Titanium dioxide as an efficient sorbent for the solid-phase extraction of glyphosate and its main metabolite in natural waters

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Glyphosate (GLP) is one of the most widely used herbicides worldwide. GLP and its main metabolite, aminomethylphosphoric acid (AMPA), are commonly detected in surface waters following herbicide application. Titanium dioxide (TiO 2 ) has emerged as a promising adsorbent for the sorption of organic phosphonates such as GLP and AMPA. Commercial TiO 2 (Adsorbsia As600) has been evaluated for use in a solid-phase extraction configuration for the concentration and determination of these two analytes in natural waters. The results confirm that quantitative adsorption of both analytes can be achieved with TiO 2 . Although adsorption is enhanced at acidic pH, when the sorbent surface is positively charged, the interaction between the analytes and TiO 2 is not solely based on electrostatic interactions. Elution requires the use of 0.5 M NaOH solutions. Improved clean-up efficiency has been observed with TiO 2 compared to conventional anion exchangers, resulting in cleaner extracts and increased sensitivity, especially when mass-spectrometry detection is applied. Sorption kinetics were found to significantly affect performance when TiO 2 was used as a sorbent; flow rates above 2 mL·min −1 result in poor retention of both analytes and non-reproducible results. GLP showed faster adsorption and was quantitatively retained at flow rates below 1.7 mL·min −1 . However, flow rates ≤0.5 mL·min −1 were required for effective AMPA sorption. No degradation of GLP on TiO 2 surface under acidic conditions was observed, even after extended contact times of up to 4 h.