Improving LC-MS analysis of human milk B-vitamins by lactose removal.

Our previously reported, first validated, UPLC-MS/MS-based simultaneous analysis of five human milk B-vitamins revealed severe matrix effects. High levels of endogenous lactose fouled the electrospray ionization source affecting the analysis. We evaluated solid-phase extraction (SPE), liquid-solid extraction (LSE), protein precipitation (PPT), and liquid chromatography effluent diversion for lactose-removal. SPE failed to separate lactose from vitamins; LSE using 2-propanol reduced lactose and vitamin recoveries. PPT-solvent, milk volume, and reconstitution solvent influenced flavin adenine dinucleotide, pyridoxal and nicotinamide recoveries. Using an optimized LC-gradient enabled chromatographic separation of lactose from vitamins and its removal using a post-column switch-valve. Only 40 µL milk was subjected to methanol-PPT and non-polar matrix removal by methyl tert-butyl ether. B-vitamin recoveries were established (81.9-118.6%; CV ≤ 11.9%; precision: 4.9-13.7%) with greatly reduced matrix effects, and improved process efficiency, and recovery.