Estimation of volatile acids in wood and bark

Abstract

To estimate the volatile acids from soft- and hardwoods a simple method was developed. Since the main part of volatile acids originates from acetyl groups of wood polyoses alkaline hydrolysis was applied, upon acidifying the free acetic acid was liberated and distilled. Acetic acid, with small amounts of other volatile acids, was then estimated by titration and expressed in two manners, as mmol acids per 100 g wood and as percent of acetyl group content. The free acids were also analyzed by high pressure liquid chromatography (HPLC), in order to compare the results obtained titrimetrically and chromatographically. Indeed, as expected, the distillate contains large amount of acetic acid and a small amount of formic acid. The titration method is simple and does not require high cost equipment to be carried out, however it delivers slightly higher results than the HPLC technique. This deviation in the results due to other acids is minute and can be tolerated. The titration method can therefore be recommended to estimate the volatile wood acids conveniently. According to the results hardwoods contain significantly more volatile acids than softwoods. Moreover, bark contains also volatile acids. Though highly acidic, heartwoods of oak and chestnut have less volatile acids than most normal hardwoods. In these woods, apparently, the nonvolatile tannins contribute largely to wood acidity.