Abstract: Methylation of trace polysaccharide was studied. Polysaccharide sample (0.1 mg) was dissolved in 0.3 mL dimethyl sulfoxide, followed by adding 10 mg powdered NaOH and sonicating for 20 min. After cooling on ice, 0.1 mL CH₃I was added and sonicated for 20 min at 18-20 ℃. After cooling, CH₃I was added again and sonicated for 20 min. Water (1 mL) containing 4 mmol/L Na₂S₂O₃ was added to stop the methylation reaction. The methylated solution was extracted four times with 0.5 mL chloroform, followed by extracted five times with 0.5 mL water. The chloroform fraction was mixed with anhydrous sodium sulfate to remove the residue water and dried with N₂. The method was simple and easy. The methylation degree of the product was high for polysaccharides soluble or insoluble in water and DMSO. In addition, the resolution of partially methylated alditol acetate was explained and the methylation methods for special carbohydrates were also illuminated.

Key words: polysaccharide, methylation, method, spectrum elucidation, Streptococcus mutans, Coprinus comatus