This method describes procedures for the determination of inorganics content in kraft, soda, and hydrolysis lignin. The method is applicable to lignin isolated from a kraft pulping process, a soda pulping process, or lignin obtained by hydrolysis of biomass.

For kraft lignin in the acid form, soda lignin, and hydrolysis lignin, the inorganics content is determined from the ash content of the sample. For kraft lignin in the base form, the inorganics content is determined from the sum of the contents of calcium, magnesium, manganese, iron, copper, sodium and potassium.