Optimization of Triacylglycerol-estolide Analysis by Matrix-Assisted Laser Desorption/Ionization-Mass Spectrometry

Acylglycerols containing more than three acyl groups (TAG-estolides) have been reported in plant seed oils and oil from ergot fungus. These TAG-estolides have considerable potential for industrial use, however, costs of producing synthetic TAG-estolides limits their use in large-scale applications. Identification and structural characterization of additional natural sources of TAG-estolides has been restricted by their complexity and limitations of current analytical techniques. In this work, detection and characterization of TAG-estolides was optimized for use with MALDI-TOF-MS. Eight commonly used matrices were compared; 2,5-dihydroxybenzoic acid (DHB) and 2,4,6-trihydroxyacetophenone (THAP) gave good quality mass spectra. Matrix additives were examined and lithium was the most suitable, since MS/MS spectra of lithiated TAG-estolides provided the most informative fragmentation using an optimized method. The matrix solution pH was examined, and for THAP, replacing LiCl with 10-40 mM LiOH resulted in a slightly basic pH and significantly more intense TAG-estolide signals (up to eightfold higher). Since DHB is acidic, a larger amount of LiOH (> 150 mM) was required for the matrix solution to become basic, leading to ion suppression and reduced signal intensities. Thus, for TAG-estolide analysis, THAP with similar to 20 to 30 mM LiOH gives the highest quality spectra and the most informative MS/MS fragmentation.