Please cite this article in press as: G. Sági, et al., Analytical approaches to the OH radical induced degradation of sulfonamide antibiotics in dilute aqueous solutions, J. Pharm. Biomed. Anal. (2014), http://dx.doi.org/10.1016/j.jpba.2014.08.028 ARTICLE IN PRESS G Model PBA-9703; No. of Pages 9 Journal of Pharmaceutical and Biomedical Analysis xxx (2014) xxx–xxx Contents lists available at ScienceDirect Journal of Pharmaceutical and Biomedical Analysis j o ur na l ho mepage: www.elsevier.com/locate/jpba Analytical approaches to the OH radical induced degradation of sulfonamide antibiotics in dilute aqueous solutions Gyuri Sági a,∗ , Tamás Csay a , László Szabó a , György Pátzay c , Emil Csonka c , Erzsébet Takács a,b , László Wojnárovits a a Institute for Energy Security and Environmental Safety, Centre for Energy Research, Hungarian Academy of Sciences, 1121, Konkoly-Thege Miklós út 29-33, Budapest, Hungary b Óbuda University, Sándor Rejt ˝ o Faculty of Light Industry and Environmental Engineering, 1034, Doberdó u. 6, Budapest, Hungary c Department of Chemical and Environmental Process Engineering, Budapest University of Technology and Economics, 1111, Budafoki út 8, Budapest, Hungary a r t i c l e i n f o Article history: Received 11 June 2014 Received in revised form 21 August 2014 Accepted 22 August 2014 Available online xxx Keywords: Sulfonamide Degradation product Advanced oxidation processes Ion chromatography LC–MS/MS a b s t r a c t By combining a large variety of analytical techniques this study aimed at elaborating methods to follow up the degradation of sulfonamides in an advanced oxidation process (AOP): irradiation with ionizing radiation in dilute aqueous solution. In this process, besides other radicals, hydroxyl radicals are produced. As pulse radiolysis experiments show the basic initial reaction is hydroxyl radical addition to the benzene ring, forming cyclohexadienyl radical intermediates. In aerated solutions these radicals transform to peroxy radicals. Among the first formed products aromatic molecules hydroxylated in the benzene rings or in some cases in the heterocyclic rings were observed by LC–MS/MS. Chemical oxygen demand (COD) measurements indicate that at the early reaction period of degradation one hydroxyl radical induces incorporation of 1.5 O atoms into the products. Comparison of the COD and TOC (total organic carbon content) results shows gradual oxidation. Simultaneously with hydroxylation ring opening also takes place. The kinetics of inorganic SO 4 2- and NH 4 + formation, analyzed by ion chromatography, is similar to the kinetics of ring degradation (UV spectroscopy), however, there is a delayed formation of NO 3 - . The latter ions may be produced in oxidative degradation of smaller N containing fragments. The S atoms of the sulfonamides remain in the solution (ICP-MS measurements) after degradation, whereas some part of the N atoms leaves the solution probably in the form of N 2 (total nitrogen content (TN) measurements). Degradation is accompanied by a high pH drop due to formation of SO 4 2- , NO 3 - and smaller organic acids. The degradation goes through many simultaneous and consecutive reactions, and with the applied methods the different stages of degradation can be characterized. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Sulfonamide antibiotics and their metabolites are classified as persistent organic pollutants, due to their resistance to biologi- cal decomposition. The degradation in surface waters may take place with the intervention of hydroxyl radicals ( • OH). In rivers and lakes • OH is suggested to form in UV photolysis of dissolved organic material or nitrates and nitrites [1]. On sunny days, the • OH formation rates are around 10 -10 M s -1 in the surface layers [2]. Sulfonamides are regularly detected in surface waters, even up to 1 g dm -3 levels, because of their widespread human and ∗ Corresponding author. Tel.: +36 13922612. E-mail address: sagi.gyuri@energia.mta.hu (G. Sági). veterinary applications [3,4]. A substantial fraction is released to the environment by the wastewater treatment plants. The tradi- tional water purification technologies are not effective enough in the degradation of non-biodegradable compounds [5,6]. Nowadays, a new class of water purification technologies, called advanced oxi- dation processes (AOP), is under development for degradation of poorly biodegradable organic compounds. Here, also • OH reactions play the key role in degradation [1,7]. Therefore, investigation of • OH reactions, identification of degradation products and study of their toxicity are essentially important for understanding the degradation in the nature and for establishing new water purifica- tion technologies. The large number of products that form during degradation and their gradually changing composition during the treatment give a great task to the analytical chemists. Sulfonamides involved in this study include sulfanilamide (SAA) and seven of its derivatives substituted on the N atom http://dx.doi.org/10.1016/j.jpba.2014.08.028 0731-7085/© 2014 Elsevier B.V. All rights reserved.