离子色谱法测定“地沟油”中钠离子和氯离子的含量及其比例关系

采用离子色谱法测定“地沟油”样品中钠离子和氯离子的含量,通过计算两者的比例关系确定样品中是否含有“地沟油”。使用去离子水提取“地沟油”样品中钠离子和氯离子。氯离子以20 nmol/L KOH溶液为淋洗液,AS19分离柱(250 mm×4 mm)分离,抑制器电流112 mA;钠离子以20 nmol/L甲基磺酸(MSA)为淋洗液,CS12分离柱(250 mm×4 mm)分离,抑制器电流59 mA;两者分离采用的其他相同色谱条件为: 柱温、检测器温度30 ℃,电导检测器检测,进样量25 μL,流量1 mL/min,峰面积定量。氯离子的检出限为0.005 mg/L,在0～5 mg/L范围内有良好的线性关系（r2=0.999988）;钠离子的检出限为0.001 mg/L,在0～5 mg/L范围内有良好的线性关系（r2=0.999926）。氯离子平均加标回收率为94.2%,相对标准偏差(RSD)为2.4%;钠离子平均加标回收率为92.5%, RSD为2.7%。经测定、计算,正常食用油中钠离子和氯离子的物质的量比约为1,而“地沟油”中钠离子与氯离子的物质的量比高于4。“地沟油”中钠离子和氯离子的含量及其比例关系可作为判断“地沟油”的重要依据。

Determination of sodium and chloride in hogwash oil and their molar ratio by ion chromatography

By reference to edible oil using process as well as hogwash oil refining technology, a method is presented to determine the contents of the sodium and chloride in hogwash oil based on ion chromatography. The molar ratio of the sodium and chloride was analyzed in order to determine whether the sample contained hogwash oil. A hogwash oil sample was extracted by deionized water before analysis. The ion chromatographic separation of the chloride was carried out on an AS19 column (250 mm×4 mm) at 30 ℃, using 20 nmol/L KOH solution as mobile phase at a flow rate of 1 mL/min and suppressor current of 112 mA. The ion chromatographic separation of the sodium was carried out on a CS12 column (250 mm×4 mm) at 30 ℃, using 20 nmol/L methanesulfonic acid (MSA) as mobile phase at a flow rate of 1 mL/min and suppressor current of 59 mA. The injection volume was 25 μL and the detector was an electron capture detector (ECD). The external standard method was used to quantify chloride and sodium. The detection limits of this method were 0.005 mg/L for chloride and 0.001 mg/L for sodium. The linear range was from 0 to 5 mg/L with r2=0.999988 for chloride and r2=0.999926 for sodium. The average recoveries and relative standard deviations were 94.2% and 2.4% for chloride and 92.5% and 2.7% for sodium, respectively. The molar ratio of sodium and chloride in edible oil was approximately 1, while that in hogwash oil was more than 4. The determination of the contents and molar ratio of the chloride and sodium in hogwash oil can be used as an important basis for the judgment of hogwash oil.