Electrochemical determination of verapamil hydrochloride using carbon nanotubes/TiO2 nanocomposite based potentiometric sensors in surface water and urine samples

β-Cyclodextrin/Zn-Fe layered double hydroxides/graphitic carbon nitride nanomaterials based potentiometric sensor for paroxetine determination in environmental water samples

Developing targeted and sensitive analytical techniques for drug monitoring in different specimens are of utmost importance. Herein, a first attempt was made for the determination of paroxetine (Prx+) in environmental water samples using a novel, sensitive, selective, stable, accurate and eco-friendly potentiometric sensor based on Zn-Fe layered double hydroxides/graphitic carbon nitride (Zn-Fe LDH/g-C3N4) nanomaterials with β-cyclodextrin (β-CD) as the sensing ionophore and dibutyl phthalate (DBP) as the plasticizer. The prepared nanomaterial was characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The surface properties of the proposed sensor were characterized by electrochemical impedance spectroscopy (EIS). The sensor exhibited an excellent Nernstian slope of 59.3 ± 0.7 mV decade-1 covering a wide linear working range of 1.0 × 10-6 to 1.0 × 10-2 mol L-1, low detection limit of 3.0 × 10-7 mol L-1, low quantification limit of 9.9 × 10-7 mol L-1, long life time, sufficient selectivity, high chemical and thermal stability within a wide pH range of 2.0-9.0. This analytical method was successfully implemented for Prx+ determination in a pure form, pharmaceutical formulation and different water samples.

Stable Pb(II) ion-selective electrodes with a low detection limit using silver nanoparticles/polyaniline as the solid contact

Solid contact-based ion-selective electrodes (SC-ISEs) based on silver nanoparticles/polyaniline (Ag@PANI) as the solid contact (SC) were successfully prepared. The Ag@PANI SC showed high capacitance and excellent electron transport performance. Owing to the synergetic effects of the Ag nanoparticles and PANI, a GC/Ag@PANI-II/Pb²⁺-ISE (where II refers to a Ag content of 0.01 wt% in the SC layer) showed a low Pb²⁺ detection limit (6.31 × 10^-10 M) with a slope of 29.1 ± 0.3 mV/dec, a fast response (< 5 s), and high stability. GC/Ag@PANI-II/Pb²⁺-ISE exhibited a Nernstian response for Pb²⁺ ions over a wide concentration range (10^-3 to 10^-9 M). After a 3-week operation, GC/Ag@PANI-II/Pb²⁺-ISE responded linearly to Pb²⁺ over the range of 10^-7-10^-3 M, demonstrating good long-term potential stability. Furthermore, the electrode showed excellent reproducibility and repeatability of the potential values and was successfully applied to detect the Pb²⁺ concentration in real samples with a recovery of 97 - 109%. Results suggest that Ag@PANI composites offer good transducer performance in trace ion detection sensors.

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.