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Initially, we investigated the distribution of chemicals in dried wood samples using a standard TOF-SIMS and obtained two-dimensional images of chemical distribution in various wood samples. However, during drying as part of the sample preparation, some artifacts could occur because water-soluble chemicals could be moved, drained, or changed at that time. To understand the function of chemicals in living trees, it is important to reveal the distribution of chemicals in planta. For this purpose, we developed the new cryo-TOF-SIMS/SEM system to analyze chemical distribution in frozen-hydrated samples. This new system consists of a glove box, a cryo-SEM, and a cryo-TOF-SIMS, which are interconnected by a cryo-vacuum shuttle. This system was then applied to freeze-fixed Cryptomeria japonica xylem. Potassium, ferruginol, a major wood chemical of C. japonica, and water were simultaneously detected in frozen-hydrated wood tissues. For accurate detection, the sublimation of ice from sample surfaces must be prevented. After the TOF-SIMS analysis of the surface, the sample was cut to make the next sample surface in the glove box and cryo-TOF-SIMS analysis was performed again. Continuing with this procedure, we obtained a three-dimensional analysis data of TOF-SIMS images. The maximum height was 1000 µm. These results suggest that this new system is useful for revealing the chemical distribution of wood tissue in planta. Copyright © 2012 John Wiley & Sons, Ltd.

Lignin, one of the main structural polymer of plant cell walls, varies in amount and monomeric composition among tissue and cell types, as well as among plant species. However, few analytical methods are available that can conveniently and accurately determine the morphological distribution of lignin units at the cellular level. In this report, we used time-of-flight secondary ion mass spectrometry (TOF-SIMS) to directly map guaiacyl (G) and syringyl (S) lignin units in several successive growth rings of the maple xylem. TOF-SIMS imaging and a semiquantitative approach revealed clear difference in the annual distribution of lignins between the fiber and vessel. While the vessel walls were constantly G-rich with varied S/G ratios through a growth ring, the fibers showed fairly regular annual distribution of lignins in which the earlywood was S-rich with an almost constant S/G ratio and the latewood was G-rich resulting from a decrease of the S unit. The reliability of TOF-SIMS results was demonstrated by its high correlation with the results of thioacidolysis on radial distribution of the S/G ratio in several contiguous tree rings and also in the latewood and earlywood of each ring. These results indicate that TOF-SIMS allows direct visualization of lignin composition in plant tissues.

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.

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to investigate the distribution of cationic starch on pulp fiber. To identify the characteristic fragment ions of the cationic starches, deuterium-labeled cationic starches were prepared and analyzed using ToF-SIMS. The starch 2-hydroxypropyltrimethylammonium chloride derivative generated characteristic fragments at m/z 58 and 59, which were identified as [H2CN(CH3)2]+ and [N(CH3)3]+·, respectively. The fragmentation patterns were also suggested. From the imaging analysis, the adsorption of the cationic starch on fibers was uneven on individual fibers, as well as between fibers. This may have been on account of fiber morphology and structure. On examining scanning electron microscope (SEM) images, the quaternary ammonium starch derivative (QS) did not penetrate the fiber. No migration of cationic starch was observed under various drying conditions. Copyright © 2007 John Wiley & Sons, Ltd.