MWCNTs/CPE exhibited excellent effect towards the oxidation of hydroxychloroquine.

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A highly sensitive electrochemical nanosensor was developed using covalent modification of a glassy carbon electrode (GCE) by self-assembly of a novel Schiff base. Scanning electron microscopy (SEM) and electrochemical techniques were used to investigate the immobilization of the self-assembled monolayer (SAM) on the GCE. The electrochemical behavior of hydroxychloroquine (HCQ) in the presence of uric acid (UA) at the surface of the modified electrode was studied using the differential pulse voltammetry (DPV) technique. Response surface methodology (RSM) is used to optimize the effects of various operating variables such as pH, immersion time, scan rate, step potential and modulation amplitude on the voltammetric response of HCQ. RSM formulates a mathematical model which correlates the independent parameters with the peak current of HCQ. The central composite rotatable design (CCRD) has been applied to conduct the experiments. Then, under the optimized conditions, HCQ was determined in the presence of UA. The electrochemical measurements demonstrated that this biosensor responded well to HCQ, confirming that the self-assembly immobilization method was effective. Also, the interference, the storage stability, and the reproducibility of the biosensor were studied and assessed. The developed nanosensor was economical and efficient, making it potentially attractive for application to real sample analysis.

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In the present study, lead titanate nano-sized powders were synthesized using citric acid gel method. The nanopowders were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Then, a nanocomposite system based on lead titanate nanopowders and carbon paste electrode (CPE) was designed and applied for determination of pentoxifylline (PTX). The prepared nanostructured electrode exhibited voltammetric responses with high sensitivity and selectivity for PTX and a detection limit of 2.1 nM was achieved. Finally, the proposed method was used for analysis of PTX in environmental and biological samples with satisfactory results.

Multivariate curve resolution by alternating least-squares (MCR-ALS) was used for voltammetric determination of dopamine (DA) in the presence of epinephrine (EP) at a gold nanoparticles chemically modified carbon paste electrode (AuNPs/CPE). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) techniques were applied for characterization of the nanostructure modified electrode. Central composite rotatable design (CCRD) was employed to generate an experimental program to offer data to model the effects of different parameters on voltammetric responses. Response surface methodology (RSM) was applied to show the individual and interactive effects of chemical and instrumental variables at five levels, combined according to CCRD. For determination of DA in the presence of unexpected interference, three-way data were achieved from various pulse heights in differential pulse voltammetry (DPV) technique. This type of data construction, analyzed by MCR-ALS, makes it possible to exploit the so-called "second-order advantage". The second-order advantage provided unbiased results even in the presence of electroactive interferences with highly overlapped peaks. Also, an algorithm was applied to correct the detected potential shift in the voltammetric data. The voltammograms of the samples were then deposited in an augmented data matrix (column-wise) and subsequently analyzed by MCR-ALS. The effect of rotational ambiguity associated with a particular MCR-ALS solution under a set of constraints was also studied. The proposed method could be applied for the determination of DA and EP in the presence of each other in a wide concentration range of 0.1-205.0 μM, and the detection limit of DA has been found to be 35.5 nM. Finally, the technique has been used for the reliable analysis of DA in real samples.