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.     

Selective determination of acenaphthene in mixtures of three-ring polycyclic aromatic hydrocarbons by fluorescence quenching in micellar medium of cetylpyridinium bromide

The interaction of acenaphthene, anthracene, and phenanthrene with cetylpyridinium bromide (CPB) was studied. The CPB acts as a quencher provoking inhibition of fluorescence intensity emitted by these hydrocarbons. The existing differences in the fluorescence inhibition for these PAHs allow us to develop a selective synchronous spectrofluorimetric method for the determination of acenaphthene in a CPB micellar medium, with a detection limit of 9.2 and 10.4 ng ml^-1 for Δλ = 10 and 40 nm, respectively. The method was applied to the selective determination of acenaphthene in mixtures of typical three-ring hydrocarbons, including anthracene, phenanthrene, and fluorene.     

Micelle-Enhanced Spectrofluorimetric Method for Determination of Cholesterol-Reducing Drug Ezetimibe in Dosage Forms

A simple and sensitive spectrofluorimetric method was developed for the determination of ezetimibe in its pharmaceutical formulations. The proposed method is based on investigation of the fluorescence spectral behavior of ezetimibe in sodium dodecyl sulfate (SDS) micellar system. In aqueous solution of acetate buffer pH 5.0, the fluorescence intensity of ezetimibe was greatly enhanced, 200% enhancement, in the presence of SDS. The fluorescence intensity of ezetimibe was measured at 380 nm after excitation at 268 nm. The fluorescence-concentration plot was rectilinear over the range of 0.03–3.0 μg/mL with lower detection limit of 3.08 × 10⁻³ μg/mL. The method was successfully applied to the analysis of ezetimibe in its commercial tablets; the results were in good agreement with those obtained with the reported method. The application of the proposed method was extended to the stability studies of ezetimibe after exposure to different forced degradation conditions, such as acidic, alkaline, photo and oxidative conditions, according to ICH guidelines.     

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.     

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.     

A New Spectrofluorimetric Method for Determination of Trace Amounts 5-Hydroxytryptamine in Human Urine and Serum

A new spectrofluorimetric method was developed for the determination of trace amount of 5-hydroxytryptamine (5-HT) in human urine and serum samples. In the NaAc-HAc buffer solution of pH=5.80, 5-HT can react with formaldehyde-acetylacetone system to form a new compound which sends yellow green fluorescence at 533nm and the enhanced fluorescence intensity is in proportion to the concentration of 5-HT. Optimum conditions for the determination of 5-HT were also investigated. The dynamic range and detection limit for the determination of 5-HT are 5.35×10⁻⁷∼1.07×10⁻⁴ mol/L and 2.08×10⁻⁷ mol/L, respectively. The developed method is simple, practical and can be successfully applied to determination of 5-HT in human urine and serum samples. Moreover, the enhancement mechanisms of the fluorescence intensity in the 5-HT - formaldehyde-acetylacetone system have been also discussed.     

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%.     

Trace Measurement of Phenothiazine Drugs in Tablets by Micellar-Enhanced Fluorophotometric Method

It was found that in buffer solution of pH 7.0, the addition of sodium dodecyl sulfate (SDS) to the solution of phenothiazine drugs, such as chlorpromazine, promethazine and trifluoperazine, showed a remarkable enhancement of their fluorescence intensity. A further study proved that the phenothiazine drugs can be determined by fluorophotometric method in micellar system. Under optimal conditions, there was a good linear relationship between fluorescence intensity and phenothiazine compounds concentration, and the detection limit of 3.0×10^-8 M chlorpromazine, 3.0×10⁻⁸ M promethazine and 1.5×10⁻⁸ M trifluoperazine (S/N=3) were also obtained. This method has been used to determine phenothiazine drugs in tablets with satisfactory results.     

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.     

Hydroxypropyl-β-Cyclodextrin Enhanced Determination for the Vitamin B<Subscript>12</Subscript> by Fluorescence Quenching Method

A novel fluorescence quenching method for the determination of Vitamin B₁₂(VB₁₂) had been developed. It was based on that the fluorescence intensity of erythrosine sodium(ES) could be enhanced by Hydroxypropyl-β-cyclodextrin(HP-β-CD) due to the formation of inclusion complex (HP-β-CD-ES), while the fluorescence intensity of HP-β-CD-ES was diminished after adding VB₁₂ into the system, and there was a linear relationship between the fluorescence quenching value of the system (ΔF) and the concentration of VB₁₂(c). The mechanism of the determination of VB₁₂was discussed. The results showed that under the optimal conditions, the linear range of calibration curve for the determination of VB₁₂ was 0.0∼2.1 × 10⁻⁵ mol/L, and the detection limit was 1.8×10⁻⁷ mol/ L. It could be satisfactorily applied to the determination of VB₁₂ in injections.     

A quenching fluoroimmunoassay for analysis of the pesticide propazine in an apolar organic solvent, reverse micelles of AOT inn-octane: Effect of the micellar matrix and labeled antigen structure

A simple way of directly observing antigen-antibody binding in a reverse micellar system,n-octane containing reverse micelles of aerosol OT (AOT), using the hydrophobic pesticide propazine as antigen, is described. We observed two processes during fluorescein-labeled propazine (FP)-antibody (Ab) interaction in reverse micelles: (1) quenching of the fluorescence of FP after mixing of Ab and FP (due immune complex formation) and (2) restoration of FP fluorescence after addition of excess propazine to the immune complex formed. We found that the quenching efficiency depends on both the properties of the reverse micellar system (surfactant concentration, hydration degreeW ₀ = [water]/[surfactant]) and the structure of the labeled antigen. A quenching fluoroimmunoassay of propazine both in apolar organic solvents and in water is developed. The method is homogeneous. The quenching time is 10–30 min, and the detection limit of propazine is 100 nM (20 Μg/L) in organic solvent and 10nM (2 Μg/L) in water. Propazine can be added to the reverse micellar system when dissolved in AOT/octane, or in an octane/chloroform mixture, or in chloroform. This makes possible the use of the analysis directly for pesticide extracts in nonpolar organic solvents.     

A Spectrofluorimetric Sequential Injection Method for the Determination of Penicillamine Using Fluorescamine in the Presence of β-cyclodextrins

A simple, robust and sensitive sequential injection spectrofluorimetric method for the determination of penicillamine (PA) in pharmaceutical formulations is developed. The method is based on the formation of a highly fluorescent derivative when penicillamine is reacted with fluorescamine (FL) in borate buffer of pH 9.3. The derivative produced is monitored at an emission wavelength of 495 nm using an excitation wavelength of 355 nm. The optimum conditions for the determination of PA with FL were: 3 mM FL, pH 9.3, 5 mM methyl-β-cyclodextrin, sample volume of 75 μL and reagent volume of 75 μL. Furthermore, the effect of various media on the fluorescence intensity of the PA–FL derivative was studied and methyl-β-cyclodextrin was found to give the largest enhancement. A linear dynamic range for the determination of PA of 5–80 ppm was obtained with a sampling frequency of 50 h⁻¹ and a relative standard deviation of less than 2.5%. The method was applied to the determination of PA in pharmaceutical formulations with reasonable recoveries ranging from 101.0–103.1%, indicating that no interference is observed from concomitants usually present in dosage forms.     

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.     

Magnetic nanoparticles as sorbent for preconcentration and determination of lead in fish and water samples

In the present work, a procedure for the preconcentration and determination of lead trace amounts of lead in fish species and water samples by graphite furnace atomic absorption spectrometry (GF AAS) is proposed, which is based on the batch solid phase extraction of lead ions by modified magnetic nanoparticles. An optimization process was performed using two-level fractional factorial designs (2^4-1) and a Box–Behnken matrix. Four variables (pH of solution, nanoparticles mass, morin mass, and shaking time) were regarded as factors in the optimization. The detection limit of the proposed method was found to be 81.0 ng/l. Six samples of fish and three samples of water (tap, river, and lake) were analyzed for lead. The lead contents ranged in fish from 0.013 to 0.038 μg/g and in water from 7.1 to 9.0 μg/l.     

Sensitive Spectrofluorimetric Determination of Cytochrome c with Spirocyclic Rhodamine B Hydrazide in Micellar Medium

A new spectrofluorimetric method for the determination of cytochrome c using spirocyclic rhodamine B hydrazide (RBH) as fluorogenic reagent in the presence of sodium dodecylbenzene sulfonate (SDBS) surfactant micelles was developed. The method was based on the reaction of cytochrome c with RBH, a colorless, nonfluorescent spirolactam of rhodamine B in SDBS micelles to give highly fluorescent rhodamine B and hence led to a large increase in fluorescence intensity. The dynamic range and detection limit for the determination of cytochrome c are 4.0–120 ng ml⁻¹ and 0.87 ng ml⁻¹ (3σ), respectively. The optimal conditions for the detection of cytochrome c were evaluated and the possible detection mechanism was also discussed.     

The Co-luminescence Effect of Eu–Gd–Ofloxacin–SDBS System and its Analytical Application

A fluorescence enhancement phenomenon in the europium (Eu)–Ofloxacin (OF)–Sodium Dodecyl Benzene Sulfonate (SDBS) fluorescence system was observed when Gd³⁺ was added. The fluorescence intensity of the systems was measured (λ _ex/λ _em = 280/612 nm) at pH 7.8. Under optimum conditions, a linear relationship between the enhanced fluorescence intensity and the Eu³⁺ concentration in the range of 5.0 × 10⁻¹⁰ ∼ 2.0 × 10⁻⁷ mol·L⁻¹ was observed. The detection limit of Eu³⁺ was 1.46 × 10⁻¹⁰ mol·L⁻¹ (S/N = 3). This method was used for the determination of trace amounts of europium in synthetic rare earth samples with satisfactory results. In addition, the interaction mechanism is also studied.     

A Chemosensing Ensemble for the Detection of Cysteine Based on the Inner Filter Effect Using a Rhodamine B Spirolactam

A fluorescent chemosensing ensemble for the detection of cysteine is designed based on the fluorescence inner filter effect. The method employs the coordination of Cu²⁺ ion with salicylaldehyde rhodamine B hydrazone (I), a colorless and non-fluorescent rhodamine B spirolactam derivative to form I-Cu(II), a pink color but weakly fluorescent complex. When rhodamine B was introduced to the I-Cu(II) complex solution, the fluorescence signal of rhodamine B is dramatically decreased because of the fluorescence inner filter effect (IFE). Upon adding cysteine to the above solution, it can complex preferentially to Cu²⁺ compared to I, and the I-Cu(II) complex dissociates, which thus decreases the fluorescence IFE of the solution, and in turn leading to the fluorescence increase of the chemosensing system. Based on the above mechanism, a fluorescent chemosensing ensemble for cysteine is developed. The fluorescence increase is linearly with cysteine concentration up to 10.0 μ mol L⁻¹, with a detection limit of 1.4 × 10⁻⁷ mol L⁻¹ (3σ). The optimal conditions of the proposed method were studied and the selectivity of the proposed method was investigated in this paper.     

Spectrofluorimetric Determination of Oxamniquine in Dosage Forms and Spiked Human Plasma through Derivatization with 1-dimethylaminonaphthalene-5-sulphonyl chloride

A sensitive, simple and selective spectrofluorimetric method was developed for the determination of oxamniquine (OXM) in pharmaceutical formulations and biological fluids. The method is based on the reaction between the drug and 1-dimethylaminonaphthalene-5-sulphonyl chloride (dansyl chloride) in presence of 0.5 M sodium carbonate (pH 10) to yield a highly fluorescent derivative that is measured at 445 nm after excitation at 335 nm. The different experimental parameters affecting the development and stability of the reaction product were carefully studied and optimized. The fluorescence concentration plot was rectilinear over the range of 0.02–0.2 μg ml⁻¹ with a lower detection limit (LOD) of 0.007 μg ml⁻¹ and limit of quantitation (LOQ) of 0.02 μg ml⁻¹. The proposed method was successfully applied to the analysis of commercial capsules. The results obtained were in good agreement with those obtained using the official spectrophotometric method. Furthermore, the method was applied for the determination of oxamniquine in spiked human plasma, the mean % recovery (n = 4) is 97.77 ± 1.19. A proposal of the reaction pathway was presented.     

Improvement in Retinol Analysis by Fluorescence and Solid Phase Extraction (SPE) in Micellar Medium

In this paper, the determination of retinol, the structure with the most activity as vitamin A, was carried out in an aqueous micellar medium with a low quantity of a short-chain alcohol. The analytical technique used in this work was fluorescence, which gave us very much information qualitative and quantitative. The sensitivity of the method is higher than that obtained in other media; the detection limit is 0.03 mg L⁻¹ and retinol was stable in solution for at least 5 days. The use of solid phase extraction (SPE) for organic samples, allowed us to change the organic matrix by a mixture CTAB 5%/n-butanol 10%/water 85% w/w/w with recoveries in retinol spiked samples close to 100%. In addition, the combination of SPE and fluorescence is a good preconcentration technique, sensitive and fast for the identification and determination of retinol, simultaneously.     

Determination of Ofloxacin using a Highly Selective Photo Probe Based on the Enhancement of the Luminescence Intensity of Eu3+—Ofloxacin Complex in Pharmaceutical and Serum Samples

A rapid, simple and sensitive spectrofluorimetric method for determination of trace amount of ofloxacin was developed. At pH 5.1 the ofloxacin enhances the luminescence intensity of the Eu³⁺ ion in Eu³⁺- ofloxacin complex at λ_ex = 365 nm. The produced luminescence intensity of Eu³⁺-ofloxacin complex was in proportional to the concentration of ofloxacin. The working range for the determination of ofloxacin was 5.0 × 10^-9–5.0 × 10^-6 mol L^-1 with lower detection limit (LOD) and quantitative detection limit (QDL) of 3 × 10^-9 and 9 × 10^-9 mol L^-1, respectively. The enhancement mechanism of the luminescence intensity in the Eu³⁺-ofloxacin system has been also explained. The method revealed good selectivity for ofloxacin in the presence of coexisting substances and used successfully for the assay of ofloxacin in pharmaceutical preparations and serum. A comparison with other standard methods was also discussed.