Colorimetric detection of glyphosate by its competitive reaction against Ponceau 4R for copper ion

Glyphosate monitoring is important for protecting the environment, biodiversity, human health, and food safety, enabling the assessment of its potential risks to inform regulatory decisions and agricultural practices. This study introduces an automated screening method that employs a cost-effective and stable Ponceau 4R-copper (P4R-Cu) complex as the chromophore probe. Glyphosate, a notably potent chelating agent for Cu, can induce a highly efficient, dose-dependent color recovery at 505 nm, arising from the unchelated reaction of P4R with Cu. Under the optimal probe condition of 120 μM P4R and 90 μM Cu (prepared in 20 mM borate buffer, pH 9), the linear range for glyphosate detection is from 1 to 90 μM (R2 = 0.9990) with good repeatability (RSD < 4.9 %, n = 5, for all concentration points). The detection limit is 0.14 μM, with a sample throughput of over 20 determinations per hour. Moreover, it is free from interference by substances such as Na+, K+, Ca2+, Mg2+, Mn2+, Zn2+, Fe2+, Pb2+, Ni2+, Co2+, Fe3+, Cr3+, CH3COO−, NO3−, CO32−, SO42−, aminomethyl phosphonic acid, glufosinate, glyphosate-based herbicide formulations, pool water, and tap water. These findings suggest that the proposed colorimetric method is reliable for the accurate and rapid quantification of glyphosate in real environmental samples.