Review: The Application of Liquid Chromatography Electrochemical Detection for the Determination of Drugs of Abuse

Recent Advances in Electrochemical Sensors for Sulfur-Containing Antioxidants

Sulfur-containing antioxidants are an important part of the antioxidant defense systems in living organisms under the frame of a thiol-disulfide equilibrium. Among them, l-cysteine, l-homocysteine, l-methionine, glutathione, and α-lipoic acid are the most typical representatives. Their actions in living systems are briefly discussed. Being electroactive, sulfur-containing antioxidants are interesting analytes to be determined using various types of electrochemical sensors. Attention is paid to the chemically modified electrodes with various nanostructured coverages. The analytical capabilities of electrochemical sensors for sulfur-containing antioxidant quantification are summarized and discussed. The data are summarized and presented on the basis of the electrode surface modifier applied, i.e., carbon nanomaterials, metal and metal oxide nanoparticles (NPs) and nanostructures, organic mediators, polymeric coverage, and mixed modifiers. The combination of various types of nanomaterials provides a wider linear dynamic range, lower limits of detection, and higher selectivity in comparison to bare electrodes and sensors based on the one type of surface modifier. The perspective of the combination of chromatography with electrochemical detection providing the possibility for simultaneous determination of sulfur-containing antioxidants in a complex matrix has also been discussed.

Vitamin D metabolites and analytical challenges

Vitamin D is an essential micronutrient for bone health and the general cellular functions of the body. Its insufficiency/deficiency leads to the pathophysiology of disorders like diabetes, cancer, autoimmune, neurodegenerative, and cardiovascular diseases. Clinical interest in Vitamin D metabolites and their role in various medical disorders have contributed to an increase in laboratory demands for vitamin D measurements. For clinical and research laboratories worldwide, analysis of vitamin D and associated metabolites is a significant problem. The best way for determining vitamin D levels is constantly being debated. Various methods such as immunoassays and chromatographic techniques are available for determining vitamin D levels. Additionally, biosensors have recently been considered promising options for routine vitamin D analysis. The existing methods and other developments in the measurement of vitamin D metabolites and associated analytical challenges are discussed in this review.

Development of a Graphene-Oxide-Deposited Carbon Electrode for the Rapid and Low-Level Detection of Fentanyl and Derivatives

The opioid overdose crisis in North America worsened during the COVID-19 pandemic, with multiple jurisdictions reporting more deaths per day due to the fentanyl-contaminated drug supply than COVID-19. The rapid quantitative detection of fentanyl in the illicit opioid drug supply or in bodily fluids at biologically relevant concentrations (i.e., <80 nM) remains a significant challenge. Electroanalytical techniques are inexpensive and can be used to rapidly detect fentanyl, but detection limits need to be improved. Herein, we detail the development of an electrochemical-based fentanyl analytical detection strategy that used a glassy carbon electrode modified with electrochemically reduced graphene oxide (ERGO) via electrophoretic deposition. The resulting surface was further electrochemically reduced in the presence of fentanyl to enhance the sensitivity. Multiple ERGO thicknesses were prepared in order to prove the versatility and ability to fine-tune the layer to the desired response. Fentanyl was detected at <10 ppb (<30 nM) with a limit of detection of 2 ppb and a calibration curve that covered 4 orders of concentration (from 1 ppb to 10 ppm). This method was sensitive to fentanyl analogues such as carfentanil. Interference from the presence of 100-fold excess of other opioids (heroin, cocaine) or substances typically found in illicit drug samples (e.g. caffeine and sucrose) was not significant.

Review of the Analytical Methods Based on HPLC-Electrochemical Detection Coupling for the Evaluation of Organic Compounds of Nutritional and Environmental Interest

This review would like to show the state of the art regarding the coupling of High-Performance Liquid Chromatography (HPLC) with Electrochemical Detection (ED). Since a universal detector for HPLC is not available, the electrochemical detection methods, thanks to their versatility and specificity, are competitive with respect to the detectors currently used. The papers present in literature on HPLC-ED technique are analyzed and discussed: for example, they regard the development of analytical determinations of resveratrol, rosmarinic acid, aromatic heterocyclic amines and glyphosate in food matrices such as meat, aromatic plants, vegetables, fruit and tomato juices. These papers show that electrochemical sensors used as detectors for HPLC can offer better sensitivity values than other detectors. Furthermore, the use of specific working potentials allows avoid matrix interferences to be avoided by almost exclusively determining the analytes of interest. It should be underlined that HPLC-ED methods have a selectivity that allows for limitation of the sample preparation and clean-up procedures to a minimum, making them quick and easy to apply. In addition, these methods offer advantages such as the possibility of direct analysis, that derivatization is often not necessary, the cost-effectiveness of the instrumentation and the possibility of regenerating the electrodes which allows numerous analyses in succession.

Analytical Method Validation for Estimation of Neurotransmitters (Biogenic Monoamines) from Cerebrospinal Fluid Using High Performance Liquid Chromatography

Biogenic amine neurotransmitters such as serotonin and dopamine are essential for signaling in both central and peripheral nervous system. Their metabolism is a multistep pathway and any defect in this results in alteration in metabolites of serotonin 5-Hydroxyindole acetic acid (5HIAA) and dopamine homovanillic acid (HVA) and 3-O-Methyl Dopa (3-OMD). Estimation of these metabolites in cerebrospinal fluid (CSF) assists in diagnosis of neurotransmitter defects. Their estimation is technically demanding and is currently available only in referral centers. We aimed to optimize a method for analysis of 5HIAA, HVA and 3-OMD. A high performance liquid chromatography (HPLC) method with electro chemical detector (ECD) was standardized for estimation. Analysis for method validation, reference range verification and clinical correlation was performed. Linearity obtained for 5-HIAA, HVA and 3-OMD was 65.35-2615.0 nmoles/l, 68.62-2745.0 nmoles/l and 236.5-4730.0 nmoles/l respectively. The coefficient of variation for internal quality controls ranged from 5 to 14% and the external proficiency testing samples (n = 16) were within peer group range. CSF metabolite levels of samples for reference range analysis overlapped with age matched ranges reported in literature. Among the 40 suspected patients analyzed for clinical testing four were found to have a neurotransmitter defect. These patients were then confirmed with molecular testing and clinical correlation. The method is validated and can be adapted in a clinical laboratory with analytical competence in HPLC.

Analytical Capabilities of Coulometric Sensor Systems in the Antioxidants Analysis

The definition of antioxidants (AOs), their classification and properties as well as electrochemical sensor systems for AOs analysis are briefly discussed. The analytical capabilities of coulometric titration with electrogenerated titrants as sensor systems for AOs determination have been considered in detail. The attention focused on the individual AO quantification that was mainly used in the pharmaceutical analysis and estimation of total antioxidant parameters (total antioxidant capacity (TAC), ferric reducing power (FRP) and ceric reducing/antioxidant capacity (CRAC)) allowing the fast screening of the target samples including their quality control. The main advantages of coulometric sensor systems are pointed out. The selective quantification of individual AO in a complex matrix using a combination of chromatography with coulometric or coulometric array detection under potentiostatic mode is discussed. The future development of coulometric sensor systems for AOs analysis is focused on the application of novel coulometric titrants and the application of coulometric detection in flow injection analysis.

A highly sensitive safrole sensor based on polyvinyl acetate (PVAc) nanofiber-coated QCM

A novel, highly sensitive and selective safrole sensor has been developed using quartz crystal microbalance (QCM) coated with polyvinyl acetate (PVAc) nanofibers. The nanofibers were collected on the QCM sensing surface using an electrospinning method with an average diameter ranging from 612 nm to 698 nm and relatively high Q–factors (rigid coating). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the PVAc nanofiber surface morphology, confirming its high surface area and roughness, which are beneficial in improving the sensor sensitivity compared to its thin-film counterpart. The as-spun PVAc nanofiber sensor could demonstrate a safrole limit of detection (LOD) of down to 0.7 ppm with a response time of 171 s and a sensitivity of 1.866 Hz/ppm. It also showed good reproducibility, rapid response time, and excellent recovery. Moreover, cross-interference of the QCM sensor response to non-target gases was investigated, yielding very low cross-sensitivity and high selectivity of the safrole sensor. Owing to its high robustness and low fabrication cost, this proposed sensing device is expected to be a promising alternative to classical instrumental analytical methods for monitoring safrole-based drug precursors.

Polyacrylonitrile Nanofiber-Based Quartz Crystal Microbalance for Sensitive Detection of Safrole

Safrole is the main precursor for producing the amphetamine-type stimulant (ATS) drug, N-methyl-3,4-methylenedioxyamphetamine (MDMA), also known as ecstasy. We devise a polyacrylonitrile (PAN) nanofiber-based quartz crystal microbalance (QCM) for detecting safrole. The PAN nanofibers were fabricated by direct electrospinning to modify the QCM chips. The PAN nanofiber on the QCM chips has a diameter of 240 ± 10 nm. The sensing of safrole by QCM modified with PAN nanofiber shows good reversibility and an apparent sensitivity of 4.6 Hz·L/mg. The proposed method is simple, inexpensive, and convenient for detecting safrole, and can be an alternative to conventional instrumental analytical methods for general volatile compounds.