Spectrofluorimetric determination of fexofenadine hydrochloride in pharmaceutical preparation using silver nanoparticles

A novel sensitive fluorimetric method was investigated for the assay of fexofenadine hydrochloride (FEX) using silver nanoparticles (NPs) as a fluorescence probe. The NPs, which were prepared by chemical reduction of silver nitrate with sodium borohydride (reducing agent) in aqueous solution (without organic stabilizers) were water soluble, stable and had narrow emission band. The addition of drug to NPs solution caused considerable quenching of the emission band of silver NPs, which was likely due to the complexation of the drug to silver NPs. Under the optimum conditions, the quenched fluorescence (FL) intensity was linear with the concentration of FEX in the range of 1 × 10^?7 to 2.5 × 10^?5 mol L^?1 (0.9985) with a detection limit of 1.2 × 10^?8 mol L^?1. The quenching mechanism of the studied drug on the emission band of silver NPs was explained by Stern–Volmer law. The developed method was applied to FEX determination in a pharmaceutical formulation (allegra tablets) and biological fluids (human serum and urine).     

Validated voltammetric method for the determination of some antiprotozoa drugs based on the reduction at an activated glassy carbon electrode

A sensitive electrochemical procedure based on reduction of secnidazole (I), tinidazole (II) and ornidazole (III) at a glassy carbon electrode (GCE) was introduced. A study of the variation of the peak current with solution variables such as pH, ionic strength, concentration of drugs, possible interference, and instrumental variables such as scan rate, pulse amplitude, preconcentration time, accumulation potential, has resulted in the optimization of the reduction signal for analytical purposes. Linear calibration plots were obtained over the concentration ranges of 50–800, 50–750 μg mL^?1 for I, and both (II, III) respectively, in Britton–Robinson buffer of pH 7. The relative standard deviations of five replicate measurements of 1.0 and 10.0 μg mL^?1 of I, II and III concentrations were 4.7%, 4.9% and 5.3%, and 2.2%, 2.6% and 2.8%, respectively. The limits of detection (LOD) for I, II and III were found to be 2 × 10^?10, 3 × 10^?10 and 2.5 × 10^?10 mol L^?1 and limits of quantification (LOQ) for I, II and III were found to be 4.0 × 10^?8, 1.2 × 10^?8 and 4.4 × 10^?8 mol L^?1, respectively. The optimal conditions were: E_acc = ?0.9 V, t_acc = 30 s, scan rate = 20 mV s^?1, pulse-height = 90 mV and Britton–Robinson buffer of pH 7. The method was applied for the determination of the cited drugs both in raw materials and in pharmaceutical preparations with satisfactory results and compared with the official reference method. Complete validation of the proposed method was also done.     

Flow injection potentiometric sensor for determination of phenylpropanolamine hydrochloride

A new polymeric membrane electrode has been constructed for the determination of phenylpropanolamine hydrochloride. The electrode was prepared by solubilizing the phenylpropanolamine-phosphomolybdate ion associate into a polyvinyl chloride matrix plasticized by dibutylphthalate as a solvent mediator. The electrode showed near-Nernstian response over the concentration range of 1 × 10^?5–1 × 10^?2 M with low detection limit of 6.3 × 10^?6 M. The electrode displays a good selectivity for phenylpropanolamine with respect to a number of common inorganic and organic species. The electrode was successfully applied to the potentiometric determination of phenylpropanolamine ion in its pure state and its pharmaceutical preparation in batch and flow injection conditions.     

Selective determination of trichloroacetic acid using silver nanoparticle coated multi-walled carbon nanotubes

Silver nanoparticle coated multi-walled carbon nanotubes (Ag/MWCNT) were prepared and used to fabricate a modified electrode. The Ag/MWCNT composites were observed by a transmission electron microscope (TEM), and the electrochemical properties of the Ag/MWCNT composite modified glassy carbon electrode were characterized by electrochemical measurements. The results showed that these composites had a favorable catalytic ability for the reduction of trichloroacetic acid (TCAA). Square wave voltammetric (SWV) technique was applied to detect TCAA. Under optimum conditions, the voltammetric determination of TCAA was performed with a linear range of 5.0 × 10^? 6–1.2 × 10^? 4 mol L^? 1 and a detection limit of 1.9 × 10^? 6 mol L^? 1 (S/N = 3).     

A simple fluorescence quenching method for berberine determination using water-soluble CdTe quantum dots as probes

A novel method for the determination of berberine has been developed based on quenching of the fluorescence of thioglycolic acid-capped CdTe quantum dots (TGA-CdTe QDs) by berberine in aqueous solutions. Under optimum conditions, the relative fluorescence intensity was linearly proportional to the concentration of berberine between 2.5 × 10^?8 and 8.0 × 10^?6 mol L^?1 with a detection limit of 6.0 × 10^?9 mol L^?1. The method has been applied to the determination of berberine in real samples, and satisfactory results were obtained. The mechanism of the proposed reaction was also discussed.     

UV-absorption and fluorimetric methods for the determination of alprazolam in pharmaceutical formulation

The development of UV and fluorescence spectrophotometric methods for the quantitative determination of alprazolam in dosage forms using As(III)?SDS system. The two simple and sensitive, spectrophotometric and spectrofluorimetric methods were developed for the determination of alprazolam (ALP) in tablets. These methods are based on formation of ALP?As(III) complex in the presence of SDS. The UV-spectrum of 30% methanolic solution of ALP (5 × 10^?5 M) at pH 6.5 (Mclivaine buffer) was run between 200 and 380 nm. The absorption spectrum of ALP exhibits two peaks with a λ_max. at 255 nm and a weak band at 325 nm. When the spectra of the drug were run at varying pH in the region 200–380 nm, one isosbestic point at 290 nm was observed, which indicated the presence of two ionic conditions in solution. The complex exhibited an absorption maximum at 265 nm and emission peak at 520 nm with respect to the excitation wavelength of 325 nm. The spectrophotometric method was found to be linear in 8.0–17.0 μg ml^?1 range with detection limit of 13.520 μg ml^?1, while 0.05–9.5 μg ml^?1 range was with detection limit of 1.048 × 10^?2 μg ml^?1 by spectrofluorimetric method. The mean percentage recovery of the added quantity was found to be 99.54 (spectrophotometric method) and 100.22 (spectrofluorimetric method) and the %RSD are lower than 0.478 and 0.296 determined spectrophotomerically and spectrofluorimtrically, respectively. This indicates that the proposed method is accurate. The apparent ionization constant of ALP was found to be 9.29. The spectra, experimental conditions were set followed by determination stoichiometry, stability constant and thermodynamic parameters of the As(III), Co(II), Ni(II), and Zn(II) complexes with ALP at pH 6.5. The proposed methods have been successfully applied to the assay of ALP in tablets and the results were statistically evaluated.     

Determination of zinc by square-wave adsorptive stripping voltammetry using alizarin as a chelating agent

The adsorptive collection of zinc(II) complex with alizarin ligand, coupled with the square-wave voltammetric technique at the hanging mercury drop electrode, yields a very sensitive electroanalytical procedure for the determination of zinc. The optimized experimental conditions include: supporting electrolyte (carbonate buffer), pH (11), alizarin concentration (1 × 10^?6 mol l^?1), accumulation time (60 s), accumulation potential (?0.1 V), scan rate (700 mV s^?1), pulse amplitude (0.06 V) and SW frequency (80 Hz). The monitored stripping voltammetric current was linear over the range of 5 × 10^?8 – 4 × 10^?7 mol l^?1 and the detection limit was 1 × 10^?8 mol l^?1. The relative standard deviation was calculated as 1.3% (n = 10) for 1 × 10^?8 mol l^?1 Zn(II) and the obtained electrochemical signal was stabile for up to 60 min. Possible interferences by either co-existing metal ions or other chelating agents were also investigated. The applicability of the proposed SW-AdSV method to the analysis of foodstuff was assessed by the determination of zinc content in instant coffee samples. The accuracy of the obtained voltammetric analytical results was validated by comparing with that obtained by atomic absorption spectrometric method and conducting the necessary statistical evaluation.     

Electrochemical determination of rosiglitazone by square-wave adsorptive stripping voltammetry method

Square-wave adsorptive stripping voltammetry technique was used to determine rosiglitazone (ROS) on the hanging mercury dropping electrode (HMDE) surface, in Britton Robinson buffer, pH = 5. The voltammetric cathodic peak was observed at ?1520 mV vs. Ag/AgCl reference electrode. The voltammetric peak response was characterized with respect to pH, supporting electrolyte, accumulation potential, preconcentration time, scan rate, frequency, pulse amplitude, surface area of the working electrode and the convection rate. Under optimal conditions, the voltammetric current is proportional to the concentration of ROS over the concentration range of 5 × 10^?8–8 × 10^?7 mol l^?1 (r = 0.9899) with a detection limit of 3.2 × 10^?11 mol l^?1 using 120 s accumulation time. The developed SW-AdSV procedure showed a good reproducibility, the relative standard deviation RSD% (n = 10) at a concentration level of 5 × 10^?7 mol l^?1 was 0.33%, whereas the accuracy was 101% ± 1.0. The proposed method was successfully applied to assay the drug in the human urine and plasma samples with mean recoveries of 90 ± 0.71% and 86 ± 1.0%, respectively.     

Flow-injection chemiluminescence determination of dihydralazine sulfate in serum using luminol and diperiodatocuprate (III) system

A novel flow-injection chemiluminescence (CL) method for the determination of dihydralazine sulfate (DHZS) is described. The method is based on the reaction of luminol and diperiodatocuprate (K₂[Cu(H₂IO₆)(OH)₂], DPC) in alkaline medium to emit CL, which is greatly enhanced by DHZS. The possible CL mechanism was first proposed based on the kinetic characteristic, CL spectrum and UV spectra. The optimum condition for the CL reaction was in detail studied using flow-injection system. The experiments indicated that under optimum condition, the CL intensity was linearly related to the concentration of DHZS in the range of 7.0 × 10^?9 to 8.6 × 10^?7 g mL^?1 with a detection limit (3σ) of 2.1 × 10^?9 g mL^?1. The proposed method had good reproducibility with the relative standard deviation 3.1% (n = 7) for 5.2 × 10^?8 g mL^?1 of DHZS. This method has the advantages of simple operation, fast response and high sensitivity. The special advantage of the system is that very low concentration of luminol can react with DPC catalyzed by DHZS to get excellent experiment results. And CL cannot be observed nearly when luminol with same concentration reacts with other oxidants, so luminol–DPC system has higher selectivity than other luminol CL systems. The method has been successfully applied to determine DHZS in serum.     

A simple and sensitive spectrophotometric method for the determination of trace amounts of nitrite in environmental and biological samples using 4-amino-5-hydroxynaphthalene-2,7-disulphonic acid monosodium salt

A very simple, sensitive, fairly selective and rapid spectrophotometric method for the determination of trace amounts of nitrite has been described. This method is based on the diazotized intramolecular coupling of electrophilic diazonium cation with the phenolic group of 4-amino-5-hydroxynaphthalene-2,7-disulphonic acid monosodium salt (AHNDMS) in a phosphate buffer solution of pH 7.5. The cyclic product has a purple color with maximum absorbance at 560 nm and is stable for 6 h. Optimum reaction conditions and other important analytical parameters for the maximum color development were established. Beer's law was found to obey for nitrite in the concentration range of 0.1–1.6 μg ml^?1 with molar absorptivity of 2.6 × 10⁴ l mol^?1 cm^?1 and Sandell's sensitivity of 0.0075 μg ml^?1. The effect of interfering ions on the determination is described. The recommended method was applied for the determination of nitrite in different water, soil and human saliva samples. The performance of the recommended method was evaluated in terms of Student's t-test and variance ratio F-test, which indicated the significance of proposed method over the reference method.     

A novel sensitive biosensor for Ca2+ based on electropolymerized melatonin modified electrode

An electropolymerized melatonin modified glassy carbon electrode (EPMT/GCE) was prepared by electrochemically polymerizing of melatonin in a 0.04 mol l^?1 perchloric acid solution. In KCl solution, Ca²⁺ was found to perform a reversible complex reaction on the EPMT/GCE to produce a sharp complex adsorption wave. The configuration of the electropolymerized membrane was characterized by scanning electron microscope and various electrochemical techniques. Based on which, a novel sensitive Ca²⁺ electrochemical sensor was established. The peak current showed a linear relationship with Ca²⁺ concentration in range of 6.2 × 10^?7–1.0 × 10^?4 mol l^?1 with detection limit of 4.5 × 10^?7 mol l^?1. The developed electrochemical sensor has been used for determination of Ca²⁺ in body fluid.     

Novel 4-carboxyphenyl-grafted screen-printed electrode for trace Cu(II) determination

This paper reports the interest of 4-carboxyphenyl-grafted screen-printed electrodes (4-CP-SPEs) for trace Cu(II) measurement in water samples. These novel sensors were easily prepared via electrochemically reduction of the corresponding diazonium salt. Detection of Cu(II) was then achieved by immersing the grafted electrode into the sample solution for 10 min, followed by the electrochemical measurement of accumulated metallic ions.The efficiency of the Cu(II) adsorption at the grafted layer was clearly demonstrated. 4-CP-SPEs were able to detect and quantify Cu(II) as low as 5 × 10^?9 and 10^?8 M in a large ionic strength range. Moreover, no major interference of Pb(II) in the determination of Cu(II) is expected in natural water. Electrodes were finally successfully applied for Cu(II) determination in tap water and in estuarine water demonstrating the convenience of such sensors for environmental analysis.     

Stability-indicating liquid chromatography for determination of clopidogrel bisulfate in tablets: Application to content uniformity testing

The present study describes a simple stability-indicating reversed-phase HPLC assay for antiplatelet drug, clopidogrel bisulfate. Separation of the drug and the degradation products, under stress conditions was successfully achieved on a C-18 column utilizing 0.01 M Na₂HPO₄ (pH 4): acetonitrile in the ratio 80:20 v/v, pumped at a flow rate of 0.5 ml min^?1 with UV detection at 235 nm. The retention time of clopidogrel was 6.84 min. The method was satisfactorily validated with respect to linearity, precision, accuracy, selectivity, sensitivity and ruggedness. The response was linear in the range of 0.2–3.5 μg ml^?1 with detection limit 0.079 μg ml^?1. The suggested method was successfully applied for the analysis of clopidogrel in bulk and in commercial tablets. The results were favorably compared to those obtained by a reference method. The proposed method was successfully applied to the content uniformity testing of tablets and for determination of clopidogrel in presence of its co-administered drug, acetyl salicylic acid.     

Molecular interaction of organic dyes in bulk and confined media

Molecular interactions of five thiazine dyes with increasing alkyl substitution have been studied in aqueous and microemulsion media at 303 K within a concentration range of (1.35–7.00) × 10^?4 M. The dimerization constant (K_d) values for the five dyes are ranged between 1.761 and 6.258 × 10³ l mol^?1 in bulk water media, where as in microemulsion media, K_d's are ranged between 1.760 and 4.110 × 10³ l mol^?1. Thionine (with no methyl substitution) and azure A (with two methyl substitution) displayed slightly larger K_d values in microemulsion water pools compared to bulk water while other dyes recorded significant drop in K_d values. The influence of microemulsion media on the molecular interaction of dyes has been explained in terms of electrostatic and hydrophobic factors. The monomer and the dimer spectra are explained in terms of molecular exciton model and the optical absorption parameters of both the species are reported in bulk and confined media.     

Utilization of oxidation reactions for the spectrophotometric determination of captopril using brominating agents

Three simple, accurate and sensitive methods (A–C) for the spectrophotometric assay of captopril (CPL) in bulk drug, in dosage forms and in the presence of its oxidative degradates have been described. The methods are based on the bromination of captopril with a solution of excess brominating mixture in hydrochloric acid medium. After bromination, the excess brominating mixture is followed by the estimation of surplus bromine by three different reaction schemes. In the first method (A), the determination of the residual bromine is based on its ability to bleach the indigo carmine dye and measuring the absorbance at 610 nm. Method B, involves treating the unreacted bromine with a measured excess of iron(II) and the remaining iron(II) is complexed with 1,10-phenanthroline and the increase in absorbance is measured at 510 nm. In method (C), the surplus bromine is treated with excess of iron(II) and the resulting iron(III) is complexed with thiocyanate and the absorbance is measured at 478 nm. In all the methods, the amount of bromine reacted corresponds to the drug content. The different experimental parameters affecting the development and stability of the color are carefully studied and optimized. Beer's law is valid within a concentration range of 0.4–6.0, 0.4–2.8 and 1.2–4.8 μg mL^?1 for methods A, B and C, respectively. The calculated apparent molar absorptivity was found to be 5.16 × 10⁴, 9.95 × 10⁴ and 1.74 × 10⁵ L mol^?1 cm^?1, for methods A, B and C, respectively. Sandell's sensitivity, correlation coefficients, detection and quantification limits are also reported. No interference was observed from common additives found in pharmaceutical preparations. The proposed methods are successfully applied to the determination of CPL in the tablet formulations with mean recoveries of 99.94–100.11% and the results were statistically compared with those of a reference method by applying Student's t- and F-test.     

Study on β-cyclodextrin inclusion of Zn(II) aromatic complex and its analytical application

A new β-cyclodextrin (β-CD) inclusion compound Zn(2H1NA)₂·2β-CD (2H1NA = 2-hydroxy-1-naphthoic acid) was prepared. The structure was characterized by ¹H NMR, IR, the fluorescence spectra, thermogravimetric analysis (TG–DTA) and elementary analysis. Meanwhile, the mechanism of the formation of the supramolecular system (2H1NA:Zn(II):β-CD) was studied and discussed by spectrofluorimetry. The results showed that the naphthalene rings of the Zn(II) aromatic complex Zn(2H1NA)₂ were encapsulated within the β-CD's cavity to form a 2:1 stoichiometry host–guest compound. The inclusion constant calculated was 1.27 × 10⁴ (L/mol)². A spectrofluorimetric method for the determination of 2H1NA in bulk aqueous solution in the presence of β-CD was developed based on the great enhancement of the fluorescence intensity of 2H1NA. The linear relationship was obtained in the range of 9.00 × 10^?7 to 2.50 × 10^?5 mol/L and the detection limit was 8.00 × 10^?7 mol/L. The proposed method was successfully applied to determine 2H1NA in waste water with recoveries of 97–104%.     

Zinc(II) selective poly(vinyl chloride) membrane ISE using a macrocyclic compound 1,12,14-triaza-5,8-dioxo-3(4),9(10)-dibenzoylcyclopentadeca-1,12,14-triene as neutral carrier

The potentiometric response characteristics of zinc ion selective PVC-based membrane electrode employing 1,12,14-triaza-5,8-dioxo-3(4),9(10)-dibenzoyl-1,12,14-triene as an inophore was investigated. The proposed electrode exhibits a Nernstian behavior with a slope of 29.2 ± 0.4 mV per decade with a working concentration range of 1.3 × 10^?7–1.0 × 10^?1 mol L^?1 and a detection limit of 1.0 × 10^?8 mol L^?1. The membrane having the composition as TDODBCPT:O-NPOE:PVC:OA; 7:57:30:6 wt.% exhibits the best results. It has a fast response time of 7 s and can be used for at least 100 days without any considerable divergence in potential. The proposed electrode show good discrimination of Zn²⁺ ion from diverse ions. The potential response remains constant over a pH range of 3.5–9.2. The electrode found well work under laboratory conditions. The proposed sensor directly used for determination of zinc ions in human hair sample, wastewater and an indicator electrode with EDTA titration.     

Ultrasensitive flow-injection electrochemical method for detection of anticancer drug tamoxifen

This paper presents the optimization of instrumental and solution parameters for determination of tamoxifen in urine and plasma and formulation by fast Fourier transform square wave voltammetry (SWV) using a gold microelectrode in flow-injection system. The samples are subjected by the same buffer solution and are injected in the flow-injection apparatus. By applying a novel square wave voltammetry method to perform as a sensitive method the voltamograms are recorded. The method used for determination of tamoxifen by measuring the changes in admittance voltammogram of a gold ultramicroelectrode (in 0.05 mol L^?1 H₃PO₄ solution) caused by adsorption of the tamoxifen on the electrode surface. The best sensitivity was achieved using a frequency of 600 Hz and a medium composed of 0.05 mol L^?1 phosphate buffers at pH 2.0. The best performance was obtained with the pH value of 2, pulse amplitude 25 mV, frequency 600 Hz, accumulation potential of ?100 mV and accumulation time of 0.5 s. Furthermore, signal-to-noise ratio has significantly increased by application of discrete fast Fourier transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. Calibration plots are given for solutions containing 1.0 × 10^?11 to 3.0 × 10^?6 mol L^?1 of tamoxifen. The detection limit is calculated to be 3.0 × 10^?12 mol L^?1 (～2 pg mL^?1). The relative standard deviation at concentration 2.0 × 10^?8 M is 6.1% for five reported measurements.     

Synthesis and physical characterization of electrically conducting polymers of polynuclear aromatic sulfonyl compounds

Potentially useful conducting polymers of sulfonyl substituted phenanthrene derivatives and non-conducting linear polymers, such as, polystyrene and poly(N-vinylcarbazole) have been synthesized and characterized using IR, thermogravimetric and dielectric measurements. The phenanthrene-based benzene, naphthalene and biphenyl copolysulfones have also been prepared and characterized through these techniques. These pendant and backbone polymer sulfones have exceptionally high thermal stability and electrical conductivity, such that dc conductivity in the range 2.80 × 10^?16 to 2.82 × 10^?7 Ω^?1 cm^?1 and ac conductivity in the range 1.69 × 10^?7 to 2.10 × 10^?6 Ω^?1 cm^?1.     

A dysprosium nanowire modified carbon paste electrode for determination of levodopa using fast Fourier transformation square-wave voltammetry method

A new detection technique called the fast Fourier transform square-wave voltammetry (FFT-SWV) is based on the measurements of electrode admittance as a function of potential. The response of the detector (microelectrode) is fast, which makes the method suitable for most applications involving flowing electrolytes. The carbon paste electrode was modified by nanostructures to improve better sensitivity. The response is generated by a redox processes. The redox property of L-dopa was used for determination of it in human serum and urine samples. The support electrolyte that provided a more defined and intense peak current for L-dopa determination was at 0.05 mol l^?1 acetate buffer pH 7.0. Synthesized dysprosium nanowires make more effective surface like nanotubes [1], [2], [3], [4] so they are good candidates for using as a modifier for electrochemical reactions. The drug presented one irreversible oxidation peaks at 360 mV versus Ag/AgCl by modified nanowire carbon paste electrode which produced high current and reduced the oxidation potential about 80 mV.Furthermore, signal-to-noise ratio has significantly increased by application of discrete fast Fourier transform (FFT) method, background subtraction and two-dimensional integration of the electrode response over a selected potential range and time window. To obtain the much sensitivity the effective parameters such as frequency, amplitude and pH was optimized. As a result, C_DL of 4.0 × 10^?9 M and an LOQ of 7.0 × 10^?9 M were found for determination for L-dopa. A good recovery was obtained for assay spiked urine samples and a good quantification of L-dopa was achieved in a commercial formulation.