Evaluation of electrochemical, UV/VIS and Raman spectroelectrochemical detection of Naratriptan with screen-printed electrodes

Selective Detection of Paraquat in Adulterated and Complex Environmental Samples Using Raman Spectroelectrochemistry

Growing demand for pesticides has created an environment prone to deceptive activities, where counterfeit or adulterated pesticide products infiltrate the market, often escaping rapid detection. This situation presents a significant challenge for sensor technology, crucial in identifying authentic pesticides and ensuring agricultural safety practices. Raman spectroscopy emerges as a powerful technique for detecting adulterants. Coupling the electrochemical techniques allows a more specific and selective detection and compound identification. In this study, we evaluate the efficacy of spectroelectrochemical measurements by coupling a potentiostat and Raman spectrograph to identify paraquat, a nonselective herbicide banned in several countries. Our findings demonstrate that applying -0.70 V during measurements yields highly selective Raman spectra, highlighting the primary vibrational bands of paraquat. Moreover, the selective Raman signal of paraquat was discernible in complex samples, including tap water, apple, and green cabbage, even in the presence of other pesticides such as diquat, acephate, and glyphosate. These results underscore the potential of this technique for reliable pesticide detection in diverse and complex matrices.

Zirconium-based hydrophobic-MOFs as innovative electrode modifiers for flibanserin determination: Exploring the electrooxidation mechanism using a comprehensive spectroelectrochemical study

Three different types of Zr-based MOFs derived from benzene dicarboxylic acid (BDC) and naphthalene dicarboxylic acid as organic linkers (ZrBDC, 2,6-ZrNDC, and 1,4-ZrNDC) were synthesized. They were characterized using X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform IR spectroscopy (FT-IR), and Transmission electron microscopy (TEM). Their hydrophilic/hydrophobic nature was investigated via contact angle measurements; ZrBDC MOF was hydrophilic and the other two (ZrNDC) MOFs were hydrophobic. The three MOFs were combined with MWCNTs as electrode modifiers for the determination of a hydrophobic analyte, flibanserin (FLB), as a proof-of-concept analyte. Under the optimized experimental conditions, a significant enhancement in the oxidation peak current of FLB was observed when utilizing 2,6-ZrNDC and 1,4-ZrNDC, being the highest when using 1,4-ZrNDC. Furthermore, a thorough investigation of the complex oxidation pathway of FLB was performed by carrying out simultaneous spectroelectrochemical measurements. Based on the obtained results, it was verified that the piperazine moiety of FLB is the primary site for electrochemical oxidation. The fabricated sensor based on 1,4-ZrNDC/MW/CPE showed an oxidation peak of FLB at 0.8 V vs Ag/AgCl. Moreover, it showed excellent linearity for the determination of FLB in the range 0.05 to 0.80 μmol L-1 with a correlation coefficient (r) = 0.9973 and limit of detection of 3.0 nmol L-1. The applicability of the developed approach was demonstrated by determination of FLB in pharmaceutical tablets and human urine samples with acceptable repeatability (% RSD values were below 1.9% and 2.1%, respectively) and reasonable recovery values (ranged between 97 and 103% for pharmaceutical tablets and between 96 and 102% for human urine samples). The outcomes of the suggested methodology can be utilized for the determination of other hydrophobic compounds of pharmaceutical or biological interest with the aim of achieving low detection limits of these compounds in various matrices.

Review on combining surface-enhanced Raman spectroscopy and electrochemistry for analytical applications

The discovery of surface enhanced Raman scattering (SERS) from an electrochemical (EC)-SERS experiment is known as a historic breakthrough. Five decades have passed and Raman spectroelectrochemistry (SEC) has developed into a common characterization tool that provides information about the electrode-electrolyte interface. Recently, this technique has been successfully explored for analytical purposes. EC was found to highly improve the performances of SERS sensors, providing, among others, controlled adsorption of analytes and increased reproducibility. In this review, we highlight the potential of EC-SERS sensors to be implemented for point-of-need (PON) analyses as miniaturized devices, and their ability to revolutionize fields like quality control, diagnosis or environmental and food safety. Important developments have been achieved in Raman spectroelectrochemistry, which now represents a promising alternative to conventional analytical methods and interests more and more researchers. The studies included in this review open endless possibilities for real-life EC-SERS analytical applications.

Occurrence, detection and ecotoxicity studies of selected pharmaceuticals in aqueous ecosystems- a systematic appraisal

Pharmaceutical compounds (PCs) have globally emerged as a significant group of environmental contaminants due to the constant detection of their residues in the environment. The main scope of this review is to fill the void of information on the knowledge on the African occurrence of selected PCs in environmental matrices in comparison with those outside Africa and their respective toxic actions on both aquatic and non-aquatic biota through ecotoxicity bioassays. To achieve this objective, the study focused on commonly used and detected pharmaceutical drugs (residues). Based on the conducted literature survey, Africa has the highest levels of ciprofloxacin, sulfamethoxazole, lamivudine, acetaminophen, and diclofenac while Europe has the lowest of all these PC residues in her physical environments. For ecotoxicity bioassays, the few data available are mostly on individual groups of pharmaceuticals whereas there is sparsely available data on their combined forms.

Detection of dithiocarbamate, chloronicotinyl and organophosphate pesticides by electrochemical activation of SERS features of screen-printed electrodes

Enhancement of Raman intensity due to the electrochemical surface-enhanced Raman scattering (EC-SERS) effect is an interesting alternative to overcome the lack of sensitivity traditionally associated with Raman spectroscopy. Furthermore, activation of metallic screen-printed electrodes (SPEs) by electrochemical route leads to the reproducible generation of nanostructures with excellent SERS properties. EC-SERS procedure proposed in this work for the detection of several pesticides (thiram, imidacloprid and chlorpyrifos) with different nature, uses gold SPEs as SERS substrates, but also includes a preconcentration step as the initial and essential stage. Taking into account the small volume of solution employed, only 60 µL, the preconcentration cannot be performed for more than 15 min in order to ensure the proper contact of the solution with WE, RE and CE. Furthermore, selected temperature, 34 °C, is not very high to allow the exhaustive control of the drop volume. Optimization of preconcentration parameters (time and temperature) displays a crucial step, particularly in the detection of low concentrations of pesticides, because it will provide higher Raman intensity in EC-SERS experiments. After the initial step, gold SPEs were electrochemically activated by cyclic voltammetry, allowing the detection of very low concentration (µg·L^-1) of pesticides due to the generation of fresh nanostructures with SERS effect.

Spectroelectrochemistry, the future of visualizing electrode processes by hyphenating electrochemistry with spectroscopic techniques

Reviewing the future of electrochemistry combined with infrared, Raman, and nuclear magnetic resonance spectroscopy as well as mass spectrometry.

Application of Factorial and Doehlert Designs for the Optimization of the Simultaneous Separation and Determination of Antimigraine Drugs in Pharmaceutical Formulations by RP-HPLC-UV

A sensitive, precise, accurate, and specific isocratic reversed-phase high-performance liquid chromatographic (RP-HPLC) method for the simultaneous separation and determination of zolmitriptan, naratriptan, dihydroergotamine, ketotifen, and pizotifen in pharmaceutical formulations has been developed and validated. An experimental design was applied for the optimization of the chromatographic parameters. A two-level full factorial 2^k was used for studying the interaction between the variables to be optimized: the percentage of acetonitrile in the mobile phase, mobile-phase pH, nature of the buffer, and column oven temperature. The most significant parameters are the percentage of acetonitrile and the mobile-phase pH. These significant parameters were optimized using the Doehlert matrix. The optimum separation was achieved by means of a Waters XBridge C18 column (250 mm × 4.6 mm, 5 μm) with a mobile phase consisting of acetonitrile and a 10 mM sodium perchlorate buffer (38 : 62, v/v) at a flow rate of 1.0 mL·min⁻¹ and UV detection at 220 nm. The selectivity, method linearity, accuracy, and precision were examined as part of the method validation. The described method shows excellent linearity over a range of 30 to 70 μg·mL⁻¹ for all compounds with correlation coefficients higher than 0.995. The standard deviations of the intraday and interday precision were between 0.75 and 1.94%. The validated method was successfully applied to perform routine analysis of these compounds in different pharmaceutical products such as syrups and tablets. In the presence of some preservatives, it was found that there were no peaks at the related peak locations.

3D-Printed Low-Cost Spectroelectrochemical Cell for In Situ Raman Measurements

Raman spectroelectrochemistry is a powerful technique for characterizing structural changes of materials during electrochemical reactions and investigating the mechanism of film deposition and adsorption processes on the surfaces of electrodes. Moreover, in situ measurements enable identification of catalytic sites and reaction intermediates, which facilitates the comprehension of reaction mechanisms. The limitations of this technique include the high-cost and the complexity of the experimental arrangement required by commercial spectroelectrochemical cells (SEC). Thus, 3D-printing technology emerges as an excellent alternative for the production of SEC, with desirable shape, low-cost, and robustness in a short period of time. In this work, an SEC and a 3D-printed working electrode were fabricated from acrylonitrile-butadiene-styrene (ABS) and conductive graphene polylactic acid (PLA) filaments, respectively. The proposed SEC and the 3D-printed electrode were printed within 3.5 h with an estimated cost of materials of less than US $2. Then, the 3D-printed SEC and the electrode were used in a study of structural changes of Prussian blue according to different voltage bias.

Spectroelectrochemical elucidation of B vitamins present in multivitamin complexes by EC-SERS

Raman spectroelectrochemistry based on electrochemical surface-enhanced Raman scattering (EC-SERS) effect is an interesting alternative to overcome the lack of sensitivity of normal Raman spectroscopy. Electrochemical activation of metallic screen-printed electrodes (SPEs) leads to the reproducible generation of nanostructures with excellent SERS properties. In that way, gold SPEs circumvent the traditional reproducibility limitation and produce the enhancement of the Raman intensity to favor the detection of low concentrations. Furthermore, fingerprint features of Raman spectroscopy make possible the dynamic spectroelectrochemical analysis of B vitamins. The accuracy assignments of Raman bands associated with B1, B2, B3, B6 and B12 vitamins present in multivitamin complexes provides valuable information, allowing us not only the detection of B vitamin present in mixtures, but also to understand the interaction between vitamins and metallic SERS surfaces.

Resolution of mixed dyes by in situ near infrared (NIR) spectroelectrochemistry

NIR spectroelectrochemistry has scarcely been used for deconvolving aqueous mixtures due to the water restriction in this spectral range. However, this work offers an interesting approach for the study of mixtures of molecules with similar electrochemical and spectroscopic behaviour by overcoming the limitations of this hybrid technique. As a proof of concept, the resolution of mixtures of two dyes with similar chemical structures demonstrates the usefulness of NIR spectroelectrochemistry.