Application of TOF-SIMS to the direct determination of syringyl to guaiacyl (S/G) ratio of lignin

The lignin syringyl to guaiacyl (S/G) ratio, the composition of monomeric units, is an important parameter that is widely used to obtain information on the complex polymer structure of lignin present in plant cell walls. We assessed the reliability of time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) for determining the S/G ratio using monomer, dimer and polymer model compounds of lignin. In the case of the monomer and dimer, the S/G ratios were much higher than the actual molar S/G ratios. In contrast, for the aryl ether 8‐O‐4′‐linked polymers, the S/G ratios estimated were similar to the actual S/G molar ratios, suggesting that the ionization efficiencies of the characteristic ions of S and G units detected from the synthetic lignin polymer compounds were similar. The results suggest that TOF‐SIMS is useful for rapid and convenient determination of the lignin S/G ratio in plants. Copyright © 2010 John Wiley & Sons, Ltd.