Antibiotics are used primarily in human and veterinary medicine to treat various infections. They have also found applications in animal farms and aquaculture as growth promotors, with the aim of increasing food production. Their uncontrolled use can lead to increased bacterial resistance to antibiotics as well as other adverse effects. Unfortunately, these can reach and accumulate in the environment. Thus, their sensitive and selective detection from various matrices, using inexpensive and portable instruments, is becoming an increasing necessity. Electrochemical techniques are a viable alternative in this regard, and carbon paste electrodes (CPEs) present electrochemical and economic characteristics that recommend them as versatile devices for this purpose. Therefore, this paper is a comprehensive synthesis of the information presented in the last 10 years in the literature regarding CPEs developed for the analysis of antibiotics in different samples. Methods for obtaining different modified CPEs and their performances in detecting compounds belonging to different classes of antibiotics were discussed and priorities for future development were suggested. Through this review, researchers interested in the (electro)analysis of antibiotics will gain information about the advantages and limitations of using CPEs and the efforts made in the last decade to improve their performance.

Benzodiazepines are psychoactive drugs with wide clinical applications. Unfortunately, due to their sedative effects, benzodiazepines are frequently used as date rape drugs or in drug-facilitated crimes. Considering the electroactive nature of benzodiazepines and the unique advantages of electrochemical techniques, this review presents a critical discussion of the state of the art of benzodiazepine electroanalysis. Aspects related to sample preparation as well as electrodes (from mercury electrodes to bare or modified solid electrodes and to disposable sensors) and techniques (mainly voltammetry) used for the quantification of benzodiazepines in different matrices (pharmaceuticals, body fluids, alcoholic and soft drinks) were discussed. Considering the actual achievements in the field, some general suggestions for possible further research were given.

Voltammetric techniques represent reliable, inexpensive and rapid alternatives for the analysis of many biologically important compounds. On the other hand, redox reactions are found in many processes essential to life and voltammetric techniques allow the understanding of the mechanisms of some of them. The heart of any electrochemical analysis instrument is the working electrode, and current research is directed towards finding sensitive and selective sensors, but which are also cheap and, above all, non-toxic and environmentally friendly. One such electrode is the pencil lead graphite electrode (PGE), which is readily available commercially at low prices and also presents excellent electrochemical properties, being applicable both in the study of anodic and cathodic processes. This work presents few examples of voltammetric methods, based on PGE as such or electroactivated, developed for the analysis of some drugs and natural polyphenolic antioxidants in different matrices.

Curcumin (CU, turmeric), a polyphenolic phytochemical that is largely used as a food spice, has benefits for human health, which have led to increased interest in its therapeutic applications and its analysis from different matrices. The two guaiacol moieties of CU are responsible for its antioxidant properties and allow for its voltammetric quantification. Cyclic and differential pulse voltammetry (DPV) investigations at a single-use pencil graphite electrode (PGE) emphasized complex pH-dependent electrode processes, involving an equal number of protons and electrons. Theoretical calculations predicted a folded geometry for the β-diketone CU conformers, which interact with the PGE surface, exposing the electroactive moieties of only one aromatic ring. The Gibbs energy variations of the structures involved in CU electro-oxidation and the theoretical electrochemical potential values were calculated. CU’s DPV cathodic peak intensity recorded at an HB-type PGE in 0.05 mol × L−1 H2SO4 varied linearly in the range 5.00 × 10−8–5.00 × 10−6 mol × L−1 CU. The method’s detection and quantification limits were 2.12 × 10−8 mol × L−1 and 6.42 × 10−8 mol × L−1, respectively. The practical applicability of the developed method, successfully tested by CU assessment in dietary supplements, provided a recovery of 99.28 ± 2.04%.

This paper summarizes the main findings of a study which aimed to examine the electrochemical oxidation of homovanillic acid (HVA), the final metabolite of dopamine. A pencil graphite electrode (PGE) was used as working electrode and the measurements were performed by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The type and the composition of the graphite leads used as PGE, the pH of the supporting electrolyte, as well as the scan rates were optimized by CV. The analyte was irreversibly oxidized in Britton–Robinson buffer (BRB) solutions. The interpretation of the voltammetric signals and the correlation of the acquired information were the key to addressing the electrode process undergone by HVA at the PGE. The outcomes of the pH and scan rate studies led to the conclusion that two electrons and two protons were involved in the diffusion-controlled process. Using the PGE, a linear relationship between peak current and HVA concentration was obtained between 1.0 × 10−6 M and 5.0 × 10−5 M by DPV in BRB with pH 2.0. The detection limit of 3.84 × 10−7 M was calculated. The accuracy, the precision, and the selectivity of the quantitative method have successfully undergone evaluation. The practical application of the developed voltammetric method was checked by determining the HVA concentration in spiked plasma samples, yielding good recovery values.

Oxytetracycline (OTC) is a broad-spectrum antibiotic that belongs to the tetracycline class. It is utilized in both human and veterinary medicine to treat a variety of bacterial infections and as a feed additive for animals. Therefore, there is an increased need in the development of simple, rapid and reliable methods for this antibiotic determination in various matrices. This work presents OTC voltammetric analysis at the disposable, cheap pencil graphite electrode (PGE). The voltammetric response was investigated at different types of working electrodes emphasized that the highest sensitivity was exhibited by PGE using HB type pencil leads. Electrochemical pretreatment of the PGE did not bring any improvement in OTC oxidation signal. The effect of solution pH on the voltammetric behavior of OTC was examined using both cyclic voltammetry (CV) and differential pulse voltammetry (DPV) in Britton-Robinson Buffer (BRB) solutions with pH values ranging from 2.00 to 11.00. The oxidation was irreversible, resulting a diffusion- controlled process that was dependent on pH and involved an equal number of electrons and protons. The highest signal was observed at pH 4.56. Applying DPV on HB PGE, the oxidation peak of the analyte increased linearly with its concentration in the range 1.00 x 10-6 to 3.60 x 10-4 mol/L. The method's limit of detection was calculated to be 6.80 x 10-7 mol /L OTC. The applicability of the developed DPV method using HB PGE was tested by quantification the antibiotic from veterinary pharmaceutical preparations. Employing the standard addition method, the obtained mean recovery was 103.12%.

A new molecularly imprinted polymer (MIP)-based disposable electrochemical sensor for dipyridamole (DIP) determination was obtained. The sensor was rapidly prepared by potentiodynamic electrochemical polymerization on a pencil graphite electrode (PGE) using curcumin (CUR) as a functional monomer and DIP as a template molecule. After the optimization of the conditions (pH, monomer–template ratio, scan rate, number of cyclic voltammetric cycles applied in the electro-polymerization process and extraction time of the template molecule) for MIP formation, DIP voltammetric behavior at the modified electrode (MIP_PGE) was investigated. DIP oxidation took place in a pH-dependent, irreversible mixed diffusion-adsorption controlled process. Differential pulse voltammetry (DPV) and adsorptive stripping differential pulse voltammetry (AdSDPV) were used to quantify DIP from pharmaceutical and tap water samples. Under optimized conditions (Britton–Robinson buffer at pH = 3.29), the obtained linear ranges were 5.00 × 10−8–1.00 × 10−5 mol/L and 5.00 × 10−9–1.00 × 10−7 mol/L DIP for DPV and AdSDPV, respectively. The limits of detection of the methods were 1.47 × 10−8 mol/L for DPV and 3.96 × 10−9 mol/L DIP for AdSDPV.

Microtubule-targeting agents (MTAs) are chemical compounds that bind to microtubules, important components of the cytoskeleton, which is essential for a wide range of cellular processes. MTAs represent one of the most successful chemotherapeutics used for cancer treatment. This review starts with a short description of the chemical and biological characteristics of the available MTAs approved as anticancer agents. After a brief general discussion of MTAs electroanalysis, the literature data regarding the electrochemistry of each compound belonging to this class was critically presented. The electrochemical techniques, the electrode materials and the modifiers used in the development of the sensors, as well as the working conditions, the linear ranges, the detection limits and their application for MTAs direct or indirect determination are summarized. On the other hand, the interaction of MTAs with metallic ions, biological important molecules and cancer cells are addressed. The main drawbacks and the gaps to be filled in this research area are emphasized, the current challenges of the electrochemical sensors and methods applied in the detection of MTAs being also outlined.

Curcumin (CU) is a polyphenolic compound extracted from turmeric, a well-known dietary spice. Since it has been shown that CU exerts beneficial effects on human health, interest has increased in its use but also in its analysis in different matrices. CU has an antioxidant character and is electroactive due to the presence of phenolic groups in its molecule. This paper reviews the data reported in the literature regarding the use of electrochemical techniques for the assessment of CU antioxidant activity and the investigation of the voltammetric behavior at different electrodes of free or loaded CU on various carriers. The performance characteristics and the analytical applications of the electrochemical methods developed for CU analysis are compared and critically discussed. Examples of voltammetric investigations of CU interaction with different metallic ions or of CU or CU complexes with DNA as well as the CU applications as electrode modifiers for the enhanced detection of various chemical species are also shown.

The article is a continuation of the book chapter entitled Recent Advances in Antioxidant Capacity Assays published by IntechOpen in 2021. The various methods for determining antioxidant capacity in a variety of materials (plant extracts, biological material, foods, etc.) are discussed, with a special emphasis on articles published in recent years and especially on reviews. Both chemical methods for determining antioxidant capacity and cellular antioxidant capacity assays were presented. In addition to the review published in 2021, the following methods for the determination of antioxidant capacity were presented: crocin bleaching assay, Briggs-Rauscher reaction inhibition assay, ferricyanide-Prussian blue assay, cerric reducing antioxidant capacity assay and Anti Oxidant Power 1 (AOP1) assay. Several applications of the cellular antioxidant capacity assay were also presented in tabular form.

Amphenicols are broad-spectrum antibiotics. Despite their benefits, they also present toxic effects and therefore their presence in animal-derived food was regulated. Various analytical methods have been reported for their trace analysis in food and environmental samples, as well as in the quality control of pharmaceuticals. Among these methods, the electrochemical ones are simpler, more rapid and cost-effective. The working electrode is the core of any electroanalytical method because the selectivity and sensitivity of the determination depend on its surface activity. Therefore, this review offers a comprehensive overview of the electrochemical sensors and methods along with their performance characteristics for chloramphenicol, thiamphenicol and florfenicol detection, with a focus on those reported in the last five years. Electrode modification procedures and analytical applications of the recently described devices for amphenicol electroanalysis in various matrices (pharmaceuticals, environmental, foods), together with the sample preparation methods were discussed. Therefore, the information and the concepts contained in this review can be a starting point for future new findings in the field of amphenicol electrochemical detection.

Sulfamethoxazole (SMX) is a sulfonamide antibiotic used in the treatment of digestive, bronchopulmonary, and urinary tract infections. [...]

Rosmarinic acid (RA) is an important bioactive phenolic acid with significant biochemical activities, including the antioxidant one. It is widely found in plants of the familiesLamiaceaeandBoraginaceaeand has many uses in the food, pharmaceutical and cosmetics industries. RA is an electroactive species owing to the presence of the two catechol groups in its structure. Due to their inherent characteristics, such as sensitivity, selectivity, ease of operation and not too high costs, electrochemical methods of analysis are interesting tools for the assessment of redox-active compounds. Moreover, there is a good correlation between the redox potential of the analyte and its capability to donate electrons and, consequently, its antioxidant activity. Therefore, this paper presents a detailed overview of the electrochemical (bio)sensors and methods, in both stationary and dynamic systems, applied for RA investigation under different aspects. These comprise its antioxidant activity, its interaction with biological important molecules and the quantification of RA or total polyphenolic content in different samples.

Ferulic acid (FA), a hydroxycinnamic acid naturally found in fruits, vegetables and alcoholic beverages, has antioxidant, antiaging, antiviral and antibacterial activity being used in the medicine, food and pharmaceutical industries [1]. [...]

The fluoroquinolones (FQ) ciprofloxacin (CIP) and norfloxacin (NOR) are used asbroad-spectrum antibacterial agents [...]

Ellagic acid (EA) is a fused four-ring polyphenol found in numerous vegetables, fruits, seeds,and some nuts. Interest in EA has increased during the past few years due to its antioxidant,antiviral, antimutagenic, and anticarcinogenic effects [...]

Generally, the temperature influence on the retention of compounds. [...]

The retention behavior of some aromatic hydrocarbons on phenylsilicagel stationary phase was studied for the temperature interval between 20 degrees C and 50 degrees C. The van't Hoff plots were studied for some mobile phase compositions, using acetonitrile or methanol as organic additive. The variation of the standard enthalpy was calculated from the slope of these linear plots and its dependence on the mobile phase composition was rather different for the two organic modifiers. The variation of the standard enthalpy was very small for the four aromatic hydrocarbons in case of using acetonitrile (from -11.07 kJ/mol for benzene to 11.49 kJ/mol for propylbenzene; mobile phase composition being 45/55, v/v, acetonitrile/water), while for methanol used as organic modifier the variation of standard enthalpy changed significantly from benzene to propylbenzene (-10.92 kJ/mol for benzene to -18.58 kJ/mol for propylbenzene; mobile phase composition - 45/55, v/v, methanol/water). The variations of the standard entropy and Gibbs free energy change for the hydrocarbons were estimated considering a phase ratio of 0.25 for the column used.

Background: In the present work, two spectrometric methods for determination of formaldehyde were studied and compared. Methods and Results: Both methods are based on the catalytic effect of formaldehyde on the oxidation of Fluorescein natrium by sodium bromate in acid media. In the first method, the decrease in fluorescence intensity of Fluorescein natrium, measured at the emission wavelength of 510 nm (excitation wavelength, 438 nm), was proportional to formaldehyde in the concentration range 0.05-1.2 mu g mL(-1) and the detection limit was found to be 0.02 mu g mL(-1). In the second method, the decrease in absorbance of Fluorescein natrium measured at the wavelength of 438 nm was proportional to formaldehyde concentration in the range 0.5-7 mu g mL(-1) and the detection limit was found to be 0.16 mu g mL(-1). As preliminary steps, the working parameters (acidity, concentration of reagents, reaction time) were established. Influence of interfering species was also investigated. Conclusion: The proposed methods were applied for the determination of formaldehyde in rainwater samples.

A novel voltammetric assay for quinine (QN) determination using an electrochemically pretreated pencil graphite electrode is described. The detection limit of QN was 2 x 10(-7) M. The method possesses some obvious advantages including extreme simplicity, rapid response, and low cost.