ISO/NP 26883

Lignin — Quantification of hydroxyl groups by 31P NMR

Scope

This Standard describes a method for the quantification of the aliphatic (R–OH), carboxylic acid (R–COOH), and phenolic (Ph–OH) hydroxyl groups present in lignin. Phenolic hydroxyl groups include
a) syringyl (S), guaiacyl (G), and p-hydroxyphenyl (H) units; and
b) condensed phenolics incorporating β-5, 4-O-5’, and 5-5’ inter-unit linkages.
The procedure utilizes derivatization with a phosphorus-containing reagent followed by 31P NMR analysis.
The procedure is applicable to dry solid lignins (e.g., in powdered form), isolated from the pulping processes in their acid form, that are completely soluble in the NMR solvent mixture. If the lignin is not fully dissolved in the NMR solvent, the data obtained will represent only the structure of the soluble portion of the lignin sample.