Colorimetric detection of glyphosate via an aromatic derivative

Glyphosate (GFT) is an organophosphorus compound which belongs to the phosphonate group. It is used as an herbicide to kill weeds and annual grasses. However, GFT shows toxicity and has a carcinogenic potential in humans.1 For this reason, it is important to develop easy, cheap and fast detection methods. An alternative is the use of derivative reactions. Herein, we propose a novel reaction of GFT with 1-Fluoro-2,4-dinitrobenzene (DNFB), which leads to a colored product, which can thereby be detected by UV-Vis spectroscopy. We evaluated the kinetics of the reaction, in order to understand and optimize the detection method. The experiments were performed under pseudo first order conditions (DNFB excess), in buffered media (pH 8 – 11) and controlled temperature (25°C). The reaction occurs with the nitrogen attack of GFT on the aromatic ring of DNFB, replacing the fluorine, forming a colored GFT derivative (GFTD) (Figure 1a) that absorbs in 400 nm, (Figure 1b). The kinetic profiles for pH 8 - 11 were obtained and at pH 9.5 the half-life time is 3,3 x 103 minutes, as shown in Figure 1c. The reaction rate increases as the pH becomes more basic because nitrogen (pKaH 8.6) is converted in free base form. The reaction presented a yellow product, in reduced time and mild conditions. This method developed is innovator and can be used to detect and quantify real GFT samples in distribution centers and plantations. NMR and mass spectroscopy analysis are being carried.