Wax esters play critical roles in biological systems, serving functions from energy storage to chemical signaling. Their diversity is attributed to variations in alcohol and acyl chains, including their length, branching, and the stereochemistry of double bonds. Traditional analysis by mass spectrometry with collisional activations (CID, HCD) offers insights into acyl chain lengths and unsaturation level. Still, it falls short in pinpointing more nuanced structural features like the position of double bonds. As a solution, this study explores the application of 213-nm ultraviolet photodissociation (UVPD) for the detailed structural analysis of wax esters. It is shown that lithium adducts provide unique fragments as a result of Norrish and Norrish-Yang reactions at the ester moieties and photoinduced cleavages of double bonds. The product ions are useful for determining chain lengths and localizing double bonds. UVPD spectra of various wax esters are presented systematically, and the effect of activation time is discussed. The applicability of tandem mass spectrometry with UVPD is demonstrated for wax esters from natural sources. The UHPLC analysis of jojoba oil proves the compatibility of MS2 UVPD with the chromatography time scale, and a direct infusion is used to analyze wax esters from vernix caseosa. Data shows the potential of UVPD and its combination with CID or HCD in advancing our understanding of wax ester structures.

• Keywords
• Double bond, Mass spectrometry, Photochemistry, UV photodissociation, Wax ester,
• Publication type
• Journal Article MeSH

The interpretation of the electron ionization mass spectra of straight-chain and methyl-branched saturated and unsaturated wax esters (WEs) is discussed in this study based on the spectra of 154 standards. The most important fragments indicative of the structure of the acid and alcohol chains are identified and summarized for WEs with various number of double bonds in the chains. Briefly, most WEs provide acylium ions allowing structural characterization of the acid part, whereas the alcohol part gives corresponding alkyl radical cations. The elemental composition of selected important fragments is established from a high-resolution accurate mass analysis. The ion abundances are discussed with respect to the length and unsaturation of the aliphatic chains. The interpretation of the spectra of branched or unsaturated WEs requires the recognition of small but important peaks that are difficult to discern among the other fragments. We demonstrate that such fragments are easily detected in differential mass spectra. This approach requires spectra of WE standards (e.g., straight-chain analogs in the case of branched WEs) recorded under the same experimental conditions. The WEs mass spectral database provided in the supplemental data can be used as a reference for the analysis of the GC/EI-MS data.

• MeSH
• Esters chemistry   MeSH
• Spectrometry, Mass, Electrospray Ionization methods   MeSH
• Fatty Acids, Unsaturated chemistry   MeSH
• Gas Chromatography-Mass Spectrometry methods   MeSH
• Reference Standards MeSH
• Waxes chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Esters MeSH
• Fatty Acids, Unsaturated MeSH
• Waxes MeSH

Human cerumen was separated by column chromatography into the following groups of compounds: hydrocarbons, squalene, wax esters and cholesterol esters, triacylglycerols, free fatty acids, free fatty alcohols, monoacylglycerols, free cholesterol, free sterols, and free hydroxy acids. The groups of compounds obtained were examined in detail by gas chromatography and gas chromatography-mass spectrometry. In total, about one thousand compounds have been identified.

• MeSH
• Cerumen chemistry   MeSH
• Chromatography methods   MeSH
• Esters chemistry   MeSH
• Humans MeSH
• Lipids analysis   MeSH
• Gas Chromatography-Mass Spectrometry methods   MeSH
• Aged MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Aged MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Esters MeSH
• Lipids MeSH