Analysis of fatty acid methyl esters with high accuracy and reliability. VI. Rapid analysis by split injection capillary gas-liquid chromatography.

Of the several facets of technique that must be addressed to allow the generation of highly accurate results by gas chromatographic analysis of fatty acid methyl esters, that of split injection to capillary columns has long been a major problem. A practical solution of this problem is now proposed. Three factors were found to be of major importance in achieving highly accurate results viz. avoidance of needle discrimination when injecting, very rapid vaporisation of the sample and complete homogenisation of the sample with the carrier gas stream. High speed of injection was found to be a highly effective means of avoiding needle discrimination. Rapid vaporisation of the sample was achieved by the use of relatively dilute solutions of analyte in the solvent, the smallest sample size commensurate with obtaining a chromatogram that could be accurately quantitated and, particularly, by the use of injector temperatures considerably higher than those generally adopted. Good mixing of the vaporized sample with the carrier gas was achieved with a number of injector insert designs, but, with improvement of design, it was found possible to achieve linear splitting over a wide range of operating conditions. The most controversial recommendation is to use very high injection temperatures, but it has been shown that the commonly held view that this may cause pyrolysis of fatty acid methyl esters is not true, even when the esters are highly unsaturated.