A sequential-injection reversed-phase chromatography method for fluorimetric determination of glyphosate and aminomethylphosphonic acid

Abstract

Glyphosate (GLYPH) is one of the most used herbicides around the world. In soil and waters, GLYPH is metabolized into aminomethylphosphonic acid (AMPA). Because of their high water solubility and half-life, both GLYPH and AMPA have been detected long after application. The present paper describes the development of a low cost Sequential Injection Chromatography (SIC) method for determination of GLYPH and AMPA based on pre-column oxidation of GLYPH to glycine (GLY) by hypochlorite, exploiting the stopped flow approach, followed by reaction with the fluorogenic reagent o-phthaldialdehyde in the presence of 2-mercaptoethanol (OPA-2ME) in borate buffer (pH > 9) to produce the fluorescent 1-(2′-hydroxyethylthio)-2-N-alkylisoindole. While GLYPH is being converted into GLY, the determination of AMPA is made by pre-column derivatization with OPA-2ME. Isocratic elution of both GLYPH and AMPA derivatives was done using a mobile phase composed of 20 : 80 (v/v) methanol : 10 mM phosphate buffer (pH 6.8) at a flow rate of 30 μL s⁻¹. The proposed method solved the mutual fluorescence interference of AMPA and GLY derivatives, and the interference of humic substances. A linear response was observed for concentrations up to 5.0 μM for both compounds, with limits of detection and quantification of 0.11 and 0.35 μM (GLYPH), and 0.06 and 0.20 μM (AMPA), respectively. Application of the method to spiked natural waters gave recoveries between 78 and 134%, suggesting that the method has potential to be applied for water sampling trials.