Simultaneous Determination of Dinitroaniline Herbicides in Spinach, Apple and Soybean by UPLC-MS/MS

A method of ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for determination of 8 kinds of dinitroaniline herbicides (trifluralin, pendimethalin, butralin, isopropalin, dinitramine, nitralin, oryzalin, prodiamine) in spinach, apple and soybean. Afer homogenization, 5.0 g sample was soaked with 7 mL water for 1 h. Then 3 g NaCl was added, and the sample was extracted twice by 25 mL hexane saturated acetonitrile solution. After concentration, the extract was put through C18 column and eluted by 5 mL acetonitrile. The eluated was then concentrated and dissolved with 2.0 mL hexane-acetone mixture (2∶8, V/V). The preparation was cleaned by Envi-Carb column and eluted with 5.0 mL hexane-acetone. The residue was dissolved by 50% acetonitrile aqueous solution (contain 0.1% formic acid), and determined by UPLC-ESI/MS/MS. Under the optimized chromatographic conditions, 8 target compounds were obtained. Confirmation was achieved using electro-spray ionization (ESI) in positive mode with multiple reaction monitoring (MRM), and external standard method was used for quantification. The results show that 8 dinitroaniline herbicides have good linearity, the linearity is more than 0.99. The limits of quantification(LOQs) are 10 μg/kg. The mean recoveries are between 70.0% and 120% at the spiked levels of 10-200 μg/kg. The RSD of the method are between 0.56% and 23.0%. The method is precise, sensitive and accurate, which is suitable for confirmation and quantification of dinitroaniline herbicides in vegetables, fruits and grains.