Analysis of wax esters by silver-ion high-performance liquid chromatography–tandem mass spectrometry

Wax esters (WEs), esters of long-chain fatty acids and long-chain alcohols, were analysed by Ag-HPLC/APCI-MS/MS. Two ChromSpher Lipids columns connected in series (a total length of 50 cm) and hexane–2-propanol–acetonitrile mobile phases were used to achieve good separation of the molecular species. The chromatographic behaviour of WEs was studied under optimised conditions: retention increased with the number of double bonds and with the temperature (15–35 °C); retention times were affected by the double-bond position, trans isomers eluted earlier than cis isomers, and the WEs were partially separated depending on the aliphatic-chain length. The WEs provided simple APCI spectra with [M+H]+ ions, the MS/MS spectra showed fragments, which allowed their identification. The method was applied for an analysis of the WE mixtures from jojoba oil and human hair and the results were compared with analogous data from an optimised RP-HPLC system.