A Quick and Simple Chromatographic Method to Investigate the Adsorption of Glufosinate on a Subtropical Oxisol: Affinity Comparisons With Glyphosate.

This work presents a fast and straightforward chromatographic method with fluorescence detection to quantify glufosinate in soil solutions. The method is based on the reaction between the primary amine group of glufosinate and o-phthaldialdehyde with 2-mercaptoethanol, producing a stable fluorescent derivative in under 2 min, which remains stable for more than 70 min (relative standard deviation [RSD] = 3.6%). The method does not require automated timing systems. Glyphosate, which lacks a primary amine, does not interfere, and potential interferences from aminomethyl phosphonic acid and ammonium are effectively circumvented by chromatographic separation, as their indole derivatives are well resolved from the glufosinate derivative. An isocratic chromatographic run using 20:80 methanol:piperazine-N,N'-bis(2-ethanesulfonic acid) buffer at 1.0 mL/min lasts 5 min. The method showed linearity over the concentration range of 0.10 and 20 µmol/L, with detection and quantification limits of 0.015 and 0.050 µmol/L, respectively. Calibration curve reproducibility is high (slope RSD < 2.1%, n = 5). The method was effectively applied to study glufosinate adsorption in an Oxisol, revealing a maximum adsorption capacity of 2.5 ± 0.2 µmol/g, significantly lower than that reported for glyphosate.