Electrochemical oxidation of sildenafil citrate (Viagra) on carbon electrodes

Electrochemical sensor for simultaneous determination of trifluoperazine and dopamine in human serum based on graphene oxide-carbon nanotubes/iron-nickel nanoparticles

Trifluoperazine (TFLP) is an important psychiatric medication that balances the dopamine (DA) level in the brain for patients suffering from neurological disorder diseases. An efficient electrochemical sensor is developed for detecting TFLP in real human serum samples. The sensor is fabricated by casting the GC surface with two consecutive thin layers, namely a graphene oxide-carbon nanotubes mixture (GRO-CNT), and iron-nickel nanoparticles (Fe-Ni). The diffusion-controlled oxidation process of TFLP at the composite surface includes one electron transfer process. Under optimized conditions, the sensor in human serum shows excellent catalytic effect for simultaneous determination of TFLP and dopamine (DA) in the same concentration range (0.5 μM to 18 μM) with low detection limits of 0.13 μM and 0.32 μM respectively. The combined effect of a large conductive surface area and the excellent catalytic activity of the nanocomposite improves the sensor's performance. The sensor exhibits a stable current response over four weeks, excellent reproducibility, and insignificant interference from common species present in human serum samples. The reliability test of using the sensor in serum samples shows good recovery of TFLP.

Sensitivity enhancement of a Cu (II) metal organic framework-acetylene black-based electrochemical sensor for ultrasensitive detection of imatinib in clinical samples

Imatinib (IMB), an anticancer drug, is extensively used for chemotherapy to improve the quality of life of cancer patients. The aim of therapeutic drug monitoring (TDM) is to guide and evaluate the medicinal therapy, and then optimize the clinical effect of individual dosing regimens. In this work, a highly sensitive and selective electrochemical sensor based on glassy carbon electrode (GCE) modified with acetylene black (AB) and a Cu (II) metal organic framework (CuMOF) was developed to measure the concentration of IMB. CuMOF with preferable adsorbability and AB with excellent electrical conductivity functioned cooperatively to enhance the analytical determination of IMB. The modified electrodes were characterized using X-rays diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared (FT-IR), ultraviolet and visible spectrophotometry (UV-vis), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), brunauer‒emmett‒teller (BET) and barrett‒joyner‒halenda (BJH) techniques. Analytical parameters such as the ratio of CuMOF to AB, dropping volumes, pH, scanning rate and accumulation time were investigated through cyclic voltammetry (CV). Under optimal conditions, the sensor exhibited an excellent electrocatalytic response for IMB detection, and two linear detection ranges were obatined of 2.5 nM-1.0 μM and 1.0-6.0 μM with a detection limit (DL) of 1.7 nM (S/N = 3). Finally, the good electroanalytical ability of CuMOF-AB/GCE sensor facilitated the successful determination of IMB in human serum samples. Due to its acceptable selectivity, repeatability and long-term stability, this sensor shows promising application prospects in the detection of IMB in clinical samples.

A Comprehensive Review on Analytical Techniques for Determination of Sex Stimulants, PDE5 Inhibitors in Different Matrices with Special Focus on the Electroanalytical Methods

Erectile dysfunction (ED) is one of the most common chronic diseases affecting men and its incidence increases with aging. Due to its substantial influence on the quality of life, phosphodiesterase type-5 (PDE5) inhibitors have been implemented to treat ED by increasing the penile blood flow that results in improving erection. PDE5 inhibitors is a class of drugs that affects many pharmacological sectors, and it is essential to review the different analytical methods described for their determination. Few reviews were published concerning this group of drugs. For this reason, this review article gathers the different analytical methods used to determine PDE5 inhibitors in pharmaceutical and biological samples over the past 20 years. Different analytical techniques were used to analyze these compounds in different matrices such as separation methods (capillary electrophoresis, LC-MS, UPLC-MS/MS, and GC-MS), spectroscopic methods (UV-visible methods, FT-IR spectroscopy and spectrofluorometry) and electrochemical methods (polarography, voltammetry and potentiometry). This review focuses on the different electrochemical methods and their use in analytical determination of PDE5 inhibitors in pharmaceutical dosage forms and biological samples. Moreover, it discusses the different modified electrodes used for their electroanalytical determination and the behavior of the studied drugs at different modified electrodes. Additionally, this review discusses the pharmacokinetics of the studied compounds and their interactions with other co-administered drugs especially the metabolic interactions between the studied compounds and other co-administered drugs in different matrices. This literature survey would provide a beneficial guide for future analytical investigation of PDE5 inhibitors.

Multi sensor compatible 3D-printed electrochemical cell for voltammetric drug screening

3D printing is a hot topic in electroanalytical chemistry, allowing the construction of custom cells and sensors at affordable prices. In this work, we describe a novel small and practical 3D-printed electrochemical cell. The cell's body, manufactured in ABS on a 3D printer, is composed by three parts easily screwed: solution vessel, stick and cover with two embedded 3D-pen-printed carbon black-polylactic acid (CB-PLA) electrodes (counter and pseudo-reference). The cell is compatible with any planar working electrode, in which boron-doped diamond, graphite sheet (GS) and 3D-printed CB-PLA were shown as examples. A new alternative protocol to quickly produce 3D-printed sensors using a 3D pen and other low-cost apparatus is also proposed. The voltammetric performance of each evaluated sensor was carried out in the presence of redox probe ferricyanide and paracetamol as model analyte, and the surfaces were characterized by electrochemical impedance spectroscopy and scanning electrochemical microscopy. To present an analytical application of the 3D-printed cell, low-cost flexible sensors (GS and CB-PLA) were used as integrated platforms for sampling and detection of solid drugs. As a proof-of-concept, traces of drugs with a historic of counterfeit or adulteration (sildenafil citrate, tadalafil, losartan and 17α-ethinylestradiol) were abrasively sampled over the sensor and assembled on 3D-printed cell to perform a fast voltammetric scan in the presence of only 500 μL of electrolyte. This protocol is attractive for pharmaceutical and forensic sciences as a simple preliminary screening method which could identify the presence or absence of the suspicious drug as well as impurities or adulterants. The 3D-printed cell was also used for the determination of 17α-ethinylestradiol in a contraceptive pill to demonstrate a quantitative analysis. The cell is quickly printed (90 min), cheap (US$ 0.30) and requires low electrolyte volumes (0.5-3.0 mL), being suitable to be used in several other electroanalyses, especially for on-site applications.

Sildenafil 4.0-Integrated Synthetic Chemistry, Formulation and Analytical Strategies Effecting Immense Therapeutic and Societal Impact in the Fourth Industrial Era

Sildenafil is a potent selective, reversible inhibitor of phosphodiesterase type 5 (PDE5) approved for the treatment of erectile dysfunction and pulmonary arterial hypertension. Whilst twenty years have passed since its original approval by the US Food and Drug Administration (USFDA), sildenafil enters the fourth industrial era catalyzing the treatment advances against erectile dysfunction and pulmonary hypertension. The plethora of detailed clinical data accumulated and the two sildenafil analogues marketed, namely tadalafil and vardenafil, signify the relevant therapeutic and commercial achievements. The pharmacokinetic and pharmacodynamic behavior of the drug appears complex, interdependent and of critical importance whereas the treatment of special population cohorts is considered. The diversity of the available formulation strategies and their compatible administration routes, extend from tablets to bolus suspensions and from per os to intravenous, respectively, inheriting the associated strengths and weaknesses. In this comprehensive review, we attempt to elucidate the multi-disciplinary elements spanning the knowledge fields of chemical synthesis, physicochemical properties, pharmacology, clinical applications, biopharmaceutical profile, formulation approaches for different routes of administration and analytical strategies, currently employed to guide the development of sildenafil-based compositions.

An immunochromatographic strip sensor for sildenafil and its analogues

In this study, a new hapten of sildenafil (Sild) was successfully synthesized and a sensitive monoclonal antibody (mAb) against Sild was produced based on this new hapten. The subclass of the mAb was IgG2a, and the half-maximal inhibitory concentration (IC50) of the mAb was 0.53 ng mL-1. Next, an immunochromatographic assay (ICA) was established for detecting Sild and its analogues in functional foods, where the visual detection limit (vLOD) and cut-off values were 0.5 and 20 μg kg-1, respectively. With the aid of a strip scan reader, the ICA can measure Sild with an LOD of 0.7 μg kg-1 and a line range of detection between 1.40 and 13.11 μg kg-1. The whole test process takes only 15 min. Therefore, the ICA provides a useful tool for the on-site detection and rapid initial screening of Sild in functional food samples.

In Situ Growth of Metal-Organic Framework HKUST-1 on Graphene Oxide Nanoribbons with High Electrochemical Sensing Performance in Imatinib Determination

Metal-organic frameworks (MOFs) have been previously investigated as electrode materials for developing electrochemical sensors. They have usually been reported to suffer from poor conductivity and improvement in the conductivity of MOFs is still a great challenge. Here, we reported the fabrication of an electrochemical sensor based on the in situ growth of framework HKUST-1 on conductive graphene oxide nanoribbons (GONRs)-modified glassy carbon electrode (GCE) (HKUST-1/GONRs/GCE). The as-fabricated modified electrode was characterized using field emission scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, Fourier transform infrared, X-ray diffraction, electrochemical impedance spectroscopy, cyclic voltammetry, and Raman spectroscopy. The voltammetric response of HKUST-1/GONRs/GCE toward Imatinib (IMA), as an anticancer drug, is dramatically higher than HKUST-1/GCE because of the synergic effect of the GONRs and HKUST-1 framework. The calibration curve at the HKUST-1/GONRs/GCE for IMA covered two linear dynamic ranges, 0.04-1.0 and 1.0-80 μmol L^-1, with a detection limit of 0.006 μmol L^-1 (6 nmol L^-1). Taking advantage of the conductivity of GONRs and large surface area of HKUST-1, a sensitive modified electrode was developed for the electrochemical determination of IMA. The present method provides an effective strategy to solve the poor conductivity of the MOFs. Finally, the obtained electrochemical performance made this modified electrode promising in the determination of IMA in urine and serum samples.

Novel synthesis of nanocomposite for the extraction of Sildenafil Citrate (Viagra) from water and urine samples: Process screening and optimization

A sensitive analytical method is investigated to concentrate and determine trace level of Sildenafil Citrate (SLC) present in water and urine samples. The method is based on a sample treatment using dispersive solid-phase micro-extraction (DSPME) with laboratory-made Mn@ CuS/ZnS nanocomposite loaded on activated carbon (Mn@ CuS/ZnS-NCs-AC) as a sorbent for the target analyte. The efficiency was enhanced by ultrasound-assisted (UA) with dispersive nanocomposite solid-phase micro-extraction (UA-DNSPME). Four significant variables affecting SLC recovery like; pH, eluent volume, sonication time and adsorbent mass were selected by the Plackett-Burman design (PBD) experiments. These selected factors were optimized by the central composite design (CCD) to maximize extraction of SLC. The results exhibited that the optimum conditions for maximizing extraction of SLC were 6.0 pH, 300μL eluent (acetonitrile) volume, 10mg of adsorbent and 6min sonication time. Under optimized conditions, virtuous linearity of SLC was ranged from 30 to 4000ngmL^-1 with R² of 0.99. The limit of detection (LOD) was 2.50ngmL^-1 and the recoveries at two spiked levels were ranged from 97.37 to 103.21% with the relative standard deviation (RSD) less than 4.50% (n=15). The enhancement factor (EF) was 81.91. The results show that the combination UAE with DNSPME is a suitable method for the determination of SLC in water and urine samples.

Automated flow system for sildenafil enrichment using surfactant coated solid-phase with fluorescence detection

In this work, Amberlite XAD-1180 resin is used for on-line surfactant-mediated pre-concentration of sildenafil as a prior step for its fluorescent detection. In order to activate the column for sildenafil pre-concentration, the cationic surfactant (hexadecyltrimethylammoniunm bromide, HTAB) is adsorbed onto the resin. In these conditions, sildenafil is retained by HTAB-resin and then it is eluted with ethanol and analyzed by spectrofluorimetry. Drug-surfactant association produces a considerable fluorescence enhancement, increasing considerably the sensitivity of detection. Therefore, sildenafil can be pre-concentrated and quantitatively determined, with a detection limit of 0.2 ng mL(-1). The proposed method was successfully applied to the analysis of bulk drug, human urine, tablets, and local herbal medicine. Validation processes were performed by recovering studies and statistical analysis with satisfactory results.

Spectrophotometric determination of sildenafil citrate in pure form and in pharmaceutical formulation using some chromotropic acid azo dyes

Two simple and highly sensitive spectrophotometric methods were developed for the quantitative determination of the drug sildenafil citrate (SC), Viagra, in pure form and in pharmaceutical formulations, through ion-associate formation reactions (method A) with mono-chromotropic acid azo dyes, chromotrope 2B (I) and chromotrope 2R (II) and ion-pair reactions (method B) with bi-chromotropic acid azo dyes, 3-phenylazo-6-o-carboxyphenylazo-chromotropic acid (III), bis-3,6-(o-hydroxyphenylazo)-chromotropic acid (IV), bis-3,6-(p-N,N-dimethylphenylazo)-chromotropic acid (V) and 3-phenylazo-6-o-hydroxyphenylazo-chromotorpic acid (VI). The reaction products, extractable in methylene chloride, were quantitatively measured at 540, 520, 540, 570, 600 and 575 nm using reagents, I-VI, respectively. The reaction conditions were studied and optimized. Beer's plots were linear in the concentration ranges 3.3-87.0, 3.3-96.0, 5.0-115.0, 2.5-125.0, 8.3-166.7 and 0.8-15.0 microg mL(-1) with corresponding molar absorptivities 1.02 x 10(4), 8.34 x 10(3), 6.86 x 10(3), 5.42 x 10(3), 3.35 x 10(3) and 2.32 x 10(4)Lmol(-1) cm(-1) using reagents I-VI, respectively. The limits of detection and Sandell's sensitivities were calculated. The methods were successfully applied to the analysis of commercial tablets (Vigoran) and the recovery study reveals that there is no interference from the common excipients that are present in tablets. Statistical comparison of the results was performed with regard to accuracy and precision using Student's t- and F-tests at 95% confidence level. There is no significant difference between the reported and proposed methods with regard to accuracy and precision.

Spectrophotometric determination of trazodone, amineptine and amitriptyline hydrochlorides through ion-pair formation with molybdenum and thiocyanate

Extraction spectrophotometric method has been developed for the determination of tricyclic drugs such as trazodone (TZH), amineptine (APH) and amitriptyline (ATPH) hydrochlorides in pure form and in the dosage forms coming from different Egyptian markets. The method based on the formation of ion-pairs between these drugs under investigation and inorganic complex of Mo(V)-thiocyanate followed by its extraction with methylene chloride. The optimum conditions for the ion-pairs formation are established. The method permits the determination of TZH, APH and ATPH over the concentration range of 2-28, 2-32 and 1-30 microg ml(-1), respectively. The Sandell sensitivity (S) is found to be 0.105, 0.138 and 0.118 g cm(-2) for TZH, APH and ATPH, respectively. The SD is found to be 0.16-0.377, 0.12-0.259 and 0.091-0.286 and the R.S.D. are 0.14-0.55, 0.12-0.399 and 0.095-0.485 for TZH, APH and ATPH, respectively. The method is applicable for the assay of the investigated drugs in different dosage forms and the results are in good agreement with those obtained by the official method.

Determination of triflumizole by differential pulse polarography in formulation, soil and natural water samples

A novel electroanalytical procedure is proposed for the determination of the triflumizole in formulation, soil and natural water samples using differential pulse polarography (DPP). Triflumizole exhibited a single well-defined cathodic peak over the pH range of 1.0-9.0 in Britton-Robinson (B-R) buffers. The peak potentials were shifted to more negative values upon increasing the pH and a plot of reduction potentials (E(p)) versus pH exhibited two linear segments with a break at pH 4.0 which corresponded to the pK(a)+/-1 value of triflumizole. The peak appeared as a maximum at pH 2.0 (-810 mV versus saturated calomel electrode (SCE)) was well resolved and suitable to be investigated for analytical use. The current-concentration plot obtained using this peak was rectilinear over the range from 2.0 to 91.0 micromol L(-1) with a correlation coefficient of 0.993. The limit of detection (LOD) and limit of quantification (LOQ) were obtained as 0.72 and 2.39 micromol L(-1), respectively. The proposed method was successfully applied to the determination of triflumizole in spiked soil and lake water. The mean recoveries of the pesticide were 102.1 and 103.6% with a relative standard deviation of 1.01 and 2.68% in soil and lake water, respectively. The method was extended to the determination of triflumizole in agrochemical fungicide formulation Trifmine and results were in agreement with that obtained by high-performance liquid chromatographic analysis (HPLC). The influence of some diverse ions and some other pesticides was also investigated.

Spectrophotometric determination of trazodone, amineptine and amitriptyline hydrochlorides through ion-pair formation using methyl orange and bromocresol green reagents

A simple and rapid extraction spectrophotometric procedure has been developed for the determination of tricyclic anti-depressant drugs such as trazodone (TZH), amineptine (APH) and amitriptyline (ATPH) hydrochlorides in pure form and in different dosage forms. The method involves the formation of intense yellow ion-pairs between these drugs under investigation and methyl orange (MO) and bromocresol green (BCG) reagents followed by their extraction with 1,2-dichloroethane and quantitative microdetermination at 420 and 410 nm using MO or BCG, respectively. The optimum experimental conditions for the ion-pairs formation are established. The method permits the determination of TZH, APH and ATPH over a concentration range of 2-50, 2-50 and 1-25 microg ml(-1) for TZH, APH and ATPH, using MO and 1-25 microg ml(-1) for TZH, APH and ATPH, using BCG, respectively. The Sandell sensitivity (S) is found to be 0.106, 0.1071 and 0.0907 g cm(-2) for TZH, APH and ATPH, respectively, using MO reagent and 0.0788, 0.0661 and 0.0494 g cm(-2) for TZH, APH and ATPH, respectively, using BCG. The method is applicable for the assay of the investigated drugs in different dosage forms and the results are in good agreement with those obtained by the official method.