Ultra-Trace Electrochemical Determination of Glyphosate Using Bimetallic Metal-Organic Frameworks (MOFs) with Differential Pulse Voltammetry

Hierarchically bimetallic Zr-Cu metal-organic framework combined with 1,3,5-benzenetricarboxylic acid (Zr-CuBTC MOFs) was synthesized using hydrothermal reaction and used as modifier for investigation of non-electroactive glyphosate. These MOFs were dropcasted on a glassy carbon electrode (GCE) and non-electroactive glyphosate were tested by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Glyphosate in water was recognized by the difference of currents in spiked and non-spiked glyphosate samples. At the same time, CuBTC and Fe-CuBTC were investigated for the best material for sensor development. The results showed the bimetallic Zr-CuBTC MOF is the most promising for the determination of glyphosate. Morphological and structural studies showed the coordination of Cu2+ with the presence of Zr4+ ions with BTC ligands provided a highly porous framework with active surface area up to 1337 m2 g-1. The pore diameter and pore volume increased to 1.75 nm and 0.687 cm3 g-1, respectively. Under optimal conditions, Zr-CuBTC modified on GCE (Zr-CuBTC/GCE) sensor is able to indirectly detect glyphosate in a water environment at a detection limit as low as 9 x 10-13 M. The developed sensor was employed to determine glyphosate in the surface water samples collected from the Red River, North Vietnam. The results showed good recoveries (94.6-107.1%) which were in agreement with liquid chromatography coupled tandem mass spectrometry (LC-MS/MS) measurements. These results demonstrate the possibility of using this MOF material in sensor applications to determine trace pesticides in the contaminated water.