Impact of the complexing cation on the sensitivity of collision‐induced dissociation spectra to fatty acid position for a set of YXY/YYX‐type triglycerides

Rationale The development of an automated platform for the positional analysis of triglycerides based on electrospray ionization tandem mass spectrometry (ESI‐MS/MS) continues to be pursued. This work compares the positional sensitivities of the collision‐induced dissociation (CID) spectra for a representative set of YXY/YYX triglycerides using ammonium, silver, sodium and lithium as complexing agents. Methods A set of triglycerides were synthesized and analyzed by ESI‐MS/MS using an ion trap mass spectrometer. Using different salt additives, the product ion spectra of the corresponding precursor ions for twelve systems of the form YXY/YYX, where Y and X represent C16:0, C18:1(c‐9), C18:2(cc‐9,12) and C20:4(cccc‐5,8,11,14), were collected. The data was used to prepare two‐point calibration plots for each of the twelve positional isomer systems using each of the four complexing agents. Results The positional sensitivities for all twelve positional isomer systems were robust for both the sodium and lithium TAG adducts. The CID data for both the sodium and lithium TAG adducts are much less sensitive to the degree of unsaturation and double bond position of the fatty acids constituents than the CID data for the ammonium adducts. Conclusions Using sodium or lithium TAG adducts may be advantageous for the development of an accurate predictive model for performing positional analysis of complex TAG mixtures based on ESI‐MS/MS. Ammonium adducts are likely complicated by the ability of the ammonium ion to provide extra stability to some precursor ions through hydrogen‐bond‐like interactions.