Electrical and Electrochemical Behavior of Carbon Paste Electrodes Modified with Ionic Liquids Based in N-Octylpyridinium Bis(Trifluoromethylsulfonyl)Imide. A Theoretical and Experimental Study

COF-43 based voltammetric sensor for Ag(I) determination: optimization of experimental conditions by Box-Behnken design

Hydrazone-linked covalent organic framework-43 (COF-43) was synthesized and the carbon paste electrode (CPE) modified with this COF was used as a voltammetric sensor to measure silver(I). Various characterization tests (XRD, FTIR, BET, SEM/EDX, electrochemical impedance (EIS), and cyclic voltammetry (CV)) were performed on the synthesized COF-43 and the prepared COF-43/CPE. Box-Behnken design was used to optimize the preparation and operation conditions of the sensor. EIS and CV investigations reveal the diffusive characteristics of silver transport in the electrode matrix. An appropriate mechanism for the sensor procedure has been suggested and ratified by electrochemical and SEM/EDX techniques. The COF-43 used has several recognition elements for the selective binding of silver ion and due to its high porosity provides a large space for the deposition and reduction of large amounts of silver. Therefore, due to the correct selection of COF used in the construction of the sensor, high selectivity and sensitivity for the prepared sensor has been achieved. The obtained data disclosed that the modification of the carbon paste electrode by COF-43 significantly improves the analytical characteristics of the sensor, which specifies the performance of COF-43 as a sensory material for determining silver(I). The obtained calibration curve is linear in the concentration range from 0.001 μM to 10.0 μM and the detection limit is 1.5 × 10^-10 M. Various statistical tests have been employed to evaluate the sensor performance. The appropriate accuracy and precision of the proposed method were confirmed using the analysis of variance (ANOVA) approach. Potential interferences were investigated and it was found that the other species did not have a significant effect on the sensor performance. The prepared sensor has been successfully used to measure silver in two samples of photographic effluents, bleaching, and fixing agents. The results from the analysis of real samples demonstrate the reliable applicability of the fabricated sensor.

Electroanalytical performance of a β-cyclodextrin and ionic liquid modified carbon paste electrode for the determination of verapamil in urine and pharmaceutical formulation

The analytical performance of sensitive and cost-effective electrochemical sensors based on ionic liquids (ILs) with the bis(trifluoromethylsulfonyl)imide anion, [NTf2]-, and the imidazolium cation with different alkyl chain lengths for electrochemical oxidation of verapamil (VER) was investigated. 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][NTf2]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]) and 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([HMIM][NTf2]) were studied as possible materials for modification of a carbon paste electrode (CPE) for trace-level determination of VER. The experimental parameters including selection of the working electrode, the pH of working media, and the amount of CPE modifiers were investigated. Among them, the [EMIM][NTf2]-CPE with 4.3 wt% of IL was selected as the most appropriate for the square wave voltammetric (SWV) determination of VER at pH 5.0. Cyclic voltammetric studies showed that the electrochemical oxidation of VER was adsorption controlled. Consequently, the square wave adsorptive stripping voltammetric (SW-AdSV) parameters were optimized with Eacc = -0.4 V and tacc = 180 s as the most suitable for accumulation of VER on the electrode surface. The electroanalytical performance of the [EMIM][NTf2]-CPE was further improved by its in situ electrochemical modification with β-cyclodextrin (β-CD) and the linear concentration range of VER was from 0.006 to 0.129 μg mL-1; the relative standard deviation did not exceed 0.7%, and the evaluated limit of detection in model solution was 0.002 μg mL-1. The β-CD/[EMIM][NTf2]-CPE showed adequate selectivity towards VER in the presence of inorganic ions and interferents usually found in human urine. The proposed sensor was successfully applied for VER determination in a spiked human urine sample and pharmaceutical formulation with good repeatability and recovery.