Environ Monit Assess (2014) 186:7431–7441 DOI 10.1007/s10661-014-3938-8

Simultaneous determination of hydroxylamine and phenol using a nanostructure-based electrochemical sensor Hadi Mahmoudi Moghaddam & Hadi Beitollahi & Somayeh Tajik & Mohammad Malakootian & Hassan Karimi Maleh

Received: 5 May 2014 / Accepted: 8 July 2014 / Published online: 16 July 2014 # Springer International Publishing Switzerland 2014

Abstract The electrochemical oxidation of hydroxylamine on the surface of a carbon paste electrode modified with carbon nanotubes and 2,7-bis(ferrocenyl ethyl) fluoren-9-one is studied. The electrochemical response characteristics of the modified electrode toward hydroxylamine and phenol were investigated. The results showed an efficient catalytic activity of the electrode for the electro-oxidation of hydroxylamine, which leads to lowering its overpotential. The modified electrode exhibits an efficient electron-mediating behavior together with well-separated oxidation peaks for hydroxylamine and phenol. Also, the modified electrode was H. M. Moghaddam : M. Malakootian Environmental Health Engineering Research Center and Department of Environmental Health, School of Public Health, Kerman University of Medical Sciences, Kerman, Iran H. M. Moghaddam Pharmaceutics Research Center, Institute of Neuropharmacology, Kerman University of Medical Sciences, Kerman, Iran H. Beitollahi (*) Environment Department, Institute of Science and High Technology and Environmental Sciences, Graduate University of Advanced Technology, Kerman, Iran e-mail: [email protected] S. Tajik Department of Chemistry, Shahid Bahonar University of Kerman, P.O. Box 76175–133, Kerman, Iran H. K. Maleh Department of Chemistry, Graduate University of Advanced Technology, Kerman, Iran

used for determination of hydroxylamine and phenol in some real samples. Keywords Hydroxylamine . Phenol . Carbon nanotubes . Chemically modified electrodes

Introduction Hydroxylamine, NH2OH, a derivative of ammonium, is an intermediate in two important microbial processes of the nitrogen cycle: it is formed during nitrification as well as during anaerobic ammonium oxidation (Arp and Stein 2003; Jetten 2001). However, it is a well-known mutagen, moderately toxic, and harmful to human, animals, and even plants (Gross 1985), which has been known to cause both reversible and irreversible physiological changes (Smith and Layne 1969). It is available commercially and frequently used industrially, widely in pharmaceutical intermediates and final drug substances synthesis, nuclear fuel reprocessing, and the manufacturing of semiconductors (Kumasaki et al. 2003). In recent years, chemists became aware of the potentials of hydroxylamine as a result of two major accidents, one occurred in the USA in February 1999, which killed five people, and the other occurred in Japan in June 2000, which killed four people. Therefore, from the industrial, environmental, and health viewpoints, the development of a sensitive analytical method for the determination of low levels of hydroxylamine is of significant importance.

7432

The reported methods of the hydroxylamine determination include spectrophotometry (Teshima et al. 2011), high-performance liquid chromatography (Korte 1992), gas chromatography (Li et al. 2005), potentiometry (Christova et al. 1976), polarography (Canterford 1978), and biamperometry (Zhao and Song 2001). However, the processes involved in many of these methods are extremely complex, and the linear ranges are relatively narrow and have low precision. Fortunately, electrochemical techniques offer the opportunity for portable, cheap, and rapid methodologies. However, hydroxylamine cannot be electro-oxidized at bare carbon electrodes. One promising approach is the use of chemically modified electrodes (CMEs) containing specifically selected redox mediators immobilized on conventional electrode materials. Recently, various chemically modified electrodes (CMEs) have been prepared and applied in the determination of hydroxylamine (Zhang and Zheng 2012; Zhang et al. 2010a, b; Kannan and Abraham John 2010; Xu et al. 2013; Li and Xie 2012, 2013), which can significantly lower the overpotentials and increase the oxidation current response. Phenolic compounds are important contaminants in food and environmental matrices (Hashemnia et al. 2012). Many of them are very toxic, showing harmful effects on plants, animals, and human health. Therefore, the identification and quantification of these compounds are important for environmental monitoring (Bartosova et al. 2014). The commonly used techniques for determination of phenolic compounds are spectrophotometry (Zain et al. 2014), chromatography (Zhou et al. 2014), and capillary electrophoresis (Wang et al. 2010). However, these methods are time-consuming and the equipments are expensive. Therefore, there is an interest in developing simple, sensitive, and effective analytical techniques for their determination. Among them, electrochemical sensors have been shown to be very simple and sensitive tools for phenolic compounds assay (Ensafi et al. 2013; Zhang et al. 2014a; Mojović et al. 2011; Janegitz et al. 2012; Yang et al. 2012). Carbon paste electrodes (CPEs) belong to the promising electrochemical or bioelectrochemical sensors of wide applicability (Xu et al. 2014; Raoof et al. 2006a; Afkhami et al. 2014). In 2008, it was exactly a half century since Ralph Norman Adams from the University of Kansas published a short one-page report in which he introduced this kind of electrode, which was originally designed as an alternative to the dropping

Environ Monit Assess (2014) 186:7431–7441

mercury electrode. Although the concept of a dynamic renewable electrode surface was not successful, it turned out that the material with paste-like consistency could be practically employed in voltammetric analysis. Carbon pastes undoubtedly represent one of the most convenient materials for the preparation of modified electrodes (Mazloum-Ardakani et al. 2010; Guo and Khoo 1997; Taleat et al. 2008). Electrochemical methods offer the practical advantages including operation simplicity, satisfactory sensitivity, wide linear concentration range, low expense of instrument, possibility of miniaturization, suitability for real-time detection, and less sensitivity to matrix effects in comparison with separation and spectral methods (Gupta et al. 2000, 2002, 2003a, 2005, 2006a, b, 2007a, b, 2011a, 2012, 2013; Mashhadizadeh and Shamsipur 1997; Prasad et al. 2004; Goyal et al. 2007, 2008a; Ghosh et al. 2006; Jain et al. 2006; Srivastava et al. 1996; Beitollahi et al. 2011b; Thriveni et al. 2007; Raoof et al. 2006b, 2007; Li et al. 2014). Modification of the electrode surface can grant some remarkable advantages in the electrochemical responses. Some special properties can be considered in modification of the electrodes using nanomaterials, e.g., catalysis, the large specific surface area and more adsorption sites (Gupta et al. 1999, 2003b, 2006c, d, 2011b; Raoof et al. 2006b; Bouffier et al. 2014; Goyal et al. 2008b; Zhang et al. 2014b; Beitollahi et al. 2011a; Fonseca et al. 2011; Azadbakht and Abbasi 2014; Liang et al. 2007; Jain et al. 1997; Wang et al. 2014). Nanostructured materials, particularly carbon nanomaterials including nanoparticles, nanowires, and nanotubes, have attracted considerable interests and have become a vast area of research owing to their unique physical and chemical properties which can provide an important and feasible platform for electroanalysis particularly in the design of modified electrodes for electrochemical sensing (Goyal et al. 2008c). Applications of carbon nanoparticles (CNPs) in electroanalytical studies display extraordinary advantages over conventional electrodes including enhanced mass transport and catalysis, highly effective surface areas, high porosity, more adsorption, and reactive sites and control over the electrode macroenvironment (Karimi-Maleh et al. 2014; Andrey Montoro et al. 2014; Beitollahi et al. 2014a, b; Tajik et al. 2013, 2014; Li et al. 2014; Yu et al. 2014; Mokhtari et al. 2012; Qiu et al. 2010; Mohammadi et al. 2013).

Environ Monit Assess (2014) 186:7431–7441

In the present work, we describe the preparation of a new electrode composed of CNPE modified with 2,7bis(ferrocenyl ethyl)fluoren-9-one (2,7-BFCNPE) and investigate its performance for the electrocatalytic determination of hydroxylamine in aqueous solutions. We also evaluate the analytical performance of the modified electrode for quantification of hydroxylamine in the presence of phenol.

7433

into the carbon paste provided the electrical contact. When necessary, a new surface was obtained by pushing an excess of the paste out of the tube and polishing with a weighing paper. For comparison, 2,7-BF modified CPE electrode (2,7-BFCPE) without CNTs, CNT paste electrode (CNPE) without 2,7-BF, and unmodified CPE in the absence of both 2,7-BF and CNT were also prepared in the same way.

Experimental Results and discussion Apparatus and chemicals Electrochemical behavior of 2,7-BFCNPE The electrochemical measurements were performed with an Autolab potentiostat/galvanostat (PGSTAT302 N, Eco Chemie, The Netherlands). The experimental conditions were controlled with General Purpose Electrochemical System (GPES) software. A conventional three-electrode cell was used at 25±1 °C. An Ag/ AgCl/KCl (3.0 M) electrode, a platinum wire, and the 2,7-BFCNPE were used as the reference, auxiliary, and working electrodes, respectively. A Metrohm 691 pH/ ion meter was used for pH measurements. All solutions were freshly prepared with doubledistilled water. Hydroxylamine, phenol, and all other reagents were of analytical grade from Merck (Darmstadt, Germany). Graphite powder and paraffin oil (DC 350, density = 0.88 g cm−3) as the binding agent (both from Merck) were used for preparing the pastes. Multiwalled carbon nanotubes (purity more than 95 %) with outer diameter (o.d.) between 10 and 20 nm, inner diameter (i.d.) between 5 and 10 nm, and tube length from 10 to 30 μm were prepared from Nanostructured & Amorphous Materials, Inc. (USA). The buffer solutions were prepared from orthophosphoric acid and its salts in the pH range of 2.0–11.0. 2,7-BF was synthesized in our laboratory as reported previously (Beitollahi et al. 2014a). Preparation of the electrode The 2,7-BFCNPEs were prepared by hand-mixing 0.01 g of 2,7-BF with 0.89 g graphite powder and 0.1 g CNTs with a mortar and pestle. Then ~0.7 ml of paraffin was added to the above mixture and mixed for 20 min until a uniformly wetted paste was obtained. The paste was then packed into the end of a glass tube (ca. 3.4-mm i.d. and 10-cm-long). A copper wire inserted

2,7-BFCNPE was constructed and its electrochemical properties were studied in a 0.1 M phosphate buffered saline (PBS, pH 7.0) using cyclic voltametry (CV). The experimental results show well-defined and reproducible anodic and cathodic peaks related to 2,7-bis (ferrocenyl ethyl)fluoren-9-one/2,7-bis(ferricenium ethyl)fluoren-9-one (Fc/Fc+) redox system, which show a quasireversible behavior in an aqueous medium (Bard and Faulkner 2001). The electrode capability for the generation of a reproducible surface was examined by CV data obtained in optimum solution pH 7.0 from five separately prepared 2,7-BFCNPEs (Table 1). The calculated relative standard deviation (RSD) for various parameters accepted as the criteria for a satisfactory surface reproducibility (about 1–4 %), which is virtually the same as that expected for the renewal or ordinary carbon paste surface. However, we regenerated the surface of 2,7-BFCNPE before each experiment according to our previous result (Beitollahi et al. 2014b). Electrocatalytic oxidation of hydroxylamine at a 2,7-BFCNPE The electrochemical behavior of hydroxylamine is dependent on the pH value of the aqueous solution, whereas the electrochemical properties of Fc/Fc+ redox couple are independent on pH. Therefore, pH optimization of the solution seems to be necessary in order to obtain the electrocatalytic oxidation of hydroxylamine. Thus, the electrochemical behavior of hydroxylamine was studied in 0.1 M PBS in different pH values (2.0

Simultaneous determination of hydroxylamine and phenol using a nanostructure-based electrochemical sensor.

The electrochemical oxidation of hydroxylamine on the surface of a carbon paste electrode modified with carbon nanotubes and 2,7-bis(ferrocenyl ethyl)...
833KB Sizes 1 Downloads 5 Views