Enhancing LC-MS sensitivity for structural characterization of lignin oligomers using acetic acid as a mobile phase

Abstract

Characterization of lignin degradation products by electrospray ionization-tandem mass spectrometry (ESI-MS/MS) greatly relies on mobile phase additives in liquid chromatography (LC). Ammonium salt, which is a common mobile phase additive for negative mode in ESI-MS-based metabolomics, has been dominantly used for lignin analysis. In this study, chromatographic separation and ionization efficiency for LC-MS analysis of lignin oligomers and lignin-derived phenolic compounds were systematically compared among seven different mobile phase additives. We found that acetic acid exhibits analytical performance greater than other mobile phase additives, including ammonium salt, for characterization of lignin degradation products by (−)-ESI-MS/MS. The use of acetic acid as a LC mobile phase additive enhanced the ionization efficiency of PCs in (−)-ESI-MS about 2 to 4 times higher than the other additives. The improved MS sensitivity with acetic acid yielded a higher fragment ion coverage in LC-MS/MS analysis, leading to a greater number of identified lignin oligomers. The use of acetic acid as a mobile phase additive providing increased chromatographic separation and enhanced sensitivity for (−)-ESI-MS will facilitate structural analysis of lignin degradation products without any additional instrumentation.