取水样50.0 mL，加盐酸调节pH至3.0，用吡咯烷酮基和二乙烯基苯修饰的磁性纳米材料50.0 mg振荡吸附20 min。乙腈3.0 mL洗脱后，将洗脱液离心5 min，过0.22 μm有机滤膜，氮吹至近干，用甲醇-0.1%（体积分数）甲酸（60+40）混合液定容至1 mL。所得溶液进行超高效液相色谱分离，以XDB-C₁₈反相色谱柱为固定相，以不同体积比的甲醇和0.1%（体积分数）甲酸溶液的混合液为流动相梯度洗脱。质谱分析采用多反应监测模式。4种苯脲类除草剂的质量浓度在0.05~5.0 μg·L^-1内与其峰面积呈线性关系，检出限（3.143s）为12.5~16.4 ng·L^-1。按标准加入法进行回收试验，回收率为83.7%~107%，测定值的相对标准偏差（n=6）均小于8.5%。

The sample (50.0 mL) was adjusted pH to 3.0 with HCl solution, and adsorbed by swirling for 20 min with 50.0 mg of magnetic nanomaterials modified with ketopyrrolidine and divinylbenzene. After elution with 3.0 mL of acetonitrile, the eluent was centrifuged for 5 min, and filtered through 0.22 μm organic filter membrane. The filtrate was dried by N₂-blowing, and made up its volume to 1 mL, with a mixture of methanol-0.1% (φ) formic acid (60+40). The sample solution was separated by UHPLC using XDB-C₁₈ reversed-phase chromatographic column as stationary phase, and mixtures of methanol and 0.1% (φ) formic acid solution in various volumic ratios as mobile phase in gradient elution. MRM was adopted in MS. Linear relationships between values of peak area and mass concentration of 4 pheulurea herbicides were found in the range of 0.05-5.0 μg·L^-1, with detection limits (3.143s) in the range of 12.5-16.4 ng·L^-1. Test for recovery was made by standard addition method, giving results in the range of 83.7%-107%, with RSDs (n=6) all less than 8.5%.