Alternaria toxin is a general term for a class of toxic metabolites produced by Alternaria, which widely exists in soil, grain, vegetables, and fruits. This mycotoxin is extremely harmful to human health. It is well known that infant milk powder containing vegetable oil is easily contaminated by Alternaria alternata. Alternaria toxins have thus become an increasingly important focus in food. Rapid and accurate detection of Alternaria toxin residues in food is of great significance for food safety. This requires pretreatment to purify the target toxins and maximize the accuracy and precision of the analysis. In this study, a rapid method based on online solid phase extraction/purification and ultra-performance liquid chromatography-tandem mass spectrometry (online SPE UPLC MS/MS) was established to detect seven Alternaria toxins (alternariol monomethyl ether, altenuene, tenuazonic acid, alternariol, tentoxin, altenusin, and altertoxin Ⅰ) in infant milk powder. First, the mass spectrometry and chromatographic conditions were optimized. A BEH-C18 column (50 mm×2.1 mm, 1.7 μm) was selected, with 0.1% formic acid aqueous solution-acetonitrile as the mobile phase. Then, the extraction conditions (extraction agent ratio and extraction method) and the solid phase extraction process (extraction column, type and volume of the eluent, and pH of the sample loading solution) were optimized. One gram of milk powder (accurate to 0.01 g) was weighed into a 50 mL tip and bottom plug centrifuge tube. Acetonitrile-water (84∶16, v/v) was set as the extraction agent for the first two cycles, and acetonitrile-methanol-water (45∶10∶45, v/v/v) was set as the third extraction agent. Horizontal shaking for 30 min was the best extraction method. The sample was centrifuged at 9500 r/min for 10 min, and the supernatant extracted many times was mixed and blown with nitrogen at 40 ℃. The sample was redissolved in first-order water (pH 5.5), purified on an HLB column, and successively activated with 6 mL methanol and 6 mL first-order water (pH 5.5). The solution was then loaded onto the column, and the SPE was adjusted to ensure that the water sample flowed through the column at the rate of 1 mL/min so that the column did not dry up during the analysis process before the end of sample loading. The column was rinsed with 12 mL of first-order water. After leaching, the negative pressure filtration was continued for approximately 5 min, followed by elution with 10 mL methanol, and the eluted solution was directly tested after passing through a 0.22 μm filter membrane, without concentration. The analytes were determined by electrospray ionization (ESI) with alternating positive and negative ions. Under the optimal analysis conditions, the linear relationships of the seven Alternaria toxins were good in the mass concentration range of 0.5-200 μg/L, with coefficients of determination (R2)>0.9903. The limits of detection and limits of quantification were 0.15-0.64 μg/kg and 0.54-2.24 μg/kg, respectively. The recoveries of the seven Alternaria toxins were 79.1%-114.3%, and the relative standard deviations were less than 8.87% at different concentrations. The method was applied to the determination and analysis of 60 samples of infant milk powder, and the results showed that no toxin was found in stage one or stage two of the milk powder. Only one sample of the stage three of milk powder was detected, which was tentoxin, and the content was 4.97 μg/kg. The developed method is accurate, rapid, simple, sensitive, repeatable, and stable. It can be used for the practical determination of seven Alternaria toxins in infant milk powder.
婴幼儿奶粉配料中的植物油易受到链格孢霉菌污染,因而链格孢霉毒素(ATs)成为该类食品的重点检测对象。该研究建立了超高效液相色谱-串联质谱法快速检测婴幼儿奶粉中链格孢酚、链孢酚单甲醚、交链孢霉烯、细交链孢菌酮酸、腾毒素、交链孢毒素Ⅰ、细格菌素7种ATs的方法。通过参数优化确定最佳的质谱与色谱条件,选取BEH-C18色谱柱,以0.1%甲酸水溶液-乙腈为流动相,然后分别对提取条件(提取剂比例及提取方式)以及固相萃取条件(萃取小柱、洗脱液种类及体积、上样液pH)进行优化,确定使用乙腈-水(84:16, v/v)为前两次提取剂,乙腈-甲醇-水(45:10:45, v/v/v)为第三次提取剂,水平摇匀30 min为最佳提取方式,以pH 5.5的一级水复溶上样,经HLB小柱净化,10 mL甲醇洗脱,不浓缩直接过0.22 μm滤膜后直接进行色谱分离,色谱分离后以电喷雾正负离子交替多反应监测模式分析。在最佳优化分析条件下,7种ATs在0.5~200 μg/L范围内线性关系良好,判定系数(R2)>0.9903,检出限为0.15~0.64 μg/kg,定量限为0.54~2.24 μg/kg。在3个不同加标水平下,7种ATs的平均回收率为79.1%~114.3%, RSD≤8.87%。将该方法用于60份实际婴幼儿奶粉样品的测定分析,结果显示一段奶粉和二段奶粉中未发现毒素;三段奶粉中只有1份样品被检出,检出毒素为腾毒素,其含量为4.97 μg/kg。该方法准确、快速、简便、灵敏度高,重复性与稳定性良好,可用于婴幼儿奶粉7种ATs的实际测定。
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