Identification of isomeric hydroxy fatty acids in aerosol samples by capillary gas chromatography—mass spectrometry

Abstract

Isomeric mixtures of 5- to (ω — 1)-monohydroxy fatty acids have been isolated from remote marine aerosols by methanolic potassium hydroxide extraction and silica gel column chromatography. Structures of the hydroxy acids were determined by comparison with high-resolution gas chromatography-mass spectrometry (GC—MS) of authentic standards, employing methyl esters and methyl ester trimethylsilyl (TMS) derivatives. A series of monohydroxy acid positional isomers have been identified in the range C 7C 15 with 5-hydroxyundecanoic and 10-hydroxyundecanoic acids as major isomers. Electron-impact mass spectra of hydroxy acid methyl esters show characteristic α-cleavage ions ( e.g. m/z 131 for the 5-hydroxy homologue) and their methanol-eliminated ions ( e.g. m/z 99). Mass spectra of the TMS derivatives also yield characteristic ions at m/z 133 + 14 m ( m ⩾ 5; m = position of carbon atom bearing the hydroxyl group). These specific ions provide a useful tool in mass chromatography to detect individual positional isomers of hydroxy fatty acids in environmental samples.