MATERIALS AND PRODUCT ENGINEERING Chinese Journal of Chemical Engineering, 22(4) 480—488 (2014) DOI: 10.1016/S1004-9541(14)60055-0 PVC Membrane Selective Electrode for Determination of Cadmium(II) Ion in Chocolate Samples Sulekh Chandra 1, * , Deepshikha Singh 1,2 and Anjana Sarkar 2 1 Department of Chemistry, Zakir Husain Delhi College, University of Delhi, New Delhi 110002, India 2 School of Applied Sciences, Netaji Subhas Institute of Technology, University of Delhi, New Delhi 110075, India Abstract Benzil bis(carbohydrazone) (BBC) is prepared and explored as new N N Schiff’s base, which plays the role of an excellent ion carrier in the construction of a Cd(II) ion membrane sensor. The tris(2-ethylhexyl) phosphate best performance corresponds to a membrane composition of 30% poly (vinyl chloride), 65% (TEHP), 3.5% BBC and 1.5% tetradodecyl-ammoniumtetrakis(4-chlorophenyl) borate (ETH 500). This sensor shows very good selectivity and sensitivity towards cadmium ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition, selectivity, pH and influence of additive on the response properties of electrode were investigated. The response mechanism was discussed in the view of UV-spectroscopy. The electrode exhibits a Nernstian behavior (with slope of 29.7 mV per decade) over a very wide concentration range from 1.0×10 −1 to 1.0×10 −8 mol·L −1 with a detection limit of 3.2×10 −8 mol·L −1 . It shows rela- tively fast response time in whole concentration range (<8 s) and can be used for at least 10 weeks in the pH range of 2.0-9.0. The proposed sensor is successfully used for the determination of cadmium in different chocolate sam- ples and as indicator electrode in titration with ethylene diamine tetraacetate (EDTA). Keywords benzil bis(carbohydrazone), ionophore, Cd(II) ion membrane sensor, selectivity coefficient, additive 1 INTRODUCTION Quick determination of minute quantities of ionic species by simple method has a great importance in analytical chemistry. Analytical methods based on potentiometric detection with ion-selective electrodes (ISEs) is considered as an advantageous alternative because they are eco-friendly techniques, provide easy construction and manipulation, present good selectivity in a wide concentration range of operatability and relatively low detection limit, show fast response and non-destructive analysis, and be used as very useful tools for clinical, chemical and environmental analysis [1-8]. In modern world, the pollution of heavy metal ions is becoming more and more severe and cadmium is one of them, which are characterized by strong tox- icity and accumulation ability in living organisms. The main sources of cadmium are natural exposure from soils or earth crust with high content of it, and an- thropogenic processes, such as combustion of coal and mineral oil, smelting, mining, alloy processing, and paint industries, are the major sources of lead and cadmium to the people in the vicinity of the industrial areas. Human uptake of cadmium takes place mainly through food. Foodstuffs that are rich in cadmium will greatly increase the cadmium concentration in human bodies. Examples are liver, mushrooms, shellfish, mussels, cocoa powder and dried seaweed. The provi- sional tolerable weekly intake of cadmium is currently 7 μg·kg −1 body mass, but the recommendation is to limit cadmium intake as it offers no nutritional benefit. Typical maximum levels of cadmium in foodstuffs are currently between 0.05-0.2 mg·kg −1 wet mass [9]. As a highly toxic element cadmium is responsible for several cases of ailment including fever, muscle ache and inflammation that can ultimately lead to res- piratory and kidney damage [10, 11]. Medical research- ers have revealed that cadmium may cause lung and prostate cancers [12]. Therefore, there is an urgent need to monitor the level of cadmium in the environment. Even though Cd-ISE is not commonly found in the marketplace, some reports [13-22] lately indicate intense interest on its fabrications. However, their setbacks are mostly due to serious interference by cations such as Ag + , Hg 2+ , Cu 2+ , Zn 2+ and Pb 2+ . Recently, there has been much focus on the con- struction of ISEs on the basis of chemical recognition principle because they can help to translate the chem- istry of new substrate-binding systems into tools for recognizing selectively various target species in the presence of potentially interfering analytes. Based on above considerations, the aim of the present work is to devise a highly selective cadmium membrane elec- trode with good response characteristics. We attempt to develop selective cadmium sensors by using benzyl bis(carbohydrazone) (BBC) as sensing materials, which show high affinity for cadmium in poly(vinylchloride) (PVC) matrix and the membrane will turn out to be sufficiently selective and sensitive cadmium sensor. The electrodes are used in titration experiments and for the determination of cadmium ion concentrations in chocolate samples. 2 EXPERIMENTAL 2.1 Reagents and apparatus Analytical reagent grade chemicals and doubly Received 2012-08-12, accepted 2013-01-08. * To whom correspondence should be addressed. E-mail: deepshikha.research@gmail.com; schandra_00@yahoo.com