Characterization of Wax Esters by Electrospray Ionization Tandem Mass Spectrometry: Double Bond Effect and Unusual Product Ions

Abstract
A series of different types of wax esters (represented by RCOOR′) were systematically studied by using electrospray ionization (ESI) collision-induced dissociation tandem mass spectrometry (MS/MS) along with pseudo MS3 (in-source dissociation combined with MS/MS) on a quadrupole time-of-flight (Q-TOF) mass spectrometer. The tandem mass spectra patterns resulting from dissociation of ammonium/proton adducts of these wax esters were influenced by the wax ester type and the collision energy applied. The product ions [RCOOH2]+, [RCO]+ and [RCO−H2O]+ that have been reported previously were detected; however, different primary product ions were demonstrated for the three wax ester types including: (1) [RCOOH2]+ for saturated wax esters, (2) [RCOOH2]+, [RCO]+ and [RCO−H2O]+ for unsaturated wax esters containing only one double bond in the fatty acid moiety or with one additional double bond in the fatty alcohol moiety, and (3) [RCOOH2]+ and [RCO]+ for unsaturated wax esters containing a double bond in the fatty alcohol moiety alone. Other fragments included [R′]+ and several series of product ions for all types of wax esters. Interestingly, unusual product ions were detected, such as neutral molecule (including water, methanol and ammonia) adducts of [RCOOH2]+ ions for all types of wax esters and [R′−2H]+ ions for unsaturated fatty acyl-containing wax esters. The patterns of tandem mass spectra for different types of wax esters will inform futu...

Source: Lipids - July 16, 2015 Category: Lipidology Source Type: research