Simultaneous quantitative determination of nine antioxidants in natural ester insulating liquid by HPLC

In this paper, high performance liquid chromatography (HPLC) was used to determine the content of nine antioxidants in natural ester insulating(NEI) liquid. After the sample to be tested was extracted with methanol, it was filtered through a $0.22 \mu \mathrm{m}$ filter membrane and entered into the chromatographic column for analysis. Ultrapure water (0.5 % formic acid)-methanol was used as the mobile phase, and a UV spectrophotometer was used to conduct qualitative analysis according to the retention time. Then the peak area was quantified to build the calibration curve. The results showed that within the concentration range of $20 \mathrm{mg} / \mathrm{L} \sim 400 \mathrm{mg} / \mathrm{L}$, the method showed a good linear relationship to the nine antioxidants, the correlation coefficient $R^{2}$ was greater than 0.999, and the recovery rate of the sample was 88%$\sim$102%. The relative standard deviation was less than 4%, and the limit of quantification was $20 \mathrm{mg} / \mathrm{L}$. This method is used in the detection of antioxidants in refined oil and the standard recovery test, and the results are accurate and the recovery rate is high.