Oxidation and Quantification of14C-lignin at Different Ages in Wheat, Pine, Oak, and Kenaf

Abstract

Plant materials, containing ¹⁴C-labeled lignins, were harvested at intervals up to 1 year after labeling. They were oxidized with sodium chlorite (NaC10₂) and nitrobenzene. Age of lignin appears to limit the degree of solubilization of lignin by NaC10₂. Nitrobenzene oxidation solubilized all lignins in wheat, oak, and kenaf but not all lignin in some pine samples. Klason and UV analysis of lignin content were compared with ¹⁴C-content to determine percent lignin soluble in 3% sulfuric acid (Klason analysis solvent), corrected lignin contents, and UV absorptivity of lignin. Ten to 20% of most lignins were soluble in 3% sulfuric acid. When corrected Klason lignin contents were used, UV absorptivities at 280 nm were about 38 g⁻¹ 1 cm⁻¹ for wheat straw and kenaf lignins and 11 g⁻¹ 1 cm⁻¹ for pine lignin.