Spectrophotometric determination of bisoprolol in pharmaceutical preparations by charge transfer reactions

A simple, rapid and sensitive method for the spectrophotometric determination, of bisoprolol was developed. The proposed methods were based on the charge-transfer reactions of bisoprolol, as n-electron donor, with 7,7,8,8-tetracyanoqumodimethane (TCNQ) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as ??-acceptors to give highly colored complexes. The proposed methods were validated according to the ICH guidelines with respect to linearity, limit of detection, limit of quantification, accuracy, precision, recovery and specificity. Beer??s law is obeyed over the concentration ranges of 10?C60 and 10?C80 ??g/mL bisoprolol with TCNQ and DDQ, respectively. The proposed methods were successfully applied to the assay of bisoprolol in pharmaceutical preparations.     

Validated spectrophotometric method for the determination,spectroscopic characterization and thermal structural analysis of duloxetine with 1,2-naphthoquinone-4-sulphonate

A novel, selective, sensitive and simple spectrophotometric method was developed and validated for the determination of the antidepressant duloxetine hydrochloride in pharmaceutical preparation. The method was based on the reaction of duloxetine hydrochloride with 1,2-naphthoquinone-4-sulphonate (NQS) in alkaline media to yield orange colored product. The formation of this complex was also confirmed by UV-visible, FTIR, ¹H NMR, Mass spectra techniques and thermal analysis. This method was validated for various parameters according to ICH guidelines. Beer’s law is obeyed in a range of 5.0–60 μg/mL at the maximum absorption wavelength of 480 nm. The detection limit is 0.99 μg/mL and the recovery rate is in a range of 98.10–99.57%. The proposed methods was validated and applied to the determination of duloxetine hydrochloride in pharmaceutical preparation. The results were statistically analyzed and compared to those of a reference UV spectrophotometric method.     

A Validated Spectrofluorimetric Method for the Determination of Citalopram in Bulk and Pharmaceutical Preparations Based on the Measurement of the Silver Nanoparticles-Enhanced Fluorescence of Citalopram/Terbium Complexes

A simple, sensitive, and accurate spectrofluorimetric method was developed for the determination of citalopram in bulk and pharmaceutical preparations. The method is based on the enhancement of the weak fluorescence signal (FL) of the Tb (III)-citalopram system in the presence of silver nanoparticles. Fluorescence intensities were measured at 555 nm after excitation at 281 nm. Prepared silver nanoparticles (AgNPs) were characterized by UV-Visible spectra and transmission electron microscopy (TEM). Various factors affecting the formation of citalopram-Tb (III)-AgNPs complexes were studied and optimized. The fluorescence intensity versus concentration plot was linear over the range 0.02–14 μg?mL^?1, with an excellent correlation coefficient of 0.9978. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 7.15?×?10^?6?μg?mL^?1 and 2.38?×?10^?5?μg?mL^?1 respectively. The proposed method was found to have good reproducibility with a relative standard deviation of 3.66 % (n?=?6). The interference effects of common excipients found in pharmaceutical preparations were studied. The developed method was validated statistically by performing recoveries studies and successfully applied for the assay of citalopram in bulk powder and pharmaceutical preparations. Percent recoveries were found to range from 98.98 % to 100.97 % for bulk powder and from 96.57 % to 101.77 % for pharmaceutical preparations.     

Development and Validation of a Spectrofluorimetric Method for the Determination of Erlotinib in Spiked Human Plasma

A rapid and sensitive spectrofluorimetric method was developed and validated for the determination of erlotinib (ETB), a potent anticancer drug, in spiked human plasma without any derivatization. The described method was validated and the analytical parameters of linearity, accuracy, precision (intra- and inter-day), limit of detection (LOD), and limit of quantification (LOQ) were evaluated. The relation between the fluorescence intensity and concentration was found to be linear (r² 0.9998) over the range 125 to 1000?ng/mL with the detection limit of 15?ng/mL. A simple liquid-liquid extraction method was followed in order to extract the drug from spiked plasma. The mean absolute recoveries of ETB were 85.59?% (±0.57), 86.91?% (±1.77) and 89.31?% (±3.01) at spiked plasma ETB concentration of 5000, 3750 and 2500?ng/mL, respectively. The spectrofluorimetric method presented here is a rapid, simple, specific, and reproducible method and can be used to characterize the plasma pharmacokinetics of ETB.     

Determination of Arsenic and Mercury in Chinese Medicinal Herbs by Atomic Fluorescence Spectrometry with Closed‐Vessel Microwave Digestion

Abstract

A simple method was developed for the determination of trace arsenic and mercury in Chinese medicinal herbs. The samples were digested in closed‐Teflon vessels in a microwave oven, and followed with hydride generation atomic fluorescence spectrometric measurements. The experimental conditions for the digestion were carefully optimized using an orthogonal design. The accuracy of the method was validated by recovery experiments, and the analytical results for arsenic in seven medicinal herbs (Codonopsis pilosula, Radix angelicae sinensis, Aconitum carmichaeli debx, crude aconite root, giant typhonium rhizome, Rhizoma typhonii, and Radix aconiti lateralis preparata) were found to agree well with those by inductively coupled plasma atomic emission spectrometry (ICP‐AES). The linear dynamic range of the calibration curve was in the range of 0.1–400 ng/mL for arsenic, and the correlation coefficient was better than 0.999. The limit of detection was 0.1 ng/mL for arsenic. For mercury, the determination was accomplished through mercury cold vapor generation in the same instrumental system. The linear dynamic range was 0.03–250 ng/mL, with a limit of detection of 0.03 ng/mL for mercury. This was a rapid, convenient, precise, and cost‐effective method.     

Simple and Sensitive Spectrofluorimetric Method for the Determination of Oseltamivir Phosphate in Capsules Through Derivatization with Fluorescamine

A new, simple and sensitive spectrofluorimetric method has been developed for the determination of oseltamivir phosphate (OSP) in capsules. The method is based on the reaction between oseltamivir and fluorescamine in borate buffer solution of pH 8.50 to give highly fluorescent derivatives that are measured at 483 nm using an excitation wavelength of 381. The different experimental parameters effecting the development and stability of the reaction product were carefully studied and optimized. The fluorescence intensity concentration plot is rectilinear over the range 50–450 ng mL⁻¹ with a lower detection limit (LOD) of 1.219 ng mL⁻¹ and limit of quantitation (LOQ) of 4.064 ng mL⁻¹. Selectivity was validated by subjecting stock solution of OSP to acidic, basic, oxidative, and thermal degradation. No interference was observed from excipients present in formulations. The developed method was successfully applied to determination of the drug in capsules. The mean % recovery (n = 6) was 100.08. The results obtained were in good agreement with those obtained using a reported spectrophotometric method.     

Flow injection determination of metoclopramide based on KMnO4—HCHO chemiluminescence in a micellar medium

A novel flow injection chemiluminescence (CL) analysis method for the determination of metoclopramide in the presence of sodium dodecyl sulfonate (SDS) surfactant micelles is described. This method is based on the luminescent properties of the KMnO₄-HCHO-metoclopramide in acid medium sensitized by SDS. The optimized experimental conditions were evaluated and the possible mechanism was discussed. The CL increase is linearly related to the concentration of metoclopramide in the range 0-80.0 μg/ml with a detection limit of 31.3 ng/mL (S/N=3).The relative standard deviation for 20.0 μg/ml samples was 2.6% (n=11). The proposed method has been successfully applied to the determination of metoclopramide in tablets.     

Spectrofluorimetric Method for Determination and Validation of Cefixime in Pharmaceutical Preparations Through Derivatization with 2-Cyanoacetamide

A simple, sensitive and accurate method has been developed for spectrofluorimetric determination of cefixime in pure form and pharmaceutical preparations. The method is based on the reaction of cefixime with 2-cyanoacetamide in the presence of 21% ammonia at 100 °C. The fluorescent reaction product showed maximum fluorescence intensity at λ 378 nm after excitation at λ 330 nm. The factors affecting the derivatization reaction were carefully studied and optimized. The fluorescence intensity versus concentration plot was rectilinear over the range of 0.02 to 4 μg mL⁻¹ with correlation coefficient of 0.99036. The limit of detection (LOD) and limit of quantification (LOQ) was found to be 2.95 ng mL⁻¹ and 9.84 ng mL⁻¹, respectively. The proposed method was validated statistically and through recovery studies. The method was successfully applied for the determination of cefixime in pure and dosage form with percent recoveries from 98.117% to 100.38%. The results obtained from the proposed method have been compared with the official HPLC method and good agreement was found between them.     

Stability-Indicating Spectrofluorimetric Method for Determination of Itopride Hydrochloride in Raw Material and Pharmaceutical Formulations

A simple, sensitive and rapid spectrofluorimetric method for determination of itopride hydrochloride in raw material and tablets has been developed. The proposed method is based on the measurement of the native fluorescence of the drug in water at 363 nm after excitation at 255 nm. The relative fluorescence intensity-concentration plot was rectilinear over the range of 0.1–2 μg/mL (2.5?×?10^?7–5.06?×?10^?6 mole/L), with good correlation (r?=?0.9999), limit of detection of 0.015 μg/mL and a lower limit of quantification of 0.045 μg/mL. The described method was successfully applied for the determination of itopride hydrochloride in its commercial tablets with average percentage recovery of 100.11?±?0.32 without interference from common excipients. Additionally, the proposed method can be applied for determination of itopride in combined tablets with rabeprazole or pantoprazole without prior separation. The method was extended to stability study of itopride. The drug was exposed to acidic, alkaline, oxidative and photolytic degradation according to ICH guidelines. Moreover, the method was utilized to investigate the kinetics of the alkaline, acidic and oxidative degradation of the drug. A proposal for the degradation pathways was postulated.     

Novel Method for Determination of Anthracene by Coupling Dispersive Liquid-Liquid Extraction to First-Derivative Synchronous Spectrofluorimetry

A novel method could be adopted successfully for determination of anthracene in environmental samples, utilizing dispersive liquid-liquid extraction followed by first-derivative synchronous fluorimetry at a constant wavelength difference Δλ?=?165 nm, where a linear calibration curve was obtained in a concentration range of 0.5–100 ng mL^?1 at 244 nm. The detection limit was 0.1 ng mL^?1. The method can be easily adopted for determination of anthracene in aqueous media including tap water and river water. The recoveries obtained were 85.40–108.02 %. The proposed method was validated according to International Conference of Harmonization (ICH) guide lines and successfully applied to determine anthracene in pure form and in water samples including real life water samples from different sources. All the results obtained were compared with those of published method, where no a significant difference was observed.     

Stability-Indicating Spectrofluorimetric Method for the Assay of Ziprasidone in Capsules

A simple, rapid and highly sensitive spectrofluorimetric method was developed for determination of ziprasidone hydrochloride (ZPS) in capsules. The method is based on measuring the native fluorescence of ZPS in acetate buffer of pH 4.5 at 398 nm after excitation at 315 nm. The fluorescence-concentration plot was rectilinear over the range of 0.05–0.80 μg mL⁻¹ with a lower detection limit (LOD) of 6.0 ng mL⁻¹ and quantification limit (LOQ) of 20.0 ng mL⁻¹. The method was fully validated and successfully applied to the determination of ZPS in its capsules with average percentage recovery of 99.7 ± 1.4. The method was extended to stability study of ZPS. The drug was exposed to acidic, alkaline, oxidative and photolytic degradation according to ICH guidelines. Moreover, the method was utilized to investigate the kinetics of the alkaline, acidic and oxidative degradation of the drug. A proposal for the degradation pathways was postulated.     

Photochemically-Induced Fluorescence Properties of Two Benzoyl- and Phenylurea Pesticides and Determination in Natural Waters

A photo-induced fluorescence (PIF) method was developed for the determination of two benzoyl- and phenylurea pesticides, namely diflubenzuron (DFB) and fenuron (FEN). The photoconversion under UV irradiation of both pesticides into strongly fluorescent photoproducts was performed in several media (methanol, ethanol, acetonitrile, pH4 aqueous solution and pH4 water–methanol (30:70, v/v) mixture). PIF parameters were optimized. Analytical figures of merit for the PIF determination of DFB and FEN were satisfactory, with rather wide linear dynamic range (LDR) values of one to two orders of magnitude, relatively low limit of detection (LOD) values of, respectively, 9–24 ng/mL for DFB and 1–28 ng/mL for FEN, and limit of quantification (LOQ) values of, respectively, 30–80 ng/mL for DFB and 4–95 ng/mL for FEN, according to the medium. Relative standard deviation (RSD) values were in the range 1.7–5.6 %. PIF was validated by comparing its analytical performances to those of a standard UV absorption spectrophotometric method. The optimized PIF method was applied to the quantitative analysis of both pesticides in various spiked natural water samples collected in a Senegal agricultural area by the standard addition procedure prior to extraction steps in dichloromethane, with satisfactory mean recovery percentage values (97.0–105.3 for DFB and 98.3–102.8 % for FEN). An interference study of foreign species, including pesticides and inorganic ions, likely to be present in natural waters, was also carried out.     

Simultaneous two color image capture for sub-diffraction localization fluorescence microscopy

A sub-diffraction limit fluorescence localization microscope was constructed using a standard cooled 1.4 mega-pixel fluorescence charge-coupled device (CCD) camera to simultaneously resolve closely adjacent paired quantum dots on a flat surface with emissions of 540 and 630 nm. The images of the overlapping Airy discs were analyzed to determine the center of the point spread function after noise reduction using Fourier transformation analysis. The Cartesian coordinates of the centers of the point spread functions were compared in serial images. Histograms constructed from serial images fit well to Gaussian functions for resolving two quantum dots separated by as little as 10 nm in the x–y coordinates. Statistical analysis of multiple pairs validated discrimination of inter-fluorophore distances that vary by 10 nm. The method is simple and developed for x–y resolution of dilute fluorophores on a flat surface, not serial z sectioning.     

Electrocatalytic determination of sulfite using a modified carbon nanotubes paste electrode: application for determination of sulfite in real samples

This paper introduces a carbon paste electrode modified with ferrocene and carbon nanotubes as a voltammetric sensor for determination of sulfite at pH 7.0. The results showed that under the optimum condition (pH 7.0) in cyclic voltammetry, the oxidation of sulfite occurred at a potential about 280?mV less positive than the unmodified carbon paste electrode. Kinetic parameters such as electron transfer coefficient (??) and heterogeneous rate constant (k) for sulfite were also determined using electrochemical approaches. Under the optimized conditions, the electrocatalytic oxidation peak current of sulfite showed two linear dynamic ranges with a detection limit of 0.1???M for sulfite. The proposed method was examined as a selective, simple, and precise method for voltammetric determination of sulfite in some real samples such as weak liquor from wood and paper industry, boiler water, river water, industrial water, and tap water.     

Optimization of the ultrasound-assisted extraction of melatonin from red rice (Oryza sativa) grains through a response surface methodology

An analytical ultrasound-assisted extraction (UAE) technique has been optimized and validated for the extraction of melatonin from rice grains. A Box–Behnken design in conjunction with a response surface methodology based on six factors and three levels was used to evaluate the effects of the studied factors prior to optimizing the UAE conditions. The significant (p < 0.05) response surface models with high coefficients of determination were fitted to the experimental data. Solvent composition and extraction temperature were found to have very significant effects on the response value (p < 0.005). The optimal UAE conditions were as follows: extraction time of 10 min, ultrasound amplitude of 30%, cycle of 0.2 s⁻¹, extraction temperature of 40 °C, 50% methanol in water as the extraction solvent at pH 3.5 and a solvent/solid ratio 2.5:1. The method validation ensured right values for linearity, LOD, LOQ, precision and recovery. Furthermore, the method was successfully applied in the analysis of a number of rice samples throughout the rice production process. Hence, it was demonstrated that this particular UAE method is an interesting tool for the determination of melatonin in rice grain samples.     

19F-NMR Analysis of Primary and Secondary Amines Following Chemical Derivatization with Trifluoroacetic Anhydride

Five amines were reacted with trifluoroacetic anhydride (TFAA) as derivatization reagent and subsequently analyzed via ¹⁹F nuclear magnetic resonance (NMR) spectroscopy. The ¹⁹F-NMR spectra of derivatives of aniline, 2,4-dimethyl aniline, and 2-methoxy aniline produce a signal that are very close to TFAA. The peaks resulting from the reaction of TFAA with N-ethyl aniline and N-methyl aniline are shifted much farther downfield than any of the other signals. Optimal ¹⁹F-NMR sensitivity based upon T ₁ relaxation time was investigated for derivatization compound and flurbiprofen as internal standard in toluene. The calibration curve was linear for amines over the range of 9.0–100.0?mg?L^?1, with detection limit (S/N?=?3) of 2.6–2.9?mg?L^?1. Solid-phase extraction cartridges were investigated for preconcentration of water samples. The method was validated through spike and recovery for secondary amines from tap water sample.     

Determination of Cd in Water Samples by Hollow-Fiber–Supported Liquid-Membrane Extraction Coupled with Thermospray-Flame–Furnace Atomic-Absorption Spectrometry

ABSTRACT

A new method of hollow-fiber–supported liquid-membrane extraction (HF-SLME) coupled with thermospray-flame–furnace atomic-absorption spectrometry (TS-FF-AAS) for the determination of cadmium in water samples was developed. 1-Octanol was immobilized in the pores of the polypropylene hollow fiber as liquid membrane and used as the acceptor solution. Cd was selectively extracted from water samples into 1-octanol that filled the inner part of hollow fiber as the acceptor solution. The authors evaluated in detail some parameters that influence extraction and determination, such as the concentration of sodium diethyldithiocarbamate (DDTC), pH of samples, stirring rate, extraction time, flow rate of the pump, and interferences. Under optimized conditions, an enrichment factor of 146 could be obtained. In combination with thermospray-flame–furnace atomic-absorption spectrometry, a very low limit of detection (LOD) (5 ng L^?1) was achieved. The relative standard deviation (RSD) was 4.3% for five determinations of 0.1 ng mL^?1 cadmium. The accuracy of this method was validated by determination of certified reference water samples (GBW(E) 08607 and GSBZ(E) 50009-88). The proposed method was also applied to the determination of cadmium in tap water and river water, with the recoveries in the range of 90–96% for spiked samples.     

Nanostructured base electrochemical sensor for voltammetric determination of homocysteine using a modified single-walled carbon nanotubes paste electrode

A carbon paste electrode modified with benzoylferrocene (BF) and carbon nanotubes (CNTs) have been applied to the electrocatalytic oxidation of homocysteine which reduced the overpotential by about 165 mV with an obvious increase in the current response. The transfer coefficient (α) for the electrocatalytic oxidation of homocysteine and diffusion coefficient of this substance under the experimental conditions were also investigated. In a phosphate buffer solution (PBS) of pH 7.0, the oxidation current increased linearly with two concentration intervals of homocysteine; one is 0.1 to 10.0 μM, and the other is 10.0 to 80.0 μM. The detection limit (3σ) obtained by square wave voltammetry (SWV) was 50.0 nM. The proposed method was successfully applied to the determination of homocysteine in real samples.     

Spectrofluorimetric Protocol for Ceftriaxone in Commercial Formulation and Human Plasma After Condensation with Formaldehyde and Ethyl Acetoacetate

A new spectrofluorimetric method has been developed and validated for the quantification of ceftriaxone in bulk powder, pharmaceutical formulations and spiked human plasma. The developed method is reproducible, accurate, sensitive and cost effective. In this method, ceftriaxone was converted into a fluorescent compound by reacting with 0.8 M ethyl acetoacetate and 25% formaldehyde in a buffered medium (pH = 4.2) at 90 °C. The excitation and emission wavelengths of the fluorescent reaction product are 316 nm and 388 nm respectively. Optimization of the experimental conditions affecting the condensation reaction were carefully carried out and the optimum experimental conditions were incorporated in the procedure. The developed method has a broad linear range (0.2–20 μg mL⁻¹) with a correlation coefficient of 0.9992. The limit of detection (LOD) and limit of quantification (LOQ) was found to be 1.94 × 10⁻² μg mL⁻¹ and 6.47 × 10⁻² μg mL⁻¹ respectively. The common excipients and co-administered drugs were investigated for their interferences effect in the assay. The developed method was validated statistically through recovery studies and successfully applied to ceftriaxone determination in bulk powder, pharmaceutical formulations and spiked human plasma samples. The percent recoveries were found to be in the range of 99.04–100.26% for bulk powder, 98.88–99.92% for pharmaceutical formulations and 94.22–98.48% for spiked human plasma. The results were verified by comparing with reference literature HPLC method and were found in good agreement.     

Selective Determination of Atropine Using poly Dopamine-Coated Molecularly Imprinted Mn-Doped ZnS Quantum Dots

In this study, a selective method for the determination of atropine in pharmaceutical formulations was proposed. L-cysteine capped Mn-doped ZnS quantum dots (QDs) were prepared in an in-situ method using sodium thiosulfate precursor and characterized by spectrofluorometer, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM) and X-ray diffractometer (XRD). Dopamine hydrochloride was used as a precursor for preparation of poly dopamine-coated molecularly imprinted Mn-doped ZnS quantum dots. Finally, these prepared molecularly imprinted Mn-doped ZnS quantum dots were used for determination of atropine in pharmaceutical formulations. The obtained linear range for determination of atropine was in the range of 2 × 10^?8 – 7 × 10^?6 M, with a correlation coefficient (R²) of 0.9889; and the detection limit (S/N = 3) was 3.2 nM.