Sensors and Actuators B 207 (2015) 291–296 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical jo ur nal home page: www.elsevier.com/locate/snb Palladium-doped mesoporous silica SBA-15 modified in carbon-paste electrode as a sensitive voltammetric sensor for detection of oxalic acid Jahan Bakhsh Raoof a,∗ , Fereshteh Chekin b , Vahid Ehsani a a Electroanalytical Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry, Mazandaran University, Babolsar, Iran b Department of Chemistry, Ayatollah Amoli Branch, Islamic Azad University, Amol, Iran a r t i c l e i n f o Article history: Received 10 August 2014 Received in revised form 14 October 2014 Accepted 15 October 2014 Available online 27 October 2014 Keywords: Pd-doped SBA-15 Oxalic acid Electrocatalysis Modified electrode a b s t r a c t We developed simple and effective method for the synthesis of Pd-doped mesoporous silica SBA-15 (Pd/SBA-15). Techniques of X-ray diffraction, scanning electron microscope, energy dispersive X-ray and nitrogen sorption isotherms techniques were used to characterize the structure and properties of the Pd/SBA-15. Due to the large surface area and high catalytic behavior of Pd/SBA-15, carbon paste elec- trode modified with Pd/SBA-15 (Pd/SBA-15/CPE) was prepared. The sensor responded linearly to oxalic acid (OA) in the concentration of 10–140 M with a detection limit of 0.4 M at 3 using linear sweep voltammetry. Also, Pd/SBA-15/CPE was used for OA detection in real samples. The proposed method showed a good result, indicating that the present modified electrode could be applied to determine OA in food samples. The accuracy of the method was evaluated as excellent comparing the detection results with that obtained using conventional KMnO 4 titration method. Possible interferences such as glycine, alanine, ascorbic acid, dopamine, uric acid, l-cysteine, glutathione, d-penicillamine, cystamine, N-acetyl- l-cysteine and lysine for the detection of OA at the Pd/SBA-15/CPE were investigated. The results showed that these mentioned compounds did not show interference. © 2014 Elsevier B.V. All rights reserved. 1. Introduction SBA-15 is a mesoporous silica sieve based on uniform hexago- nal pores with a narrow pore size distribution and a tunable pore diameter of between 5 and 15 nm [1]. The thickness of the frame- work walls is about 3.1–6.4 nm, which gives the material a higher hydrothermal and mechanical stability than, for instance, MCM- 41 [2]. The high internal surface area of typically 400–900 m 2 g -1 makes SBA-15 a well suited material for various applications. It can be used in environmental analytics for adsorption and separa- tion [3,4], advanced optics [5,6], as a support material for catalysts [7,8] and as a template for the production of nanostructured carbon or platinum replica [9,10]. SBA-15 is synthesized in a cooperative self-assembly process under acidic conditions using the triblock copolymer Pluronic 123 as template and tetraethoxysilane as the silica source [11]. After synthesis, the template can be removed by calcinations [1,12], washing [13,14], reflux extraction [1,12], acid ∗ Corresponding author. Tel.: +98 11 35302392; fax: +98 11 35302350. E-mail address: j.raoof@umz.ac.ir (J.B. Raoof). [15], H 2 O 2 treatment [16], extraction with supercritical CO 2 [17] and microwave digestion [18]. It has been demonstrated that the large structural meso- porous of SBA-15 are accompanied by disordered microporous or mesoporous located within the silica pores wall, likely providing connectivity between the ordered large pore channels [19]. In order to generate catalytic activity, elements such as aluminum [20], tita- nium [21], chromium [22], iron [23], lanthanum [24], platinum [25], and palladium [26] were incorporated into the framework of mesoporous SBA-15 molecular sieve. Oxalic acid (OA) widely exists in plants, animals and microbes. Since it can easily combine with Ca 2+ and Mg 2+ to form less soluble salts, high levels of OA in the digestive system lead to formation of kidney stones [27]. Therefore, the accurate detection of OA has attracted considerable interest in arrangement of a rational diet and management of food qualities, as well as in diagnosis and preven- tion of renal stone formation [28]. There have been many methods for the determination of oxalic acid. Thus, various instrumental analytical techniques such as gas chromatography [29], liquid chro- matography [30], spectroscopy [31,32], and enzymatic methods [33,34] have been developed to quantify oxalic acid or oxalate species. However, these instrumental methods have suffered from http://dx.doi.org/10.1016/j.snb.2014.10.064 0925-4005/© 2014 Elsevier B.V. All rights reserved.