either 0.2 g of an oven-dried precipitated sample of lignin or 1.2 g of filtrated liquor is weighed and 3 mL of 72% sulphuric acid is added to the sample. The sample is then evacuated for 15 min and placed in a water bath at 30 °C for 1 hour 84 g of deionized water is added to the sample and then heated to 125 °C in an autoclave for 1 hour. After hydrolysis, the sample is filtrated and the insoluble solid residue, which is referred to Klason lignin, is measured gravimetrically according to the Tappi T222 cm-00 method.