Abstract
A novel method is presented for transesterification of fatty acid esters in phospholipids and triglycerides to benzyl esters while simultaneously recovering free fatty acids as methyl esters. Transesterification is catalyzed by 0.2 M (m-trifluoromethyl phenyl)trimethyl ammonium hydroxide in methylene chloride, 10% (v/v) benzyl alcohol, and 1% (w/v) potassium tert-butoxide, and is complete in 30 min at room temperature. Methyl esters of all common fatty acids separate from the benzyl esters formed from phospholipids. This method has broad utility and is applicable to the formation of esters optimized for detection by absorbance or fluorescence (high performance liquid chromatography), electron capture (gas-liquid chromatography), or negative ion chemical ionization (gas-liquid chromatography-mass spectrometry).
Highlights
In this report we present a rapid method to obtain fatty acid benzyl esters by direct transesterification of phospholipids or other glycerides using benzyl alcohol in methylene chloride with a quaternary ammonium base and potassium tmt-butoxide as catalysts
Methanol was removed from 0.1 ml of a 0.2 M methanolic solution of (m-trifluoromethyl phenyl) trimethyl ammonium hydroxide by rotary vacuum evaporation and the sample was kept under vacuum for 10 min after it reached dryness to remove the last traces of methanol
Methanol contained 50 pg/ml of butylated hydroxytoluene, and water contained 2 mM EDTA, pH 7.0.The dichloromethane phase containing phospholipids and free fatty acids was dried over sodium sulfate, the sample was removed from the drying agent, and the solvent was completely evaporated under nitrogen
Summary
Di-heptadecanoyl-sn-glycero-3-phosphocholineand 1palmitoyl-2-linoleoyl-sn-glycero-3-phosphocholinweere obtained from Sigma Chemical Company (St. Louis, MO). Methanolic (m-trifluoromethyl phenyl) trimethyl ammonium hydroxide (0.2 M) (called Methyl Prep 11) was a product of Applied Sciences Laboratories, Inc. Potassium tot-butoxide (Aldrich) was sublimed before use [7]. Gas-liquid chromatographic analyses were performed with a Perkin-Elmer model 3920 gas chromatograph with an all-glass sample stream, a 6 ft x 4 mm glass column containing 3% SP 2100 on Supelcoport, a nitrogen flow rate of 20 mlfmin, and a flame ionization detector. The temperature was programmed from 175 to 25OOC at 4OC/min. A Spectra-physics minigrator was used to establish retention times and peak areas
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