The simultaneous electrochemical determination of Zn(II), Cd(II), Pb(II), and Cu(II) in the aqueous solution has been developed on the basis of the bismuth film glassy carbon electrode (GCE) using differential pulse anodic stripping voltammetry (DP-ASV). The bismuth film electrode (BiFE) was prepared by adding 500 ppb bismuth(III) directly to the sample solution and simultaneously depositing bismuth and the metal analytes on GCE. The optimal operational parameters, namely, accumulation potential (–1.6 V), accumulation time (110 s), pulsed amplitude (0.07 V), and scan rate (0.021 V·s−1), were found using a Box–Behnken design. Under the optimum conditions, a linear relationship exists between the current and the concentration of Zn(II), Cd(II), Pb(II), and Cu(II) in the range between 5.0 ppb and 110.0 ppb with the detection limits of 1.07 for Zn(II), 0.93 ppb for Cd(II), 0.65 ppb for Pb(II), and 0.94 ppb for Cu(II) calculated on the basis of a signal-to-noise ratio equal to 3 (S/N = 3). The interference experiments show that Co(II), Ni(II), and Fe(III) have a little influence on the DP-ASV signals of Zn(II), Cd(II), Pb(II), and Cu(II). In addition, a high reproducibility was indicated from small relative standard deviations (1.03%, 1.74%, 1.32%, and 4.74%) for 25 repeated measurements of 15 ppb copper, lead, cadmium, and zinc solutions. BiFE was successfully applied to determine Zn(II), Cd(II), Pb(II), and Cu(II) in river samples, and the results are in a good agreement with those determined with graphite furnace atomic absorption spectrometry (GF-AAS).

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In the present paper, the adsorption of Astrazon Black AFDL dye onto Vietnamese diatomite has been demonstrated. The diatomite was characterized by XRD, SEM, TEM, EDS, and nitrogen adsorption/desorption isotherms. The results show that diatomite mainly constituted centric type frustules characterized by pores as discs or as cylindrical shapes. The adsorption kinetics and isotherms of dye onto Vietnam diatomite were investigated. The experimental data were fitted well to both Freundlich and Langmuir in the initial concentration range of 400–1400 mg L−1. The average value of maximum adsorption capacity,qm, calculated from Freundlich equation is statistically similar to the average value of maximum monolayer adsorption capacity calculated from Langmuir equation. The thermodynamic parameters evaluated from the temperature dependent on adsorption isotherms in the range of 303–343 K show that the adsorption process was spontaneous and endothermic. The Webber and pseudo-first/second-order kinetic models were used to analyze the mechanism of adsorption. The piecewise linear regression and Akaike’s Information Criterion were used to analyze experimental data. The results show that the dye adsorption onto diatomite was film diffusion controlled and the goodness of fit of experimental data for kinetics modes was dependent on the initial concentration.

The synthesis of magnetic iron oxide/reduced graphene oxide (Fe 3 O 4 /rGO) and its application to the electrochemical determination of paracetamol using Fe 3 O 4 /rGO modified electrode were demonstrated. The obtained materials were characterized by means of X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms, X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), and magnetic measurement. The results showed that Fe 3 O 4 /rGO composite exhibited high specific surface area, and its morphology consists of very fine spherical particles of Fe 3 O 4 in nanoscales. Fe 3 O 4 /rGO was used as an electrode modifier for the determination of paracetamol by differential pulseanodic stripping voltammetry (DP-ASV). The preparation of Fe 3 O 4 /rGO-based electrode and some factors affecting voltammetric responses were investigated. The results showed that Fe 3 O 4 /rGO is a potential electrode modifier for paracetamol detection by DP-ASV with a low limit of detection. The interfering effect of uric acid, ascorbic acid, and dopamine on the current response of paracetamol has been reported. The repeatability, reproducibility, linear range, and limit of detection were also addressed. The proposed method could be applied to the real samples with satisfactory results.

In the present paper, graphene oxide was directly electrodeposited by means of cyclic voltammetric techniques on the glassy-carbon electrode (GCE) to obtain a reduced graphene-oxide-modified electrode (ErGO/GCE). Cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DP-ASV) had been utilized to study the electrochemical behavior of ErGO/GCE toward ascorbic acid (AA), paracetamol (PA), and caffeine (CA). Differential pulse voltammetry results show that AA, PA, and CA could be detected selectively and sensitively on ErGO/GCE with peak-to-peak separation of 312 mV and 756 mV for AA–PA and PA–CA, respectively. The factors affecting the voltammetric signals such as pH, scan rate, and interferents were addressed. The results reveal that the ErGO/GCE-modified electrode exhibits excellent electrochemical activity in the oxidation of PA, CA, and AA. The detection limits are 0.36 μM, 0.25 μM, and 0.23 μM for AA, PA and CA, respectively, suggesting that the ErGO/GCE can be utilized with high sensitivity and selectivity for the simultaneous determination of these compounds. Finally, the proposed method was successfully used to determine AA, PA, and CA in pharmaceutical preparations.