Electrospray mass spectrometry of human hair wax esters

Wax esters extracted from human hair have been examined by capillary GC-MS and by nano electrospray ionization (ESI) mass spectrometry using a tandem quadrupole mass spectrometer. Initially, the wax esters were examined by capillary GC-MS using conventional means, thus revealing an incomplete chromatographic resolution of the complex array of >200 wax esters ranging from 28 to 40 carbons in length, including saturated/straight-chained, unsaturated/straight-chained, saturated/branched, and unsaturated/branched molecular species. ESI of wax esters produced ammonium adduct ions [M+NH4]+, and collisional activation of these ions formed abundant [RCO2H2]+ product ions. Wax esters containing a double bond in the fatty acyl or fatty alcohol portion of the molecule revealed identical behavior, suggesting little influence of the double bond on the ionization process or subsequent decomposition. The wax ester mixture was analyzed by ESI and tandem mass spectrometry using multiple reaction monitoring and neutral loss scanning. The neutral loss experiment [loss of NH3 and CH2=CH-(CH2)nCH3] was particularly effective at rapidly surveying the complex biological mixture, identifying>160 different wax esters that range from 24 to 42 total carbons.