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In this article, a serially connected dual column liquid chromatography-tandem mass spectrometry (LC-MS/MS) method is described for the simultaneous separation and enantioseparation of proteinogenic amino acids. For this purpose, different achiral and chiral stationary phases (CSP) and mobile phase compositions have been tested. As a result of the optimization studies, the best enatioseparation for amino acids were achieved with a combination of zwitterionic and crown ether stationary phases using a gradient of two mobile phases: A (water:TFA 99.5:0.5, % v/v) and B (acetonitrile:ethanol:TFA 85:15:0.5, % v/v/v). The developed method provided simultaneous enantioseparation of all proteinogenic amino acids under this study including isomeric and isobaric ones except for proline. The method was successfully applied to human lung adenocarcinoma cells (A549) and healthy human lung epithelial cells (BEAS-2B) cultivated with d-amino acid containing cocktails in order to evaluate d-amino acids transfer rate in normal and cancer lines. Thed/l amino acid ratios were different in cancer and normal cell lines cultivated as mentioned above for aspartic acid, cysteine, methionine, phenylalanine, and serine.

The aim of the present study is to develop the polymeric nanoparticulate drug delivery systems of piroxicam and to evaluate the in-vitro characteristics such as entrapment efficiency, surface morphology, in-vitro drug release performance, etc. For this reason, a novel HPLC methodology was developed for the determination of piroxicam from its bulk form, pharmaceutical preparation, and nanoparticulate delivery systems. Furthermore, the developed formulation was applied to the rats and the biological samples (plasma, liver, heart, spleen, kidney, and lung homogenates) were analyzed by the developed HPLC method following a salting-out assisted liquid-liquid extraction strategy for the first time in the literature. A Kinetex C18 analytical column (150 mm × 4.6 mm i.d., 5 µm) was used as a stationary phase with a 0.8 mL/min flow rate of acetonitrile: phosphate buffer (40:60, v/v), the column oven was adjusted to 40 °C and detection wavelength is set to 360 nm. Developed method were validated as per selectivity, linearity, LOD, LOQ, precision, and accuracy specified in the International Council for Harmonisation guidelines. As a result of the present study, it has been shown that the analysis of piroxicam from the bulk form, pharmaceutical preparation, developed polymeric-based drug delivery system, and biological samples can be successfully performed and no interferences were observed in any matrix. The developed method was also successfully utilized to study the tissue distribution of piroxicam in rats.

Drug resistance is one of the main problems of cancer treatment. For this reason, combination therapy is commonly used for years. The combination of a chemotherapeutic, carboplatin, and the epigenetic drug decitabine is a new approach to modulate drug resistance. Nanoparticulate systems can overcome the drawbacks associated with the drug combinations. An analytical method that can detect and quantify carboplatin and decitabine which is encapsulated into the nanoparticles is necessary for nanoparticle development. In the literature, there is no analytical method in which carboplatin and decitabine are determined simultaneously. The primary purpose of this study is to develop and validate a novel, and stability-indicating high-performance liquid chromatography method for simultaneous determination of carboplatin and decitabine in pharmaceutical preparations in addition to developing the first nanoformulation for this drug combination. Therefore, various experimental parameters were optimized. The chromatographic separation was achieved using an XSelect(R)CSH C18 (250 x 4.6 mm I.D., 5 mu m) column and a mobile phase consisting of methanol:water (containing 0.1% phosphoric acid) (3:97, v/v). The mobile phase pH was adjusted to 7.0 with 5 M NaOH. The developed method was successfully applied for the simultaneous determination and quantification of carboplatin and decitabine co-encapsulated in nanoparticles and released into in vitro dissolution medium.

In the present study, the enantiomer migration order (EMO) of enilconazole in the presence of various cyclodextrins (CDs) was investigated by capillary electrophoresis (CE). Opposite EMO of enilconazole were observed when β-CD or the sulfated heptakis(2-O-methyl-3,6-di-O-sulfo)-β-CD (HMDS-β-CD) was used as the chiral selectors. Nuclear magnetic resonance (NMR) spectroscopy was used to study the mechanism of chiral recognition between enilconazole enantiomers and those two cyclodextrins. On the basis of rotating frame nuclear Overhauser (ROESY) experiments, the structure of an inclusion complex between enilconazole and β-CD was derived, in which (+)-enilconazole seemed to form a tighter complex than the (-)-enantiomer. This correlates well with the migration order of enilconazole enantiomers observed in CE. No evidence of complexation between enilconazole and HMDS-β-CD could be gathered due to lack of intermolecular nuclear Overhauser effect (NOE). Most likely the interaction between enilconazole and HMDS-β-CD leads to formation of a shallow external complex that is sufficient for separation of enantiomers in CE but cannot be evidenced based on ROESY experiment. Thus, in this particular case CE documents the presence of intermolecular interactions which are at least very difficult to be evidenced by other instrumental techniques.

High performance liquid chromatography-electrochemical detector (HPLC-EC) is employed as a reliable device for the detection of catecholamines in blood or urine samples without any time-consuming extraction procedure. However, there is a need for the construction of cheap and easy-to-operate electrode assemble systems embedded in HPLC-EC. In this study, we present a disposable and low-cost paper-based electrode (PBE) assemble utilizing a nitrocellulose membrane, which serves support material in flow-cell device for HPLC-EC. A custom-built flow cell was inventively designed as specific to the prepared PBEs via stereolithography 3D printing. To gain the electrochemical signal enhancement, the working electrode was modified with gold nanoparticles and carboxylated-multi-walled carbon nanotubes (MWCNTs). Here, we focused on the construction of the paper-based electrode assemble and characterization of the flow cell device performance. To demonstrate the functionality of the flow cell device, we analyzed common catecholamines from spiked biological fluids using the optimized experimental parameters. Amperometric detection of the catecholamines was carried out at the potential of + 0.5 V and linear range was found to be 0.5–20.0 μg/mL, with a limit of detection in the range of 4.0–15.0 ng/mL. The obtained results confirmed our disposable paper-based electrode assemble to be promising for the construction of an electrochemical platform for reliable and fast detection of electroactive species.

Background:Probiotics are living microorganisms that have a healthy influence on a host.Objective:The aim of this study was to isolate a probiotic Pediococcus acidilactici strain from newborn faeces and develop and optimize a selective high-performance liquid chromatography method for the determination and validation of its lactic acid content and also evaluate some probiotic characteristics.Methods:Isolated strains were identified by the API 50 CH system and 16S rDNA gene sequence analysis and tested for antibiotic susceptibility, bile salt tolerance, low pH resistance, proteolytic, haemolytic activity, as well as the production of bacteriocin, hydrogen peroxide, and lactic acid. Antimicrobial activity of selected strain against standard test microorganisms was determined by the spot lawn method and the quantitation of lactic acid was carried out by high-performance liquid chromatography on a Rezex ROA organic acid (300x7.8 mm) analytical column.Results:P. acidilactici M7 strain was evaluated as a potential probiotic due to its ability to survive at low pH values or in the presence of pepsin, pancreatin, and bile salts. The lactic acid amount of strain was found in the range between 5.59-5.94 mg mL-1 by HPLC. M7 strain was also found to be resistant to vancomycin, had no bacteriocin, and hydrogen peroxide production and was able to inhibit the growth of P. aeruginosa and E. faecalis by its lactic acid content.Conclusion:This study explains a simple, selective, and fully validated procedure for the determination of lactic acid from probiotic bacteria.

High performance liquid chromatography (HPLC) and ultrahigh performance liquid chromatography (UHPLC or UPLC) have been the most widely used tools for research and routine quality control of active pharmaceutical ingredients (API). The most important challenge in these techniques is fast and efficient separation. Both techniques are preferred due to their selectivity, high accuracy and remarkable precision. On the other hand, they have some limitations: In some cases, traditional HPLC uses high amounts of organic solvents with longer analysis time, and furthermore UHPLC has high back pressure and frictional heating. To overcome these limitations, scientists have developed new type of column particles. In general, two different silica types of column packing material based on their backbone have been used for HPLC and UHPLC. Stationary phases that have fully porous silica particles comply with the essential criteria of analysis, but these show all the limitations of HPLC. However, in recent years, core–shell silica particles (a combination of solid core and porous shell) have been increasingly used for highly efficient separation with reduced run times. Thus, core–shell technology provides the same efficient separations as the sub 2 µm particles that are used in UHPLC, while eliminating the disadvantages (potentially lower backpressure). The key factors for core–shell particles are size and thickness of porous shell layer, the latter of which can be explained using the Van Deemter equation. The columns packed with core–shell particles have been employed in a wide range of applications for analysis and quality control of pharmaceutical active substances. This review will underline the advantages of core–shell silica particles in the analysis of pharmaceutically active ingredients based on liquid chromatography from the perspective of column properties, system suitability test parameter results and validation steps.

In a recent study, opposite enantiomer elution order was observed for ketoprofen enantiomers on two amylose-phenylcarbamate-based chiral columns with the same chemical composition of the chiral selector but in one case with coated while in the other with an immobilized chiral selector. In the present study, the influence of this uncommon effect on method validation parameters for the determination of minor enantiomeric impurity in dexketoprofen was studied. The validated methods with two alternative elution orders for enantiomers were applied for the evaluation of enantiomeric impurity in six marketed dexketoprofen formulations from various vendors. In most of these formulations except one the content of enantiomeric impurity exceeded 0.1% (w/w).

The affinity pattern of terbutaline enantiomers towards various cyclodextrins was studied using capillary electrophoresis. The affinity pattern of terbutaline enantiomers was the same towards all studied cyclodextrins except heptakis(2-O-methyl-3,6-di-O-sulfo)-β-CD. Nuclear magnetic resonance spectroscopy was used for understanding of fine structural mechanisms of interactions of β-cyclodextrin and its two sulfated derivatives with the enantiomers of terbutaline. The structure of terbutaline complexes with all 3 cyclodextrins studied was different from each other. In confirmation with our earlier studies it was shown again that capillary electrophoresis represents very sensitive technique for studies of affinity patterns in cyclodextrin complexes with chiral guests. Other instrumental (e.g. NMR spectroscopy and X-ray diffraction analysis) and theoretical techniques, although very useful for obtaining the information regarding the stoichiometry, binding constants and structure of intermolecular complexes, as well as about the forces involved in selector-selectand binding and chiral recognition, may sometimes fail to properly sense those fine differences in the affinity patterns. Therefore, it is recommended to use capillary electrophoresis in order to examine correctness of affinity pattern determined for intermolecular complexes of cyclodextrins with guest molecules by other instrumental or computation techniques.

The major goal of this study was to determine the affinity pattern of brombuterol (BB) enantiomers toward various cyclodextrins (CD) and to evaluate the potential of NMR spectroscopy for understanding fine mechanisms of interactions between CDs and BB enantiomers. Separation of BB enantiomers was performed in a fused-silica capillary using a phosphate buffer, pH 2.5, at the room temperature in the normal polarity mode. It was shown once again that CE in combination with NMR spectroscopy represents a very sensitive tool for studies of affinity patterns and structure of CD complexes with chiral guests. Although opposite affinity patterns of BB enantiomers were observed toward native β- and γ-CDs, no significant differences between the structures of the complexes of these two CDs with BB were detected by NMR spectroscopy. In contrary to this, the opposite affinity pattern of BB enantiomers toward β-CD and its two sulfated derivatives, heptakis (2,3-O-diacetyl-6-sulfo)-β-CD (HDAS-β-CD) and heptakis (2-O-methyl-3,6-di-O-sulfo)-β-CD (HMDS-β-CD) was associated with major differences in the structure of the complexes. In addition, it was shown again that HMDS-β-CD provides separation of enantiomers without formation of inclusion-type complex with the chiral analyte.

In this study separation of enantiomers of 8 chiral ?-agonists were studied on 6 polysaccharide-based chiral columns in polar-organic and alcohol-hydrocarbon mobile phases. No separation of enantiomers was observed on any column with polar-organic mobile phase eluents such as pure methanol, ethanol or acetonitrile. Most of the chiral analytes were resolved into enantiomers when alcohol-hydrocarbon type mobile phases were used. The most successful column was Lux Cellulose-2 on which all 8 chiral analytes were baseline resolved into enantiomers at least with one mobile phase used. The reversal of enantiomer elution order was observed dependent on the chemistry of the chiral selector and the composition of the mobile phase. © 2016 Elsevier B.V.

Capillary electrophoretic (CE) and high performance liquid chromatographic (HPLC) methods were developed and optimized for the determination of antazoline (ANT) and tetrahydrozoline (TET) in ophthalmic formulations. Optimum electrophoretic conditions were achieved using a background electrolyte of 20mM phosphate buffer at pH 7.0, a capillary temperature of 25°C, a separation voltage of 22 kV and a pressure injection of the sample at 50 mbar for 17s. HPLC analysis was performed with Kinetex (150 × 4.6mm ID × 5 μm) (Phenomenex, USA) analytical column with 1 mL min(-1) flow rate of mobile phase which consisted of 0.05% TFA in bidistilled water (pH adjusted to 3.0 with 5M NaOH) and acetonitrile/buffer in the ratio of 63:37 (v/v) at room temperature. Injection volume of the samples was 10 μL and the wavelength of the detector was set at 215 nm for monitoring both analytes. Calibration graphs showed a good linearity with a coefficient of determination (R(2)) of at least 0.998 for both methods. Intraday and interday precision (expressed as RSD%) were lower than 2.8% for CE and 0.92% for HPLC. The developed methods were demonstrated to be simple and rapid for the determination of ANT and TET in ophthalmic solutions providing recoveries in the range between 97.9 and 102.70% for CE and HPLC.

A selective and sensitive stability indicting HPLC method was developed for the analysis of enantiomers of miconazole. For this purpose, six different polysaccharide-based chiral columns were evaluated. Optimization was performed using several polar organic and alcohol-hydrocarbon mobile phases. As a result of optimization studies, the analysis was carried out using Lux Cellulose-3, methanol as a mobile phase at a flow rate of 1 mL·min-1 , and the detection wavelength was arranged to 230 nm. Developed method has been fully validated according to International Council on Harmonization guidelines. Method was found linear in the concentration range of 1 to 200 μg·mL-1 . Coefficient of determination (R2 ) was calculated as 0.9996, intraday precision of the method was found with the RSD% of 0.56, and the recovery of the method was calculated close to 100%. Furthermore, some other validation parameters like specificity, selectivity, LOD, and LOQ were also investigated. Stability indicating capability of this method was shown by forced degradation studies, and the run time for each analysis was less than 6 minutes. As a result, simple, fast, reliable HPLC method was developed for the separation and determination of the enantiomers of miconazole. Applicability of the developed method was shown with the application of marketed pharmaceutical preparations.

Our earlier studies have demonstrated the applicability of polysaccharide-based chiral selectors in combination with superficially porous (or core-shell) silica (SPS) particles for the preparation of highly efficient chiral stationary phases (CSP). In earlier studies, CSPs were prepared by coating (adsorption) of the chiral selector onto the surface of silica. In this study we report for the first time the CSP obtained by covalent immobilization of a chiral selector onto the surface of SPS particles. The applicability of this CSP for the separation of enantiomers in pure methanol and acetonitrile, as well as in n-hexane/2-propanol mobile phases is shown. The effect of the injected sample amount, mobile phase flow rate and detection frequency on separation performance were studied, as well as high efficiency separation of enantiomers with the analysis time less than 30 s was attempted. (C) 2018 Elsevier B.V. All rights reserved.

In the past decades, patients who have chemotherapy treatment have considerably increased number. At this point, the development of rapid precise, and reliable methods are very important to analyze cancer drugs from their dosage forms, animals or human biological samples. Among all the analytical methods, electrochemical methods hold an important position with their unique properties such as specificity in the biological recognition process, fast response, and their reliability and do not need a pretreatment process. Chromatographic methods are also used in a wide range of analytical applications for the analyses of anticancer drugs. The power of chromatography comes from its ability to separate a mixture of analytes and determination of their concentrations. Chromatographic techniques can mainly be divided into gas, liquid, and supercritical fluid chromatography. In the frame of this information, this review is aimed to provide basic principles of electroanalytical and high-performance liquid chromatography methods for the analysis of cancer drugs. In addition, some selected applications for electrochemistry-related techniques and high-performance liquid chromatography, for the determination of anti-cancer pharmaceuticals published in the last five years are also discussed. © 2018, © 2018 Taylor & Francis Group, LLC.

This is the first report in literature using hydrophilic interaction liquid chromatography (HILIC) in combination with diode array detector (DAD) for stability indicating determination of 5-Fluorouracil (5-FU) from its bulk form, pharmaceutical preparations, developed solid lipid nanoparticle (SLN) and nano structured lipid carrier (NLC) drug delivery systems as well as the rat skin extracts. The separation was performed at 45 °C, on Sequant Zic HILIC (250 mm × 4.60 mm ID, 5 μm, 200 Ao), peek HPLC column. Mobile phase is consisting of a mixture of acetonitrile: buffer containing 5 mM ammonium acetate (95:5; v/v). The pH of the mobile phase was adjusted to 7.0 using 1 M NaOH. The analysis was carried out at 0.75 mL min?1 flow rate with a detection wavelength of 265 nm and the injection volume was arranged as 10 μL. The developed method was fully validated in accordance with the International Council on Harmonization (ICH) Guidelines. Specificity of this method was demonstrated by forced degradation studies. As a result of calibration studies, the calibration curve was found linear in the concentration range of 1–250 μg mL-1 (R2 = 0.999). The precision of this technique calculated within the frame of intra-day and inter-day based on a percentage of relative standard deviation (RSD%) values (

In the present study, new isocratic stability-indicating reverse phase chromatographic methods were developed using HPLC and UPLC systems for the determination of entacapone (ENT) in its pharmaceutical dosage forms. Ultra performance liquid chromatography (UPLC) using small sub-2 μm particles and high-performance liquid chromatography (HPLC) were compared for separation and determination of the ENT using Acquity HSS C18 (50 × 2.1 mm, 1.8 µm) and Xbridge C18 (150 × 4.6 mm, 5.0 µm) columns by UPLC and HPLC, respectively. When using UPLC, the run time could be reduced five fold and actually the solvent consumption decreased 10 times. The proposed UPLC method would decrease the consumption of organic solvents and reagents. The present methods were validated according to ICH guideline. All analytical procedures including sample preparation, flow rate, run time of the analytical systems were at low levels. Forced degradation studies were also performed for both compounds in bulk drug samples to demonstrate the specificity and stability-indicating comparative advantage of both methods.

One-dimensional dynamic computer simulation was employed to investigate the separation and migration order change of ketoconazole enantiomers at low pH in presence of increasing amounts of (2-hydroxypropyl)-β-cyclodextrin (OHP-β-CD). The 1:1 interaction of ketoconazole with the neutral cyclodextrin was simulated under real experimental conditions and by varying input parameters for complex mobilities and complexation constants. Simulation results obtained with experimentally determined apparent ionic mobilities, complex mobilities, and complexation constants were found to compare well with the calculated separation selectivity and experimental data. Simulation data revealed that the migration order of the ketoconazole enantiomers at low (OHP-β-CD) concentrations (i.e. below migration order inversion) is essentially determined by the difference in complexation constants and at high (OHP-β-CD) concentrations (i.e. above migration order inversion) by the difference in complex mobilities. Furthermore, simulations with complex mobilities set to zero provided data that mimic migration order and separation with the chiral selector being immobilized. For the studied CEC configuration, no migration order inversion is predicted and separations are shown to be quicker and electrophoretic transport reduced in comparison to migration in free solution. The presented data illustrate that dynamic computer simulation is a valuable tool to study electrokinetic migration and separations of enantiomers in presence of a complexing agent.

Electroanalytical methods are chosen for the sensitive analysis of pharmaceutically active compounds in their dosage forms and biological samples. Electroanalytical method validation is the process used to confirm that the determination procedure employed for a specific test is suitable for its intended use like other analytical methods. Results from electroanalytical method validation can be used to judge the quality, applicability, accuracy, reliability and

Fulvestrant is used for the treatment of hormone receptor-positive metastatic breast cancer in postmenopausal women with disease progression following anti-estrogen therapy. Several reversed-phase columns with variable silica materials, diameters, lengths, etc., were tested for the optimization study. A good chromatographic separation was achieved using a Waters X-Terra RP(18) column (250 × 4.6 mm i.d. × 5 µm) and a mobile phase, consisting of a mixture of acetonitrile-water (65:35; v/v) containing phosphoric acid (0.1%). The separation was carried out 40 °C with detection at 215 nm.The calibration curves were linear over the concentration range between 1.0-300 and 1.0-200 µg/mL for standard solutions and biological media, respectively. The proposed method is accurate and reproducible. Forced degradation studies were also realized. This fully validated method allows the direct determination of fulvestrant in dosage form and biological samples. The average recovery of the added fulvestrant amount in the samples was between 98.22 and 104.03%. The proposed method was also applied for the determination of fulvestrant from the polymeric-based nanoparticle systems. No interference from using polymers and other excipients was observed in in vitro drug release studies. Therefore an incorporation efficiency of fulvestrant-loaded nanoparticle could be determined accurately and specifically.

The detailed electrochemical oxidation and selective determination of fosamprenavir were studied in aqueous-alcohol medium at a carbon paste electrode. Electrochemical behavior of fosamprenavir was investigated as details by different electrochemical techniques in the absence and presence of Triton X-100. The electrochemical mechanism was also carried out and aromatic amine part of the molecule was found to be involved in electrochemical oxidation of fosamprenavir. The oxidized form takes part in hydrolysis; the products are also electroactive and participate in redox reaction. Voltammetric studies were realized between pH 1.0 and 12.0. In the presence of Triton X-100, the signal increased almost 5 times. The promising analytical performance was obtained with developed method. A systematic study of the experimental parameters such as pH, scan rate, accumulation potential and accumulation time that affect the square wave stripping response was carried out and the optimized experimental conditions were arrived. Developed electroanalytical procedure is based on a carbon paste working electrode in Britton–Robinson buffer (pH ∼ 2) using square wave voltammetry. Concentration range was linear in the range of 1 × 10 −6 –5 × 10 −5 M fosamprenavir. In sense of low detection limit (4.8 × 10 −7 M) and good repeatability (4.07%) and reproducibility (4.53%) of the results, the method was used for the determination of fosamprenavir in pharmaceutical dosage form successfully. The results are satisfying compared with that of already published high-performance liquid chromatographic results.

Liquid chromatography (LC) is a separation technique used in many different areas to aid the identification and quantification of substances in various matrices. LC techniques with various detection modes have been widely used for the sensitive and selective determination of trace amounts of pharmaceutical active compounds in biological samples and their dosage forms. A completely new system design with advanced technology has been developed, called ultra high performance liquid chromatography, which has evolved from high performance liquid chromatography. The application of LC methods to drug analysis introduces a powerful tool for therapeutic drug monitoring as well as for clinical research. The advantages of short turnaround time, method reliability, method sensitivity, and drug specificity justify the use of LC techniques for various groups of the drug active compounds. This review describes some of the principles of ultra high performance liquid chromatography and high performance liquid chromatography, validation of these methods, system suitability tests for the methods, and application of methods to pharmaceutical analysis in the last 3 years.

A RP-LC method is presented, which is sensitive and selective for the simultaneous determination of enalapril-lercanidipine and enalapril-nitrendipine binary mixtures in their pharmaceutical dosage forms. The analyte peaks were detected using the LC method with the mobile phase ratio of methanol: water (70:30 v/v, pH 3.0) and a 1.0 mL min-1 flow rate. The detection wavelength was selected at 210 nm using photo diode array detector and column temperature was optimized to 30 C. Linearity was obtained at different concentration ranges for all working pharmaceutically active compounds between 0.5 and 25 ?g mL-1. The proposed methods were extensively validated according to USP 27 requirements and ICH guidelines. The methods were applied to the analysis of pharmaceutical dosage forms containing binary mixtures of enalapril-lercanidipine and enalapril-nitrendipine. Moreover, the proposed methods were applied for the degradation studies of the selected compounds. Degradation studies were conducted using stress conditions such as UV light, acidic and alkaline hydrolysis, oxidation and heat in oven, to evaluate the ability of the separation of the response of standard compounds from their degradation products. © 2013 Springer-Verlag Berlin Heidelberg.

The aim of the present study was to develop a fast, sensitive and reliable method for rapid screening of cephalosporin injectable dosage forms namely ceftazidime and ceftizoxime to the detection of counterfeit and substandard drugs that might be illegally commercialized. Ceftazidime, ceftizoxime and cefixime (IS) were separated in a X-Terra RP-18 column (250 × 4.60 mm ID × 5 μ) and DAD detector set at 290 and 260 nm. The mobile phase consisted of a mixture of methanol:water 20:80 (v/v) at a flow rate of 1.0 mL min−1. Additionally, in order to find the optimum pH value of separation the pK a values of studied compounds were determined by using two different methodologies. Aqueous pK a values of studied compounds have been determined by UV-spectrophotometry and liquid chromatography were used for the determination and direct characterization of the dissociation constants by using the dependence of the capacity factor on the pH of the mobile phase in 20% (v/v) methanol–water binary mixture in which separation was performed. The pH of the mobile phase was adjusted with 25 mM H3PO4 to 3.2. The method was shown to be linear, sensible, accurate, and reproducible over the range of analysis and it can be used to pharmaceutical formulations containing a single active ingredient within a short analysis time.

Ziprasidone is a psychotropic agent used for the treatment of schizophrenia. Its oxidation was investigated electrochemically at boron-doped diamond and glassy carbon electrodes using cyclic, differential pulse, and square wave voltammetry. The dependence of the peak current and peak potentials on pH, concentration, nature of the buffer, and scan rate were examined. The process was diffusion and adsorption controlled for boron-doped diamond and glassy carbon electrodes, respectively. The possible mechanism of oxidation was discussed with some model compounds that have indole and piperazine oxidations. A linear response was obtained between 8 × 10-7 and 8 × 10-5 M for the first peak in acetate buffer (pH 5.5) and between 2 × 10-6 and 2 × 10-4 M for the second peak in 0.1 M H2SO4 with boron-doped diamond electrode for differential pulse and square wave voltammetric techniques. The reproducibility and accuracy of the proposed methods were found between 0.31 and 1.20, 99.27 and 100.22, respectively. The recovery studies were also achieved to check selectivity and accuracy of the methods. The proposed methods were applied for the determination of ziprasidone from pharmaceutical dosage forms and human serum samples without any time-consuming extraction, separation, evaporation or adsorption steps prior to drug assay except precipitation of the proteins using acetonitrile. The results were statistically compared with those obtained through an established LC-UV technique, no significant differences were been found between the voltammetric and LC methods. © 2010 Elsevier B.V. All rights reserved.

A combination of antiretroviral agents is frequently used in effective treatment of the human immunodeficiency virus infection. In this study, two different separation methods are presented for the simultaneous determination of emtricitabine, rilpivirine and tenofovir from raw materials and urine samples. Developed liquid chromatography and capillary electrophoresis methods were thoroughly optimized for high analytical performances. Optimization of multiple variables at the same time by performing a minimum number of experiments was achieved by the Box–Behnken design, which is an experimental design in response surface methodology, in capillary electrophoresis. The results of the experimental design ensure minimum analysis time with well-separated analytes. Separation conditions, such as different stationary phases, pH level, organic modifiers and temperatures in liquid chromatography method, were also optimized. In particular, among stationary phases, the core–shell column especially enhanced the effectiveness of separation in liquid chromatography. Both methods were fully validated and applied to real samples. The main advantage of the developed methods is the separation of the drug combination in a short time with high efficiency and without any time-consuming steps. Copyright © 2017 John Wiley & Sons, Ltd.

Etoposide is a topoisomerase II enzyme inhibitor type chemotherapeutic agent which is widely used in the therapy of various cancers. Its short half-life and toxicity to normal tissues are the major drawbacks in its clinical applications. Polymeric nanoparticulate drug delivery systems are rational carriers to deliver etoposide with higher efficiency and fewer side effects. In addition tubular shaped drug carriers are found to show a great potential for drug delivery on the basis of promising results regarding particle shape and cellular uptake. In this study, etoposide loaded polymeric tubular nanocarriers have been developed by template wetting method using porous anodic aluminum oxide membranes as templates. The developed poly(methyl methacrylate) nanocarriers were evaluated for structural analysis, in vitro drug release studies and drug release kinetics. Accurate and reliable determination of the drug release from newly developed nanocarriers, is of great importance. For this reason a selective and sensitive reversed phase liquid chromatography method was developed and fully validated from the point of system suitability, specificity, linearity and range, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy and robustness for the reliable determination of etoposide. Stability indicating capability was shown with forced degradation studies and the chromatographic conditions were optimized on ACE 5C18 (150 mm × 4.6mm I.D., 5 μm) analytical column. Related to the calibration results ETP was found linear in the range between 0.2 from 100 μg mL(-1) with the LOD as 0.015 μg.mL(-1). The resultant conditions were applied for the selective and sensitive determination of etoposide from its commercial dosage form with the high accuracy values (99.82-100.65%). The method was successfully detected assay of etoposide release from newly developed polymeric tubular nanocarriers, which was found as 72.2% at the end of 24h.

Ratio derivative spectrophotometric technique is presented for the rapid, accurate and precise simultaneous determination of olmesartan medoxomil (OLM), hydrochlorothiazide (HCT), and zofenopril (ZOF) as well as HCT binary mixtures in their dosage forms. First derivative of the ratio spectra (DD1) by measurements using different amplitudes was used and calibration graphs were established for 0.5–12 mg/mL HCT and 0.5–20 mg/mL OLM and ZOF. This method depends on first derivative of the ratio spectra by division of the absorption spectrum of the binary mixture by a standard spectrum of one of the components and then calculating the first derivative of the ratio spectrum. The first derivative of the ratio amplitudes at 250.4 and 291.5 nm for OLM, 250.4 and 298.1 nm for ZOF and 231.8, 332.2, 232.3 and 280.4 nm for HCT were selected for the determination. The proposed methods were successfully applied for determining of both drug combinations (ZOF-HCT and OLM-HCT) in their synthetic mixtures and in pharmaceutical dosage forms. The described procedures are extensively validated, non-destructive and do not require any separation steps. © 2014, Pleiades Publishing, Ltd.

A stability-indicating RP-LC assay method was developed for the simultaneous determination of the cardiovascular drugs amlodipine and perindopril in the presence of degradation products generated from forced decomposition studies. The developed method is applicable for the determination of related substances in bulk drugs and simultaneous assay in a tablet pharmaceutical dosage form. Separation of the drugs and their degradation products was obtained using an RP Waters Spherisorb ODS1 column (250 × 4.6 mm id, 5 μm particle size) with the mobile phase acetonitrile–water (30 + 70, v/v) containing 15 mM phosphoric acid. The pH of the mobile phase was adjusted to 5.0. A flow rate of 1.2 mL/min was used for the separations, with detection at 215 nm. The chromatographic separation was performed at a column temperature of 45°C. Atenolol was chosen as the internal standard. Amlodipine and perindopril were exposed to thermal, photolytic, hydrolytic, and oxidative stress conditions, and the stressed samples were analyzed by the proposed method. Degradation studies showed that both compounds were degraded under these stress conditions. The method was found to be stability-indicating and can be used for the routine analysis of amlodipine and perindopril in the studied combined tablet dosage form.

Voltammetric, chromatographic, and spectrophotometric methods were developed for the simultaneous determination of bisoprolol fumarate (BIS) and hydrochlorothiazide (HCZ). Differential pulse and square wave voltammetry techniques were used to analyze BIS and HCZ simultaneously by measuring at about 1400 and 1100 mV, respectively. RP-HPLC was the second method for simultaneous analysis of the compounds. The mixture of BIS, HCZ, and moxifloxacin as an internal standard was separated on an RP Zorbax Eclipse XDB-C18 column (150 × 4.6 mm, id, 5 μm particle size) using acetonitrile–15 mM phosphate (25 + 75, v/v) mobile phase at a 1.0 mL/min flow rate. The third method was based on first derivative of the ratio-spectra method obtained from the measurements of the amplitudes at 246 and 257 nm for BIS and HCZ, respectively. All the proposed methods were effectively applied for the simultaneous determination of BIS and HCZ in tablet dosage forms without any time-consuming extraction, sample preparation, or derivatization procedures.

Two reversed phase liquid chromatographic (RP-LC) techniques are presented for the rapid, accurate, precise, simultaneous determination of olmesartan-hydrochlorothiazide and zofenopril-hydrochlorothiazide binary mixtures in their dosage forms. The separation of these binary mixtures was carried out by using two new stationary phases that have different surface chemistries which were used for the first time in the determination of these binary mixtures. The analyte peaks were detected at 216nm. Linearity was obtained in different concentration ranges between 0.5 and 20?gmL-1 for all compounds. The proposed methods have been extensively validated and sample preparation, flow rate, run time of the analytical systems were at low levels. The proposed methods would decrease the consumption of organic solvents and reagents further safeguarding to our environment. © 2012 Elsevier B.V.

PubMed ID: 22483669 The detailed electrooxidative behavior of benidipine (BEN) has been studied by using glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Using cyclic voltammetry, depending on the pH values and the working electrodes, BEN showed one or two sharp and irreversible oxidation responses. The voltammetric experiments on some model compounds allowed elucidation of the oxidation mechanism of BEN. Highly sensitive, selective, rapid, and fully validated voltammetric methods for the determination of BEN in tablet dosage form were also presented. Under optimized conditions, the peak current showed a linear dependence with concentration in the range between 3.25?gmL -1 and 54.20?gmL -1 for GC and 1.08?gmL -1 and 54.20?gmL -1 for BDD electrodes by using differential pulse (DPV) and square wave (SWV) voltammetric techniques. In this study, acid dissociation constant (pK a) value of BEN was determined by using the dependence of the retention factor on the pH of the mobile phase using reverse phase-liquid chromatographic (RP-LC) method. The effect of the composition of the mobile phase on the ionization constant was studied by measuring the pK a at different acetonitrile-water mixtures, ranging between 50 and 65% (v/v). Also simple, accurate, precise and fully validated RP-LC method for the assay of BEN in dosage form has been developed. XTerra RP-18 column at 25°C with the mobile phase of acetonitrile:water 55:45 (v/v) adjusted to pH 3.0 with 15mM o-phosphoric acid was used. Isocratic elution was performed in less than 5.0min with a flow rate of 1.0mLmin -1. The RP-LC method allowed quantitation over the 0.25-15.00?gmL -1 range for BEN. The proposed voltammetric and RP-LC methods allow a number of cost and time saving benefits. BEN was also exposed to thermal, photolytic, oxidative stress, acid-base catalyzed hydrolyses, and the stressed samples were detected by the proposed RP-LC method. © 2012 Elsevier B.V.

The pK a values of cefdinir and cefixime, which are used in the treatment of bacterial infections, have been determined precisely in water and methanol–water binary mixtures (20% v/v) using spectrophotometric titration and LC, respectively. A simple, fast and precise isocratic high-performance liquid chromatographic (LC) procedure has been developed for the determination of cefdinir and cefixime in drug formulations. This method was validated successfully for specificity, precision, linearity, range, accuracy, limit of detection, and limit of quantitation as per the ICH guidelines. The proposed method can be used for routine analysis of studied cephalosporin compounds and as an alternative tool for drug quality control laboratories.

In this study, pKa values were determined using the dependence of the retention factor on the pH of the mobile phase for three ionizable substances, namely, enalapril, lercanidipine and ramipril (IS). The effect of the mobile phase composition on the ionization constant was studied by measuring the pKa at different methanol-water mixtures, ranging between 50 and 65% (v/v), using LC-DAD method. Two simple, accurate, precise and fully validated analytical methods for the simultaneous determination of enalapril and lercanidipine in combined dosage forms have been developed. Separation was performed on an X-Terra RP-18 column (250 mm × 4.60 mm ID × 5 μm) at 40 °C with the mobile phase of methanol-water 55:45 (v/v) adjusted to pH 2.7 with 15 mM orthophosphoric acid. Isocratic elution was performed in less than 12 min with a flow rate of 1.2 mL min-1. Good sensitivity for the analytes was observed with DAD detection. The LC method allowed quantitation over the 0.50-20.00 μg mL-1 range for enalapril and lercanidipine. The second method depends on first derivative of the ratio-spectra by measurements of the amplitudes at 219.7 nm for enalapril and 233.0 nm for lercanidipine. Calibration graphs were established for 1-20 μg mL-1 for enalapril and 1-16 μg mL-1 lercanidipine, using first derivative of the ratio spectrophotometric method. Both methods have been extensively validated. These methods allow a number of cost and time saving benefits. The described methods can be readily utilized for analysis of pharmaceutical formulations. The methods have been applied, without any interference from excipients, for the simultaneous determination of these compounds in tablets. There was no significant difference between the performance of the proposed methods regarding the mean values and standard deviations. © 2010 Elsevier B.V. All rights reserved.

Fosamprenavir is a pro-drug of the antiretroviral protease inhibitor amprenavir and is oxidizable at solid electrodes. The anodic oxidation behavior of fosamprenavir was investigated using cyclic and linear sweep voltammetry at boron-doped diamond and glassy carbon electrodes. In cyclic voltammetry, depending on pH values, fosamprenavir showed one sharp irreversible oxidation peak or wave depending on the working electrode. The mechanism of the oxidation process was discussed. The voltammetric study of some model compounds allowed elucidation of the possible oxidation mechanism of fosamprenavir. The aim of this study was to determine fosamprenavir levels in pharmaceutical formulations and biological samples by means of electrochemical methods. Using the sharp oxidation response, two voltammetric methods were described for the determination of fosamprenavir by differential pulse and square-wave voltammetry at the boron-doped diamond and glassy carbon electrodes. These two voltammetric techniques are 0.1 M H2SO4 and phosphate buffer at pH 2.0 which allow quantitation over a 4×10-6 to 8×10 -5 M range using boron-doped diamond and a 1×10-5 to 1×10-4 M range using glassy carbon electrodes, respectively, in supporting electrolyte. All necessary validation parameters were investigated and calculated. These methods were successfully applied for the analysis of fosamprenavir pharmaceutical dosage forms, human serum and urine samples. The standard addition method was used in biological media using boron-doped diamond electrode. No electroactive interferences from the tablet excipients or endogenous substances from biological material were found. The results were statistically compared with those obtained through an established HPLC-UV technique; no significant differences were found between the voltammetric and HPLC methods. © 2009 Springer-Verlag.