Abstract: The free alkylphenol in the sulfurized calcium alkylphenolate were determined first by methanol extraction, followed by high performance liquid chromatography (HPLC) and finally by calculation. The HPLC conditions are: C8 column at 30 ℃, water and methnol as mobile phases with a water/methanol volume ratio of 0.1:0.9, flow rate 1 mL/min, UV detection wavelength of 280 nm. The recovery of this method is 97.37%-99.84 %, and the relative standard deviation is 0.19%-0.62%. The method has the advantages of simple operation, fast and high accuracy.

Key words: free alkylphenol, sulfurized calcium alkyl phenolate, high performance liquid chromatography