Gas Chromatographic Analysis of Geometrical Isomers of Unsaturated Fatty Acids as O-Isopropyliden Derivatives with Simultaneous Analysis of Positional Isomers by Use of Gaschro-Mass Spectrometer

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概要

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• A method for gas chromatographic analysis of geometrical isomers of unsaturated fatty acid is described. Unsaturated fatty acid methyl esters were first converted to dihydroxy (polyhydroxy-) derivatives by osmium tetroxide hydroxylation in dioxane in the presence of Pyridine as catalyst. The osmate formed was then split by Na<SUB>2</SUB>SO<SUB>3</SUB>. The dihydroxy-(polyhydroxy-) derivatives were subsequently transformed into O-isopropyliden derivatives by a reaction with acetone, forming 1, 3-dioxolane ring at the position of double bond, in the presence of anhydrous CuSO<SUB>4</SUB> and dimethoxypropane as dehydrating catalysts. Cis and trans isomers of unsaturated fatty acid methyl esters were clearly separated as O-isopropyliden derivatives as seen in Fig. 1. These procedures were designed to an alyze a small amount (about one mg) of samples. The reactions were quantitative for monoenoate. However, yields for dienoate or polyenoate were low.<BR>Several kinds of fat were analyzed by this method. About 45% of octadecenoates from margarine was of trans configuration as seen in Fig. 2. About 10% of octadecenoates from beef fat was also of trans configuration (Fig. 3).<BR>When the O-isopropyliden derivatives were analyzed by mass spectrometer connected to gas chromatography, the mass spectra revealed the presence of peaks corresponding to cleavage of bonds α to the 1, 3-dioxolane ring. Since the dioxolane ring marks the position of double bond in the parent unsaturated fatty acid, cleavage at the bonds α to the dioxolane ring yields ions specific to each positional isomer as seen in TABLE III. Octadecenoate from parsley seed oil which is a major constituent of the oil was identified qualitatively as cispetroselinate by this method as seen in TABLE III. It will also be possible to estimate positional isomers quantitatively by analyzing the mass spectral data with computer. The outline of this method has been already referred to by McCloskey and McClelland6). During preparation of this report, Wood 7) reported independently a similar method of gas chromatographic analysis of geometrical isomers. However, he performed hydroxylation with potassium permanganate, and did not utilize mass spectrometer for analysis of the positional isomers.

• Japan Society of Clinical Chemistryの論文

著者

• 田中 圭

  東京大学医学部中尾内科

• HORNING Evan

  Baylor大学医学部脂質研究所

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• Gas Chromatographic Analysis of Geometrical Isomers of Unsaturated Fatty Acids as O-Isopropyliden Derivatives with Simultaneous Analysis of Positional Isomers by Use of Gaschro-Mass Spectrometer

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