1604 J. Sep. Sci. 2013, 36, 1604–1611 Luisa Pasti 1 Elena Sarti 1,2 Alberto Cavazzini 1 Nicola Marchetti 1,2 Francesco Dondi 1 Annalisa Martucci 3 1 Department of Chemistry and Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy 2 Terra&AcquaTech Laboratory, University of Ferrara, Ferrara, Italy 3 Physics and Earth Sciences Department, University of Ferrara, Ferrara, Italy Received December 11, 2012 Revised February 13, 2013 Accepted February 14, 2013 Research Article Factors affecting drug adsorption on beta zeolites The adsorption behaviour of three commonly used drugs, namely ketoprofen, hy- drochlorothiazide and atenolol, from diluted aqueous solutions on beta zeolites with differ- ent SiO 2 /Al 2 O 3 ratio (i.e. 25, 38 and 360) was investigated by changing the ionic strength and the pH, before and after thermal treatment of the adsorbents. The selective adsorption of drugs was confirmed by thermogravimetry and X-ray diffraction. The adsorption capacity of beta zeolites was strongly dependent on both the solution pH and the alumina content of the adsorbent. Such a remarkable difference was interpreted as a function of the interac- tions between drug molecules and zeolite surface functional groups. Atenolol was readily adsorbed on the less hydrophobic zeolite, under pH conditions in which electrostatic inter- actions were predominant. On the other hand, ketoprofen adsorption was mainly driven by hydrophobic interactions. For undissociated molecules the adsorption capability increased with the increase of hydrophobicity. Keywords: Adsorption selectivity / Beta zeolites / Pharmaceuticals enrichment DOI 10.1002/jssc.201201142  Additional supporting information may be found in the online version of this article at the publisher’s web-site 1 Introduction Zeolites are environmentally compatible crystalline solids, whose micro-pore dimensions and physico-chemical prop- erties strongly depend on their framework composition [1]. The hydrophilic/hydrophobic character of these materials can be tailored by varying the SiO 2 /Al 2 O 3 ratio (SAR) [2], while the 3D framework, generating nanometre-sized channels and cages, imparts to them high porosity and large surface ar- eas [3]. On the other hand, the shape of the internal pore structure strongly affects the adsorption selectivity towards host molecules. For these reasons, zeolites have been used as adsorbent media for specific classes of chemicals, includ- ing hydrocarbons [4–6], halocarbons [7–10] and pharmaceu- ticals [11–13]. Beta zeolites (BEAs), firstly described by the Mobile Oil Corporation [14], are synthetic highly siliceous large-pore ma- terials obtained by using tetraethylammonium as structure- directing agent. Their high thermal and chemical stability, together with the presence of strong acid sites on the sur- face has made BEAs active and efficient catalysts for a wide spectrum of reactions of industrial importance [15–21]. The Correspondence: Dr. Luisa Pasti, Department of Chemistry and Pharmaceutical Sciences, University of Ferrara, Via L. Borsari, 46, 44123 Ferrara, Italy E-mail: luisa.pasti@unife.it Fax: +39 0532 240709 Abbreviations: ATN, atenolol; BEA, beta zeolite; HCT, hy- drochlorothiazide; KTP, ketoprofen; SAR, SiO 2 /Al 2 O 3 ratio; TG, thermogravimetric framework structure of beta zeolite was independently re- solved by Newsam et al. [22] and Higgins et al. [23] using a combination of various techniques. The structure consists of an intergrowth of two or more polymorphs [22] comprising a 3D system of 12-membered ring channels. Polytype A, is tetragonal (space group P4 1 22, or P4 3 22 and cell parameters a = b ≈ 12.5 ˚ A and c ≈ 26.4 ˚ A), whereas polytype B is mon- oclinic (space group C2/c and cell parameters a ≈ b ≈ 17.6 ˚ A, c ≈ 14.4 ˚ A and β ≈ 114°) [22, 23]. According to Higgins et al. [23] a third polytype, called polytype C, (monoclinic with space group P2/c and with a ≈ b ≈ 12.5 ˚ A, c ≈ 27.6 ˚ A, and β ≈ 107°) was also suggested. In recent years, solid phase micro-extraction and micro- SPE have become widely practiced solvent-minimised ap- proaches in sample preparation, especially for the analysis of drugs from aqueous environmental samples [24, 25]. Some of these molecules such as the analgesics, anti- inflammatories, antiepileptics,  blockers, etc. have been identified as environmental pollutants or contaminants of emerging concern [26–30]. They are usually found in the aquatic environment at low concentration level and their an- alytical determination requires accurate sample preparation, an application field where zeolites, thanks to their unique physico-chemical properties, seem to be particularly useful adsorbents [31–33]. Another field where the study of the adsorption of pharmaceuticals by zeolites could be of great interest is the drug delivery in nanomedicine applications. Due to their high chemical and thermal stabilities, siliceous porous materials can be employed for hosting and in situ delivering a variety of molecules of pharmaceutical interest [34–36]. They C  2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.jss-journal.com