Study on the Fluorescence Quenching Reaction of Amitriptyline and Clomipramine Hydrochlorides with Eosin Y and its Analytical Application

Amitriptyline.HCl (AMI) and clomipramine.HCl (CMI) react with eosin Y (EY) in pH 3.8 NaAc-AcH buffer solution to form ion association complex which results in quenching of fluorescence of EY and appearance of a new resonance Rayleigh scattering (RSS) spectrum at 620 nm. The spectral characteristics of absorption, fluorescence and RSS spectra have been investigated. The factors influencing the reaction were studied and optimum conditions for the reaction have been determined. Based on fluorescence quenching, a simple and sensitive spectrofluorimetric method for determination of AMI and CMI has been developed. The fluorescence quenching intensity was measured at 550 nm using an excitation wavelength of 310 nm. The calibration graph was found to be rectilinear in the range 0.08–2.0 μg?mL^?1 with detection limit of 0.017 μg?mL^?1 for AMI and 0.06–2.0 μg?mL^?1 with detection limit of 0.015 μg?mL^?1 for CMI. The method can be satisfactorily applied to the determination of AMI and CMI in tablets without interference from commonly occurring exicipients. The recovery and RSD values obtained indicate good accuracy and precision of the method. The mechanism of the reaction and fluorescence quenching has also been discussed.     

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.     

Novel Comparative Synchronous Spectrofluorimetric Study of Benzo(a)pyrene Using Beta-Cyclodextrin and Calix(8)arene as Fluorescence Enhancers

Successfully benzo(a)pyrene could be quantitified in environmental samples by a novel synchronous spectrofluorimetric techniques at a constant wavelength difference Δλ?=?120 nm, using beta-cyclodextrin ‘β-CD’ and calix(8)arene as fluorescence enhancers, where a linear calibration curve was obtained in a concentration range of 900–14,400 pg mL^?1 and 18–360 pg mL^?1 and the detection limit of 380.00 pg mL^?1 and 12.08 pg mL^?1 (which is well below the maximum contaminant concentration for benzo(a)pyrene set by the Environmental Protection Agency ‘EPA’) using both enhancers, respectively. The method can be easily adopted for determination of benzo(a)pyrene in aqueous media including tap water, river water and complex water samples. The recoveries obtained were 85.13–113.36 % with RSD?<?4 %. The proposed method was validated according to International Conference of Harmonization (ICH) guide lines and successfully applied to determine benzo(a)pyrene in pure form and in water samples including contaminated environmental water samples. All the results obtained were compared with those of a published method, where no significant difference was observed.     

Determination of Protein by Fluorescence Enhancement of Curcumin in Lanthanum-Curcumin-Sodium Dodecyl Benzene Sulfonate-Protein System

We found that the fluorescence intensity of the lanthanum (La³⁺)-curcumin (CU) complex can be highly enhanced by proteins in the presence of sodium dodecyl benzene sulphonate (SDBS). Based on this finding, a new fluorimetric method for the determination of protein was developed. Under optimized conditions, the enhanced intensities of fluorescence are quantitatively in proportion to the concentrations of proteins in the range 0.0080?C20.0 ??g·mL^?1 for bovine serum albumin (BSA) and 0.00080?C20.0 ??g·mL^?1 for human serum albumin (HSA) with excitation of 425 nm, and 0.00020?C20.0 ??g·mL^?1 for bovine serum albumin (BSA) and 0.00080?C20.0 ??g·mL^?1for human serum albumin (HSA) with excitation of 280 nm, while corresponding qualitative detection limits (S/N????3) are as low as 5.368, 0.573, 0.049, 0.562 µg·mL^?1, respectively. Study on reaction mechanism reveals that proteins can bind with La³⁺, CU and SDBS through self-assembling function with electrostatic attraction, hydrogen bonding, hydrophobic interaction and van der Waals forces, etc. The proteins form a supermolecular association with multilayer structure, in which La³⁺-CU is clamped between BSA and SDBS. The unique high fluorescence enhancement of CU is resulted through synergic effects of favorable hydrophobic microenvironment provided by BSA and SDBS, and efficient intermolecular energy transfer among BSA, SDBS and CU. In energy transfer process, La³⁺ plays a crucial role because it not only shortens the distance between SDBS and CU, but also acts as a ??bridge?? for transferring the energy from BSA to CU.     

Spectrofluorimetric Determination of Topiramate and Levetiracetam as Single Components in Tablet Formulations and in Human Plasma and Simultaneous Fourth Derivative Synchronous Fluorescence Determination of their Co-Adminstered Mixture in Human Plasma

Two highly sensitive, rapid, simple, economic and validated spectrofluorimetric methods have been developed for determination of Topiramate and Levetiracetam in pharmaceutical tablets and in human plasma. Topiramate and Levetiracetam were determined separately by derivatization using 4-Chloro-7-nitrobenzofuran-2-oxo-1,3-diazole (NBD-Cl) and measured spectrofluorimetrically. The Relative fluorescence intensities were measured at λ_em/_ex of 547/465 nm and 551/465 nm for Topiramate and Levetiracetam, respectively. While a binary mixture of Topiramate and Levetiracetam were determined by the fourth derivative synchronous fluorescence measurement after their reaction with NBD-Cl. In this method, the fourth derivative synchronous spectra were estimated as peak to peak measurement at 493–497 and 490.5–495 nm corresponding with zero-contribution of Levetiracetam and Topiramate, respectively. Linearity ranges for Topiramate and Levetiracetam in both methods were found to be 0.15–1.2 and 0.2–1.5 μg/mL, respectively. The different experimental parameters affecting the fluorescence of the two drugs were carefully studied and optimized. The proposed methods were validated in terms of linearity, accuracy, precision, limits of detection and quantification and other aspects of analytical validation. The proposed methods were successfully applied for the determination of the investigated drugs in human plasma samples obtained from healthy volunteers after single oral administration of the two drugs.     

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.     

Fluorimetric Method Based on Diazotization-Coupling Reaction for Determination of Clenbuterol

A novel fluorimetric method based on diazotization-coupling reaction (DCR) for the determination of clenbuterol is described. In acidic solution, clenbuterol was first diazotized with sodium nitrite, followed by coupling with bisphenol A to produce an azo-compound in NH₃- NH₄Cl buffer. It has found the diazotized clenbuterol- bisphenol A- NH₃- NH₄Cl (DCBN) system has strong fluorescence efficiency compare with the bisphenol A solution. There is a linear relationship between the increased intensity of the fluorescence emission spectra (λ_ex/λ_em?=?276 nm/306 nm) and the concentration of clenbuterol. The effects of the amount of sodium nitrite, diazo reaction time, the amount of bisphenol A, coupling reaction time and coupling reaction temperature have been examined. Under the optional conditions, clenbuterol can be determined over the concentration range of 0.02 to 2.0 μg mL^?1 with a correlation coefficient of 0.9953. The detection limit is 0.01 μg mL^?1 at a signal-to-noise ratio of 3. The relative standard deviation (RSD) for 11 repetitive determinations of 0.9 μg mL^?1 clenbuterol is 0.22 %. The utility of this method was demonstrated by determining clenbuterol in meat samples.     

Effect of Room Temperature Ionic Liquid on the Formation of the Complex Oxalate-Sodium Morin-5-Sulfonate-Aluminium(III): Application to the Fluorescence Determination of Oxalate Ion

The effect of room temperature ionic liquid (RTIL) on the formation of the fluorescence ternary complex oxalate-sodium morin-5-sulfonate (NaMSA)-Aluminium(III) has been studied. In weakly acidic medium and in the presence of RTIL, 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF₆), total complex formation is achieved as compared with the formation of the binary complex of NaMSA-Aluminium(III). The fluorescence characteristics of the system allowed the establishment of a very sensitive method for the spectrofluorimetric determination of oxalate ion. The ternary complex formed its highest fluorescence signal at 513 nm and excitation at 420 nm. In these conditions, the method produces a detection limit of 0.57 ng mL^?1. The procedure has been satisfactorily applied to the determination of oxalate ion in a vegetal tissue (spinach leaves).     

Sensitive Fluorescence Detection of Etimicin Based on Derivatives of Formaldehyde and Acetylacetone

A novel fluorescence method for the determination of etimicin is described. Etimicin reacts with acetylacetone and formaldehyde in pH 4.0 Britton-Robinson (B.R.) buffer solution to from a fluorescent substance [I]. Emission spectra of [I] and the reagent blank were overlapped, so the arithmetic emission spectra of the fluorescent substance were obtained by subtracted form the spectra of [I] to the spectra of the reagent blank using the Fluorescence Data Software. There is a linear relationship between the intensity of the arithmetic emission spectra and the concentration of etimicin. Effects of pH, amount of acetylacetone-formaldehyde, and heating time on the determination of etimicin have been examined. Etimicin can be determined over the concentration range of 1.0 to 10.0 μg?mL^?1 with a correlation coefficient of 0.9991. The relative standard deviation (RSD) for 11 repetitive determinations of 5.0 μg?mL^?1 etimicin is 0.22 %. The utility of this method was demonstrated by determining etimicin in commercial samples.     

Spectrofluorimetric quantification of bilirubin using yttrium–norfloxacin complex as a fluorescence probe in serum samples

A simple and sensitive spectrofluorimetric method was developed to determine trace amounts of bilirubin (BR) using yttrium (Y³⁺)–norfloxacin (NFLX) complex as a fluorescence (FL) probe. NFLX can form a stable binary complex with Y³⁺ and markedly enhances the weak FL signal of the NFLX. The FL intensity of the Y³⁺–NFLX complex decreased significantly in the presence of BR in a buffer solution at pH=7.2. Under optimal conditions, the FL intensity decreased according to the BR concentration and showed a good linear relationship in the range of 0.03–2.3 μg mL^?1 of BR with a correlation coefficient of 0.9988. The limit of detection for the determination of BR was 2.8 ng mL^?1 with a relative standard deviation (RSD) of 1.55% for five replicate determination of 0.05 μg mL^-1 BR. The presented method offers higher sensitivity with simple instrumentation and was applied successfully in detecting BR at low concentrations.     

One-step aqueous synthesis of CdS nanoparticles as a novel fluorescence probe for the ultrasensitive detection of DNA

One-step aqueous synthesis of CdS nanoparticles as a novel fluorescence probe for sensitive and selective determination of DNA with synchronous fluorescence spectrometric method has been developed. Different from the traditional organometallic route, in which toxic precursors or solvents might be used, the wet chemical approach demonstrated in this paper is superior in terms of simplicity, using of nontoxic materials, mild synthetic condition and good reproducibility. When Δλ=255 nm, maximum synchronous fluorescence is produced at 264 nm, the synchronous fluorescence intensity of the composite nanoparticles is significantly decreased in the presence of trace DNA at PH 0.91. Under optimal conditions, the linear ranges of the calibration curves are 0.08-30.0 μg mL⁻¹ for ctDNA and 0.05-35.0 μg mL⁻¹ for hsDNA, respectively. The detection limits are 1.5 ng mL⁻¹ for ctDNA and 2.2 ng mL⁻¹ for hsDNA, respectively. Furthermore, the method is successfully applied to the quantification of DNA in synthetic samples. The results show that this proposed method is stable, sensitive and practical for the determination of trace DNA.     

Determination of Protoporphyrin IX Disodium Salt Based on Fluorescence Quenching of Glutathione-Capped Cadmium/Tellurium Quantum Dots

ABSTRACT

Aqueous glutathione-capped cadmium/tellurium quantum dots with a diameter of about 3 nm were synthesized. The fluorescence was quenched in the presence of protoporphyrin IX disodium salt, with the excitation wavelength at 320 nm. Under the optimal conditions, the quenched fluorescence intensity was linear in the range of 0.096–16 µg · mL^?1 with a concentration of protoporphyrin IX disodium salt, and the detection limit (3σ) was 2.8 × 10^?2 µg · mL^?1. The proposed method has been applied to the determination of protoporphyrin in serum samples with satisfactory results. The interaction mechanism was investigated.     

Selectivity Improvement for Spectrofluorimetric Determination of Oseltamivir Phosphate in Human Plasma and in the Presence of Its Degradation Product

A simple and sensitive spectrofluorimetric method has been developed and validated for determination of oseltamivir phosphate (OSP). The proposed method is based on condensation reaction of the primary amino group of OSP with ninhydrin and phenylacetaldehyde in buffered medium (pH 6.5). The formed yellow fluorescent product exhibits excitation and emission maxima at 390 and 460 nm, respectively. The selectivity improvement of our proposed method is based on the water insolubility of the oseltamivir carboxylic acid (OSC) the active metabolite of OSP, which contains the same primary amino group as OSP but cannot, condensed with ninhydrin and phenylacetaldehyde reagents. The different experimental parameters affecting the formation and stability of the reaction product were carefully studied and optimized. The fluorescence intensity concentration plot is rectilinear in the range of 2–15 μg ml^?1 with detection and quantitation limits of 0.32 and 0.98 μg ml^?1, respectively. The proposed method was successfully applied for determination of OSP in commercial capsules, suspension and spiked human plasma with good percentage recovery. In addition, the developed procedure was extended to study the stability of OSP under different stress conditions; including acid and alkali hydrolysis, oxidation, photolysis, and thermal degradation. Furthermore, the kinetic of alkaline and acidic degradation of the cited drug were investigated. The apparent first order degradation rate constants were 0.258 and 0.318 K h^?1 with half times of 2.68 and 2.17 h, for acidic and alkaline degradation, respectively.     

Comparative Study on Three Different Systems of Chemiluminescence Flow‐Injection Determination of Leucogen

Abstract

The effects of three systems on the chemiluminescence (CL) intensity have been studied in this paper, such as leucogen–potassium permanganate–rhodamine B, leucogen–cerium (IV)–rhodamine B, and leucogen–luminol–hydrogen peroxide (called system 1, system 2, and system 3, respectively). The mechanism of these reactions is also discussed. Surfactant (CTMAB) has a remarkably sensitive effect on these systems mentioned above. Therefore, three new flow injection chemiluminescence methods for the determination of leucogen have been established. For system 1, the linear range is 8.0×10^?8 to 4.0×10^?5 g mL^?1, with limits of detection 2×10^?8 g mL^?1; the relative standard deviation is 2.5% (n=11, Cs=4.0×10^?6 g mL^?1). For system 2, the linear range is 1.0×10^?8 to 5.0×10^?6 g mL^?1, with limits of detection 3×10^?9 g mL^?1; the relative standard deviation is 5.1% (n=11, Cs=1.0×10^?6 g mL^?1). For system 3, the linear range is 4.0×10^?8 to 2.0×10^?6 g mL^?1, with limits of detection 1×10^?8 g mL^?1; the relative standard deviation is 1.3% (n=11, Cs=1.0×10^?7 g mL^?1). Compared with the three methods above, system 3 is confirmed as the best method. This method has been applied to the determination of leucogen with satisfactory results.     

Micelle-Enhanced Spectrofluorimetric Method for Determination of Cyproheptadine Hydrochloride in Tablets: Application to In-Vitro Drug Release and Content Uniformity Test

A highly sensitive and simple spectrofluorimetric method was developed for the determination of cyproheptadine hydrochloride (CYP) in its pharmaceutical formulations. The proposed method is based on the investigation of the fluorescence spectral behaviour of CYP in a sodium dodecyl sulphate (SDS) micellar system. In aqueous solution, the fluorescence intensity of CYP was greatly enhanced (150 %) in the presence of SDS. The fluorescence intensity was measured at 410 nm after excitation at 280 nm. The fluorescence–concentration plot was rectilinear over the range 0.2–2.0 μg/mL, with lower detection limit of 0.06 μg/mL. The proposed method was successfully applied to the assay of commercial tablets as well as content uniformity testing. The application of the proposed method was extended to test the in-vitro drug release of CYP tablets, according to USP guidelines. The results were statistically compared with those obtained by official USP method and were found to be in good agreement.     

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.     

Flow‐Injection Chemiluminescence Study of Luminol–Hydrogen Peroxide–Carbendazim System

Abstract

A new flow‐injection chemiluminescence (CL) method is described for the determination of carbendazim. The method is based on the CL reaction of luminol and hydrogen peroxide (H₂O₂). Carbendazim can greatly enhance the chemiluminescence intensity in sodium hydroxide–sodium dihydrogen phosphate (NaOH–NaH₂PO₄) medium (pH=12.6). Under the optimum conditions, the linear range for the determination of carbendazim is 2.00×10^?8 to 2.00×10^?6 g mL^?1 with a detection limit (S/N=3) of 7.24×10^?9 g mL^?1. The relative standard deviation is 1.8% for 1.0×10^?7 g mL^?1 carbendazim (n=8). The proposed method has been applied to the determination of carbendazim in tap‐water samples. Furthermore, the possible enhanced CL mechanism is discussed by examining the CL spectra and fluorescence spectra.     

Vortex-Assisted Liquid–Liquid Microextraction for the Determination of Residual Sulfonamides in Meat Samples with Spectrofluorophotometer

A simple and fast extraction termed vortex-assisted liquid–liquid microrextraction coupled with molecular fluorescence spectroscopy has been developed and used for the detection of three sulfonamides (sulfadiazine sodium, sulfamethoxazole, and sulfaguanidine) in the meat samples. In the vortex-assisted liquid–liquid microrextraction method, 400 µL of nonanoic acid was used as extractant and directly injected into 10 mL centrifuge tube containing a derivative, which sulfonamides derived with o-phthaladehyde. And the extraction solvent was dispersed into the water phase under mechanical force with the vortex-mix. The polar side was reduced and the strong fluorescence produced at λ_ex = 295 nm. Variable parameters affecting the derivatization and vortex-assisted liquid–liquid microrextraction procedure were evaluated and optimized. The vortex-mix substituted effect of disperser solvent in this procedure. The limits of detection were 2.0 ng mL^?1 for sulfadiazine sodium and sulfamethoxazole, 0.5 ng mL^?1 for sulfaguanidine with the relative standard deviations of the method ranging from 2.5% to 6.1%. And the calibration graph was linear from 5 to 5000 ng mL^?1 with coefficient of determinations more than 0.9995. Recoveries of the three sulfonamides on spiked meat samples at different levels were 92.2–102.5%. Finally, the method has been successfully applied to the determination of sulfonamides from meat samples.     

Sensitive Detection of Luteolin Using Thioglycolic Acid–Capped Cadmium Telluride/Cadmium Sulphide Quantum Dots as the Fluorescent Probe

ABSTRACT

A sensitive and simple method for the determination of luteolin (LTL) was developed based on the fluorescence quenching effect of LTL for thioglycolic acid–capped (TGA-capped) CdTe/CdS quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 0.3 to 20.0 µg · mL^?1 with a correlation coefficient of 0.9972, and the detection limit was 7.2 ng · mL^?1. The fluorescence quenching mechanism has been proposed on the basis of electron transfer supported by ultraviolet-visible (UV-Vis) absorption, fluorescence (FL) spectroscopy. The proposed method was successfully applied to the determination of LTL in commercial capsules and human urine samples. It manifested several advantages such as high sensitivity, short analysis time, low cost, and ease of operation.     

Native Fluorescence Determination of Pyridoxine Hydrochloride (Vitamin B6) in Pharmaceutical Preparations After Sorption on Sephadex SP C‐25

A simple, batch mode, solid phase spectrofluorimetric procedure has been developed for the determination of pyridoxine hydrochloride (PY) (vitamin B₆). The method is based on the measurement of the native fluorescence of the analyte at 395 nm (λ_exc = 295 nm) sorbed on Sephadex SP C‐25 beads. The cation‐exchange gel, previously equilibrated with the sample solution, is packed in a 1‐mm quartz cell in which the measurements are performed (diffuse transmitted fluorescence).

The method responds linearly in the measuring range of 50–500, 10–100 and 5–40 μg·l^? 1 with detection limits of 9.5, 2.3 and 0.60 μg·l^? 1 for 10, 25 and 50 ml of sample volume, respectively.

The relative standard deviation (n = 10) for the determination of 100 (10 ml), 60 (25 ml) and 30 μg·l^? 1 (25 ml) of PY is 1.3%, 2.2% and 3.7%, respectively. The method, which shows increasing sensitivity as the sample volume increases, was satisfactorily applied to the determination of vitamin B₆ in pharmaceutical preparations using the procedure for 10 ml of sample.