Environmentally friendly protocol for the determination of sitagliptin phosphate in pharmaceutical preparations and biological fluids using l-tyrosine as a fluorescence probe

A responsive spectrofluorometric method was developed for the determination of sitagliptin phosphate using l -tyrosine as a fluorescence probe. The fluorescence intensity of l -tyrosine was quenched with sitagliptin phosphate. The fluorescence intensity was recorded at 307 nm using a 272 nm excitation wavelength. The calibration plot between fluorescence intensity and the concentration of drug was linear in the range of 0.1 to 2.0 mM with a good correlation value of 0.997. The limit of detection and quantification were established to be 3.7 × 10⁻⁴ and 1.23 × 10⁻³ mM, respectively. Commonly used excipients did not interfere with sitagliptin phosphate measurement. The proposed method was used to measure the sitagliptin phosphate in its standard type, dosage form, and biological samples. The percent recovery ranged from 97.41–103.36%. The static quenching was shown to be responsible for quenching as indicated by the Stern–Volmer plot. The method was validated using ICH guidelines and profitably applied for the content uniformity test, resulting in a high percent recovery and small relative standard deviation. The proposed approach is effortless, susceptible, selective, economic, and provides a high precision and accuracy, and can be used to determine sitagliptin phosphate in the pharmaceutical industry.     

Chemiluminescence determination of moxifloxacin in pharmaceutical and biological samples based on its enhancing effect of the luminol–ferricyanide system using a microfluidic chip

A sensitive determination of a synthetic fluoroquinolone antibacterial agent, moxifloxacin (MOX), by an enhanced chemiluminescence (CL) method using a microfluidic chip is described. The microfluidic chip was fabricated by a soft‐lithographic procedure using polydimethyl siloxane (PDMS). The fabricated PDMS microfluidic chip had three‐inlet microchannels for introducing the sample, chemiluminescent reagent and oxidant, and a 500 µm wide, 250 µm deep and 82 mm long microchannel. An enhanced CL system, luminol–ferricyanide, was adopted to analyze the MOX concentration in a sample solution. CL light was emitted continuously after mixing luminol and ferricyanide in the presence of MOX on the PDMS microfluidic chip. The amount of MOX in the luminol–ferricyanide system influenced the intensity of the CL light. The linear range of MOX concentration was 0.14–55.0 ng/mL with a correlation coefficient of 0.9992. The limit of detection (LOD) and limit of quantification (LOQ) were 0.06 and 0.2 ng/mL respectively. The presented method afforded good reproducibility, with a relative standard deviation (RSD) of 1.05% for 10 ng/mL of MOX, and has been successfully applied for the determination of MOX in pharmaceutical and biological samples. Copyright © 2013 John Wiley & Sons, Ltd.     

Sensitive spectrofluorometric method for the determination of ascorbic acid in pharmaceutical nutritional supplements using acriflavine as a fluorescence reagent

An easily performed, specific, sensitive, rapid, reliable and inexpensive procedure for the spectrofluorometric quantitation of ascorbic acid was proposed using acriflavine as a fluorescence quenching reagent. The procedure was based on the determined quenching effect of ascorbic acid on the natural fluorescence signal of acriflavine and the reaction between ascorbic acid and acriflavine in Britton–Robinson buffer solution (pH 6) to produce an ion‐associated complex. The reduction in acriflavine fluorescence intensity was detected at 505 nm, while excitation occurred at 265 nm. The relationship between quenching fluorescence intensity (?F) and concentration of ascorbic acid was linear (R² = 0.9967) within the range 2–10 μg/ml and with a detection limit of 0.08 μg/ml. No significant interference was detected from other materials often found in pharmaceutical nutritional tablets. The obtained results were compared with those from high‐performance liquid chromatography and appeared in good agreement, with no important differences in precision or accuracy. The proposed spectrofluorimetric method was used to determine the amount of ascorbic acid in a number of commercial pharmaceutical nutritional supplement tablets with a 95% confidence performance.     

Validated spectrofluorimetric method for the determination of clonazepam in pharmaceutical preparations

A simple, highly sensitive and validated spectrofluorimetric method was applied in the determination of clonazepam (CLZ). The method is based on reduction of the nitro group of clonazepam with zinc/CaCl₂, and the product is then reacted with 2‐cyanoacetamide (2‐CNA) in the presence of ammonia (25%) yielding a highly fluorescent product. The produced fluorophore exhibits strong fluorescence intensity at ?_em = 383 nm after excitation at ?_ex = 333 nm. The method was rectilinear over a concentration range of 0.1–0.5 ng/mL with a limit of detection (LOD) of 0.0057 ng/mL and a limit of quantification (LOQ) of 0.017 ng/mL. The method was fully validated and successfully applied to the determination of CLZ in its tablets with a mean percentage recovery of 100.10 ± 0.75%. Method validation according to ICH Guidelines was evaluated. Statistical analysis of the results obtained using the proposed method was successfully compared with those obtained using a reference method, and there was no significance difference between the two methods in terms of accuracy and precision. Copyright © 2015 John Wiley & Sons, Ltd.     

Kinetic spectrophotometric method for the determination of ramipril in pharmaceutical formulations

The objective of this research was to develop a kinetic spectrophotometric method for determination of ramipril in pure form and pharmaceutical formulations. The method was based on the reaction of carboxylic acid group of the drug with a mixture of potassium iodate (KIO₃) and potassium iodide (KI) in aqueous medium at room temperature. The reaction is followed spectrophotometrically by measuring the increase in absorbance at 352 nm as a function of time. The initial-rate and fixed-time methods were adopted for constructing the calibration curves. Both the calibration curves were linear in the concentration range of 10.0–70.0 μg mL⁻¹. The detection limits were 0.02μg mL⁻¹ and 0.15-μg mL⁻¹ for initial rate and fixed time methods, respectively. The proposed methods are validated statistically and through recovery studies. The point and interval hypothesis tests have been performed confirming that there is no significant difference between the proposed methods and the reference method. The experimental true bias of all samples is less than ±2%. The methods have been successfully applied to the determination of ramipril in tablets and capsules. Published: October 27, 2005     

CdS nanoparticles‐ enhanced chemiluminescence and determination of baicalin in pharmaceutical preparations

CdS nanoparticles (CdS NPs) of different sizes were synthesized by the citrate reduction method. It was found that CdS NPs could enhance the chemiluminescence (CL) of the luminol‐potassium ferricyanide system and baicalin could inhibit CdS NPs‐enhanced luminol‐potassium ferricyanide CL signals in alkaline solution. Based on this inhibition, a flow‐injection CL method was established for determination of baicalin in pharmaceutical preparations and human urine samples. Under optimized conditions, the linear range for determination of baicalin was 5.0 x 10^?6 to 1.0 x 10^?3 g/L. The detection limit at a signal‐to‐noise ratio of 3 was 1.7 x 10 ^?6 g/L. CL spectra, UV‐visible spectra and transmission electron microscopy (TEM) were used to investigate the CL mechanism. The method described is simple, selective and obviates the need of extensive sample pretreatment. Copyright © 2012 John Wiley & Sons, Ltd.     

Synchronous spectrofluorometric methods for simultaneous determination of diphenhydramine and ibuprofen or phenylephrine in combined pharmaceutical preparations

Simple and rapid synchronous fluorometric methods were adopted and validated for the simultaneous analysis of a binary mixture of diphenhydramine (DIP) and ibuprofen (IBU) ( Mix I) or DIP and phenylephrine (PHE) (Mix II) in their co‐formulated pharmaceuticals without prior separation. Analysis of Mix I is based on the measurement of the peak amplitudes (D¹) of synchronous fluorescence intensities at 265.1 nm for DIP and 260 nm for IBU. The relationship between the concentration and the amplitude of the first‐derivative synchronous fluorescence spectra showed good linearity over the concentration ranges 0.50–10.00 μg ml^?1 and 0.50–7.90 μg ml^?1 for DIP and IBU, respectively. Analysis of Mix II was based on measurement of the peak amplitude (D¹) synchronous fluorescence intensities at 230 nm for DIP and at 253.9 nm for PHE. Moreover, for Mix II, the peak amplitude (D²) synchronous fluorescence intensities were measured at 227.9 nm for DIP and at 264.9 nm for PHE. Calibration plots were rectilinear over the concentration range 0.30–3.50 μg ml^?1 and 0.03–0.75 μg ml^?1 for DIP and PHE, respectively. The proposed methods were successfully applied to determine the studied compounds in pure form and in pharmaceutical preparations.     

New spectrofluorimetric method for determination of cephalosporins in pharmaceutical formulations

A simple, accurate, precise spectrofluorimetric method has been proposed for the determination of three cephalosporins, namely, cefixime (cefi), cephalexine (ceph), and cefotaxime sodium (cefo) in pharmaceutical formulations. This method is based on a reaction between cephalosporins with 8‐hydroxy‐1,3,6‐pyrenetrisulfonic acid trisodium salt (HPTS) in alkaline medium, at pH 12.0 for cefi and 13.0 for ceph and cefo to give highly fluorescent derivatives extracted with chloroform and subsequent measurements of the formed fluorescent products at 520, 500 and 510 nm after excitation at 480, 470 and 480 nm for cefi, ceph and cefo respectively. The optimum experimental conditions have been studied. Beer's law is obeyed over concentrations of 10–60 ng/mL, 5–35 ng/mL and 10–60 ng/mL for cefi, ceph and cefo, respectively. The detection limits were 4.20 ng/mL, 2.54 ng/mL and 4.09 ng/mL for cefi, ceph and cefo, respectively, with a linear regression correlation coefficient of 0.99783, 0.99705 and 0.9978 and recoveries in ranges 96.96–105.77, 96.13–102.55 and 95.45–105.39% for cefi, ceph and cefo, respectively. This method is simple and can be applied for the determination of cefi, ceph and cefo in pharmaceutical formulations in quality control laboratories. Copyright © 2012 John Wiley & Sons, Ltd.     

Sensitive determination of enoxacin in pharmaceutical formulations by its quench effect on the fluorescence of glutathione‐capped CdTe quantum dots

A sensitive and simple method for the determination of enoxacin (ENX) was developed based on the fluorescence quenching effect of ENX for glutathione (GSH)‐capped CdTe quantum dots (QDs). Under optimum conditions, a good linear relationship was obtained from 4.333 × 10^?9 mol?L^?1 to 1.4 × 10^?5 mol?L^?1 with a correlation coefficient (R) of 0.9987, and the detection limit (3σ/K) was 1.313 × 10^?9 mol?L^?1. The corresponding mechanism has been proposed on the basis of electron transfer supported by ultraviolet–visible (UV) light absorption, fluorescence spectroscopy, and the measurement of fluorescence lifetime. The method has been applied to the determination of ENX in pharmaceutical formulations (enoxacin gluconate injections and commercial tablets) with satisfactory results. The proposed method manifested several advantages such as high sensitivity, short analysis time, low cost and ease of operation. Copyright © 2015 John Wiley & Sons, Ltd.     

The fluorescence quenching of Ru(bipy)32+: an application for the determination of bilirubin in biological samples

A simple, sensitive and efficient fluorescence method has been established for the quantitative analysis of bilirubin. The fluorometric determination method was based on the kinetic quenching of ruthenium(II) fluorescence. The quenching effect may be due to the complexation reaction of bilirubin with ruthenium(II). Therefore, the effects of ruthenium concentrations and different surfactants have been studied. Under the optimized experimental parameters, the fluorescence intensity decreased proportionally with the bilirubin concentration and linearity was established in the range of 3.3 × 10⁻⁷ to 3.0 × 10⁻⁴ M bilirubin. The detection limit calculated from the calibration graph was found to be 5.2 × 10⁻⁸ M. The relative standard deviation (RSD) of 10 consecutive measurements of 8.0 × 10⁻⁶ M bilirubin was 3.0%, while the recoveries of bilirubin in both human serum and urine samples were obtained in the range 94.0–99.5%. The interference study shows that the developed fluorescence based technique is fast, easy to carry out and shows negligible interference. The developed technique was successfully applied for the analysis of bilirubin in human urine and serum samples. All the experimental results and quality parameters confirmed the sensitivity and reproducibility of the proposed technique for bilirubin determination in human urine and serum samples .     

Fullerene-C60-modified edge plane pyrolytic graphite electrode for the determination of dexamethasone in pharmaceutical formulations and human biological fluids

Electrochemical behaviour of dexamethasone at the fullerene-C(60)-modified pyrolytic graphite electrode (PGE) has been investigated using Osteryoung square wave voltammetry (SWV). Compared to a bare PGE and fullerene-C(60)-modified glassy carbon electrode (GCE), the fullerene-C(60)-modified edge plane PGE exhibited an apparent shift of the peak potential to less negative potentials with a marked enhancement in the current response of dexamethasone. The peak potential was linearly dependent on pH with dE(p)/dpH as 59 mV/pH. Calibration plot having good linearity with a correlation coefficient 0.9983 is obtained in the concentration range of 0.05-100 microM and the sensitivity of the method has been found to be 0.685 microA microM(-1). The detection limit is estimated to be 5.5 x 10(-8)M. The electrode showed good sensitivity, stability and reproducibility. The practical analytical utility of the method is illustrated by quantitative determination of dexamethasone in several commercially available pharmaceutical formulations and human blood plasma of patients being treated with dexamethasone. HPLC method was used to compare the results obtained for the quantitative estimation of dexamethasone in biological fluids.     

Spectrofluorimetric determination of tobramycin in human serum and pharmaceutical preparations by derivatization with fluorescamine

A simple, sensitive and selective spectrofluorimetric method has been developed for the determination of tobramycin (TOB) in human serum and pharmaceutical preparations. The method is based on the reaction between the primary amino group of TOB and fluorescamine in borate buffer, pH 8.5, to give a highly fluorescent derivative which is measured at 469 nm after excitation at 388 nm. The fluorescence intensity was directly proportional to the concentration over the range 300–1500 ng/mL, with a limit of detection of 65 ng/mL and limit of quantitation of 215 ng/mL. All variables were investigated to optimize the reaction conditions. The method was validated according to International Conference on Harmonization guidelines in terms of specificity, linearity, limit of detection, limit of quantification, accuracy, precision and robustness. Good recoveries were obtained ranging from 97.4 to 100.64%, indicating that no interference was observed from concomitants usually present in pharmaceutical dosage forms. The method was successfully, applied for the analysis of the drug substance in its pharmaceutical preparations and spiked serum samples. Copyright © 2013 John Wiley & Sons, Ltd.     

A selective determination of copper ions in water samples based on the fluorescence quenching of thiol‐capped CdTe quantum dots

CdTe quantum dots (QDs) capped with different stabilizers, i.e. thioglycolic acid (TGA), 3‐mercaptopropionic acid (MPA) and glutathione (GSH) were investigated as fluorescent probes for the determination of Cu²⁺. The stabilizer was shown to play an important role in both the sensitivity and selectivity for the determination of Cu²⁺. TGA‐capped CdTe QDs showed the highest sensitivity, followed by the MPA and GSH‐capped CdTe QDs, respectively. The TGA‐ and MPA‐capped CdTe QDs were not selective for Cu²⁺ that was affected by Ag⁺. The GSH‐capped CdTe QDs were insensitive to Ag⁺ and were used to determine Cu²⁺ in water samples. Under optimal conditions, quenching of the fluorescence intensity (F₀/F) increased linearly with the concentration of Cu²⁺ over a range of 0.10–4.0 µg/mL and the detection limit was 0.06 µg/mL. The developed method was successfully applied to the determination of Cu²⁺ in water samples. Good recoveries of 93–104%, with a relative standard deviation of < 6% demonstrated that the developed simple method was accurate and reliable. The quenching mechanisms were also described. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimization and validation of spectrofluorimetric method for determination of cefadroxile and cefuroxime sodium in pharmaceutical formulations

A simple, accurate, precise and validated spectrofluorimetric method is proposed for the determination of two cephalosporins, namely, cefadroxile (cefa) and cefuroxime sodium (cefu) in pharmaceutical formulations. The method is based on a reaction between cephalosporins with 1,2‐naphthoquinone‐4‐sulfonate in alkaline medium, to form fluorescent derivatives that are extracted with chloroform and subsequently measured at 610 and 605 nm after excitation at 470 and 460 nm for cefa and cefu respectively. The optimum experimental conditions have been studied. Beer's law is obeyed over the concentrations of 20–70 ng/mL and 15–40 ng/mL for cefa and cefu, respectively. The detection limits were 4.46 ng/mL and 3.02 ng/mL with a linear regression correlation coefficient of 0.9984 and 0.998, and recoveries ranging 97.50–109.96% and 95.73–98.89% for cefa and cefu, respectively. The effects of pH, temperature, reaction time, 1,2‐naphthoquinone‐4‐sulfonic concentration and extraction solvent on the determination of cefa and cefu, have been examined. The proposed method can be applied for the determination of cefa and cefu in pharmaceutical formulations in quality control laboratories. Copyright © 2013 John Wiley & Sons, Ltd.     

Two green and sensitive spectrofluorimetric approaches for determination of Ambroxol and guaifenesin in their single and combined pharmaceutical formulations

Ambroxol hydrochloride (AMX) and guaifenesin (GFN) are approved drugs utilized to treat coughs through their potent mucolytic and expectorant properties. Due to their massive, combined administration in many illnesses, there is a persistent need for their concurrent estimation in different pharmaceutical formulations. Two sensitive, environmentally friendly spectrofluorimetric methods were developed. AMX was determined using the first method (I) without interference from GFN. This method depends on the quenching of Erythrosine B (EB) native fluorescence at 552 nm after excitation at 527 nm due to the formation of a non-fluorescent AMX-EB ion-pair complex in Britton–Robinson buffer (BRB) solution pH (3.5). The concentration plot is linear over the 0.25–5.0 μg/mL range, with a mean percent found value of 99.74%. Method (II) depends on measuring the native fluorescence of aqueous GFN solution at two analytical wavelengths, either 300 or 600 nm, after excitation at 274 nm. Relative fluorescence intensity (RFI)–concentration plots are linear over the ranges of 0.02–0.5 and 0.1–2.0 μg/ml, with mean percent found at 99.96% and 99.91% at dual wavelengths, respectively. The proposed methods were successfully applied to assay both drugs in raw materials and different single and combined pharmaceutical formulations. These methods have been thoroughly validated following International Committee on Harmonisation (ICH) guidelines. National Environmental Methods Index, Analytical Eco-Scale, and Green Analytical Procedure Index were used to prove greenness, thereby enhancing their applicability. The proposed techniques provide straightforward, precise, and cost-effective solutions for routine formulation analysis in quality control laboratories.     

Utilization of erythrosine B in spectrofluorimetric quenching analysis of amlodipine and perindopril in pharmaceutical and biological matrices

A spectrofluorimetric approach that is sensitive, simple, validated, and cost-effective has been proposed for the estimation of amlodipine (AML) and perindopril (PER) in their bulk powders, pharmaceutical formulations, and spiked human plasma. The recommended approach utilized the quantitative quenching effect of the two cited drugs on the fluorescence intensity of erythrosine B, as a result of complex binary reactions among each drug with erythrosine B at pH 3.5 (Teorell and Stenhagen buffer). The quenching of erythrosine B fluorescence was recorded at 554 nm after excitation at 527 nm. The calibration curve was detected in the range 0.25–3.0 μg ml⁻¹, with a correlation coefficient of 0.9996 for AML, and 0.1–1.5 μg ml⁻¹, with a correlation coefficient of 0.9996 for PER. The established spectrofluorimetric approach was validated for the estimation of the cited drugs with high sensitivity regarding International Council on Harmonization guidelines. Therefore, the established approach could be utilized for quality control of the cited drugs in their pharmaceutical formulations.     

Rapid chemiluminometric determination of gabapentin in pharmaceutical formulations exploiting pulsed‐flow analysis

In this study, a straightforward and automated pulsed flow‐based procedure was developed for the chemiluminometric determination of gabapentin [1‐(aminomethyl)cyclo‐hexaneacetic acid], a new generation antiepileptic drug, in different formulated dosage forms. The software‐controlled time‐based injection method capitalizes on the decrease of the background chemiluminescence (CL) readout of the luminol–hypochlorite reaction in the presence of gabapentin. In short, gabapentin works as a hypochlorite scavenger. The analytical procedure was implemented in a multi‐pumping flow network furnished with a suite of microdispensing solenoid‐actuated pumps. The diaphragm‐type micropumps might be configured to operate as fluid propellers, commutation units and metering injectors. A dynamic linear working range for gabapentin concentrations in the range 60–350 µmol/L was obtained, with an estimated detection limit of 40 µmol/L. The flow analyser handles about 41 injections/h and yields precise results (RSD < 2%). The miniaturized flow analyser thus has potential to be exploited for in‐line monitoring of drug manufacturing within the quality assurance framework of modern pharmaceutical companies. Copyright © 2008 John Wiley & Sons, Ltd.     

Sensitive spectrofluorimetric determination of tizanidine in pharmaceutical preparations,human plasma and urine through derivatization with dansyl chloride

A sensitive spectrofluorimetric method was developed for the determination of tizanidine in human plasma, urine and pharmaceutical preparations. The method is based on reaction of tizanidine with 1‐dimethylaminonaphthalene‐5‐sulphonyl chloride (dansyl chloride) in an alkaline medium to form a highly fluorescent derivative that was measured at 511 nm after excitation at 383 nm. The different experimental parameters affecting the fluorescence intensity of tizanidine was carefully studied and optimized. The fluorescence–concentration plots were rectilinear over the ranges 50–500 and 20–300 ng/mL for plasma and urine, respectively, detection limits of 1.81 and 0.54 ng/mL and quantification limits of 5.43 and 1.62 ng/mL for plasma and urine, respectively. The method presents good performance in terms of linearity, detection and quantification limits, precision, accuracy and specificity. The proposed method was successfully applied for the determination of tizanidine in pharmaceutical preparations. The results obtained were compared with a reference method, using t‐ and F‐tests. Copyright © 2011 John Wiley & Sons, Ltd.     

A sensitive fluorescence quenching method for the detection of tartrazine with acriflavine in soft drinks

In this work, a simple, rapid, sensitive, selective spectrofluorimetric method was applied to detect tartrazine. The fluorescence of acriflavine could be efficiently quenched by tartrazine. The method manifested real time response as well as presented satisfied linear relationship to tartrazine. The linear response range of tartrazine (R² = 0.9995) was from 0.056 to 5 μmol L^?1. The detection limit (3σ/k) was 0.017 μmol L^?1, indicating that this method could be applied to detect traces of tartrazine. The accuracy and precision of the method was further assured by recovery studies via a standard addition method, with percentage recoveries in the range of 96.0% to 103.0%. Moreover, a quenching mechanism was investigated systematically by the linear plots at varying temperatures based on the Stern–Volmer equation, fluorescence lifetime and UV–visible absorption spectra, all of which proved to be static quenching. This sensitive, selective assay possessed a great application prospect for the food industry owing to its simplicity and rapidity for the detection of tartrazine.     

Optical ascorbic acid sensor based on the fluorescence quenching of silver nanoparticles

A sensitive and selective fluorimetric sensor for the assay of ascorbic acid (AA) using silver nanoparticles as emission reagent was investigated. In this study, silver nanoparticles were prepared based on aqueous–gaseous phase reaction of silver nitrate solution and ammonia gas. The nanoparticles were water‐soluble, stable and had a narrow emission band. They were used as a fluorescence probe for the assay of ascorbic acid on its quenching effect on the emission of silver nanoparticles. The principal reason for quenching is likely to be a complexation between ascorbic acid and silver nanoparticles. The quenching mechanism was established by Stern–Volmer law. Under the optimum conditions, the quenched fluorescence intensity was linear with the concentration of ascorbic acid in the range of 4.1 × 10^?6 to 1.0 ×10^?4 m (r = 0.9985) with a detection limit of 1.0 × 10^?7 m . The RSD for repeatability of the sensor for the assay of ascorbic acid concentration of 3.0 × 10^?5 and 4.0 × 10^?6 m was found to be 1.5 and 1.3%, respectively. The proposed method was applied to the determination of ascorbic acid in vegetables and vitamin C tablets. Copyright © 2009 John Wiley & Sons, Ltd.