Green SPE–Spectrophotometric Determination of Trace Atrazine in Environmental and Agricultural Matrices

A sensitive, selective, and cost-effective analytical method integrating solid-phase extraction (SPE) with visible-region spectrophotometry was developed and validated for the quantitative determination of the s-triazine herbicide atrazine. The method is based on the reaction of atrazine with pyridine to form a quaternary pyridinium halide, which undergoes carbinol-base formation and heterocyclic ring cleavage under alkaline conditions, releasing glutaconic dialdehyde. Subsequent condensation of the dialdehyde with *p*-amino acetanilide produces a stable yellow-orange polymethine chromogen, which was quantified at 420 nm following preconcentration on a C18 SPE cartridge. The method exhibited excellent linearity over the concentration range of 0.5–6.5 µg mL⁻¹, with a molar absorptivity of 6.16 × 10⁵ L mol⁻¹ cm⁻¹ and a Sandell sensitivity of 0.00035 µg cm⁻². The SPE procedure provided a tenfold enrichment factor and improved the analytical sensitivity, affording a limit of detection (LOD) of 0.048 µg mL⁻¹ and a limit of quantification (LOQ) of 0.146 µg mL⁻¹. The method demonstrated good precision, with intra-day relative standard deviation (RSD) values below 1.5%. Analytical validation was performed in accordance with ICH Q2(R2) guidelines, covering accuracy, precision, linearity, and robustness. The environmental performance of the method was further assessed using the AGREE and Analytical Eco-Scale metrics, both of which indicated a favourable green analytical profile compared with conventional chromatographic approaches. The practical applicability of the method was demonstrated in fortified plant, soil, water, and grain yielding recoveries of 90.0–98.8% with RSD values below 3%. The combination of high sensitivity, low instrumentation requirements, satisfactory analytical performance, and favourable environmental characteristics makes the proposed method a promising alternative to LC–MS/MS and GC–ECD for routine atrazine residue monitoring, particularly in resource-limited laboratories.