Current Analytical Chemistry - Volume 15, Issue 3, 2019

Background: The article presents the state of research on conductive composite materials constructed on the basis of poly (3,4-ethylenedioxythiophene) (PEDOT), a conductive polymer, as well as selected nanoparticles and nanostructures. Combining two or more materials in a composite which is later used in electrode modification can result in obtaining an electrode with new, more desirable properties. One of such fields is pharmacological analysis which, due to the continuous emergence of new substances and often also a need for analyte determination in complex samples, requires newer instruments in the form of suitably sensitive and selective sensors. Contents: The review contains the description of properties of PEDOT and composite PEDOT with polystyrenesulfonates. In the following part, composite materials are described: PEDOT-CNT, PEDOT- nanoparticles, PEDOT-graphene. The review closes with the examples of multi-component composite materials. Conclusion: The on-going development of new substances used in medicine, pharmacy and related fields, as well as the continuous increase in the production and consumption of this type of substances, necessitates constant development and modernization of analytical techniques used for their determination. Biomedical assays require being able to carry out determinations in different systems, including in vitro ones, without separating individual compounds. It is necessary to be able to identify several substances simultaneously or determine one compound in the presence of chemically similar substances. Modern electrode materials such as PEDOT and nanostructured materials allow for the development of sensors which are getting increasingly better at meeting the requirements of the analysts.

Background: Captopril is the synthetic dipeptide used as an angiotensin converting enzyme inhibitor. Captopril is used to treat hypertension as well as for the treatment of moderate heart failure. Analytical instrumentation and methodology plays an important role in pharmaceutical analysis. Methods: This review presents some important applications of electrochemical modes used for the analysis of captopril. So far captopril has been analyzed by using different bare and modified working electrodes with a variety of modifiers from organic and inorganic materials to various types of nano particles/materials. Results: This paper presents some of the methods which have been published in the last few years i.e. from 2003 to 2016. This review highlights the role of the analytical instrumentation, particularly electrochemical methods in assessing captopril using various working electrodes. Conclusion: A large number of studies on voltammetry noted by means of various bare and modified electrodes. Among all of the published voltammetric methods, DPV, SWV, CV and miscellaneous modes were trendy techniques used to analyze captopril in pharmaceutical formulations as well as biological samples. Electrodes modified with nanomaterials are promising sensing tools as this showed high sensitivity, good accuracy with precision as well as selectivity. In comparison to chromatographic methods, the main advantages of electrochemical methods are its cheaper instrumentation, lower detection limit and minimal or no sample preparation.

Background: Calcium Channel Blockers (CCBs) are widely used in the treatment of cardiovascular and ischemic heart diseases in recent years. They treat arrhythmias by reducing cardiac cycle contraction and also benefit ischemic heart diseases. Electroanalytical methods are very powerful analytical methods used in the pharmaceutical industry because of the determination of therapeutic agents and/or their metabolites in clinical samples at extremely low concentrations (10-50 ng/ml). The purpose of this review is to gather electroanalytical methods used for the determination of calcium channel blocker drugs in pharmaceutical dosage forms and biological media selected mainly from current articles. Methods: This review mainly includes recent determination studies of calcium channel blockers by electroanalytical methods from pharmaceutical dosage forms and biological samples. The studies of calcium channel blockers electroanalytical determination in the literature were reviewed and interpreted. Results: There are a lot of studies on amlodipine and nifedipine, but the number of studies on benidipine, cilnidipine, felodipine, isradipine, lercanidipine, lacidipine, levamlodipine, manidipine, nicardipine, nilvadipine, nimodipine, nisoldipine, nitrendipine, diltiazem, and verapamil are limited in the literature. In these studies, DPV and SWV are the most used methods. The other methods were used less for the determination of calcium channel blocker drugs. Conclusion: Electroanalytical methods especially voltammetric methods supply reproducible and reliable results for the analysis of the analyte. These methods are simple, more sensitive, rapid and inexpensive compared to the usually used spectroscopic and chromatographic methods.

Background: The electrochemical sensing of drugs in pharmaceutical formulations and biological matrices using molecular-imprinting polymer (MIP) as a recognition element combined with different electrochemical signal transduction has been widely developed. The MIP electrochemical sensors based on nanomaterials such as graphene, carbon nanotubes, nanoparticles, as well as other electrode modifiers incorporated into the MIPs to enhance the performance of the sensor, have been discussed. The recent advances in enantioselective sensing using MIP-based electrochemical sensors have been described. Methods: The molecular imprinting has more than six decades of history. MIPs were introduced in electrochemistry only in the 1990s by Mosbach and coworkers. This review covers recent literature published a few years ago. The future outlook for sensing, miniaturization and development of portable devices for multi-analyte detection of the target analytes was also given. Results: The growing pharmaceutical interest in molecularly imprinted polymers is probably a direct consequence of its major advantages over other analytical techniques, namely, increased selectivity and sensitivity of the method. Due to the complexity of biological samples and the trace levels of drugs in biological samples, molecularly imprinted polymers have been used to improve the response signal, increase the sensitivity, and decrease the detection limit of the sensors. The emergence of nanomaterials opened a new horizon in designing integrated electrochemical systems. The success of obtaining a high-performance electrochemical sensor based on MIPs lies in the kind of material that builds up the detection platform. Conclusion: The novel approaches to produce MIP materials, combined with electrochemical transduction to develop sensors for screening different pharmaceutically active compounds have been overviewed. MIPs may appear indispensable for sensing in harsh conditions, or sensing that requires longterm stability unachievable by biological receptors. The electrochemical sensors provide several benefits including low costs, shortening analysis time, simple design; portability; miniaturization, easy-touse, can be tailored using a simple procedure for particular applications. The performance of sensor can be improved by incorporating some conductive nanomaterials as AuNPs, CNTs, graphene, nanowires and magnetic nanoparticles in the polymeric matrix of MIP-based sensors. The application of new electrochemical sensing scaffolds based on novel multifunctional-MIPs is expected to be widely developed and used in the future.

Background: Qualitative and quantitative analysis of atypical antipsychotic drugs used for the treatment of schizophrenia, depression, anxiety, and bipolar disorder obtaining satisfactory results can be ensured by voltammetric techniques. The aim of this review is to present the application of voltammetric techniques developed for the determination of the atypical antipsychotic drugs, which are amisulpride, aripiprazole, clozapine, olanzapine, quetiapine fumarate, risperidone, sertindole, and ziprasidone, in pharmaceutical dosage forms and biological samples. Methods: Studies in the literature published between 2004 and 2017 based on the voltammetric determination of atypical antipsychotic drugs were gathered using scientific databases. The results obtained from these studies were combined and interpreted. Results: Voltammetric techniques applied for the sensitive determination of trace amounts of the selected atypical antipsychotic drugs in their pharmaceutical dosage forms and biological fluids were compared. The best analysis conditions were obtained after the optimization of some parameters such as buffer type, pH, and scan rate. For diffusion controlled electrode processes, it was observed that differential pulse and square wave voltammetry methods were generally used for the sensitive quantitative determination of the drugs, whereas stripping methods were used for the adsorption controlled electrode processes. Detection limits were between 1.53×10-3 μM for clozapine and 0.97 μM for risperidone. Conclusion: The electrodes used in the studies showed high selectivity, sensitivity, and good accuracy with precision. The developed methods were also applied to pharmaceutical preparations of the drugs and biological fluids with satisfactory results, without any interference from inactive excipients.

Background: Electroanalytical techniques play a very important role in the areas of medicinal, clinical as well as pharmaceutical research. Amongst these techniques, the voltammetric methods for the determination of drugs using nanomaterials based chemically modified electrodes (CMEs) have received enormous attention in recent years. This is due to the sensitivity and selectivity they provide on qualitative as well as quantitative aspects of the electroactive analyte under study. The aim of the present review was to discuss the work on nanomaterials based CMEs for the analysis of drugs covering the period from 2000 to present employing various voltammetric techniques for different classes of the drugs. Methods: The present review deals with the determination of different classes of drugs including analgesics, anthelmentic, anti-TB, cardiovascular, antipsychotics and anti-allergic, antibiotic and gastrointestinal drugs. Also, a special section is devoted for enantioanalysis of certain chiral drugs using voltammetry. The detailed information of the voltammetric determination for the drugs from each class employing various techniques such as differential pulse voltammetry, cyclic voltammetry, linear sweep voltammetry, square wave voltammetry, stripping voltammetry, etc. are presented in tabular form below the description of each class in the review. Results: Various nanomaterials including carbon nanotubes, graphene, carbon nanofibers, quantum dots, metal/metal oxide nanoparticles, polymer based nanocomposites have been used by researchers for the development of CMEs over a period of time. The large surface area to volume ratio, high conductivity, electrocatalytic activity and biocompatibility make them ideal modifiers where they produce synergistic effect which helps in trace level determination of pharmaceutical, biomedical and medicinal compounds. In addition, macrocyclic compounds as chiral selectors have been used for the determination of enantiomeric drugs where one of the isomers captured in the cavities of chiral selector shows stronger binding interaction for one of the enantiomorphs. Conclusion: Various kinds of functional nanocomposites have led to the manipulation of peak potential due to drug - nanoparticles interaction at the modified electrode surface. This has facilitated the simultaneous determination of drugs with almost similar peak potentials. Also, it leads to the enhancement in voltammetric response of the analytes. It is expected that such modified electrodes can be easily miniaturized and used as portable, wearable and user friendly devices. This will pave a way for in-vivo onsite real monitoring of single as well as multi component pharmaceutical compounds.

Introduction: Ultra-Performance Liquid Chromatographic (UPLC) method enables analyst to establish an analysis at higher pressure than High Performance Liquid Chromatographic (HPLC) method towards liquid chromatographic methods. UPLC method provides the opportunity to study a higher pressure compared to HPLC, and therefore smaller column in terms of particle size and internal diameter are generally used in drug analysis. The UPLC method has attracted gradually due to its advantages such as short analysis time, the small amount of waste reagents and the significant savings in the cost of their destruction process. In this review, the recent selected studies related to the UPLC method and its method validation are summarized. The drug analyses and the results of the studies which were investigated by UPLC method, with certain parameters from literature are presented. Background: Quantitative determination of drug active substances by High-Performance Liquid Chromatography (HPLC) from Liquid Chromatography (LC) methods has been carried out since the 1970's with the use of standard analytical LC methods. In today's conditions, rapid and very fast even ultra-fast, flow rates are achieved compared to conventional HPLC due to shortening analysis times, increasing method efficiency and resolution, reducing sample volume (and hence injection volume), reducing waste mobile phase. Using smaller particles, the speed and peak capacity are expanding to new limit and this technology is named as Ultra Performance Liquid Chromatography. In recent years, as a general trend in liquid chromatography, ultra-performance liquid chromatography has taken the place of HPLC methods. The time of analysis was for several minutes, now with a total analysis time of around 1-2 minutes. The benefits of transferring HPLC to UPLC are much better understood when considering the thousands of analyzes performed for each active substance, in order to reduce the cost of analytical laboratories where relevant analysis of drug active substances are performed without lowering the cost of research and development activities. Methods: The German Chemist Friedrich Ferdinand Runge, proposed the use of reactive impregnated filter paper for the identification of dyestuffs in 1855 and at that time the first chromatographic method in which a liquid mobile phase was used, was reviewed. Christian Friedrich Chönbein, who reported that the substances were dragged at different speeds in the filter paper due to capillary effect, was followed by the Russian botanist Mikhail S. Tswet, who planted studies on color pigment in 1906. Tswet observes the color separations of many plant pigments, such as chlorophyll and xanthophyll when he passes the plant pigment extract isolated from plant through the powder CaCO3 that he filled in the glass column. This method based on color separation gives the name of "chromatographie" chromatography by using the words "chroma" meaning "Latin" and "graphein" meaning writing. Results and Conclusion: Because the UPLC method can be run smoothly at higher pressures than the HPLC method, it offers the possibility of analyzing using much smaller column sizes and column diameters. Moreover, UPLC method has advantages, such as short analysis time, the small amount of waste reagents and the significant savings in the cost of their destruction process. The use of the UPLC method especially analyses in biological samples such as human plasma, brain sample, rat plasma, etc. increasingly time-consuming due to the fact that the analysis time is very short compared to the HPLC, because of the small amount of waste analytes and the considerable savings in their cost.

Background: Diclofenac is a widely used nonsteroidal anti-inflammatory drug. Recent studies have shown that frequent consumption of this drug in high concentrations can cause heart diseases, so strict control of diclofenac’s quantity in commercial drugs is necessary. This paper presents the development of an optimized voltammetric methodology for the quantification of diclofenac, which offers some advantages over other electrochemical and accepted methods. Objective: Optimize with a Box-Behnken design the differential pulse voltammetry parameters towards the quantification of diclofenac in pharmaceutical samples. Methods: Diclofenac behavior in the working electrode was evaluated by cyclic voltammetry, in order to stablish the best conditions for diclofenac’s quantification. A Box-Behnken design was then used to optimize the differential pulse voltammetry parameters and stablish the analytical behavior of the proposed methodology. Commercial tablets were prepared for analysis according to the Pharmacopeia, the DPV optimized methodology was used to quantify diclofenac in the samples, and the results were statistically compared with those obtained with the official methodology. Results: After optimization, the analytical parameters found were: correlation coefficient of 0.998, detection limit of 0.001 μM, quantification limit of 0.0033 μM and sensitivity of 0.299 μA.μM-1. The statistical analysis showed there were no significant differences between the results obtained with the proposed methodology and those obtained with the official methodology. Conclusion: The statistical analysis showed that the proposed methodology is as reliable as the official spectrophotometric one for the quantification of diclofenac in commercial drugs, with very competitive analytical parameters, and even better to others found with more complex electrodes.

Background: Nanomaterials have a significant role in improving the performance of electrochemical sensing systems. Unique physical and chemical properties have extended the application of nanomaterials in the fields of engineering, materials and biomedical science. In the last few years, these materials with unique properties have been preferred in the design of experimental approaches for the analysis of metal ions, proteins, biomarkers and pharmaceutical compounds. This paper reports preparation, characterization of two different nanomaterials and their electrochemical application on doublestranded calf-thymus DNA signals. Methods: The multi-walled carbon nanotubes were functionalized with amine groups (MWCNTs-NH2) by employing the dielectric barrier discharge plasma treatment and then applied as MWCNTs- NH2/glassy carbon electrode. Moreover, the synthesized mesoporous silica MCM-41 was chemically amine functionalized and used as MCM-41-NH2/carbon paste electrode. For biosensor preparation, a thin layer of calf thymus double stranded deoxyribonucleic acid (ct-dsDNA) was immobilized over the modified electrodes. Results: The influence of dsDNA immobilized substrate was investigated based on the electrochemical signals. While dsDNA/MCM-41-NH2/carbon paste biosensor showed a selective effect for guanine signals, the dsDNA/MWCNTs-NH2/glassy carbon biosensor presented electrocatalytic effect for dsDNA signals. Both dsDNA modified electrodes were employed to explore the interaction between the dsDNA and the anticancer drug etoposide (ETP) in aqueous solution through voltammetric techniques. By increasing the interaction time with ETP, the adenine peak current was quenched in the presence of MWCNTs-NH2 based glassy carbon electrode. Whereas, in the presence of MCM-41-NH2 based CP electrode, selective interaction with guanine occurred and oxidation peak intensity was diminished. Conclusion: The selective effect of MCM-41-NH2 can be used when the studied substances give a signal with the same potential of adenine.

Background: New Chemical Entities (NCEs) could be generally exposed to several stress conditions of hydrolysis, oxidation, photolysis and thermal degradation in order to better characterize the compounds and to know if the degradation processes lead to generate undesired (or toxic) products. Objective: This paper reports the development and validation of an HPLC-PDA method for the qualiquantitative profiles determination and chemical-physical stability evaluation after forced decomposition studies of thiosemicarbazone-derived compounds endowed with interesting pharmacological activities. Methods: All compounds and two possible degradation products were resolved by using a Grace® C-18 (ODS) column (250 mm 4.6 mm; 5 mm particle size) in gradient elution mode. The chromatographic analysis was run in 28 min. The analytical method was correctly validated using weighted-matrix matched standard curves in the following ranges: 1-100 μg mL-1 for the lead compounds, and 0.1-8 μg mL-1 for the two possible degradation products showing a good correlation coefficients (≥0.9756). Precision and trueness comply with International Guidelines on method validation. Results: The obtained results demonstrated an excellent stability of the thiosemicarbazone-derived products following the treatment with UV set at 254 nm and heat (at 80°C). In solution, however, the compounds showed different stability profiles. Conclusion: The results obtained through the forced degradation studies provided important information not only for handling, formulation and storage of the substances, but also for the possible chemical changes in order to increase the stability. Given the importance of the non-conventional dosage forms, the stability of the substances was also analyzed in the presence of widely used surfactants.