Fatty acids are a category of lipids which primarily serve functions such as energy storage, signalling and making up the structural support for cell membranes. Fatty acids are composed of an aliphatic chain and at least one carboxylic acid group. Despite their relatively simple composition, countless isomers exist as a result of difference in their degree of unsaturation, double bond positions and branching of groups. Inspired by the charge inversion ion/ion reaction developed by McLuckey and coworkers, we have demonstrated that charge inversion ion/ion reactions using ion mobility-mass spectrometry (IM-MS) can be used as mobility shift reagents to increase the resolution of IM separations The results we will present apply this method to lipid analysis by IM-MS.<br/><br/>Our initial methods developed for oligosaccharide isomer separations involve generation of a doubly charged alkaline earth metal-tris-phenanthroline cations with a singly deprotonated di- and trisaccharide anions to form a singly, positively charged long-lived complex in the trap cell of the Synapt. The cation alkaline earth metal-tris-phenanthroline complex breaks down to form three different products as a result of each phenanthroline group being removed due to increase in trap bias. We observed that the product peaks with one phenanthroline group attached showed distinctly different features between reducing and non-reducing disaccharide isomers thereby resulting in structural elucidation. Different sizes of alkaline earth metals (e.g., magnesium, calcium, strontium, and barium) and the presence of either one or zero phenanthrolines gave different mobility fingerprints for reducing and non-reducing sugars.<br/>We are applying this same approach to fatty acids based on previous studies undertaken by McLuckey et al. In their experiments they highlight the use of shotgun lipidomics for profiling and quantitating isomeric fatty acids in binary mixtures from different standards using CID. We are using alkali earth metal-tris-phenanthroline ion/ion chemistry with various cis/trans and unsaturation site isomers to give unique mobility fingerprints for each isomer. This, coupled with the increased ability to separate the isomers from each other with the application of charge-inversion chemistry, results in their facile structural determination in a mixture. We are currently evaluating trends observed in product ion peak drift times using complexation with calcium, strontium and barium metal adducts.

Charge inversion Ion/Ion chemistry improves isomer separation by ion mobility

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