Objective To establish a method for determining the amount of silicone oil on the surface of rubber closures,which is one of the packaging material standards in the Pharmacopoeia of the People's Republic of China.Methods The development process of the method for determining silicone oil content on the surface of rubber closures was described,taking the infrared transmission mode as example.Through method validation,the scientific and rational aspects of the method were examined.Key points of the determination method were analyzed,including the selection of quantitative peaks,selection of measurement solvent,selection of extraction solvent and conditions,selection of instrument measurement methods,selection of liquid cell windows for infrared transmission mode,selection of quantification methods,and selection of dimethyl silicone oil reference standards.Results The infrared spectroscopy mode was chosen to determine the amount of polydimethylsiloxane on the surface of rubber closures based on the peak height of the Si-CH3 bond vibration absorption at 1 260 cm-1.Cyclohexane was used as the measurement solvent.The same concentration of polydimethylsiloxane reference solution was measured using both infrared transmission mode and attenuated total reflection mode,and quantification was performed based on peak height.The results from the two measurement modes were essentially the same.The linear range of polydimethylsiloxane was about 0.3-10.0 mg·mL-1,and its correlation coefficient was 0.999 8.The average recovery of the method was 102.3%-105.6%.The LOD of polydimethylsiloxane was 0.1 mg·mL-1.The silicone oil measurement results of seven batches for rubber closures were consistent with the silicone oil amounts provided by the manufacturer.Conclusion Enterprises can choose either the infrared transmission mode or the attenuated total reflection mode to measure the amount of polydimethylsiloxane on the surface of rubber closures based on their actual conditions.