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[Simultaneous determination of three inorganic anions in food-grade lubricating oils by chromatography with suppressed conductivity detection].

An ion chromatographic (IC) method with suppressed conductivity detection was developed for the simultaneous determination of Cl-, NO3(-), SO(2-)(4) in food-grade lubricating oils. After ultrasonic extraction with 50% (v/v) methanol aqueous solution and centrifugation, the sample in aqueous phase was purified with 0. 22 µm hybrid fiber membranes, then analyzed by IC using 15 mmol/L KOH solution as eluent, and detected by a suppressed conductivity detector. Effects of the concentration and flow rate of the eluent, and the concentration of the methanol aqueous solution on the detection of the three anions were investigated. Under the optimized separation conditions, the three anions were separated completely and the system peaks didn't interfere with the determination. The calibration curves showed good linearity (R2> 0. 999) in the range of 0. 10-20. 00 mg/L. The limits of detection (LODs, S/N= 3) were 0. 01 - 0. 03 mg/kg. The average recoveries of Cl-, NO(-)3, SO(2-)4 anions were 90. 0% - 103. 6% with the relative standard deviations (RSDs) of 2. 8% - 5. 7%. This method avoids the time-consuming pretreatment process to burn or ash the oil phase matrix, and can determine the amounts of three inorganic anions (Cl-, NO(-)3, SO(2-)(4)) in food-grade lubricating oils fast and accurately. It is suitable for simultaneously separating and detecting trace inorganic anions in lubricating oils or other oil products.