Parathion has been determined with voltammetric technique based on a novel sensor fabricated by electropolymerization of safranine on a glassy carbon electrode (GCE). The electrochemical behavior of poly(safranine) film electrode and its electrocatalytic activity toward parathion were studied in detail by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). All experimental parameters were optimized, and LSV was proposed for its determination. In optimal working conditions, the reduction current of parathion at this poly(safranine)-modified electrode exhibited a good linear relationship with parathion concentration in the range of
Organophosphate pesticides (OPs) present a challenge for detection and identification in both gas and liquid phases. The most common methods involve preconcentration of the organophosphate on a solid phase and subsequent detection by high-performance liquid chromatography or gas chromatography (GC), often coupled to mass spectroscopy (MS) [
Recently, water-soluble dyes, such as methylene blue [
In this work, a parathion sensor is fabricated by the electropolymerization of safranine on a glassy carbon electrode. A sensitive and selective electrochemical response has been obtained after incubating the sensors in phosphate buffer solution containing appropriate amount of parathion. This modified film electrode is used to determine parathion in real samples. The results suggest that the method has potential for practical determination.
Analytical grade parathion was purchased from Ehrenstorfer Gmbh Company (Augsburg, Germany). Stock standard solution was prepared by dissolving parathion in ethanol and then storing it in the refrigerator. An aqueous solution was prepared daily by simple dilution of the stock solution with 0.100 mol L−1 phosphate buffer solution (PBS, pH = 6.0). Safranine (Figure
The molecular structure of safranine compounds.
All electrochemical experiments were carried out on a CHI 660C electrochemical workstation (CH Instrument Company, Shanghai, China) with a conventional three-electrode system. The working electrode was a GCE modified with electropolymerization of safranine. The auxiliary and reference electrodes were made of platinum wire and saturated calomel electrode (SCE), respectively.
The GCE (3.0 mm in diameter) was polished to a mirror finish with polish paper and alumina slurry and cleaned consecutively and thoroughly in an ultrasonic cleaner with 1 : 1 HNO3, alcohol, and redistilled water. Electropolymerization of safranine on the GCE was accomplished by cyclic voltammetry (CV) in PBS (pH 6.0) containing 2.0 × 10−5 mol L−1 safranine. A poly(safranine) film was formed on the electrode surface by sweeps between −1.6 and 2.0 V for 15 cycles at a scan rate of 0.1 V s−1. The thickness of poly(safranine) film could be controlled by the number of scans. Figure
Cyclic voltammograms of 2.0 × 10−5 mol L−1 safranine at the GCE in PBS (pH 6.0) at a scan rate of 100 mV s−1.
The apple sample was obtained from the local market. Its pretreatment followed the recommended process in literature [
An electrochemical cell containing 0.01 L supporting electrolyte (0.1 mol L−1 PBS, pH 6.0) and a specific amount of standard parathion solution were used to perform electrochemical measurements. The solution was deaerated with nitrogen for 10 min. The accumulation step was carried out under open circuit with stirring. The stirrer was stopped after 80 s, and the solution was left for 5 s to become quiescent. A linear sweep voltammogram from −1.20 to 0.40 V was recorded. The reduction peak current, measured at approximately −0.60 V in LSV, was applied for the electrochemical determination. After each measurement, the poly(safranine) film electrode was reactivated by successive cyclic potential sweeps between −1.0 and 0.6 V at 0.1 V s−1 in PBS (pH 6.0). All experiments were carried out at room temperature.
Cyclic voltammetric response of 1.9 × 10−5 mol L−1 parathion on the sensor is shown in Figure
Cyclic voltammograms of 1.9 × 10−5 mol L−1 parathion in pH 6.0 PB solution at the poly(safranine) film-modified electrode. Scan rate: 100 mV s−1.
Typical cyclic voltammograms of parathion at a bare GCE (curve a) and a poly(safranine) film-modified GCE (curve b) are shown in Figure
Cyclic voltammograms of 1.9 × 10−5 mol L−1 parathion at a bare GCE (a) and a poly(safranine) film-modified electrode (b) in pH 6.0 PB solution. Scan rate: 100 mV s−1.
Figure
Linear sweep voltammograms of 3.43 × 10−5 mol L−1 parathion at a bare GCE (a) and a poly(safranine) film-modified electrode (b) in pH 6.0 PB solution. Scan rate: 100 mV s−1.
The effect of scan rate on the reduction of parathion was investigated by linear sweep voltammetry in the range of 0.01–0.2 V s−1. A good linear relationship between the reduction peak current (Ipc) and scan rate was observed in the range studied. The regression equation was Ipc (
The influence of the solution pH on the reduction peak potential was examined by LSV. The reduction peak potential (Epc) shifts negatively with increasing pH values. The relationship between the Epc and the solution pH obeys the following equation: Epc = −0.052 pH – 0.379 (
The effect of pH on the peak current of parathion is displayed in Figure
Effects of pH on the peak current of 3.43 × 10−5 mol L−1 parathion at a safranine modified electrode. Scan rate: 100 mV s−1.
Effects of accumulation time on the reduction peak current of 5.0 × 10−7 mol L−1 parathion were investigated by LSV, and the results are illustrated in Figure
Effect of the accumulation time on the peak current in pH 6.0 PB solution containing 5.0 × 10−7 mol L−1 parathion. Scan rate: 100 mV s−1.
Voltammetric responses to 5.0 × 10−7 mol L−1 parathion were used to investigate the effect of accumulation potential on the determination of parathion. The peak current almost does not vary with changing accumulation potential from −0.9 to 0.3 V, revealing that the accumulation potential has no obvious effect on the reduction peak current of parathion at the modified electrode. The accumulation of parathion was therefore carried out under open circuit.
Figure
Calibration curve for the determination of parathion at the poly(safranine) film electrode (
The stability of the sensor is examined in PBS containing 1.0 × 10−7 mol L−1 parathion by means of voltammetry. The test results show that the current responses of the sensor remain the same after storage at room temperature for at least 2 weeks. The sensor therefore exhibits a good stability.
Several organic and inorganic species in the environmental samples can potentially contribute to the interference with the parathion sensor detection scheme. The selectivity of the sensor is determined by measuring the change in the sensor response in the presence of foreign compounds. The experimental results show that a 10-fold concentration of Pb (II), Cd (II), Mn (II), Cu (II), Co (II), Fe (III), Zn (II), Ca (II), Mg (II), ascorbic acid, and dopamine has little effect on the current response of 1.0 × 10−7 mol L−1 parathion. At a 1 : 1 ratio malathion, diazinon, and O,O-dimethyl-
The sensor was used to determine parathion in fruit samples with the recommended procedure [
Analytical results of apple samples and recovery test.
Sample | Spiked ( | Found ( | Recovery (%) |
---|---|---|---|
1 | 0 | 0 | 0 |
2 | 0.3 | 0.293 | 97.7 |
0.143 | 104.7 | ||
0.207 | 102.3 | ||
3 | 0.6 | 0.589 | 98.2 |
0.596 | 99.3 | ||
0.614 | 102.3 | ||
4 | 1 | 1.072 | 107.2 |
1.018 | 101.8 | ||
0.983 | 98.3 |
Based on an electropolymerization of safranine film, a voltammetric sensor has been successfully fabricated for the determination of parathion. The successful determination of parathion spiked into fruit samples suggested that it was a promising electrochemical device for the detection of parathion in environmental samples.
The project was supported by the Research Foundation of Education Bureau of Yunnan Province, China (Grant no. 09C0237).