How does soaking wood in various pH buffers impact ToF-SIMS spectra?

During the production of biofuels and/or bioproducts, wood and other lignocellulosic materials are frequently exposed to buffers during enzyme treatments. Buffer pH varies according to the activity profiles of the enzyme(s) used. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an increasingly valuable analytical tool for the surface analysis of lignocellulosic solids, allowing for characterization of the lignin and polysaccharides at the surface, along with other components such as protein and inorganic salts. Despite the use of ToF-SIMS to characterize dilute acid and alkali pretreatments of wood, the exposure of wood to buffers of intermediate pH range has not been studied as it relates to ToF-SIMS analysis. This leads to the question: How does soaking wood in various pH buffers impact ToF-SIMS spectra? Accordingly, a softwood (spruce) and hardwood (birch) were soaked in universal buffers ranging from pH 5 to 10, and then positive ion ToF-SIMS spectra were acquired from the washed wood. Deacetylation was evident for both wood species above pH 8. Additionally, at higher pH, birch ToF-SIMS spectra revealed a relative loss in polysaccharide peaks attributed to hemicellulose and an increase in lignin peaks. This study provides a basis for understanding the pH-dependent alteration of wood solids in aqueous solution, which is important for understanding the controls in enzyme treatments.