Ammonia Concentration in the Eluent Influences Fragmentation Pattern of Triacylglycerols in Mass Spectrometry Analysis

Correct assessment of the fatty acyl at the glycerol sn-2 position in triacylglycerol (TAG) analysis by liquid chromatography and mass spectrometry (LC-MS) is challenging. Ammonium hydroxide (NH(4)OH) is the preferred choice for the solvent additive for the formation of the ammonium adduct ([M + NH(4)](+)). In this study, the influence of different NH(4)OH concentrations in the eluents on TAG adduct formation and fragmentation under LC-MS analysis was assessed. Increasing NH(4)OH concentrations delayed the chromatographic elution time according to a power function. The [M + NH(4)](+) and [M + ACN + NH(4)](+) adducts (where ACN means acetonitrile) were formed at all ammonium concentrations assayed. [M + ACN + NH(4)](+) predominated above 18.26 mM [NH(4)OH], and the intensity of [M + NH(4)](+) dropped. TAG fragmentation for fatty acyl release in the MS(E) was reduced with increasing [M + ACN + NH(4)](+) adduct, which suggests that ACN stabilizes the adduct in a way that inhibits the rupture of the ester bonds in TAGs. A linear equation (H(sn-I) = a × H([M+NH4]+), where sn-I refers to the sn position of the glycerol (I = 1, 2, or 3) and H is the peak height) was deduced to quantify the dehydroxydiacylglycerol fragment intensity in relation to [M + NH(4)](+) intensity in the full scan. This equation had a slope mean value of 0.369 ± 0.058 for the sn-1 and sn-3 positions, and of 0.188 ± 0.007 for the sn-2 position.