Fatty Acid Methods and Measurements

Fatty acids are typically present in plant and animal tissues as triglycerides, which are saponified (hydrolyzed) and converted to fatty acid methyl esters (FAMEs) for analysis by gas chromatography. When this conversion is required, the fatty acids are reported as the triglycerides. Free fatty acids do not require saponification, but do require esterication prior to analysis by gas chromatography. For value assignment of fatty acid levels in SRMs, two independent methods are utilized. Multiple deuterated fatty acids are added to the samples for use as internal standards. If necessary, the samples are extracted and the triglycerides are converted to free fatty acids through saponification. The derivatized fatty acid mixtures are analyzed by either gas chromatography with flame ionization detection (GC-FID) or by GC with mass spectrometric detection (MS). 

Biodiesel materials represent a special case since the materials that are produced from plant or animal fats are converted to FAMEs during manufacturing. The analysis of biodiesel SRMs is simplified, since the materials can be spiked with the internal standards and injected directly without further processing.