Unexpected Errors in Gas Chromatographic Analysis of Methane Production by Thermophilic Bacteria

Unexpected errors in methane measurement by gas chromatography occurred when samples at thermophilic temperatures were analyzed. With a standard curve prepared at room temperature (25 degrees C), stoppered bottles incubated and sampled at 37 to 85 degrees C showed more methane upon analysis than bottles incubated at 25 degrees C: values at 50, 63, and 85 degrees C were 109, 126, and 125%, respectively, of the 25 degrees C value. All variation between 4 and 50 degrees C can be explained by the temperature difference between culture bottle and sampling syringe, and the variation of methane concentration can be predicted by the gas law. Between 50 and 63 degrees C, there was a more dramatic rise than predicted by theory. These variations are important to consider if thermophilic methane production is to be measured accurately. Methods to avoid errors are discussed.