Each sample (0.1–1 g) was weighed in 50 mL hydrolysis bottle with Teflon-lined screw-cap and then treated with 20 mL of 5 N sodium hydroxide solutions under nitrogen atmosphere. After hydrolysing in an oven at 120 C for 12 h,
Each sample (0.1–1 g) was weighed in 50 mL hydrolysis bottlewith Teflon-lined screw-cap and then treated with 20 mL of 5 Nsodium hydroxide solutions under nitrogen atmosphere. Afterhydrolysing in an oven at 120 C for 12 h,