Lignin determination is carried out according to TAPPI T 222. This method (also Klason Lignin) describes a procedure that can be used for the determination of the acid-insoluble lignin content in wood and in all types of unbleached pulp.

Direct lignin methods are based on gravimetric lignin determination after total hydrolysis of the carbohydrate fiber components. There are different methods, which differ mainly in the hydrolyzing agent. In the TAPPI method, sulfuric acid is used.

Mineral acid is used to hydrolyze the carbohydrate components of the sample and make them water-soluble. The lignin (and possibly ash) that is undissolved in the acid is separated from the hydrolysate by filtration and determined gravimetrically.

In the presence of lignin, the papers turn yellow due to the effects of light and heat.