The gas chromatography used for detecting antioxidizing additive ionol at transformer oil presence helps to ensure reliable operation of oil-filled electrical equipment. Changes in the ionol preliminary extraction temperature do affect the reliability of measurement result. This study aim consisted in investigating the temperature effect on the value of extraction degree and distribution coefficients for ionol in the system “oil — ionol — ethanol” at extraction temperatures 15...75 °C. The experiment included optimization of gas chromatographic ionol in transformer oil detection conditions using method of ionol ethanol extraction and an estimated equation for a single extraction. Found is that the ionol extraction temperature increase in the range of 15...75 °C reduces the values of the ionol distribution coefficients and increases the value of ionol extraction degree and its concentration in the extract reducing the extraction duration, lowering the value of the detection threshold and the total duration of ionol in transformer oil detection. The recommended values for ionol extraction in the temperature range of 15...32 °C at a temperature of extraction 20 °C with precision temperature Δt ≤ ±1 °C, in the range of 32…40 °C, with a temperature of extraction 36 °C and Δt ≤ ±2 °C, in the range of 40...75 °C, with a temperature of extraction 65 °C and Δt ≤ ±5 °C.