Determination of Residue of Glyphosate in Environmental Samples Based on Europium Ion-Tetracycline-Glyphosate Fluorescence Enhancement System Combined with Molecular Imprinted Solid Phase Extraction

A method for the determination of residue of glyphosate in environmental samples based on europium ion-tetracycline-glyphosate fluorescence enhancement system combined with molecular imprinted solid phase extraction was proposed. Using ethyl orthosilicate as sol-gel functional monomer, glyphosate molecular imprinted solid phase extraction membrane was prepared in a silica sol-gel system at pH 1.0 for the pretreatment of environmental water and soil samples. The pretreated sample solution was mixed with 1.5×10^-2 mol·L^-1 EuCl₃ solution, 3.0×10^-3 mol·L^-1 tetracycline solution and 100 mmol·L^-1 borate buffer solution (pH 10.0) at a definite ratio, then the mixed solution was reacted for settling 3 min. The content of glyphosate was calculated according to the increase of fluorescence intensity (ΔF value) of the system at emission wavelength of 615 nm, with 403 nm as excitation wavelength. It was shown that the fluorescence intensity of the system at 615 nm was significantly enhanced by the addition of glyphosate under higher alkaline condition, and linear relationship between the logarithm of glyphosate concentration and ΔF value of the system was kept in the range of 5.0×10^-8-1.5×10^-4 mol·L^-1, with detection limit (3s/k) of 1.0×10^-8 mol·L^-1. Glyphosate-ammonium, and aminomethylphosphonic acid, common metal ions and amino acids with similar structure did not interfere with the fluorescence intensity of europium ion-tetracycline-glyphosate system, but Fe³⁺ and Hg²⁺ did, so triethanolamine was used during sample pretreatment for masking. The method was applied to analysis of water and soil samples in real environment, and the determined values of glyphosate were basically consistent with those obtained by electrochemical method. Test for recovery was made on the water sample according to the standard addition method, giving the result of 101%.