阀切换-非抑制离子色谱法测定奶粉中的左旋肉碱

Determination of L-carnitine in milk by valve-switching non-suppressed ion chromatography

建立了阀切换-非抑制型电导检测离子色谱法测定奶粉中的左旋肉碱的方法。奶粉样品经高纯水溶解后，以乙腈沉淀蛋白，离心，过RP固相萃取小柱和Na柱净化，再通过阀切换的方式进样，经浓缩柱浓缩并冲洗去除基体。以3mmol／L的甲基磺酸为淋洗液等度洗脱，IonPacCS17阳离子柱交换分离，非抑制电导检测。结果表明：左旋肉碱在17．5—175mg／kg范围内线性关系良好（r=0．9995）；奶粉中左旋肉碱的加标回收率为92．3％～105．2％，相对标准偏差（RSD）在1．4％-4．3％之间；检出限为5mg／kg。该方法能满足奶粉中左旋肉碱的检测及质量控制要求。

A novel assay was developed for the determination of L-carnitine in milk powder by valve-switching non-suppressed ion chromatography. In this method, milk powder samples were dissolved in high purity water, Acetonitrile was used to precipitate protein and online SPE （ Ionpac TCC-ULP1 ） to serve as a concentrator after samples were purifeied by a Dionex RP column and a Na column. The chromatographic method was based on a Dionex IonPac CS17 ＋ IonPac CG17 cation-exchange column with an aqueous methanesulfonic acid （3 mmol/L） as the isocratic eluent at a flow rate of 1 mL/min. The column temperature was maintained at 30~C. A good linear relationship was observed in the concentration range of 17.5 ~ 175 mg/kg（r = 0. 9995 ） for L-carnitine . The recoveries of L-carnitine in milk powder were 92. 3% ~ 105.2% with RSDs of 1.4% -4. 3%. The limit of detection was 5 mg/kg. No interference from other ions was found. The pretreatment and chromatographic conditions were discussed in this article. The results indicate that the assay is simple, rapid, accurate and suitable for the determination of L-carnitine in milk powder samples.