Determination of multiresidues of three acid herbicides in tobacco by liquid chromatography/tandem mass spectrometry.

A method to determine residues of the three acid herbicides, 2,4,5-trichlorophenoxyacetic acid, 2,4-dichlorophenoxyacetic acid, and 3,6-dichloro-2-methoxybenzoic acid (dicamba), in tobacco using LC/MS/MS is presented. Because these herbicide residues in tobacco might exist in different forms (free acid, salt, and ester), tobacco samples were first pretreated by alkaline hydrolysis and then the pH was adjusted in order to convert the residues completely to their free acid forms. Dichloromethane extraction and dispersive SPE using C18 sorbent were carried out before LC/MS/MS analysis, and quantification was performed using the internal standard method. Linearity was good for all analytes (R(2) ≥ 0.999) in the concentration range of 0.02 to 0.5 mg/kg. LODs were below 0.05 mg/kg. Recoveries ranged from 80.4 to 93.5%, and RSD was below 10%. This simple, efficient, and sensitive method can be applied to the determination of residues of the three acid herbicides in tobacco.