Lignin Monomer Quantification Without Standards: Using Gas Chromatography with Dual Quantitative Carbon Detection and Mass Spectrometry

Lignin depolymerization yields a complex mixture of monomeric products, including a wide range of highly oxygenated molecules. Quantifying these lignin monomers using existing gas chromatography (GC) with a flame ionization detector and effective carbon number methods is highly challenging due to the response variability for molecules containing heteroatoms and the inability to quantify unknown monomers. In this work, we demonstrate the potential of a GC equipped with dual detectors, a modified flame ionization detector (FID) for quantitative carbon detection (Polyarc reactor) and a mass spectrometer (GC-QCD/MS) for identifying and quantifying lignin monomers without the use of standards. Lignin depolymerization products were generated from Organosolv poplar lignin and poplar biomass through methods such as hydrogenolysis, solvolysis, and reductive catalytic fractionation. In the GC-QCD/MS, the QCD component converts all organic molecules into methane before quantification via FID, providing nearly uniform response factors for diverse compounds found within the sample, while a flow splitter directs a portion of the sample to the mass spectrometer for simultaneous molecular identification. This setup enables cost-effective, flexible, and streamlined measurements of lignin monomer carbon yields without the need for standards. Additionally, GC-QCD/MS supports the quantification of unidentified compounds within the lignin product mixture.