Trimethylaminoethyl ester derivatization and stable isotope derivatization for enhanced analysis of fatty acids in biological samples by electrospray ionization tandem mass spectrometry.

Background: Abnormal fluctuations in free fatty acids (FFAs) are associated with cardiovascular diseases. However, conducting a thorough analysis of individual FFAs via mass spectrometry has historically posed challenges due to their low ionization efficiency and the absence of distinctive fragment ions.

Results: In this study, we introduce a method utilizing paired stable isotope derivatization coupled with liquid chromatography-triple quadrupole mass spectrometry (ID-LC-QQQ-MS) for thorough identification and relative quantification of fatty acids in serum samples. This method involves the derivatization of the carboxyl groups of FFAs using a pair of isotope reagents, resulting in the formation of FA trimethylaminoethyl ester (FA-TMAE-h/d), which can yield two distinct neutral fragments with masses of 59 and 62 Da during collision-induced dissociation (CID). Consequently, a quadruple neutral loss scan (QNLS) approach was utilized for the non-targeted profiling of FFAs in serum samples. The derivative peak pairs displaying matching retention times and distinct mass differences were extracted from the two QNLS spectra and recognized as potential FFAs. Subsequently, a multiple reaction monitoring (MRM) detection protocol was established for the relative quantification of fatty acids in the serum of Syrian Golden Hamsters subjected to various treatments, utilizing a pooled sample labeled with a heavy isotope as an internal standard. Partial least squares discriminant analysis (PLS-DA) revealed notable variations in these 23 fatty acids across the four groups.

Significance: The current stable isotope derivatization (ID) method, in conjunction with tandem mass spectrometry (MS/MS) analysis, stands out as a promising approach for identifying and quantifying FFAs in real samples.