Square-wave Cathodic Voltammetry Research Articles

A Magnetic Nanocomposite Modifier for Improved Ultrasensitive Detection of Hexavalent Chromium in Water Samples

In this work, different electrodes were employed for the determination of Cr(VI) by the cathodic square-wave voltammetry (SWV) technique and the square-wave adsorptive stripping voltammetry (SWAdSV) technique in combination with diethylenetriaminepentaacetic acid. Using SWV, a comparison of the analytical performance of the bare glassy carbon electrode (GCE), ex situ electrodes (antimony-film—SbFE, copper-film—CuFE, and bismuth-film—BiFE), and the GCE modified with a new magnetic nanocomposite (MNC) material was performed. First, the MNC material was synthesized, i.e., MNPs@SiO2@Lys, where MNPs stands for magnetic maghemite nanoparticles, coated with a thin amorphous silica (SiO2) layer, which was additionally functionalized with derived lysine (Lys). The crystal structure of the prepared MNCs was confirmed by X-ray powder diffraction (XRD), while the morphology and nano-size of the MNCs were investigated by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), where TEM was additionally used to observe the MNP core and silica layer thickness. The presence of functional groups of the MNCs was investigated by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and surface analysis was performed by X-ray photoelectron spectroscopy (XPS). The hydrophilicity of the modified electrodes was also tested by static contact angle measurements. Then, MNPs@SiO2@Lys was applied onto the electrodes and used with the SWV and SWAdSV techniques. All electrodes tested with the SWV technique were effective for Cr(VI) trace determination. On the other hand, the SWAdSV technique was required for ultra-trace determination of Cr(VI). Using the SWAdSV technique, it was shown that a combination of ex situ BiFE with the deposited MNPs@SiO2@Lys resulted in excellent analytical performance (LOQ = 0.1 µg/L, a linear concentration range of 0.2–2.0 µg/L, significantly higher sensitivity compared to the SWV technique, an RSD representing reproducibility of 9.0%, and an average recovery of 98.5%). The applicability of the latter system was also demonstrated for the analysis of a real sample.

Magnetite nanoparticles/chitosan-modified glassy carbon electrode for non-enzymatic detection of the endocrine disruptor parathion by cathodic square-wave voltammetry

A glassy carbon electrode modified with magnetite nanoparticles dispersed in chitosan was employed as electrochemical detector for the determination of parathion in food samples by cathodic square-wave voltammetry. The modified electrode surface was characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Under optimized experimental conditions, the square-wave voltammograms for parathion obtained with the proposed modified electrode exhibited a well-defined peak at −0.59 V, corresponding to the reduction of the nitro group to the hydroxylamine group. The resultant cathodic peak current was linear for parathion concentrations in the range of 0.34 to 4.46 μmol L−1 (r = 0.997). The limits of detection and quantification were 0.187 and 0.567 μmol L−1, respectively. The novel detector was successfully employed for the analysis of parathion in five food samples (carrot, orange, tomato, lettuce and rice) using the standard addition method. The results were statistically compared with data obtained using the UV–vis technique.

Environmentally-friendly in situ plated bismuth-film electrode for the quantification of the endocrine disruptor parathion in skimmed milk

An in situ bismuth-film electrode (BiFE) together with square-wave cathodic voltammetry (SWCV) was used to determine the concentration of the endocrine disruptor parathion in skimmed milk. The experimental conditions (deposition time, deposition potential and Bi (III) concentration) were optimized for the preparation of the BiFE. A glassy carbon electrode was used as the substrate. The selection of the chemical composition of the supporting electrolyte and the solution pH was aimed at improving the reduction of parathion at the BiFE surface. In addition, the parameters of the square-wave cathodic voltammetry were adjusted to improve the sensor performance. A cathodic current identified at −0.523V increased linearly with the parathion concentration in the range of 0.2–2.0μmolL−1 (R=0.999). The sensitivity of the calibration curve obtained was 4.09μALμmol−1, and the limits of detection (LOD) and quantification (LOQ) were 55.7nmolL−1 and 169.0 nmolL−1, respectively. The performance of the sensor was tested using a sample of skimmed milk with parathion added. The same determination was carried out by UV–vis spectroscopy and the results obtained were used for the statistical evaluation of the data obtained.

In situ bismuth-film electrode for square-wave cathodic voltammetric detection of pendimethalin at nanomolar level

An in situ plated bismuth-film electrode (BiFE) was used for the study of the herbicide pendimethalin. A single peak was observed by cyclic voltammetry at −0.520V associated with the reduction of pendimethalin in HCl solution at pH3.0. Square-wave cathodic voltammetry (SWCV) was used for the analytical procedures after the preparation of the BiFE using 10.0μmolL−1 Bi(III) for 80s at −0.250V. A peak current at −0.585V related to the reduction of the herbicide was obtained, which increased linearly with the pendimethalin concentration in the range of 0.3 to 1.0μmolL−1. The limit of detection attained was 37.0nmolL−1. The sensor prepared in situ was applied for the determination of pendimethalin in simulated samples of tap water and sea water with satisfactory results being obtained compared with the UV–vis spectroscopy technique. In addition, pendimethalin was spiked and determined at nanomolar level in samples of water collected from a local river. The recovery values for such experiments were between 93% and 96%.

Determination of Selenium in Foodstuffs by Cathodic Stripping Voltammetry at a Mercury–Graphite Electrode

A universal procedure was developed for the voltammetric determination of total selenium in various foodstuffs. The procedure involves the mineralization of a test sample with magnesium nitrate followed by the reduction of selenium(VI) to selenium(IV) in 6 M HCl and the determination of selenium by cathodic square-wave voltammetry at a mercury–graphite electrode in an HCl solution in the presence of copper and mercury ions.

Cathodic Stripping Voltammetric Determination of Tellurium(IV) in Chloride Media Using a Tosflex/8-Quinolinol Mercury Film Electrode

A Tosflex/8-quinolinol (oxine) coated mercury film electrode (TOMFE) was developed for the determination of tellurium(IV) by square-wave cathodic voltammetry. The electrode is prepared by spin-coating a Tosflex/oxine solution onto the glassy carbon electrode surface. Subsequently, mercury is plated onto the electrode surface. Tellurium(IV) is preconcentrated, as TeCl62−in the chloride medium, onto the modified electrode by the ion-exchange effect of the Tosflex and the chelating effect of oxine. Good sensitivity was achieved through the catalytic process between oxine and tellurium. In comparison with the conventional mercury electrode, the TOMFE showed improved resistance to interferences from surface-active compounds on the determination of tellurium(IV). The interferences from metal ions, such as cadmium(II) and molybdenum(VI), which are capable of forming complexes with oxine were effectively eliminated by the addition of ethylenediaminetetraacetate (EDTA) in the sample solution. The TOMFE is easy to prepare and chemically more stable than other anion-exchange polymer modified electrodes such as polyvinylpyridine modified mercury film electrode.