emulsification. 100 gms. of alkali stool mixture is neutralized with strong sulphuric acid and 175 to 200 cc. of a 10% mercuric chloride solution added. This amount of mercuric chloride is soluble in 1.5% hydrochloric acid. The mercury is precipitated with solid calcium hydrate, which is added until the stool is strongly alkaline to litmus. The volume is made up to 500 cc. which is centrifuged in 100 cc. centrifuge tubes. Two 100 cc. portions of supernatant fluid are measured off and made acid to litmus with sulphuric acid. Excess mercury is precipitated with hydrogen sulphide, the excess being blown off with a current of air. After filtering 100 cc., portions of filtrate are distilled in the manner reported. These filtrates from stools are almost nitrogen free (95% being removed) and free from higher insoluble fatty acids and sugar. On distilling the stool filtrates the rates of distillation obtained closely resemble those obtained from mixtures of pure volatile fatty acids. When formic, acetic, propionic or butyric acids are added to stools they may be recovered to within 5 to 10%. Duplicate determinations usually agree to within 5%. From the observed rates of distillation, it is concluded that the principal volatile fatty acids in the stools are acetic and butyric.