离子色谱-抑制型电导检测法同时测定食品级润滑油中的3种无机阴离子

建立了离子色谱-抑制型电导检测同时测定食品级润滑油中Cl^-、NO₃^-、SO₄^2- 3种代表性无机阴离子的方法。样品经50%(v/v)甲醇水溶液超声提取,离心后所得下层水相用0.22 μm混合纤维过滤膜净化,以15 mmol/L KOH溶液为淋洗液,采用抑制型电导检测器进行检测,外标法定量。在上述条件下,Cl^-、NO₃^-、SO₄^2- 3种无机阴离子在0.10~20.00 mg/L范围内具有良好的线性关系(R²>0.999);检出限(S/N=3)为0.01~0.03 mg/kg;在1.00、5.00、10.00 mg/kg添加水平下,实际样品中3种阴离子的加标回收率为90.0%~103.6%,相对标准偏差为2.8%~5.7%。结果表明,该方法无需燃烧、灰化油相基质等繁琐耗时的前处理过程,可以快速、准确定量测定食品级润滑油中Cl^-、NO₃^-、SO₄^2- 3种无机阴离子的含量,适用于润滑油等油品中痕量无机阴离子的同时分离与测定。

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

An ion chromatographic (IC) method with suppressed conductivity detection was developed for the simultaneous determination of Cl^-, NO₃^-, SO₄^2- 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^-, NO₃^-, SO₄^2- 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^-, NO₃^-, SO₄^2-) 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.