Determination of the fatty acid composition of saponified vegetable oils using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

A method using matrix-assisted laser desorption/ionization time-of-flight m ass spectrometry (MALDI-TOFMS) for the determination of the fatty acid comp osition of vegetable oils is described and illustrated with the analysis of palm kernel oil, palm oil, olive oil, canola oil, soybean oil, vernonia oi l, and castor oil. Solutions of the saponified oils, mixed with the matrix, meso-tetrakis(pentafluorophenyl)porphyrin, provided reproducible MALDI-TOF spectra in which the ions were dominated by sodiated sodium carboxylates [ RCOONa + Na](+). Thus, palm kernel oil was found to contain capric acid, la uric acid, myristic acid, palmitic acid, oleic acid, and stearic acid. Palm oil had a fatty acid profile including palmitic, linoleic, oleic, and stea ric. The relative percentages of the fatty acids in olive oil were palmitol eic (1.2 +/- 0.5), palmitic (10.9 +/- 0.8), linoleic (0.6 +/- 0.1), linolei c (16.5 +/- 0.8), and oleic (70.5 +/- 1.2). For soybean oh, the relative pe rcentages were: palmitoleic (0.4 +/- 0.4), palmitic (6.0 +/- 1.3), linoleni c (14.5 +/- 1.8), linoleic (50.1 +/- 4.0), oleic (26.1 +/- 1.2), and steari c (2.2 +/- 0.7). This method was also applied to the analysis of two commer cial soap formulations. The first soap gave a fatty acid profile that inclu ded: lauric (19.4% rt 0.8), myristic (9.6% +/- 0.5), palmitoleic (1.9% +/- 0.3), palmitic (16.3% +/- 0.9), linoleic (5.6% +/- 0.4), oleic (37.1% +/- 0 .8), and stearic (10.1% +/- 0.7) and that of the second soap was: lauric (9 .3% +/- 0.3), myristic (3.8% +/- 0.5), palmitoleic (3.1% +/- 0.8), palmitic (19.4% +/- 0.8), linoleic (4.9% +/- 0.7), oleic (49.5% +/- 1.1), and stear ic (10.0% +/- 0.9). The MALDI-TOFMS method described in this communication is simpler and less time-consuming than the established transesterification method that is coupled with analysis by gas chromatography/mass spectromet ry (GC/MS). The new method, could be used routinely to determine the qualit ative fatty acid composition of vegetable oils, and, when fully validated b y comparison with standard analytical methodologies, should provide a relat ively fast quantitative measurement of fatty acid mixtures and/or soap form ulations that contain saturated and unsaturated hydrocarbon moieties. Copyr ight (C) 2000 John Whey & Sons, Ltd.