考虑到现有前处理方法不能有效去除牛奶样品中的磷脂且糖皮质激素离子化效果差,提出了题示方法。5.0 g牛奶样品经10 mL乙腈涡旋提取2 min,加入1.0 g氯化钠盐析。分取5 mL上清液,加入常用QuEChERS吸附剂[50 mg十八烷基键合硅胶(C₁₈)、50 mg N-丙基乙二胺(PSA)、500 mg无水硫酸镁]和二氧化钛吸附剂50 mg净化,涡旋1 min,离心5 min后过0.22 μm滤膜,滤液进入超高效液相色谱仪,在Agilent ZORBAX SB-C₁₈色谱柱上以不同体积比的乙腈-0.1%(体积分数)甲酸溶液的混合溶液为流动相进行梯度洗脱,分离后的15种糖皮质激素用配有电喷雾离子源的串联质谱仪在正离子模式、多反应监测(MRM)模式下检测。为消除基质抑制效应的影响,用基质匹配法定量。结果显示:15种糖皮质激素的质量浓度在0.5~50 μg·L^-1内与其对应的峰面积呈线性关系,检出限为0.1~0.3 μg·kg^-1;以阴性样品为基质进行3个浓度水平的加标回收试验,所得回收率为89.7%~104%,测定值的相对标准偏差(n=6)为3.2%~12%。方法用于10批牛奶样品的分析,仅在1批样品中检出了氢化可的松,检出量为0.37 μg·kg^-1。

Considering that the existing pretreatment methods cannot effectively remove phospholipids in milk samples, and the ionization effect of glucocorticoids was poor, the title method was proposed. Milk sample (5.0 g) was extracted with 10 mL of acetonitrile for 2 min by vortex, and 1.0 g of sodium chloride was added for salting out. An aliquot (5 mL) of supernatant was mixed with commonly used QuEChERS adsorbents[50 mg of octadecyl-bonded silica gel (C₁₈), 50 mg of N-propylethylenediamine (PSA) and 500 mg of anhydrous magnesium sulfate] and 50 mg of titanium dioxide adsorbent. After whirling for 1 min, the mixture was centrifuged for 5 min, passed through a 0.22 μm filter membrane, and the filtrate was introduced into ultra-high performance liquid chromatography. The mixed solution of acetonitrile and 0.1% (volume fraction) formic acid solution at varous volume ratios was used for gradient elution as the mobile phase on Agilent ZORBAX SB-C₁₈ column, and the separated 15 glucocorticoids were detected by tandem mass spectrometer equipped with electrospray ion source in positive ion mode and multiple reaction monitoring (MRM) mode. In order to eliminate the effect of matrix inhibitory effect, the matrix-matched method was used for quantification. It was shown that the mass concentrations of the 15 glucocorticoids were linearly related to their corresponding peak areas in the range of 0.5-50 μg·L^-1, and the detection limits were 0.1-0.3 μg·kg^-1. Test for spiked recovery was made at the 3 concentration levels with negative milk samples as matrice, giving recoveries in the range of 89.7%-104%, and RSDs (n=6) of the determined values ranged from 3.2% to 12%. The proposed method was used for the analysis of 10 batches of milk samples, hydrocortisone was detected in one batch of the sample, with the detected amount of 0.37 μg·kg^-1.