Acid-insoluble lignin, also known as Klaassen lignin, is a lignin-like compound commonly used to assess wood and pulp quality. The following is a common method for determining acid-insoluble lignin content:
principle
The content of acid-insoluble lignin is determined by hydrolyzing lignin with acid to free phenol, and then decolorizing it with sodium hydroxide solution to make the solution appear light yellow, and then measure its absorbance by UV-visible Spectrophotometer or Colorimeter, and then calculate Acid-insoluble lignin content.
Instruments and Reagents
Acetic acid-sulfuric acid mixture: mix according to the ratio of 1:1, can make 0.5 mol/L mixed acid.
5% NaOH solution: Dissolve 5g of sodium hydroxide in 100 mL of pure water.
Pure water cuvette: A certain quality cuvette can be obtained by washing, drying and weighing.
UV-Vis Spectrophotometer or Colorimeter.
Steps
Prepare pulp sample: Take about 1 g of pulp sample into a cuvette, add about 25 mL of acetic acid-sulfuric acid mixture, seal the cuvette and heat it in a Water Bath at 105 °C for acid hydrolysis about 2 hours.
Filtration and washing: The acid hydrolyzed sample was filtered and washed repeatedly with pure water until it was colorless.
Decolorization: Add about 25 mL of 5% NaOH solution to the cuvette, mix the solution evenly with a magnetic stirrer, then dilute with pure water to make the volume of the solution in the cuvette about 50 mL, mix well.
Determination of absorbance: Use a UV-vis Spectrophotometer or a Colorimeter to measure the absorbance of the solution. The acid-insoluble lignin content in the sample can be calculated according to the standard curve.
North and South Chao reminds you: This method has less influence on other components such as hemicellulose and polysaccharides, but it will be affected by other lignin substances, so proper sample pretreatment and correction are required.
