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 mu g/mL in sodium hydroxide electrolyte as well as low detection limit (0.39 mu g/mL) and a good repeatability (RSD = 3.4% for 264 mu g/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 mu g/mL and a detection limit of 2.6 mu g/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.

Simultaneous analysis of five antidepressant drugs using direct injection of biofluids in a capillary restricted-access media-liquid chromatography-tandem mass spectrometry system

Direct analysis, with minimal sample pretreatment, of antidepressant drugs, fluoxetine, imipramine, desipramine, amitriptyline, and nortriptyline in biofluids was developed with a total run time of 8 min. The setup consists of two HPLC pumps, injection valve, capillary RAM-ADS-C18 pre-column and a capillary analytical C 18 column connected by means of a six-port valve in backflush mode. Detection was performed with ESI-MS/MS and only 1 mu m of sample was injected. Validation was adequately carried out using FLU-d(5) as internal standard. Calibration curves were constructed under a linear range of 1-250 ng mL(-1) in plasma, being the limit of quantification (LOQ), determined as 1 ng mL(-1), for all the analytes. With the described approach it was possible to reach a quantified mass sensitivity of 0.3 pg for each analyte (equivalent to 1.1-1.3 fmol), translating to a lower sample consumption (in the order of 103 less sample than using conventional methods). (C) 2008 Elsevier B.V. All rights reserved.

Determination of amino acids by capillary electrophoresis-electrospray ionization-mass spectrometry: An evaluation of different protein hydrolysis procedures

In this work, a CE equipment, online hyphenated to an IT MS analyzer by a linear sheath liquid interface promoting ESI, was used to develop a method for quantitative determination of amino acids. Under appropriate conditions (BGE composition, 0.8% HCOOH, 20% CH(3)OH; sheath liquid composition, 0.8% HCOOH, 60% methanol; V(ESI), +4.50 W), analytical curves of all amino acids from 3 to 80 mg/L were recorded presenting acceptable linearity (r > 0.99). LODs in the range of 16-172 mu mol/L were obtained. BSA, a model protein, was submitted to different hydrolysis procedures (classical acid and basic, and catalyzed by the H(+) form of a cation exchanger resin) and its amino acid profiles determined. In general, the resin-mediated hydrolysis yields were overall similar or better than those obtained by classical acid or basic hydrolysis. The resulting experimental-to-theoretical BSA concentration ratios served as correction factors for the quantitation of amino acids in Brazil nut resin generated hydrolysates.

Determination of fluoroacetate and fluoride in blood serum by capillary zone electrophoresis using capacitively coupled contactless conductivity detection

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Formation of bright solitons and soliton trains in a fermion-fermion mixture by modulational instability

We employ a time- dependent mean- field- hydrodynamic model to study the generation of bright solitons in a degenerate fermion - fermion mixture in a cigar- shaped geometry using variational and numerical methods. Due to a strong Pauli- blocking repulsion among identical spin- polarized fermions at short distances there cannot be bright solitons for repulsive interspecies interactions. Employing a linear stability analysis we demonstrate the formation of stable solitons due to modulational instability of a constant-amplitude solution of the model equations for a sufficiently attractive interspecies interaction. We perform a numerical stability analysis of these solitons and also demonstrate the formation of soliton trains by jumping the effective interspecies interaction from repulsive to attractive. These fermionic solitons can be formed and studied in laboratory with present technology.

On local analysis of oscillations of a non-ideal and non-linear mechanical model

It is of major importance to consider non-ideal energy sources in engineering problems. They act on an oscillating system and at the same time experience a reciprocal action from the system. Here, a non-ideal system is studied. In this system, the interaction between source energy and motion is accomplished through a special kind of friction. Results about the stability and instability of the equilibrium point of this system are obtained. Moreover, its bifurcation curves are determined. Hopf bifurcations are found in the set of parameters of the oscillating system.

Indirect determination of chloride and sulfate ions in alcohol fuel by capillary electrophoresis

A capillary zone electrophoresis method using indirect UV detection for the analysis of chloride and sulfate in alcohol fuel samples was developed. The anions were analyzed in less than 3 min using an electrolyte containing 10 mmol 1(-1) chromate and 0.75 mmol 1(-1) hexamethonium bromide (HMB) as electroosmotic flow modifier. Coefficients of variation were better than 0.6% for migration time (n = 10) and between 2.05 and 2.82% for peak area repeatabilities. Analytical curves of peak area versus concentration in the range of 0.065-0.65 mg kg(-1) for chloride and 0.25-4.0 mg kg(-1) for sulfate were linear with coefficients of correlation higher than 0.9996. The limits of detection for sulfate and chloride were 0.033 and 0.041 mg kg(-1), respectively. Recovery values ranged from 85 to 103%. The method was successfully applied for the quantification of sulfate and chloride in five alcohol fuel samples. The concentration of sulfate varied from 0.45 to 3.12 mg kg(-1). Chloride concentrations were below the method's LOD.

Active flutter suppression in a 2-D airfoil using linear matrix inequalities techniques

Flutter is an in-flight vibration of flexible structures caused by energy in the airstream absorbed by the lifting surface. This aeroelastic phenomenon is a problem of considerable interest in the aeronautic industry, because flutter is a potentially destructive instability resulting from an interaction between aerodynamic, inertial, and elastic forces. To overcome this effect, it is possible to use passive or active methodologies, but passive control adds mass to the structure and it is, therefore, undesirable. Thus, in this paper, the goal is to use linear matrix inequalities (LMIs) techniques to design an active state-feedback control to suppress flutter. Due to unmeasurable aerodynamic-lag states, one needs to use a dynamic observer. So, LMIs also were applied to design a state-estimator. The simulated model, consists of a classical flat plate in a two-dimensional flow. Two regulators were designed, the first one is a non-robust design for parametric variation and the second one is a robust control design, both designed by using LMIs. The parametric uncertainties are modeled through polytopic uncertainties. The paper concludes with numerical simulations for each controller. The open-loop and closed-loop responses are also compared and the results show the flutter suppression. The perfomance for both controllers are compared and discussed. Copyright © 2006 by ABCM.

Determination of 2-methylimidazole and 4-methylimidazole in caramel colors by capillary electrophoresis

The use of chemical preservative compounds is common in the food products industry. Caramel color is the most usual additive used in beverages, desserts, and breads worldwide. During its fabrication process, 2- and 4-methylimidazole (MeI), highly carcinogenic compounds, are generated. In these cases, the development of reliable analytical methods for the monitoring of undesirable compounds is necessary. The primary procedure for the analysis of 2- and 4-MeI is using LC- or GC-MS techniques. These procedures are time-consuming and require large amounts of organic solvents and several pretreatment steps. This prevents the routine use of this procedure. This paper describes a rapid, efficient, and simple method using capillary electrophoresis (CE) for the separation and determination of 2- and 4-MeI in caramel colors. The analyses were performed using a 75 μm i.d. uncoated fused-silica capillary with an effective length of 40 cm and a running electrolyte consisting of 160 mmol L-1 phosphate plus 30% acetonitrile. The pH was adjusted to 2.5 with triethylamine. The analytes were separated within 6 min at a voltage of 20 kV. Method validation revealed good repeatability of both migration time (<0.8% RSD) and peak area (<2% RSD). Analytical curves for 2- and 4-MeI were linear in the 0.4-40 mg L-1 concentration interval. Detection limits were 0.16 mg L-1 for 4-MeI and 0.22 mg L-1 for 2-MeI. The extraction recoveries were satisfactory. The developed method showed many advantages when compared to the previously used method. © 2013 American Chemical Society.

Quantum versus classical instability of scalar fields in curved backgrounds

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Validation of a stability indicating capillary electrophoresis method for the determination of darunavir in tablets and comparison with the of infrared absorption spectroscopic method

Darunavir (DRV) is a protease inhibitor used in the treatment of HIV infection, which constitutes a keystone in the therapy of patients infected with this virus. There is no monograph described in official compendia. The literature provides few methods of analysis for the determination of DRV in pharmaceuticals which include TLC, IR, UPLC, HPLC, HPLC-MS, HPLC-MS/MS, but there are no reports of the use of capillary electrophoresis (CE) for the determination of this drug. Thus, this research proposed the development and validation of a CE method for the determination of DRV in tablets. The method was completely validated according to the International Conference on Harmonization guidelines, showing linearity, selectivity, precision, accuracy and robustness. The migration was achieved in less than 1 minute using fused-silica uncoated capillary with an id of 50 μm and total length of 21 cm and voltage of +20 kV. The sample injection was performed in the hydrodynamic mode. The method was linear over the concentration range of 50-200 μg mL-1 with correlation coefficient 0.9998 and limits of detection and quantification of 7.29 and 22.09 μg mL-1, respectively. The drug was subjected to acid, base, oxidation and photolysis degradation. Degradation products were found interfering with the assay of DRV, therefore the method can be regarded as stability indicating. The validated method is useful and appropriate for the routine quality control of DRV in tablets.

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 mu g mL(-1) in acetate buffer solution and a detection limit of 0.11 mu g 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 mu mol 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. (C) 2012 Elsevier B.V. All rights reserved.

Capillary electrophoretic enantioselective determination of zopiclone and its impurities

A capillary electrophoretic enantioselective method with UV detection was developed and validated for the simultaneous quantification of zopiclone enantiomers and its impurities, zopiclone-N-oxide enantiomers, and 2-amino-5-chloropyridine, in tablets. The analytes were extracted from the tablets using ACN and were separated in an uncoated fused-silica capillary (50 mu m, 42 cm effective length, 50 cm total length) using 80 mM sodium phosphate buffer pH 2.5 and 5 mM carboxymethyl-beta-cyclodextrin as running buffer. The analytes and the internal standard (trimethoprim) were detected at 305 and 200 nm, respectively. A voltage of 27 kV was applied and the capillary temperature was maintained at 25 degrees C. All enantiomers were analyzed within 8 min and linear calibration curves over the concentration range of 0.40.8 mg mL-1 for each zopiclone enantiomer, 0.81.6 mu g mL-1 for 2-amino-5-chloropyridine and 0.40.8 mu g mL-1 for each zopiclone-N-oxide enantiomer were obtained. The coefficients of correlation obtained for the linear curves were greater than 0.99. The intra-day and inter-day accuracy and precision were lower than 2% for all analytes. This validated method was employed to study the degradation and racemization of zopiclone under stress conditions. This application demonstrated the importance of a stability-indicating assay method for this drug.

Stability-indicating methods for the enantioselective determination of dihydropyridines by high performance liquid chromatography and capillary electrophoresis

This paper presents simple, rapid, precise and accurate stability-indicating HPLC and CE methods, which were developed and validated for the determination of nitrendipine, nimodipine and nisoldipine. These drugs are calcium channel antagonists of the 1,4-dihydropyridine type which are used in the treatment of cardiovascular diseases. Experimental results showed a good linear correlation between the area and the concentration of drugs covering a relatively large domain of concentration in all cases. The linearity of the analytical procedures was in the range of 2.0-120.0 mu g mL-1 for nitrendipine, 1.0-100.0 mu g mL(-1) for nimodipine and 100.0-600.0 mu g mL(-1) for nisoldipine, the regression determination coefficient being higher than 0.99 in all cases. The proposed methods were found to have good precision and accuracy. The chemical stability of these drugs was determined under various conditions and the methods have shown adequate separation for their enantiomers and degradation products. In addition, degradation products produced as a result of stress studies did not interfere with the detection of the drugs' enantiomers and the assays can thus be considered stability-indicating.

Morphological instability analysis of a misfit strained core-shell nanowire for the growth of quantum dots

Nell'ambito delle nanostrutture, un ruolo primario è svolto dai punti quantici. In questo lavoro siamo interessati all'analisi teorica del processo di creazione dei punti quantici: esso può avvenire per eteroepitassia, in particolare secondo il metodo studiato da Stranski-Krastanov. Un film di Germanio viene depositato su un substrato di Silicio in modo coerente, cioè senza dislocazioni, e, a causa del misfit tra le maglie dei due materiali, c'è un accumulo di energia elastica nel film. A una certa altezza critica questa energia del film può essere ridotta se il film si organizza in isole (punti quantici), dove la tensione può essere rilassata lateralmente. L'altezza critica dipende dai moduli di Young (E, υ), dal misfit tra le maglie (m) e dalla tensione superficiali (γ). Il trasporto di materiale nel film è portato avanti per diffusione superficiale. Il punto focale nell'analisi delle instabilità indotte dal misfit tra le maglie dei materiali è la ricerca delle caratteristiche che individuano il modo di crescita più rapido dei punti quantici. In questo lavoro siamo interessati ad un caso particolare: la crescita di punti quantici non su una superficie piana ma sulla superficie di un nanofilo quantico a geometria cilindrica. L'analisi delle instabilità viene condotta risolvendo le equazioni all'equilibrio: a tal fine sono state calcolate le distribuzioni del tensore delle deformazioni e degli sforzo di un nanofilo core-shell con una superficie perturbata al primo ordine rispetto all'ampiezza della perturbazione. L'analisi è stata condotta con particolari condizioni al contorno ed ipotesi geometriche, e diverse scelte dello stato di riferimento del campo degli spostamenti. Risolto il problema elastico, è stata studiata l'equazione dinamica di evoluzione descrivente la diffusione di superficie. Il risultato dell'analisi di instabilità è il tasso di crescita in funzione del numero d'onda q, con diversi valori del raggio del core, spessore dello shell e modo normale n, al fine di trovare il più veloce modo di crescita della perturbazione.