Rapid screening of glyphosate in environmental water based on Ponceau 4R-Cu²⁺ competitive complexation

Glyphosate, a widely used organophosphorus herbicide in agriculture, poses potential threats to aquatic ecosystems and human health due to its long-term environmental persistence. This study presents a spectroscopic detection system based on a competitive reaction utilizing the Ponceau 4R (P4R)-Cu²⁺ complex. Leveraging glyphosate's high affinity for chelating copper ions, the method enables indirect, rapid, and visual quantitative analysis of glyphosate. In the presence of glyphosate, Cu²⁺ preferentially binds to it, causing the release of P4R and the restoration of its characteristic absorption spectrum, resulting in a measurable absorbance change at 505 nm. Systematic optimization of buffer pH, P4R concentration, Cu²⁺ concentration, and their ratio established the optimal detection conditions (120 μmol L^-1 P4R, 120 μmol L^-1 Cu²⁺, 40 mmol L^-1 borate buffer, pH 9.0). Under these conditions, the method exhibited a good linear relationship within the concentration range of 5.9-295.8 μmol L^-1 (R² = 0.998). The limit of quantitation (LOQ) and limit of detection (LOD) were determined to be 14.0 μmol L^-1 and 4.6 μmol L^-1, respectively. This method was successfully applied to the analysis of spiked surface water samples and soils collected from the upper reaches of the Liao River, yielding average recoveries of 98.7-107.6% with relative standard deviations (RSDs) below 5%. Interference tests indicated that citric acid interference was manageable (recovery: 88.9%) when its concentration ratio to glyphosate was ≤2 : 1, while tartaric acid and oxalic acid required masking strategies to suppress their interference. This method, characterized by its simplicity, rapid response, and low instrumental dependence, provides reliable technical support for the rapid screening of glyphosate in environmental samples.