ЖУРНАЛ АНАЛИТИЧЕСКОЙ ХИМИИ, 2014, том 69, № 6, с. 610-620
ОРИГИНАЛЬНЫЕ СТАТЬИ
УДК 543
ELECTROCATALYTIC OXIDATION OF HYDRAZINE AT POLY(4,5-DIHYDROXY-1,3-BENZENEDISULFONIC ACID) MULTIWALL CARBON NANOTUBES MODIFIED-GLASSY CARBON ELECTRODE: IMPROVEMENT OF THE CATALYTIC ACTIVITY © 2014 Ali A. Ensafi, Mahsa Lotfi
Department of Chemistry, Isfahan University of Technology Isfahan 84156-83111, Iran Received 30.01.2012; in final form 11.11.2013
A stable electroactive thin film of poly(4,5-dihydroxy-1,3-benzenedisulfonic acid) was electrochemically deposited at the surface of multiwall carbon nanotubes-glassy carbon electrode. The electrocatalytic oxidation of hydrazine has been studied at the surface of the modified electrode using cyclic voltammetry, chrono-amperometry and linear sweep voltammetry as diagnostic techniques. The modified electrode exhibits good electrocatalytic activity for the oxidation of hydrazine with a good sensitivity. Linear calibration range was in the wide concentration range of 10—3540 ^M hydrazine with a detection limit of 1.8 ^M and a sensitivity of 85.3 nA/^M. A Tafel plot, derived from voltammograms, indicated a one-electron transfer process to be the rate-limiting step and the overall number of electrons involved in the catalytic oxidation of hydrazine was found to be four. The influences of potentially interfering substances were studied. The diffusion coefficient of hydrazine was also evaluated. Finally, the proposed modified electrode was used for the determination of hydrazine in spiked water samples.
Keywords: hydrazine, electrocatalytic determination, poly(4,5-dihydroxy-1,3-benzenedisulfonic acid), vol-tammetry.
DOI: 10.7868/S0044450214060073
There is an increasing demand for simple, inexpensive and rapid analytical tests to determine the concentrations of biological and environmental compounds. A great deal of interest still exists in the development of materials capable of the catalytic electrooxidation of hydrazine; in order to diminish the typically large overpotential encountered in its direct oxidation at most electrode surfaces. Electrochemical techniques have been particularly studied for these applications and much interest has centered on the use of carbon as an inexpensive substrate for electrochemical techniques. But owing to the often impractical high activation overpotential required for the oxidation or reduction of many substances at a carbon surface, one field that offers great scope is chemically modified electrodes [1-5].
Hydrazine is used as an oxygen scavenger in industry and has wide applications as an antioxidant, a photographic developer and an insecticide [6]. It is also used as fuel in fuel cells due to its high capacity and lack of contamination [7]. Hydrazine and its derivatives have found various applications such as catalysts, corrosion inhibitors and antioxidants, emulsifiers, reducing agents, pesticides and plant-growth regulators,
dye, stuffs and explosives. In addition, hydrazine is very important in pharmacology because it has been recognized as a carcinogenic and hepatotoxic substance, which affects liver and brain glutathione. Consequently, drug regulatory authorities are becoming increasingly aware of the need to control the levels of hydrazones in isoniazid and other hydrazide drugs and in their formulations. Because it is highly toxic and irritating and is suspected of being carcinogenic and mutagenic [8], its detection has attracted considerable analytical interest. Adverse health effects on people living near hazardous waste sites caused by hydrazine and its derivatives have been described in the literature [9], and the maximum recommended level of hydrazine in trade effluents is 1 ^g/mL [10]. Because of hydrazine's industrial and pharmacological significance, a sensitive method is required for its reliable measurement. Unfortunately, hydrazine has a large anodic overpotential at ordinary carbon electrodes.
Different methods for the determination of hydra-zine have been developed including potentiometric [11, 12], spectrophotometric [10, 13-15], and flow-injection methods [14-16], optical sensors [17], chemiluminescence method [18] and liquid chroma-
Table 1. Characteristics of modified electrodes for the determination of hydrazine
Electrode Modifier pH Linear range, цМ Limit of detection, Interference Reference
Glassy carbon Pyrocatechol violet 7.5 5-40 4.2 Not reported [6]
Glassy carbon Pyrogallol red 9.0 5-600 2 nh2oh [8]
Glassy carbon electrode Curcumin multiwall carbon nanotubes 8.0 2-44 1.4 Not reported [20]
Titanium electrode Nanoporous gold particles - 500-4000 0.042 Not reported [21]
Glassy carbon Chlorogenic acid 7.5 50-1000 - Not reported [22]
Glassy carbon Hydroquinone salophen Derivatives 7.0 10-400 1.6 Not reported [23]
Titanium electrode Ag - 0-6000 - Not reported [24]
Glassy carbon electrode Carbon nanotubes and catechol derivatives 7.0 25-2000 2 Not reported [25]
Glassy carbon Overoxidized polypyrrole 9.0 1.3-2000 3.6 Not reported [26]
Gold electrode Iron phthalocyanine 7.0 0.13-0.92 5 Not reported [27]
Glassy carbon Fe-tetraaminophthalocyanine 13 1-10000 - Not reported [28]
Glassy carbon Hybridhexacyanoferrates of copper and cobalt films 7.0 100-12000 - Not reported [29]
Microelectrodes Carbon nanotube powder 7.0 1-10000 - Not reported [30]
Glassy carbon Cobalt pentacyanonitrosylferrate - 0-12000 - Not reported [31]
Carbon nanotubes Poly(4,5-dihydroxy-1,3-benzenedisul-fonic acid) 8.0 10-3540 1.8 nh2oh This work
tography with UV detection [19]. Accordingly, during the last decade many efforts have been made to lower the oxidation potential of hydrazine in order to facilitate its voltammetric and amperometric detection at various chemically modified electrodes. There are several electrochemical methods for determination of hydrazine in the literature with different detection limits, pH, linear range and the potential of hydrazine oxidation. Table 1 summarized details of the methods from available references along with their analytical parameters and compares them with the proposed electrode in this work. Although some of them are sensitive, they have short linear dynamic range, and/or suffer from many interfering substances. In this work, 4,5-dihy-droxy-1,3-benzenedisulfonic acid (DHBDSA) was electrochemically polymerized at a surface of a glassy carbon electrode for electrocatalytic determination of hydrazine as a simple, highly selective, rapid and new assay method for hydrazine.
EXPERIMENTAL
Reagents. All chemicals were of analytical reagent grade and used without further purification. Doubly distilled water was used throughout the e[periments. Phosphate buffer solutions (PBS, 0.05 M) were prepared by mixing different volumes of 0.10 M Na2HPO4 and 0.10 M NaH2PO4 and deionized water. The pH values were adjusted by addition of H3PO4 or NaOH. Hydrazine stock solution was prepared by dissolving 0.10497 g N2H4 • 2HCl (Merck) in water in a 100-mL volumetric flask. Multiwall carbon nanotubes (MWCNTs, >90%, d x l = (100-70 nm) x (5-9 |im)) from Fluka were used.
Apparatus. All electrochemical experiments including cyclic voltammetry (CV) and differential pulse voltammetry were performed with a Metrohm instrument, Model 797 VA processor. A conventional three-electrode electrochemical system was used for all electrochemical experiments, which consisted of a working electrode (modified multiwall carbon nanotubes/glassy
Fig. 1. SEM image of PDHBDSA-modified MWCNTs-GCE.
carbon electrode), a platinum wire counter electrode and an Ag/AgCl (3.0 M KCl) reference electrode. A Corning pH-meter, Model 140, with a glass electrode (conjugated with an Ag/AgCl reference electrode, Model 6.0232.100) was used to determine pH of the solutions. Scanning electron microscope, Philips, Model XLC, was used to characterize the prepared electrodes.
Procedure. To eliminate any oxide catalysts within the nanotubes, MWCNTs were refluxed in 100 mL of 2.0 M HNO3 for 20 h, washed twice with distilled water and dried at room temperature. The purified MWCNTs were dispersed in acetonitrile (1.0 mg/mL MWCNTs) using ultrasonic agitation to obtain a black suspension. The glassy carbon electrode (GCE) was carefully polished with 0.05 ^m alumina slurry on a polishing cloth for 3 min and then washed in an ultrasonic bath of methanol/water (20/80, v/v). The cleaned GCE was coated by casting 5 ^L of the suspension of MWCNTs and dried in oven at 60°C. Then, the electrode was placed in a solution containing 0.7 M NaOH and 5.0 mM DHBDSA. The potential runned for the potential range of -0.30 and 0.70 V with a scan rate 50 mV/s for 10 times using cyclic voltammetry to polymerize DHBDSA at surface of the electrode. After polymerization the modified electrode was washed with distilled water and cycled the scan at pH 8.0 between 0 and 0.60 V four times to eliminate unreacted DHBDSA, to increase its reproducibility.
Ten milliliters of the buffer solution (pH 8.0) were transferred into an electrochemical cell using the
three-electrode system containing DHBDSA modified MWCNTs—GCE as a working electrode. Then, linear sweep voltammogram (LSV) was recorded from 0 to 0.55 V with a potential scan rate of 50 mV/s. The peak current was measured and recorded as a blank signal (/b). After the background voltammogram was obtained, aliquot of the sample solution containing hydrazine was introduced into the cell. Then, the LSV was recorded as described above to give the sample peak current. The peak current was measured and recorded as a sample signal (Is). All data was obtained at room temperature. The difference in the currents (Is — Ib) was considered as a net signal (AI) for each of the experiments. Calibration graph was prepared by plotting the net peak currents vs. the hydrazine concentrations in solution.
Real sample preparation. Before sampling of water, polyethylene bottles were cleaned with conc. HNO3, conditioned over 1 day with 1 : 100 (v/v) hydr
Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.