Quantitation of Dicamba Herbicide in Pharmaceutical Raw Materials: Developing a Selective Chromatographic Method

INTRODUCTION. The content of pesticides in pharmaceutical raw materials is regulated by the Russian legislation, namely General pharmacopoeial monograph, OFS.1.5.3.0011 Determination of Residual Pesticides in Pharmaceutical Raw Materials and Medicinal Plant Preparations of the State Pharmacopoeia of the Russian Federation, XV edition (SP RF). Residual pesticides are one of safety parameters for medicinal plant raw materials. SP RF stipulates the content of 65 compounds; however, the pesticide market is actively expanding (at least 10% per year), while not all compounds used are subject to quality control. Pesticides widely used in agriculture to control weeds, such as dicamba (3,6-dichloro-2-methoxybenzoic acid), a derivative of chlorobenzoic acid, are of particular interest. Dicamba is used to produce Lintur and Dialen Super, formulations for weed eradication.

AIM. This study aimed to develop a selective identification method for dicamba herbicide in the pharmaceutical raw materials of Echinacea purpurea for its subsequent introduction into pharmacopoeial standards.

MATERIALS AND METHODS. The study used a reference standard of dicamba (Kit-54, pesticide 4-4600, Polycience Corporation); the pharmaceutical raw material Echinacea purpurea, Livadia strain, cultivated from the seeds (seed manufacturer Aelita, Russia, best before 06/2028); and herbicide mixture Lintur, active substance dicamba 659 g/kg and triasulfuron 41 g/kg, (Gardener’s Green Pharmacy Co. Ltd.). High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was performed on Agilent Technologies 1260 Infinity modular liquid chromatograph with Agilent Technologies 6420 Triple Quad LS/MS tandem mass spectrometer; gas chromatography-mass spectrometry (GC-MS) was performed on a gas chromatograph connected to QP-2020 monoquadrupole mass spectrometer (Shimadzu). Chromatograms and mass spectra obtained using HPLC-MS/MS were analyzed in Agilent MassHunter Quantitative Analysis B.06.00 databases, GC-MS chromatograms — in Аgilent G1710 MSD Data Analysis ChemStation. NIST MS Search Program 17 Mass Spectral Library was used to analyze mass spectra obtained by GC-MS.

RESULTS. We developed an assay method of dicamba herbicide in pharmaceutical raw materials using HPLC-MS/MS and evaluated the validation parameters (chromatographic system suitability, specificity, linearity, accuracy, and precision). The possibility of using GC-MS method with/without silylation was examined. The maximum permissible value of dicamba herbicide in pharmaceutical raw materials was calculated, and it was concluded that Echinacea purpurea raw materials cultivated using this herbicide do not meet the compendial requirements.

CONCLUSIONS. The findings demonstrate suitability of the HPLC-MS/MS method and the inadequacy of the GC-MS method, both with and without derivatization, for dicamba quantitation in the pharmaceutical raw materials. The developed procedure can be offered as the main method used to quantify dicamba in the pharmaceutical raw materials to be included in the compendial requirements.

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