A gas chromatographic analysis of fecal short-chain fatty acids, using the direct injection method.

A simple, reproducible, and rapid gas chromatographic method for short-chain fatty acid determination in human feces was developed. It involves direct injection of fecal supernatants into the gas chromatograph, without any pretreatment. Contamination of the gas chromatographic column with nonvolatile fecal material was prevented by the use of a glass liner in the injector. This liner, which acted as a precolumn, was stoppered with a glass wool plug at the lower end of the liner. Injection was performed against the glass wall of the liner, ensuring an immediate contact of the injected sample with the hot glass wall. More than 100 injections of fecal supernatants could be carried out before the liner had to be replaced by a new one. Peak tailing and ghosting was prevented by the use of formic acid in the fecal samples. The method gave sharp peaks with baseline separation for all the fatty acids.