Fabiana S. Felix

Fast and Accurate Analysis of Drugs Using Amperometry Associated With Flow Injection Analysis

This review presents a general overview about the amperometric detection potentialities associated to flow injection analysis (FIA). Fundamental aspects, developments, applications and advantages accrued from the coupling of voltammetry with FIA for pharmaceutical analyses are discussed. The selected references present several examples for this association in various classes of drugs and support their advantages. Examples illustrate that the amperometric techniques coupled with flow system can usually be used in drug routine analysis without sample pretreatment. Amperometry/FIA has proved to be an excellent alternative to the chromatographic techniques and it has been used in routine analysis, from the simplest analytes to more complex species, solving even special cases such as the enantiomeric analysis of pharmaceutical compounds with a chiral moiety, which requires time-consuming sample preparation or expensive instrumentation. This revision also aims to contribute for reducing the gap between the vast possibilities enabled by electroanalytical techniques and their effective utilization for pharmaceutical analysis.

Quantification of terbinafine in pharmaceutical tablets using capillary electrophoresis with contactless conductivity detection and batch injection analysis with amperometric detection

Terbinafine hydrochloride (TerbHCl) is an allylamine derivative with fungicidal action, especially against dermatophytes. Different analytical methods have been reported for quantifying TerbHCl in different samples. These procedures require time-consuming sample preparation or expensive instrumentation. In this paper, electrochemical methods involving capillary electrophoresis with contactless conductivity detection, and amperometry associated with batch injection analysis, are described for the determination of TerbHCl in pharmaceutical products. In the capillary electrophoresis experiments, terbinafine was protonated and analyzed in the cationic form in less than 1 min. A linear range from 1.46 to 36.4 μg mL(-1) in acetate buffer solution and a detection limit of 0.11 μg mL(-1) were achieved. In the amperometric studies, terbinafine was oxidized at +0.85 V with high throughput (225 injection h(-1)) and good linear range (10-100 μmol L(-1)). It was also possible to determine the antifungal agent using simultaneous conductometric and potentiometric titrations in the presence of 5% ethanol. The electrochemical methods were applied to the quantification of TerbHCl in different tablet samples; the results were comparable with values indicated by the manufacturer and those found using titrimetry according to the Pharmacopoeia. The electrochemical methods are simple, rapid and an appropriate alternative for quantifying this drug in real samples.

ELECTROCHEMICAL IMMUNOSENSORS – A POWERFUL TOOL FOR ANALYTICAL APPLICATIONS

Immunosensors are biosensors based on interactions between an antibody and antigen on a transducer surface. Either antibody or antigen can be the species immobilized on the transducer to detect antigen or antibody, respectively. Because of the strong binding forces between these biomolecules, immunosensors present high selectivity and very high sensitivity, making them very attractive for many applications in different science fields. Electrochemical immunosensors explore measurements of an electrical signal produced on an electrochemical transductor. This signal can be voltammetric, potentiometric, conductometric or impedimetric. Immunosensors utilizing electrochemical detection have been explored in several analyses since they are specific, simple, portable, and generally disposable and can carry out in situ or automated detection. This review addresses the potential of immunosensors destined for application in food and environmental analysis, and cancer biomarker diagnosis. Emphasis is given to the approaches that have been used for construction of electrochemical immunosensors. Additionally, the fundamentals of immunosensors, technology of transducers and nanomaterials and a general overview of the possible applications of electrochemical immunosensors to the food, environmental and diseases analysis fields are described.

Determination of ciclopirox olamine in pharmaceutical products by capillary electrophoresis with capacitively coupled contactless conductivity detection

This paper describes the determination of ciclopirox olamine in pharmaceutical formulations using capillary electrophoresis with capacitively coupled contactless conductivity detection. In an alkaline medium, ciclopirox olamine is converted into an anionic species and its detection is possible in capillary electrophoresis with capacitively coupled contactless conductivity detection without an electroosmotic flow modifier, because it is a low‐mobility species. A linear working range from 2.64 to 264 μg/mL in sodium hydroxide electrolyte as well as low detection limit (0.39 μg/mL) and a good repeatability (RSD=3.4% for 264 μg/mL ciclopirox solution (n=10)) were achieved. It was also possible to determine olamine in its cationic form when acetic acid was used as the electrolyte solution. The results obtained include a linear range from 26.4 to 184.8 μg/mL and a detection limit of 2.6 μg/mL olamine. The proposed methods were applied to the analysis of commercial pharmaceutical products and the results were compared with the values indicated by the manufacturer as well as those obtained using a titrimetric method recommended by American Pharmacopoeia.

Flow injection analysis using carbon film resistor electrodes for amperometric determination of ambroxol

Flow injection analysis (FIA) using a carbon film sensor for amperometric detection was explored for ambroxol analysis in pharmaceutical formulations. The specially designed flow cell designed in the lab generated sharp and reproducible current peaks, with a wide linear dynamic range from 5x10(-7) to 3.5x10(-4) mol L(-1), in 0.1 mol L(-1) sulfuric acid electrolyte, as well as high sensitivity, 0.110 Amol(-1) L cm(-2) at the optimized flow rate. A detection limit of 7.6x10(-8) mol L(-1) and a sampling frequency of 50 determinations per hour were achieved, employing injected volumes of 100 microL and a flow rate of 2.0 mL min(-1). The repeatability, expressed as R.S.D. for successive and alternated injections of 6.0x10(-6) and 6.0x10(-5) mol L(-1) ambroxol solutions, was 3.0 and 1.5%, respectively, without any noticeable memory effect between injections. The proposed method was applied to the analysis of ambroxol in pharmaceutical samples and the results obtained were compared with UV spectrophotometric and acid-base titrimetric methods. Good agreement between the results utilizing the three methods and the labeled values was achieved, corroborating the good performance of the proposed electrochemical methodology for ambroxol analysis.

A simple and precise conductometric method for the determination of losartan in pharmaceutical products

AbstractLosartan is an antihypertensive agent that lost its patent protection in 2010, and, consequently, it has been available in generic form. The latter motivated the search for a rapid and precise alternative method. Here, a simple conductometric titration in aqueous medium is described for the losartan analysis in pharmaceutical formulations. The first step of the titration occurs with the protonation of losartan producing a white precipitate and resulting in a slow increase in conductivity. When the protonation stage is complete, a sharp increase in conductivity occurs which was determined to be due to the presence of excess of acid. The titrimetric method was applied to the determination of losartan in pharmaceutical products and the results are comparable with values obtained using a chromatographic method recommended by the United States Pharmacopoeia. The relative standard deviation for successive measurements of a 125 mg L−1 (2.71×10−4 mol L−1) losartan solution was approximately 2%. Recovery study in tablet samples ranged between 99 and 102.4%. The procedure is fast, simple, and represents an attractive alternative for losartan quantification in routine analysis. In addition, it avoids organic solvents, minimizes the risk of exposure to the operator, and the waste treatment is easier compared to classical chromatographic methods.

Amperometric determination of promethazine in tablets using an electrochemically reduced graphene oxide modified electrode

Graphene films were prepared on a glassy carbon electrode for amperometric determination of promethazine hydrochloride in pharmaceutical products. This modified sensor was prepared by chemical oxidation of graphite powder followed by product exfoliation in ultrapure water using an ultrasonic bath. Then, the resultant graphene oxide was electrochemically reduced in 0.10 mol L−1 acetic acid–sodium acetate (pH = 5.0) on a glassy carbon electrode surface. The proposed sensor exhibited reproducible amperometric responses in a wide linear range from 1.99 × 10−6 to 1.03 × 10−3 mol L−1 at +0.78 V (vs. Ag/AgCl). Low detection and quantification limits (1.99 × 10−7 mol L−1 and 6.63 × 10−7 mol L−1, respectively) were achieved. This method was applied to the analyses of commercial tablet samples and all results were in good agreement with those obtained using spectrophotometry and high-performance liquid chromatography.

Determination of Cd, Pb and Ni by square wave stripping voltammetry in particulate matter collected in workplace atmosphere of some Brazilian industrial foundries

The concentration of Cd, Pb and Ni in atmospheric particulate matter collected in the workplace of three foundries located in the municipality of Loanda, Parana, Brazil, was determined by square wave voltammetry and ICP OES. The results show that workers are being systematically exposed to concentrations of Cd and Pb that are significantly above the Limit of Concentration recommended by the American Conference of Governmental Industrial Hygienists (ACGIH). Results obtained by the proposed electroanalytical method do not differ statistically from the results obtained by ICP OES, indicating its potential application to environmental monitoring at much lower cost of installation, operation and maintenance. According to the results obtained, technological changes in the production process were recommended, as well as the use of personal protective equipment in order to keep the health and well being of workers, minimizing damages to the external environment.

Gold random microarrays: design, characterization and amperometric determination of ciclopirox olamine in pharmaceutical products

In this work, a disposable gold random microarray (GRM) sensor was developed and applied for the determination of ciclopirox olamine in 0.10 mol L−1 Britton Robinson buffer (pH 5.0). The GRM was fabricated by the deposition of two toner pattern masks, the first mask delimiting the disc area and the second one (with 90% of toner) defining the microarrays. Following the optimization of the experimental parameters, the proposed sensor presented excellent analytical properties for the amperometric detection of ciclopirox olamine at +0.85 V vs. Ag/AgCl(KClsat). The usefulness of the GRM sensor was confirmed by determining ciclopirox olamine in commercial products. The results obtained were in good agreement with those found by potentiometric titration and the labelled values. The proposed GRM platform can be produced with high throughput and is cost-effective and disposable, hence no pre-treatment is required between measurements.

Determinação de manganês em material particulado atmosférico de ambientes de trabalho utilizando eletrodo de diamante dopado com boro e voltametria de onda quadrada com redissolução catódica

A boron-doped diamond electrode is used for determination of Mn(II) in atmospheric particulate matter by square wave cathodic stripping voltammetry. The analytical curve was linear for Mn(II) concentrations between 5.0 and 37.5 µg L-1, with quantification limit of 3.6 µg L-1. The precision was evaluated by the relative standard deviation, with values between 5.1% and 9.3%. The electrode is free of adsorption, minimizing memory effects. Samples collected in the workplace atmosphere of a foundry had Mn(II) concentrations between 0.4 and 4 µg m-3. No significant differences were observed between the proposed method and inductively coupled plasma optical emission spectroscopy.