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Diclofenac (DCF) is a common anti-inflammatory drug. In this work, we have developed two new modified electrodes based on attapulgite clay mineral for the determination of DCF. The first one is made of an amino-functionalized attapulgite modified glassy carbon electrode (GCE/Amino-AT) issued from the grafting of attapulgite particles with [3-(2aminoethylamino)propyl]trimethoxysilane. Voltammetric data indicate slightly easier oxidation of DCF on such modified electrode (irreversible anodic peak at +0.750 V vs.Ag/AgCl i.e., about 85 mV lower than on bare GCE), and pH-dependent response resulting from interactions between the probe and the electrode material. The second one is an aminoattapulgite-mesoporous silica composite film generated by electro-assisted self-assembly of a surfactant-templated silica layer entrapping the amino-functionalized attapulgite particles on GCE pretreated by electrografting of [3-aminopropyl]triethoxysilane (GCE/APTES-Amino-AT-Silica), which was designed in order to avoid the loss of clay particles in solution over prolonged use of the modified electrode. After characterization of the film morphology, composition and permeability, respectively by scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDX) and cyclic voltammetry (CV), the modified electrodes were applied to the detection of DCF by square wave voltammetry (SWV). Both electrodes gave rise to SWV peak currents varying linearly with DCF concentration in the range of 0.3 -20 µΜ (in phosphate buffer at pH 5.7). The detection limits were 0.204 μM on GCE/Amino-AT and 0.053 μM on GCE/APTES-Amino-AT-Silica. The proposed method was successfully applied to the determination of DCF in pharmaceuticals and water samples.

In the present work, a simple and economic analytical method based on attapulgite/nafion coated glassy carbon electrode (AT/Naf/GCE) has been developped for the electrochemical determination of caffeine. Prior to its use, the ionic exchange properties and conductivity of AT/Naf/GCE were studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Caffeine gave an irreversible oxidation peak around +1.41 V (vs Ag/AgCl reference electrode) in 0.1 M H2SO4 at pH 1.5. The peak current varied linearly with the square root of the scan rate, showing that the transfer process is controlled by diffusion. The heterogeneous rate constant, the transfer coefficient and the number of electrons involved were calculated. Upon optimization of key analytical parameters involved in the electroanalysis of caffeine by DPV, the recorded oxidation peak current varied linearly with caffeine concentration in the range from 0.1 to 4 μm, leading to a detection limit of 4.57×10−8 M (S/N=3). The developed electrode exhibited good stability and was easily regenerated. The effect of some important potential interfering compounds (ascorbic acid, dopamine, uric acid, sulphite ions and glucose) on the signal of caffeine was also examined. The obtained electrode was successfully employed in the determination of caffeine content in a commercial drug.

The aminated metal–organic framework H 2 N-MIL-101(Cr) was used as the carbon paste electrode (CPE) modifier for the determination of tartrazine (Tz) in soft drinks. The amino material was characterized by electrochemical impedance spectroscopy and showed significantly faster electron transfer with lower charge-transfer resistance (0.13 kΩ) compared to the electrode modified with the unfunctionalized MIL-101(Cr) material (1.1 kΩ). The H 2 N-MIL-101(Cr)-modified CPE [H 2 N-MIL-101(Cr)-CPE] was then characterized by cyclic voltammetry (CV) using [Fe(CN) 6 ] 3– and [Ru(NH 3 ) 6 ] 3+ ions as the redox probes, showing good accumulation of [Fe(CN) 6 ] 3– ions on the electrode surface. A CV scan of Tz in Britton Robinson buffer solution revealed an irreversible system with an oxidation peak at +0.998 V versus Ag/AgCl/KCl. Using CV and differential pulse voltammetry, an electrochemical method for quantifying Tz in aqueous medium was then developed. Several parameters that affect the accumulation and detection steps were optimized. Optimal detection of Tz was achieved after 180 s of accumulation in Britton Robinson buffer solution (pH 2) using 2 mg of H 2 N-MIL-101(Cr) material. Under optimal conditions, the sensor exhibited a linear response in the concentration range of 0.004–0.1 μM and good detection sensitivity (35.4 μA μM –1 ), and the detection limit for Tz was found to be 1.77 nM (S/N = 3). Satisfactory repeatability, stability, and anti-interference performance were also achieved on H 2 N-MIL-101(Cr)-CPE. The sensor was applied to commercial juices, and the results obtained were approximately similar to those given by UV–vis spectrophotometry.

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This work describes a new sensitive sensor for the simultaneous electrochemical determination by square wave anodic stripping voltammetry of Cd 2+ and Pb 2+ ions in aqueous solution, based on a disposable ink-jet-printed graphene electrode (IPGE) modified by a thin film of montmorillonite (Mont) clay mineral. The clay was characterized by X-ray diffraction and scanning electron microscopy while the Mont-IPGE was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry before its exploitation for sensing studies. EIS results revealed a low electron transfer rate on Mont-IPGE during the electro-oxidation of [Fe(CN) 6 ] 3−. The stripping response on both Cd 2+ and Pb 2+ analytes was improved by the in situ co-deposition with bismuth, added to the electrolyte solution, on the clay substrate. The proposed electrode showed great stability and good reproducibility. The key experimental parameters governing the stripping analysis of Cd 2+ and Pb 2+ were optimized. A linear relationship between peak currents and concentrations of the analytes was obtained in the range from 0.01 to 0.21 µM, leading to detection limits of 0.42 nM for Cd 2+ and 1.14 nM for Pb 2+ ions, respectively (S/N = 3). The sensitivities to Cd 2+ and Pb 2+ ions were 921.8 A cm −2 M −1 and 1960.8 A cm −2 M −1 , respectively. The Mont-IPGE sensor was used for the quantification of lead and cadmium in a mineral water.

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