In turn, post-column charge switch derivatization was utilized to enhance structural information obtained from fragmentation experiments. Briefly, the introduction of bis-terpyridine magnesium complex dications as the derivatization reagent via a post-column tee injunction (Figure ) facilitated the formation of charge-switched [FA -H + MgTerpy] + ions from chromatographically resolved FA structures. The extracted ion chromatograms (EICs) of the charge-switched FA products (m/z 498) in Figure denote that the slight shift in retention time (c.f. Figures and) is attributed to the increase in dead time associated with the tee junction setup. The LC-MS/MS spectra of post-column derivatized FAs 15:0, 14:0(12Me), and 14:0(13Me) are shown in Figure and display key diagnostic fragmentation patterns analogous to those described before utilizing the gas-phase ion/ion approach. Specifically, the product ion observed at m/z 468 serves as a diagnostic signature of anteiso-methyl chain branching. The indicator product ion at m/z 468 is readily observed in the LC-MS/MS spectrum of charge-switched FA 14:0(12Me), as shown with Figure , and is notably suppressed in the LC-MS/MS spectra of charge-switched FA 14:0(13Me) (Figure ) and FA 15:0 (Figure ) structures respectively. We note that, while the product ion spectra of the saturated straight chain FA 15:0 and iso-branched FA 14:0(13Me) are nearly identical, excellent chromatographic separation of these isomers prior to MS/MS affords unambiguous FA identification via retention time matching utilizing authentic straight-chain FA reference standards which are readily available from a surplus of commercial vendors. Therefore, the combination of LC and post-column charge switch derivatization can readily distinguish saturated straight chain and methyl branched FA isomers with detailed structural information of methyl branching sites for respective FA structures.