Improvement of sugar analysis sensitivity using anion-exchange chromatography–electrospray ionization mass spectrometry with sheath liquid interface

• Sheath liquid is first applied for improving sugar ESI sensitivity.
• Sheath liquid interface not T-joint allows NH4+ to replace Li/NaCl for ESI signal.
• HPAEC-ESI-MS successfully separates and identifies co-eluted sugars in pectins.

A novel interface that enables high-performance anion-exchange chromatography (HPAEC) to be coupled with electrospray ionization (ESI) mass spectrometry (MS) is reported. A sheath liquid consisting of 50 mM NH4Ac in isopropanol with 0.05% acetic acid, infused at a flow rate of 3 μL/min at the tip of the electrospray probe, requires less ESI source cleaning and promotes efficient ionization of mono- and di-carbohydrates. The results suggest that use of a sheath liquid interface rather than a T-joint allows volatile ammonium salts to replace non-volatile metal salts as modifiers for improving sugar ESI signals. The efficient ionization of mono- and di-carbohydrates in the ESI source is affected by the sheath liquid properties such as buffer concentration and type of organic solvent. HPAEC-ESI-MS was used for the analysis of monocarbohydrates in pectins, particularly co-eluted sugars, and the performance was evaluated. Addition of a make-up solution through the sheath liquid interface proved to be an efficient tool for enhancing the intensities of sugars analyzed using HPAEC-ESI-MS.