Identification of conjugated linoleic acid elongation and β-oxidation products by coupled silver-ion HPLC APPI-MS

Atmospheric pressure photoionisation (APPI) was used in combination with silver-ion (Ag+)-HPLC for detection of (conjugated) fatty acid methyl esters (FAME) by tandem-mass spectrometry. APPI-MS of methyl esters of conjugated linoleic acid showed an increase in signal-to-noise ratio by a factor of 40 compared to atmospheric pressure chemical ionization in the positive mode. It was possible to identify double bond position, configuration and chain length of FAME based on chromatographic separation and mass detection. The developed LC–MS method is useful for the analysis of CLA elongation and β-oxidation products, especially with trans,trans-configuration, which are difficult to analyze by conventional GC–MS techniques.