取5.00 g土壤样品,加入4 mL水,涡旋混匀后加入10 mL乙腈提取剂,涡旋提取3 min。加入1 g氯化钠,在室温下离心10 min,分取7.5 mL上清液,加入0.3 g无水硫酸镁,涡旋30 s后在25 ℃下离心5 min。分取5 mL上清液,于35 ℃氮吹至干。用1 mL甲醇复溶,过0.22 μm滤膜,滤液中13种硝基咪唑类抗生素在Phenomenex Kinetex F5 100色谱柱上用不同体积比0.1%(体积分数,下同)甲酸溶液和甲醇的混合溶液进行梯度洗脱分离,以喷射流电喷雾离子源正离子(AJS ESI⁺)模式电离,以多反应监测(MRM)模式检测,以基质匹配法定量。结果显示,各抗生素的质量浓度均在0.5~100.0 μg·L^-1与对应的峰面积呈线性关系,测定下限(10S/N)为0.01~0.07 μg·kg^-1。按标准加入法进行回收试验,回收率为71.5%~116%,测定值的相对标准偏差(n=5)为1.1%~7.8%。方法用于20份实际样品的分析,仅在一份样品中检出了迪美唑,检出量为8.39 μg·kg^-1。

An aliquot (5.00 g) of soil sample was taken, and mixed with 4 mL of water by vortex. The extractant (10 mL of acetonitrile) was added, and the mixture was vortexed for 3 min. After adding 1 g of sodium chloride, the mixture was centrifuged for 10 min at room temperature, and 7.5 mL of the supernatant was taken, and mixed with 0.3 g of anhydrous magnesium sulfate. The mixture was vortexed for 30 s and centrifugated for 5 min at 25 ℃. An aliquot (5 mL) of the supernatant was taken and blown to dryness by nitrogen at 35 ℃. The residue was redissolved by 1 mL of methanol, and the mixed solution was passed through a 0.22 μm filtration membrane. Thirteen nitroimidazole antibiotics in the filtrate were separated on Phenomenex Kinetex F5 100Å column with mixed solutions composed of methanol and 0.1% (volume fraction) formic acid solution at different volume ratios by gradient elution, and ionized by AJS ESI⁺ mode, detected by MRM mode, quantified by matrix matched method. As shown by the results, linear relationships between values of the mass concentration and the peak area of each antibiotic were kept in the same range of 0.5-100.0 μg·L^-1, with lower limits of determination (10S/N) in the range of 0.01-0.07 μg·kg^-1. Test for recovery was made by standard addition method, giving recoveries in the range of 71.5%-116%, and RSDs (n=5) of the determined values ranged from 1.1% to 7.8%. The proposed method was applied to the analysis of 20 actual samples, dimetridazole was detected in 1 sample with detection amount of 8.39 μg·kg^-1.