On-line monitoring of the photocatalytic degradation of 2,4-D and dicamba using a solid-phase extraction-multisyringe flow injection system

•Photocatalytic degradation processes of dicamba and 2,4-D were monitored by on line SPE-MSFIA system.•Real-time measurement of pesticides during a remediation process was demonstrated.•Filtration, sample clean-up and detection were automatically achieved by the on-line system.•A fast, inexpensive, reproducible, and environment-friendly method was developed.

A fully automated on-line system for monitoring the photocatalytic degradation of herbicides was developed using multisyringe flow injection analysis (MSFIA) coupled to a solid phase extraction (SPE) unit with UV detection. The calibration curves were linear in the concentration range of 100–1000 μg L−1 for 3,6-dichloro-2-methoxybenzoic acid (dicamba) and 500–3000 μg L−1 for 2,4-dichlorophenoxyacetic acid (2,4-D), while the detection limits were 30 and 135 μg L−1 for dicamba and 2,4-D, respectively. The monitoring of the photocatalytic degradation (TiO2 anatase/UV 254 nm) of these two herbicides was performed by MSFIA-SPE system using a small sample volume (2 mL) in a fully automated approach. The degradation was assessed in ultrapure and drinking water with initial concentrations of 1000 and 2000 μg L−1 for dicamba and 2,4-D, respectively. Degradation percentages of approximately 85% were obtained for both herbicides in ultrapure water after 45 min of photocatalytic treatment. A similar degradation efficiency in drinking water was observed for 2,4-D, whereas dicamba exhibited a lower degradation percentage (75%), which could be attributed to the presence of inorganic species in this kind of water.