Differentiation of positional isomers of branched-chain fatty acids using ion mobility-mass spectrometry based on...

This study presents a rapid, non-derivatization method using ion mobility-mass spectrometry (IM-MS) to differentiate short-chain branched-chain fatty acid (BCFA) positional isomers in food products. The core strategy involves selectively forming host-guest complexes between the target isomers and crown ethers (B12C4 or 18C6) in combination with metal ions (Co²⁺ or Ca²⁺), thereby amplifying structural differences for effective mobility separation. Experimental results demonstrated significant peak-to-peak resolution (R_p-p) of 0.622 for methyloctanoic acid isomers using the B-12C4/Co²⁺ system and 0.560 for ethyloctanoic acid isomers using the 18C6/Ca²⁺ system. Quantum chemical calculations and visual analysis elucidated that the differences in intermolecular interaction sites and forces lead to distinct spatial configurations of the complexes, which is the fundamental mechanism enabling high-resolution separation. Furthermore, quantification methods established showed excellent linearity (R² > 0.99), and was successfully applied to quantify trace BCFA isomers in goat milk and fruit juice, confirming its practical utility for food flavor analysis.