Identification of lignin oligomers in Kraft lignin using ultra-high-performance liquid chromatography/high-resolution multiple-stage tandem mass spectrometry (UHPLC/HRMSn)

Jens Prothmann,Charlotta Turner,Margareta Sandahl,Peter Spégel

doi:10.1007/s00216-018-1400-4

Jens Prothmann, Charlotta Turner + Show 2 more

Open Access

https://doi.org/10.1007/s00216-018-1400-4

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Journal: Analusis	Publication Date: Oct 10, 2018
Citations: 33	License type: open-access

Affiliation: Lund University

Abstract

Kraft lignin is the main source of technically produced lignin. For the development of valuable products based on Kraft lignin, its molecular structure is important. However, the chemical composition of Kraft lignin is still not well known. So far, the analysis of Kraft lignin by mass spectrometry (MS) has been mainly focused on monomeric compounds. Previous MS studies on lignin oligomers (LOs) considered only synthesised LO standards and/or lignins produced by processes other than the Kraft process. Furthermore, published MS methods suffer from using high resolution only in the MS1 stage in multiple-stage tandem MS methods. A high resolution in all MSn stages would provide more detailed information about LO fragmentation pathways. Since lignin samples are complex mixtures of a large number of similar phenolic compounds, the selection of tentative LOs in the MS data is challenging. In this study, we present a method for non-targeted analysis of LOs in Kraft lignin using ultra-high-performance liquid chromatography/high-resolution multiple-stage tandem mass spectrometry (UHPLC/HRMSn). A pre-selection strategy for LOs has been established based on a data-dependent neutral loss MS3 method in combination with a principal component analysis-quadratic discriminant analysis classification model (PCA-QDA). The method was optimised using a design of experiments (DOE) approach. The developed approach improved the pre-selection of tentative LOs in complex mixtures. From 587 detected peaks, 36 peaks were identified as LOs.Graphical abstractᅟ

Highlights

The aromatic biopolymer lignin is a promising biorenewable raw material, which has the potential to reduce our dependency on crude oil
We present a non-targeted UHPLC/HRMSn approach for identification of lignin oligomers (LOs) in Kraft lignin
An initial principal component analysis-quadratic discriminant analysis classification model (PCA-quadratic discriminant analysis (QDA)) classification model for dimers and trimers was created based on a suspect list containing 90 LOs found in literature (Fig. 3)

Summary

Introduction

The aromatic biopolymer lignin is a promising biorenewable raw material, which has the potential to reduce our dependency on crude oil. The lignin biopolymer has a complex molecular structure. Nuclear magnetic resonance spectroscopy (NMR) allows for determination of functional groups and interunit linkages, and has been extensively used to investigate the chemical composition of Kraft lignin [11, 12]. With techniques like Py-GC/ MS and NMR, it is difficult to identify and characterise single lignin oligomers (LOs) in complex Kraft lignin samples. Several methods based on atmospheric pressure ionisation (API) in combination with tandem mass spectrometry (MS/MS) or multiple-stage tandem mass spectrometry (MSn) have been established for the investigation of LOs in different types of lignin samples [8, 13]

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