Int. J. Electrochem. Sci., 7 (2012) 2633 - 2642 International Journal of
ELECTROCHEMICAL SCIENCE www.electrochemsci.org
Electrochemical Anion Sensor for Monohydrogen Phosphate Based on Nano-composite Carbon Paste P. Norouzi1,*, M. R. Ganjali1, F. Faridbod1, S. J. Shahtaheri2, H. A. Zamani3 1
Center of Excellence in Electrochemistry, University of Tehran, Tehran, Iran Department of Occupational Health, School of Public Health, Center for Environmental Research, Tehran University of Medical Sciences, Tehran, Iran 3 Department of Applied Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran * E-mail: [email protected]
Received: 21 January 2012 / Accepted: 16 February 2012 / Published: 1 March 2012
Spectroscopic studies of the interaction between cerium acetylacetonate complex (CAA) and a number of inorganic anions showed a selective interaction between CAA and monohydrogen phosphate anion respect to the other anion tested. Therefore, CAA was used as a suitable ionophore (sensing element) in construction of a nano-composite carbon paste electrode. The nano-compoite paste was composed of 5% Multi-walled Carbon Nanotube (MWCNT), 65% graphite powder, 15% room temperature ionic liquid (RTIL) and 15% of CAA. The proposed electrode composition was selected after a series of experiments and optimizations. The sensor worked well with a Nernstian response of -29.3±0.4 mV decade-1 of HPO42- anion in a wide dynamic concentration range of 1.0×10-6-1.0×10-1 mol L-1. The electrode had relatively short response time (20 s), and it was found to produce stable responses for more than two months. It was also used for monitoring of monohydrogen phosphate ion concentration in waste water samples.
Keywords: Monohydrogen phosphate, Multi-walled Carbon Nanotube, Ionic liquid, Sensor, Ion selective electrode, Potentiometry
1. INTRODUCTION Monohydrogen phosphate is one of the anions which play important roles in biological, environmental and many industrial processes. Phosphate levels in water have increased in recent years because of leaching from agricultural soil after wide use of phosphate fertilizers, which may have a negative effect on water quality [1,2].
Int. J. Electrochem. Sci., Vol. 7, 2012
There are some analytical methods for measurement of monohydrogen phosphate ion at low concentrations including UV–Vis spectrophotometric methods such as molybdenum blue, complex of molybdophosphate with basic dye compounds . An alternative method for determination of monohydrogen phosphate ion is potentiometry using a selective electrode. Such methods are simple, low cost, accurate and rapid, which is the reason behind the increasing interest in them [4-16]. Carbon paste electrodes are a class of ion selective electrodes with a high physical stability, long lifetime, the versatility of chemical modification, miniaturization, and rapid renewal of the electrode surface [17-24]. Multi-walled carbon nanotubes (MWCNTs) have been recently used in the compositions of carbon paste electrodes [20-26] due to their extraordinary physicochemical properties, such as ordered structures with high aspect ratios, ultra-light weight, high thermal conductivity, metallic or semimetallic behavior, high surface area, high electrical conductivity and remarkable mechanical strength [27, 28]. Ionic liquids are also a good choice as binder in carbon paste electrodes due to their interesting properties, such as stability, low vapor pressure, low toxicity, low melting temperature, ion-exchange properties, extraction and catalytic activity, high ionic conductivity and good electrochemical and thermal stability [20,21]. Recently, room temperature ionic liquids (RTILs) have been widely used as efficient pasting binders instead of non-conductive organic binders in preparation of carbon composite electrodes. Carbon paste electrode based on MWCNTs and RTILs types of electrodes show superior performance over traditional carbon paste electrodes. Solution studies shows a selective interaction between CAA and monohydrogen phosphate respect to a number of anions tested, therefore, the complex was used as sensing material in construction of a HPO42- nano-composite carbon paste sensor based on MWCNTs and RTILs.
2. EXPERIMENTAL SECTION 2.1. Equipments A glass cell where the carbon paste electrode was used consisting of an R684 model Analion Ag/AgCl double junction electrode as a reference electrode. A Corning ion analyzer 250 pH/mV meter was used for the potential measurements at 25.0±0.1 °C. 2.2. Reagents Graphite powder with a