Journal of Pharmaceutical and Biomedical Analysis 80 (2013) 147–154 Contents lists available at SciVerse ScienceDirect Journal of Pharmaceutical and Biomedical Analysis jou rn al h om epage: www.elsevier.com/locate/jpba Study of the quenching effect of quinolones over CdTe-quantum dots using sequential injection analysis and multicommutation L. Molina-García a , E.J. Llorent-Martínez a , M.L. Fernández-de Córdova a , J.L.M. Santos b , S.S.M. Rodrigues b , A. Ruiz-Medina a,∗ a Department of Physical and Analytical Chemistry, Faculty of Experimental Sciences, University of Jaén, Campus las Lagunillas, E-23071 Jaén, Spain b REQUIMTE, Laboratory of Applied Chemistry, Department of Chemical Sciences, Faculty of Pharmacy of Porto University, Rua Jorge Viterbo Ferreira, 228, 4050-313 Porto, Portugal a r t i c l e i n f o Article history: Received 3 February 2013 Received in revised form 6 March 2013 Accepted 11 March 2013 Available online xxx Keywords: Quinolones Automation Quantum dots MCFIA SIA a b s t r a c t The field of light-emitting nanoparticles has experienced an enormous development over the past two decades. The fluorescence of these nanometer-size crystalline particles, called quantum dots (QDs), can be both quenched and enhanced by different compounds. Since a high percentage of articles related to QDs are focused on theoretical studies, the development of analytical methods with real applications is an important step in order to progressively demonstrate the versatility of these particles. Moreover, taking into account that most of the QDs-based analytical methods are non-automated, the development of automated flow methodologies is still a field that presents an important analytical potential. With this purpose, two automatic methodologies, multicommutated flow injection analysis and sequential injection analysis, have been here applied to the analysis of quinolones in pharmaceutical formulations, making use of the quenching effect caused by the analytes over mercaptopropionic acid-capped CdTe QDs fluorescence. Both methodologies were compared in terms of versatility, sample throughput, sensitivity, etc., and applied to the determination of five quinolones in pharmaceutical preparations available in the Spanish Pharmacopoeia. The detection limits ranged between 26 and 50 mol L -1 , and Relative Standard Deviations lower than 3% were observed in all cases. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Colloidal nanocrystals, also known as quantum dots (QDs), are nanometer-scale semiconductor crystals, defined as particles with physical dimensions smaller than the exciton Bohr radius. These monodispersed nanoparticles are made of a core of semiconductor material (elements from the IIB-VIB (e.g. CdSe, CdTe, CdS, ZnSe), IIIB-VB (e.g. InP, InAs) or IVB-VIB (e.g. PbSe) [1,2]) surrounded by an organic capping layer or passivating molecule, in a diameter typ- ically in the range from 1 to 10 nm. QDs have gained increasing interest over the past decade due to their superior photochemical properties, such as higher quantum yields, photostability, tunabi- lity and broad absorption and narrow emission in comparison to conventional organic dyes [3]. They can be directly prepared in aqueous media or can be made water-soluble by appropriate cap- ping with hydrophilic ligands [4]. Compared to traditional organic metallic method, in the aqueous synthesis, QDs are stabilized by some functional ligands (mercaptopropionic acid (MPA), thiogly- colic acid (TGA), glutathione (GSH) and so on) and exhibit some ∗ Corresponding author. Tel.: +34 953 212759; fax: +34 953 212940. E-mail address: anruiz@ujaen.es (A. Ruiz-Medina). unique properties such as lower cost, less toxicity, water-solubility and biocompatibility [5]. In this way, it has been possible to use these nanomaterials in biological and biomedical applications. The promising prospects of QDs-bioconjugates and the bio-applications that they have made possible to demonstrate the use of these QDs as an advantageous alternative to the commonly used molecular probes. Hence, QDs have been extensively used with bio-labelling, bio-imaging and bio-targeting purposes [6–9]. Several works have shown that changes on the QDs pho- toluminescence could occur and be significantly influenced by changes on the QDs surface charge or ligands that affect electron- hole recombination. Therefore, the direct binding of an analyte on the QDs surface could induce changes on their fluorescence response resulting in either enhancing or quenching effects [10]. Furthermore, recent advances in QDs nanotechnology have slowly introduced these nanomaterials in analytical areas mostly as chem- ical sensors involving fluorescence-based measurements [11,12]. Concerning analytical applications, there is already a reasonable amount of published methodologies regarding quantification pro- cedures for the detection of different analytes (macromolecules, vitamins, heavy metals, etc.) involving surface interactions with the nanocrystals [13–15]. However, most of these methods have been non-automatic schemes and they have been based on manual sample handling and measuring. 0731-7085/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jpba.2013.03.003