Structural characterization of wax esters using ultraviolet photodissociation mass spectrometry

TL;DR

This paper introduces a new method using ultraviolet photodissociation to better understand the complex structures of wax esters in biological systems.

Contribution

The study demonstrates the use of 213-nm UVPD for detailed structural analysis of wax esters, revealing features like double bond positions.

Findings

Lithium adducts produce unique fragments via Norrish and Norrish-Yang reactions, aiding in structural analysis.

UVPD spectra help determine chain lengths and localize double bonds in wax esters.

UVPD is compatible with UHPLC and effective for analyzing wax esters from natural sources like jojoba oil and vernix caseosa.

Abstract

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.

The online version contains supplementary material available at 10.1007/s00216-024-05434-2.

Figures