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.     

Fluorescence Quenching Reaction of Polyvinylpyrrolidone-Eosin Y System for the Determination of Polyvinylpyrrolidone

In pH 1.8 ∼ 2.8 weak acid medium, polyvinylpyrrolidone (PVP) and Eosin Y reacted to form complex that could result in Eosin Y (EY) fluorescence quenching. The maximum quenching wavelength was at 542 nm. The fluorescence quenching (ΔF) was proportional to the concentration of polyvinylpyrrolidone in a certain range. The linear range, the correlation coefficient and the detection limit were 0.33 ∼ 2.0 μg•mL⁻¹, 0.9994 and 99.6 ng•mL⁻¹, respectively. The influences of the coexistence substances were tested and the results showed that the method had good selectivity. Therefore, a new method based on fluorescence quenching of eosin Y by PVP for the determination of trace PVP was developed. The method was sensitive, simple and rapid, which was applied to the determination of trace PVP in the beer with satisfactory results. The reaction mechanism was also discussed.     

Fluorescence Enhancement of the Silver Nanoparticales – Curcumin - Cetyltrimethylammonium Bromide-nucleic Acids System and its Analytical Application

It is found that silver nanoparticles (AgNPs) can further enhance the fluorescence intensity of curcumin (CU) - cetyltrimethylammonium bromide (CTAB) – nucleic acids and improve its anti-photobleaching activity. Under optimum conditions, the enhanced fluorescence intensity is proportion to the concentration of nucleic acids in the range of 2.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for fish sperm DNA (fsDNA), 2.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for calf thymus DNA (ctDNA), 1.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for yeast RNA (yRNA), and their detection limits (S/N = 3) are 8.0 ng mL⁻¹, 10.5 ng mL⁻¹ and 5.8 ng mL⁻¹, respectively. This method is used for determining the concentration of DNA in actual sample with satisfactory results. The interaction mechanism is also studied.     

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.     

Spectrofluorimetric Methods for the Determination of Gemifloxacin in Tablets and Spiked Plasma Samples

Two new, sensitive and selective spectrofluorimetric methods have been developed for the determination of gemifloxacin (GFX) in tablets and spiked plasma samples. Gemifloxacin, as a primary amine compound, reacts with 7-chloro-4-nitrobenzofurazon (NBD-Cl) (for method A) and fluorescamine (for method B) which are a highly sensitive fluorogenic reagents used in many investigations. For method A, the reaction product was measured spectrofluorimetrically at 516 nm with excitation at 451 nm. The reaction proceeded quantitatively at pH 8.5, 80 °C in 7 min. For method B, the method was based on the reaction between GFX and fluorescamine in borate buffer solution of pH 8.5 to give highly fluorescent derivatives that were measured at 481 nm using an excitation wavelength of 351 nm. The fluorescence intensity was directly proportional to the concentration over the range 40–200 ng mL⁻¹ and 100–1,200 ng mL⁻¹ for method A and B, respectively. Successful applications of the developed methods, for the drug determination in pharmaceutical preparations and spiked plasma samples, were performed.     

Silver Nanoparticle-Enhanced Chemiluminescence Method for Determining Naproxen Based on Europium(III)-Sensitized Ce(IV)-Na<Subscript>2</Subscript>S<Subscript>2</Subscript>O<Subscript>4</Subscript> Reaction

A simple and sensitive chemiluminescence (CL) method coupled with flow-injection technique is proposed to determine naproxen (NAP). The method is based upon the enhancement of the weak CL signal arising from the reaction of Ce(IV) and Na₂S₂O₄ with Eu³⁺ to form the Eu³⁺-Ce(IV)-Na₂S₂O₄ system. The CL intensity was significantly increased by the introduction of NAP into this system in the presence of silver nanoparticles (Ag NPs). Examination of the recorded UV–vis spectra and fluorescence spectra indicated that the energy of the intermediate SO₂*, which originated from the redox reaction of Ce(IV) and Na₂S₂O₄, was transferred to Eu³⁺ via NAP and that the process was accelerated by Ag NPs due to their catalytic activity. Under the optimum conditions, the CL intensity was increased with increasing NAP concentration and the correlation was linear (r = 0.9992) over the NAP concentration range of 1–420 ng mL⁻¹. The limit of detection (LOD) was 0.11 ng mL⁻¹ with a relative standard deviation (RSD) of 1.15% for 5 replicate determinations of 200 ng mL⁻¹ NAP. The method was successfully applied to determine NAP in pharmaceutical and biological samples.     

Spectrofluorimetric Assessment of Metoclopramide Hydrochloride Using Terbium Doped in PMMA Matrix Optical Sensor

A new, simple and accurate spectrofluorimetric method for the determination of metoclopramide hydrochloride was developed. The metoclopramide hydrochloride can remarkably enhance the luminescence intensity of the Tb³⁺ ion doped in PMMA matrix at λ_ex = 360 nm in methanol at pH 6.9. The intensity of the emission band at 545 nm of Tb³⁺ ion doped in PMMA matrix is increased due to the energy transfer from metoclopramide hydrochloride to Tb³⁺ in the excited stated. The effect of different parameters, e.g., pH, temperature, Tb³⁺ concentration, foreign ions that control the fluorescence intensity of the produced ion associate was critically investigated. The calibration curve of the emission intensity at 545 nm shows linear response of metoclopramide over a concentration range of 5 × 10⁻⁵–5.0 × 10⁻⁸ M with detection limit of 8.7 × 10⁻¹⁰ M. The method was used successfully for the determination of metoclopramide in pharmaceutical preparations and human serum. The average recovery of 99.48% with standard deviation of 0.32% and 96.98% with standard deviation of 0.4%, of pharmaceutical preparations and human serum respectively, were obtained which compared will with the results obtained from standard LC method of average recovery 99.04% and standard deviation of 0.6% and average recovery of 98.19% with standard deviation of 0.6% of pharmaceutical preparations and human serum, respectively.     

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.     

Second-derivative Synchronous Fluorometric Method for the Simultaneous Determination of Cinnarizine and Domperidone in Pharmaceutical Preparations. Application to Biological Fluids

A rapid, simple and highly sensitive second derivative synchronous fluorometric method has been developed for the simultaneous analysis of binary mixture of cinnarizine (CN) and domperidone (DOM). The method is based upon measurement of the native fluorescence of these drugs at Δλ = 80 nm in aqueous methanol (50% V/V). The different experimental parameters affecting the native fluorescence of the studied drugs were carefully studied and optimized. The fluorescence-concentration plots were rectilinear over the range of 0.1 to 1.3 μg mL⁻¹ and 0.1–3.0 μg mL⁻¹ for CN and DOM, respectively with lower detection limits of 0.017 and 5.77 × 10⁻³ μg mL⁻¹ and quantification limits of 0.058 and 0.02 μg mL⁻¹ for CN and DOM. The proposed method was successfully applied for the determination of the studied compounds in synthetic mixtures and in commercial tablets. The results obtained were in good agreement with those obtained with reference methods. The high sensitivity attained by the synchronous fluorometric method allowed the determination of CN in real and spiked human plasma. The mean % recoveries in case of spiked human plasma (n = 3) were 96.39 ± 1.18 while that in real human plasma (n = 3) was 104.67 ± 4.16.     

Spectrofluorimetric Determination of Dopamine Using Chlorosulfonylthenoyltrifluoroacetone–Europium Probe

A new spectrofluorimetric method was developed for the determination of trace amounts of dopamine (DA). Using chlorosulfonylthenoyltrifluoroacetone (CTTA)–europium ion (Eu³⁺) as a fluorescent probe, in a buffer solution at pH = 10.0, DA can remarkably enhance the fluorescence intensity of the CTTA-Eu³⁺ complex at λ = 612 nm; the enhanced fluorescence intensity of Eu³⁺ is proportional to the concentration of DA. Optimum conditions for the determination of DA were also investigated. The linear range and detection limit for the determination of DA were 5.0 × 10⁻⁸∼1.6 × 10⁻⁵ mol/l and 3.2 × 10⁻⁸ mol/l. This method is simple, practical and relatively free of interference from coexisting substances, and can be applied to assess DA in injection and human serum samples with good precision and accuracy.     

Synthesis of Novel Eu(III) Luminescent Probe Based on 9- Acridinecarboxylic Acid Skelton for Sensing of ds-DNA

Eu(III)-9-acridinecarboxylate (9-ACA) complex was synthesized and characterized by elemental analysis, conductivity measurement, IR spectroscopy, thermal analysis, mass spectroscopy, ¹H-NMR, fluorescence and ultraviolet spectra. The results indicated that the composition of this complex is [Eu(III)-(9-ACA)₂(NCS)(C₂H₅OH)₂] 2.5 H₂O and the oxygen of the carbonyl group coordinated to Eu(III). The interaction between the complex with nucleotides guanosine 5′- monophosphate (5′-GMP), adenosine 5′-diphosphates (5′-ADP), inosine (5′-IMP) and CT-DNA was studied by fluorescence spectroscopy. The fluorescence intensity of Eu(III)-9-acridinecarboxylate complex was enhanced with the addition of CT-DNA. The effect of pH values on the fluorescence intensity of Eu(III) complex was investigated. Under experimental conditions, the linear range was 9–50 ng mL⁻¹ for calf thymus DNA (CT- DNA) and the corresponding detection limit was 5 ng mL⁻¹. The results showed that Eu(III)-(9-ACA)₂ complex binds to CT-DNA with stability constant of 2.41 × 10⁴ M .     

Fluorophotometric Determination of Hydrogen Peroxide with Fluorescin in the Presence of Cobalt (II) and Reaction Against Other Reactive Oxygen Species

A fluorophotometric method for the determination of hydrogen peroxide (H₂O₂) using fluorescin was developed. This method was based on the oxidative reaction of fluorescin, a colorless, non-fluorescent lactoid fluorescein, by H₂O₂ to give highly fluorescein fluorescence emission. In the determination of H₂O₂, the calibration curve exhibited linearity over the H₂O₂ concentration range of 1.5–310 ng mL⁻¹ at an emission wavelength of 525 nm with an excitation of 500 nm and with relative standard deviations (n = 6) of 2.51%, 2.48%, and 1.31% for 3.1 ng mL⁻¹, 30.8 ng mL⁻¹, and for 308 ng mL⁻¹ of H₂O₂, respectively. The detection limit for H₂O₂ was 1.9 ng mL⁻¹ six blank determinations was performed (ρ = 6). This proposed method was applied to detection of other reactive oxygen species and nitrogen species (ROS/RNS) such as singlet oxygen (¹O₂), hydroxyl radical (^•OH), peroxynitrite (ONOO⁻) etc., and it was possible to detect them with a high sensitivity. In addition, this proposed method was applied to the recovery tests of H₂O₂ in calf serum, human saliva, rain water, and wheat noodles; the results were satisfactory.     

Spectrofluorimetric Assessment of Chlorzoxazone and Ibuprofen in Pharmaceutical Formulations by using Eu-Tetracycline HCl Optical Sensor Doped in Sol–Gel Matrix

A novel, simple, sensitive and selective spectrofluorimetric method was developed for the determination of trace amounts of chlorzoxazone and Ibuprofen in pharmaceutical tablets using optical sensor Eu-Tetracycline HCl doped in sol–gel matrix. The chlorzoxazone or Ibuprofen can remarkably enhance the luminescence intensity of Eu-Tetracycline HCl complex doped in a sol–gel matrix in dimethylformamide (DMF) at pH 9.7 and 6.3, respectively, λ_ex = 400 nm. The enhancing of luminescence intensity peak of Eu-Tetracycline HCl complex at 617 nm is proportional to the concentration of chlorzoxazone or Ibuprofen a result that suggested profitable application as a simple optical sensor for chlorzoxazone or Ibuprofen assessment. The dynamic ranges found for the determination of chlorzoxazone and Ibuprofen concentration are 5 × 10⁻⁹–1 × 10⁻⁴ and 1 × 10⁻⁸–7 × 10⁻⁵ mol L⁻¹, and the limit of detection (LOD) and quantitation limit of detection (LOQ) are 3.1 × 10⁻¹⁰ , 9.6 × 10⁻¹⁰ and 5.6 × 10⁻¹⁰, 1.7 × 10⁻⁹ mol L⁻¹, respectively.     

Spectrofluorimetric Determination of 3-hidroxy-2-naphthoic Acid by Use of Its Ternary Complex with Zirconium (IV) and Beta-Cyclodextrin: Application to Determination in River Water

A spectrofluorimetric method has been developed for the determination of 3-hydroxy-2-naphthoic acid (3H2NA) by formation of a ternary complex with zirconium (IV) and β-cyclodextrin (β-CD). It has been observed that the fluorescence intensity of 3H2NA is greatly enhanced when the ternary complex is formed and is accompanied with shifts in the excitation and emission wavelengths. The conditions for the formation of the ternary complex have been optimized and the stoichiometry has been calculated, resulting a 1:2:1 complex (3H2NA:Zr: β-CD). The linear range was 20–2000 ng mL⁻¹ and the detection and quantification limits calculated were 17 and 58 ng mL⁻¹, respectively. The proposed method was applied to the determination of 3H2NA in river water. To eliminate interferences an off-line solid phase extraction (SPE) procedure using C18 cartridges was used. The extraction procedure was optimized and good recoveries were obtained (around 100%) with relative standard deviations (RSDs) of less than 5%.     

Fluorescence enhancement effect for the determination of adenosine 5'-monophosphate with 9-anthracene carboxylic acid-cetyl trimethyl ammonium bromide system

A fluorimetric method based on fluorescence enhancement effect was developed for the determination of adenosine 5′-monophosphate (AMP) with 9-anthracene carboxylic acid (9-ANCA)–cetyl trimethyl ammonium bromide (CTAB) system. Fluorescence intensity of 9-ANCA was decreased by the addition of CTAB but addition of AMP again rose the intensity of 9-ANCA gradually. The observed fluorescence enhancement is attributed to the competitive binding reaction of 9-ANCA and adenosine to CTAB. The enhancement in the fluorescence intensity was found proportional to the concentration of AMP over the range 2.0 × 10⁻⁴ to 1.2 × 10⁻³ mol dm⁻³. The ion pair complex is formed spontaneously between 9-ANCA and CTAB. Since the binding interaction is larger for the adenosine–CTAB pair, the fluorophore 9-ANCA will be released. The quantum yield of free 9-ANCA is higher therefore its fluorescence observed at 417 nm wavelength is enhanced. This mechanism of competitive molecular interaction is further confirmed by conductometric measurements. The method was applied successfully for the determination of AMP from pharmaceutical sample. The method is more selective, sensitive and relatively free from interferences.     

Spectrofluorimetric Assessment of Doxycycline Hydrochloride in Pharmaceutical Tablets and Serum Sample Based on the Enhancement of the Luminescence Intensity of the Optical Sensor Sm<Superscript>3+</Superscript> Ion

A simple and sensitive spectrofluorimetric method for determination of trace amount of doxycycline hydrochloride (DC) in pharmaceutical tablets and serum samples was developed. In ammonia buffer solution of pH 8.9 the doxycycline hydrochloride can remarkably enhance the luminescence intensity of the Sm³⁺ ion in Sm³⁺- DC complex at λ_ex = 400 nm. The produced luminescence intensity of Sm³⁺- DC complex in DMSO is in proportion to the concentration of DC and used as optical sensor for its determination. The dynamic range for the determination of DC is 1 × 10⁻⁸ – 5 × 10⁻⁶ mol L⁻¹ and in case of quantum yield calculations is 7 × 10⁻⁹ – 5 × 10⁻⁶ mol L⁻¹ with detection limit of 6.5 × 10⁻¹⁰ mol L⁻¹. The enhancement mechanism of the luminescence intensity in the Sm³⁺- DC system has been also discussed. A comparison with other spectrofluorimetric methods for tetracycline derivatives in which Eu³⁺ ion is used instead of Sm³⁺ ion is also studied.     

Sensitive Phosphorimetric Determination of Bumetanide in Human Urine with Its Inhibition Effect on the Formation of [Fe-morin] <Superscript>3+</Superscript> Complex

A novel solid substrate-room temperature phosphorimetry (SS-RTP) was developed for determination of bumetanide (BMTN). It was validated by determining selectivity, linearity, accuracy, precision, and signal to noise ratio (S/N) for analysis. And all the experiments presented in this work were based on that BMTN inhibited the formation of [Fe-morin]³⁺ ([FeR]³⁺) complex by the reaction between Fe³⁺ and R, which led to severe quenching of room temperature phosphorescence (RTP) signal. The rate constant of the reaction (k) was 2.44 × 10⁻⁴ s⁻¹, the activation energy (E) was 21.39 kJ mol⁻¹. Detection limit of this method (LD, 5.0 ag spot⁻¹, corresponding concentration was 1.2 × 10⁻¹⁴ g mL⁻¹) was evaluated and compared with other methods, indicating better sensitivity for BMTN determination using this technique. And due to the high sensitivity of the method, it has been successfully applied to determine BMTN in human urine samples. The linear range was from 0.040 pg mL⁻¹ to 4.0 pg mL⁻¹, allowing wide determined range of BMTN. Meanwhile, the mechanism of this method was also discussed.     

Determination of Paracetamol Based on its Quenching Effect on the Photoluminescence of CdTe Fluorescence Probes

L-Cysteine capped CdTe nanoparticles (NPs) were synthesized in aqueous medium, and their application as fluorescence probes in the determination of paracetamol was studied. The L-cysteine capped CdTe NPs were characterized by transmission electron microscopy, X-ray diffraction spectrometry, spectrofluorometry, ultraviolet-visible and Fourier transform infrared spectrometry. Based on the distinct fluorescence quenching of CdTe fluorescence probes in the presence of paracetamol, a simple, rapid and specific method for paracetamol determination was presented. Under optimum conditions, the relative fluorescence intensity of CdTe NPs was linearly proportional to paracetamol concentration from 1.0 × 10⁻⁸ mol/L to 1.6 × 10⁻⁷ mol/L with a detection limit of 4.2 × 10⁻⁹ mol/L. The proposed method was applied to detect paracetamol in commercial tablets with satisfactory results.     

Study of Enhanced Chemiluminescence of Diperiodatocuprate (III) on 1,10-Phenanthroline/Hydrogen Peroxide/Cetyltrimethylammonium Bromide System

In the paper, a chemiluminescence (CL) system was developed based on the catalytical effect of diperiodatocuprate (III) (DPC) on the 1,10-phenanthroline (phen)/hydrogen peroxide (H₂O₂) in the presence of cetyltrimethylammonium bromide (CTAB). The effects of experimental conditions were investigated. Meanwhile the increase of CL intensity of the DPC/phen/H₂O₂/CTAB system is proportional to the concentration of phen in the range of low concentration. The linear range of the calibration curve is 5.0 × 10⁻⁹–1.0 × 10⁻⁶ mol L⁻¹, and the corresponding detection limit is 1.9 × 10⁻⁹ mol L⁻¹. The effects of phenolic compounds (PCs) on the system were investigated. Hydroquinone was used as an example to investigate the application of the CL system to the determination of PCs. The quenched CL intensity is linearly related to the logarithm of concentration of hydroquinone. The linear range of the calibration curve is 2.5 × 10⁻⁹–1.0 × 10⁻⁵ g mL⁻¹, and the corresponding detection limit is 1.8 × 10⁻⁹ g mL⁻¹. This phen and hydroquinone can be synchronously determined. The method was applied to the determination of hydroquinone in water samples and the recoveries were from 92% to 106%.