Experimental-Theoretical Approach for the Chemical Detection of Glyphosate and Its Potential Interferents Using a Copper Complex Fluorescent Probe

The present contribution proposes an optical method for the detection of glyphosate (GLY) using a Cu(II) bis-(oxamate) complex ([Cu(opba)]2−) as the fluorescent probe. It wa found that in acetonitrile solution, its fluorescence increases in the presence of GLY and scales linearly (R2 = 0.99) with GLY concentration in the range of 0.7 to 5.5 µM, which is far below that established by different international regulations. The probe is also selective to GLY in the presence of potential interferents, namely aminomethyl phosphonic acid and N-nitrosoglyphosate. Theoretical results obtained by time-dependent density functional theory coupled to a simplified treatment of the liquid environment by using a self-consistent reaction-field revealed that GLY molecules do not coordinate with the central Cu2+ ion of [Cu(opba)]2−; instead, they interact with its peripheral ligand through hydrogen bond formation. Thereby, GLY plays mainly the role of the proton donor. The results also suggest that GLY increases the dielectric constant of the medium when it contributes to the stabilization of the excited state of the [Cu(opba)]2− and enhancement of its fluorescence.