Perfluoroalkyl ketones: novel derivatization products for the sensitive determination of fatty acids by gas chromatography/mass spectrometry in electron impact and negative chemical ionization modes

Analytically useful pentafluoro ketone derivatives of fatty acids are descr ibed. The gas chromatographic/mass spectrometric characteristics of these n ew derivatives are compared with those of methyl, trimethylsilyl and pentaf luorobenzyl esters. Pentafluoro ketones exhibit excellent chromatographic p roperties and significantly shorter chromatographic retention times than th ese other esters. The electron impact mass spectra of these new compounds s how informative acylium ions, whose intensity decreases with the degree of unsaturation of the parent fatty acid. The formation of strong and informat ive fragment ions in negative chemical ionization (CH4) mass spectra of pen tafluoro ketone derivatives allows the detection and the characterization ( length of the chain and number of double bonds) of fatty acids at trace lev els (femtomole), even in the case of polyunsaturated compounds. The scope a nd limitations of this new derivatization technique are also discussed. Cop yright (C) 2000 John Wiley & Sons, Ltd.