银离子固相萃取-程序升温大体积进样-气相色谱法定量分析市售巧克力中的饱和烷烃矿物油

摘要

建立了银渍硅胶固相萃取柱离线(Ag-SPE)净化,程序升温进样-气相色谱-氢火焰离子化检测器(PTV-GC-FID)定量分析巧克力中饱和烷烃矿物油(MOSH)的方法.以正己烷浸泡提取巧克力中的MOSH,离心后取1 mL上清液,过0.3％ Ag渍硅胶SPE柱净化,氮吹浓缩,定容至0.2 mL,注入GC分析; GC的进样口程序升温过程:初始温度45℃,保持1 min(分流比200∶1),以250℃/min升温至360℃(分流阀关闭2 min),并保持27 min(分流比100∶1); 进样量40 μL; 柱温箱升温程序为:35℃保持3 min,以25℃/min升温至350℃,以5℃/min升温至370℃,保持10 min,载气为高纯氮气,流速1.3 mL/min(压力60 kPa); FID温度为380℃.结果表明,本方法的MOSH定量限为0.5 mg/kg,加标回收率为84.9％～108.6％,相对标准偏差(RSD)为0.2％～1.5％.运用本方法对25个市售巧克力样品中的MOSH含量进行了测定,3个样品未检出,其余22个样品中MOSH含量为1.09～8.15 mg/kg(其中C16～C35 的含量为0.56～4.43 mg/kg),有3个样品含量高于5.00 mg/kg,为严重污染样品.本方法操作简便,检出限低,适用于巧克力中MOSH的定量测定.%An offline silver-impregnated silica gel solid-phase extraction (Ag-SPE) approach combined with a programmed temperature vaporization-gas chromatography-flame ionization detector (PTV-GC-FID) was proposed for routine analysis of mineral oil saturated hydrocarbons (MOSH) in chocolates. The MOSH in chocolates were extracted by n-hexane and 1 mL of extract was purified by offline Ag-SPE column. The SPE columns packed with 0.3％ Ag-activated silica gel were used to separate MOSH from triglycerides and olefins in chocolates. The eluent of MOSH fraction was only 5 mL and then concentrated to 0.2 mL through nitrogen blowing with little evaporation loss. The PTV parameters were as follows: the initial temperature was set at 45℃ and held for 1 min (split ratio was 200∶1), then warmed up to 360℃ at linear gradient of 250℃ minSymbolm@@_1 and held for 27 min (split valve was closed for 2 min followed by split ratio of 100∶1). The GC injection volume was 40 μL. The GC column was heated from 35℃ (3 min) to 350℃ at 25℃/min, and then raised to 370℃ (10 min) at 5℃/min. The flow rate of the carrier gas was 1.3 mL/min (and pressure was 60 kPa), FID temperature was set at 380℃. The limit of quantification (LOQ) and the recoveries of the method were 0.5 mg/kg and 84.9％-108.6％, respectively, with the relative standard deviations (RSD) of 0.2％-1.5％. Twenty-five commercial chocolate samples were analyzed with the proposed method, and it was found that the MOSH in three samples were not detected, and the concentrations of MOSH in other 22 samples were 1.09-8.15 mg/kg (the concentrations of MOSH with C16-C35 component were 0.56-4.43 mg/kg). The results suggested that it was necessary to routinely detect mineral oil contamination in chocolates for food safety.