Ultra high performance liquid chromatography–tandem mass spectrometry method for the determination of soluble milk glycans in rat serum

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• Multi-analyte method for the determination of soluble milk glycans in rat serum.
• Validation of the method: quality parameters, accuracy (trueness and precision).
• Evaluation of the time-course of SMGs in rat serum after an oral challenge.
• In vivo absorption of SMGs from the intestine to the systemic circulation is demonstrated.

The main objective of the present work was to develop and validate a multicompound method to measure soluble milk glycans (SMGs) in biological fluids such as serum. An ultra high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method for the identification and quantification of the following SMGs and their precursors 2′-fucosyllactose, 3′-sialyllactose, 6′-sialyllactose, lacto-N-neotetraose, N-acetylneuraminic acid, fucose, lactose and glucose in rat serum samples was set up. These analytes were separated in an Acquity UPLC BEH Amide column using acetonitrile–water gradient with ammonia as additive, in a 10 min run, and were detected and quantified using a triple quadrupole (QqQ) mass spectrometer. The mass spectrometric conditions in negative electrospray ionization mode (ESI−) were individually optimized for each analyte to obtain maximum sensitivity in the Selected Reaction Monitoring (SRM) mode. Selection of two specific fragmentation reactions for each compound allowed simultaneous quantification and identification in one run, ensuring a high specificity of the method. The limits of detection (LODs) ranged from 5 to 70 ng mL−1 and the limits of quantification (LOQs) from 20 to 200 ng mL−1. The inter- and intra-day variability was lower than 15% and the recoveries ranged from 85% to 115%. A biological application of the method was also described, specifically the time-course of SMGs in rat serum after an oral challenge.