On-line monitoring of the photocatalytic degradation of 2,4-D and dicamba using a solid-phase extraction-multisyringe flow injection system Carmín Chávez-Moreno a , Laura Ferrer b , Laura Hinojosa-Reyes a , Aracely Hernández-Ramírez a , Víctor Cerdà c , Jorge Guzmán-Mar a, * a Universidad Autónoma de Nuevo León, UANL, Facultad de Ciencias Químicas, Cd. Universitaria, San Nicolás de los Garza, Nuevo León C.P. 66451, Mexico b Laboratory of Environmental Radioactivity (LaboRA), University of the Balearic Islands, E-07122 Palma de Mallorca, Spain c Laboratory of Environmental Analytical Chemistry (LQA), University of the Balearic Islands, E-07122 Palma de Mallorca, Spain article info Article history: Received 12 May 2013 Received in revised form 29 July 2013 Accepted 6 August 2013 Available online Keywords: Dicamba 2,4-D Photocatalytic degradation TiO 2 MSFIA system On-line monitoring abstract 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 100e1000 mgL 1 for 3,6-dichloro-2-methoxybenzoic acid (dicamba) and 500e3000 mgL 1 for 2,4-dichlorophenoxyacetic acid (2,4-D), while the detection limits were 30 and 135 mgL 1 for dicamba and 2,4-D, respectively. The monitoring of the photocatalytic degradation (TiO 2 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 mgL 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. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The use of herbicides provides benefits for increasing agricul- tural production; however, the intensive use of pesticides has led to the contamination of surface waters by drift, runoff, drainage and leaching (Popp et al., 2013). Among the herbicides used to prevent the growth of undesirable plants, auxinic herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D) and 3,6-dichloro-2- methoxybenzoic acid (dicamba) (Fig. 1), are widely used in agri- cultural applications to selectively control broadleaf weeds in cereal crops (González et al., 2006). Phenoxyacetic and benzoic acid herbicides are highly soluble in water, stable to chemical hydrolysis, and highly mobile (Ghoshdastidar and Tong, 2013; Phillips and Bode, 2004). Consequently, these compounds are often wide- spread in aquatic matrices. Surface water contamination may have ecotoxicological effects for aquatic flora and fauna, and for human health if used for public consumption (Shin et al., 2011). The U.S. Environmental Protection Agency (USEPA) has established drinking water health advisory levels for 2,4-D and dicamba of 70 and 200 mgL 1 , respectively (Hamilton et al., 2003). Therefore, the development of simple, efficient and low-cost process is strongly urged for the on-site treatment of water. Recently, an increasing interest has been focused on the use of advanced oxidation processes (AOPs) for water treatment. AOPs are based on the generation of very reactive species, such as hydroxyl radicals (  OH), that rapidly and non-selectively oxidize a broad range of pollutants. Among the AOPs, heterogenous photocatalysis is one of the most promising techniques for the complete oxidative mineralization of pollutants to CO 2 . The process is photo-induced and requires UVeVis irradiation to activate the catalyst, which is a semiconductor oxide usually suspended in water. Among the most common photocatalysts, TiO 2 has been demonstrated to be the most suitable catalyst for widespread environmental applica- tions due to its biological and chemical inertness, strong oxidizing power, nontoxicity and long-term stability against photo and * Corresponding author. Tel.: þ52 81 8329 4000x3424; fax: þ52 81 8352 9025. E-mail addresses: jorge.guzmanmr@uanl.edu.mx, jorge74mar@gmail.com (J. Guzmán-Mar). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman 0301-4797/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jenvman.2013.08.007 Journal of Environmental Management 129 (2013) 377e383