Abstract: A method for the preparation of dispersed liquid-liquid micro-extraction (DLLME) samples was developed and applied to the extraction and purification of phenolic antioxidants from industrial lubricating oil. Combined with gas chromatography and flame ionization detector (GC-FID), the measurement of phenolic antioxidants in the full life cycle of transformer oil was realized. This method was used to determine the content of phenolic antioxidants in different industrial lube oil samples and to monitor the change of phenolic antioxidants in transformer oil during its full life cycle. The results showed that the detection limit of the established method for 2,6-di-tert-butylphenol and 2,6-di-tert-butyl-methylphenol could be low to 0.03 μg/mL, respectively, the recoveries of the two phenolic antioxidants were between 84.7% - 94.2% , the intra-day and inter-day precision were between 1.2% - 4.1%, and linear correlation coefficients of the fitting curves were both 0.999 9, respectively. This method is simple, convenient, universal, high sensitive and environmental friendly.

Key words: transformer oil, full life circle, antioxidant, dispersive liquid liquid micro-extraction, chromatography