Validated spectrofluorimetric method for the determination of carbamazepine in pharmaceutical dosage forms after reaction with 4‐chloro‐7‐‐nitrobenzo‐2‐oxa‐1,3‐diazole (NBD‐Cl)

A sensitive and simple spectrofluorimetric method has been developed and validated for the determination of the anti‐epileptic drug carbamazepine (CBZ) in its dosage forms. The method was based on a nucleophilic substitution reaction of CBZ with 4‐chloro‐7‐nitrobenzo‐2‐ oxa‐1,3‐diazole (NBD‐Cl) in borate buffer (pH 9) to form a highly fluorescent derivative that was measured at 530 nm after excitation at 460 nm. Factors affecting the formation of the reaction product were studied and optimized, and the reaction mechanism was postulated. The fluorescence–concentration plot is rectilinear over the range of 0.6–8 µg/mL with limit of detection of 0.06 µg/mL and limit of quantitation of 0.19 µg/mL. The method was applied to the analysis of commercial tablets and the results were in good agreement with those obtained using the reference method. Validation of the analytical procedures was evaluated according to ICH guidelines. Copyright © 2015 John Wiley & Sons, Ltd.     

Steady‐state and synchronous spectrofluorimetric methods for simultaneous determination of aliskiren hemifumarate and amlodipine besylate in dosage forms

Aliskiren hemifumarate (ALS) and amlodipine besylate (AML) were simultaneously determined by two different spectrofluorimetric techniques. The first technique depends on direct measurement of the steady‐state fluorescence intensities of ALS and AML at 313 nm and 452 nm upon excitation at 290 and 375 nm, respectively, in a solvent composed of methanol and water (10: 90, v/v) . The second technique utilizes synchronous fluorimetric quantitative screening of the emission spectra of ALS and AML at 272 and 366 nm, respectively using Δλ of 97 nm. Effects of different solvents and surfactants on relative fluorescence intensity were studied. The method was validated according to ICH guidelines. Linearity, accuracy and precision were found to be satisfactory in both techniques over the concentration ranges of 1–15 and 0.4–4 µg/mL for ALS and AML, respectively. In the first technique, limit of detection and limit of quantification were estimated and found to be 0.256 and 0.776 µg/mL for ALS as well as 0.067 and 0.204 µg/mL for AML, respectively. Also, limit of detection and limit of quantification were calculated in the synchronous method and found to be 0.293 and 0.887 µg/mL for ALS as well as 0.034 and 0.103 µg/mL for AML, respectively. The methods were successfully applied for the determination of the two drugs in their co‐formulated tablets. The results were compared statistically with reference methods and no significant difference was found. The developed methods are rapid, sensitive, inexpensive and accurate for the quality control and routine analysis of the cited drugs in bulk and in pharmaceutical preparations without pre‐separation. Copyright © 2014 John Wiley & Sons, Ltd.     

Second‐derivative synchronous spectrofluorimetric determination of nebivolol hydrochloride and amlodipine besylate in their combined dosage form

A rapid, simple, accurate and highly sensitive spectrofluorimetric method was developed for the simultaneous analysis of nebivolol hydrochloride (NEB) and amlodipine besylate (AML). The method was based on measuring the synchronous fluorescence intensity of the drugs at Δλ = 40 nm in methanol. Various experimental parameters affecting the synchronous fluorescence of the studied drugs were carefully studied and optimized. The calibration plots were rectilinear over concentration ranges of 0.05–1.5 µg/mL and 0.5–10 µg/mL for NEB and AML with limits of detection (LOD) of 0.010 and 0.051 µg/mL and limits of quantitation (LOQ) of 0.031 and 0.156, respectively. The peak amplitudes (²D) of the second derivative synchronous fluorimetry (SDSF) were estimated at 282 nm for NEB and at 393 nm for AML. Good linearity was obtained over the concentration ranges. The proposed method was successfully applied to the determination of the studied compounds in laboratory‐prepared mixtures, commercial single and laboratory‐prepared tablets. The results were in good agreement with those obtained using the comparison method. The mean percent recoveries were found to be 100.12 ± 0.77 and 99.91 ± 0.77 for NEB and AML, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Enhanced spectrofluorimetric determination of esomeprazole and pantoprazole in dosage forms and spiked human plasma using organized media

A simple, sensitive and rapid spectrofluorimetric method was developed for the determination of esomeprazole (EMZ) and pantoprazole (PRZ) in their pharmaceutical formulations and human plasma. The proposed method is based on the fluorescence spectral behavior of EMZ in methanol in the presence of 0.1 m NaOH containing 0.5% methyl cellulose (MC) at 306/345 nm. The fluorescence intensity of EMZ was enhanced about 1.3‐fold and good linearity in the range 0.4–4.0 µg/mL with a lower detection limit of 0.04 µg/mL and lower quantification limit of 0.14 µg/mL. For PRZ, its methanolic solution exhibited marked native fluorescence at 290/325 nm after enhancement (about 2.1‐ or 1.4‐fold) using either 0.025% sodium dodecyl sulfate (SDS) or 0.05% MC in the presence of 0.2 m borate buffer of pH 9.5. The fluorescence–concentration plots of PRZ were rectilinear over the ranges 0.2–2.0 and 0.3–3.0 µg/mL with lower detection limits of 0.02 and 0.03 µg/mL and lower quantification limits of 0.07 and 0.09 µg/mL using sodium dodecyl sulfate and MC, respectively. The method was successfully applied to the analysis of EMZ and PRZ in their commercial dosage forms and the results were in good agreement with those obtained with the comparison method. Furthermore, in a preliminary investigation, the proposed method was extended to the in vitro determination of the two drugs in spiked human plasma and the results were satisfactory. Copyright © 2014 John Wiley & Sons, Ltd.     

Spectrofluorimetric determination of oseltamivir phosphate through derivatization with o‐phthalaldehyde. Application to pharmaceutical preparations with a preliminary study on spiked plasma samples

A simple and sensitive spectrofluorimetric method has been developed and validated for the determination of oseltamivir phosphate (OST) in pharmaceutical preparations. The method is based on the reaction between oseltamivir phosphate and o‐phthalaldehyde in presence of 2‐mercapto‐ethanol in borate buffer, pH 10.8, to give a highly fluorescent product measured at 450 nm after excitation at 336 nm. The different experimental parameters affecting the development and stability of the reaction product were studied and optimized. The fluorescence intensity–concentration plot is rectilinear over the range 0.05–1.0 µg/mL, with a lower detection limit of 5 ng/mL and limit of quantitation of 16 ng/mL. The developed method was successfully applied to the analysis of the drug in its commercial capsules and suspension, mean recoveries of OST were 99.97 ± 1.67% and 100.17 ± 1.18%, respectively (n = 3). Statistical comparison of the results obtained by the proposed and comparison method revealed no significant difference in the performance of the two methods regarding accuracy and precision. The proposed method was further extended to in vitro determination of the studied drug in spiked human plasma as a preliminary investigation; the mean recovery (n = 3) was 98.68 ± 5.8%. A reaction pathway was postulated. Copyright © 2012 John Wiley & Sons, Ltd.     

Fluorimetric determination of proteins using 4‐chloro‐(2′‐hydroxylophenylazo)rhodanine–Ti(IV) complex as a spectral probe

A novel method for the determination of proteins was developed, based on the enhancement of fluorescence with 4‐chloro‐(2′‐hydroxylophenylazo)rhodanine–Ti(IV) [ClHARP–Ti(IV)] complex as a fluorescence probe. The excitation and emission wavelengths of the system were 335 nm and 376 nm, respectively. The presence of bis(2‐ethylhexyl)sulphosuccinate sodium salt (AOT) microemulsion greatly increased the sensitivity of the system. Under optimal conditions, four kinds of proteins, including bovine serum albumin (BSA), human serum albumin (HSA), egg albumin (Ova), and γ‐globin (γ‐G) were studied. The detection limits were 0.182 µg/mL for BSA, 0.0788 µg/mL for HSA, 0.216 µg/mL for Ova and 0.484 µg/mL for γ‐G. The linear ranges of the calibration were 0–12.0, 0–10.0, 0–18.0 and 0–18.0 µg/mL, respectively. The method possessed high sensitivity, good selectivity and was applied to the analysis of protein in milk powder and cornmeal with satisfactory results. Copyright © 2008 John Wiley & Sons, Ltd.     

Development and validation of a sensitive spectrofluorimetric method for the determination of amoxapine in human plasma and urine

A selective and sensitive spectrofluorimetric method was developed and validated for the determination of amoxapine in human plasma and urine. The developed method is based on labeling with 5‐dimethylaminonaphthalene‐1‐sulfonyl chloride (dansyl chloride) and monitoring at 397 nm (excitation)/514 nm (emission). The method was validated for linearity, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy, recovery and robustness. The calibration curves were linear over a concentration range of 250–2500 and 50–1250 ng/mL for plasma and urine, respectively. The LOD values were calculated to be 13.31 and 13.17 ng/mL for plasma and urine, respectively. The proposed method was applied to study of amoxapine in human plasma and urine. Copyright © 2013 John Wiley & Sons, Ltd.     

Validated spectrofluorimetric and spectrophotometric methods for the determination of brimonidine tartrate in ophthalmic solutions via derivatization with NBD‐Cl. Application to stability study

Two simple, selective and accurate methods were developed and validated for the determination of brimonidine tartrate (BT) in pure state and pharmaceutical formulations. Both methods are based on the coupling of the drug with 4‐chloro‐7‐nitro‐2,1,3‐benzoxadiazole in borate buffer (pH 8.5) at 70 °C and measurement of the reaction product spectrophotometrically at 407 nm (method I) or spectrofluorimetrically at 528 nm upon excitation at 460 nm (method II). The calibration graphs were rectilinear over the concentration ranges of 1.0–16.0 and 0.1–4.0 µg/mL with lower detection limits of 0.21 and 0.03, and lower quantification limits of 0.65 and 0.09 µg/mL for methods I and II, respectively. Both methods were successfully applied to the analysis of commercial ophthalmic solution with mean recovery of 99.50 ± 1.00 and 100.13 ± 0.71%, respectively. Statistical analysis of the results obtained by the proposed methods revealed good agreement with those obtained using a comparison method. The proposed spectrofluorimetric method was extended to a stability study of BT under different ICH‐outlined conditions such as alkaline, acidic, oxidative and photolytic degradation. Furthermore, the kinetics of oxidative degradation of the drug was investigated and the apparent first‐order reaction rate constants, half‐life times and Arrhenius equation were estimated. The proposed methods are practical and valuable for routine applications in quality control laboratories for the analysis of BT. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of human albumin in serum and urine samples by constant‐energy synchronous fluorescence method

A sensitive spectrofluorimetric method using constant‐energy synchronous fluorescence technique is proposed for the determination of human albumin without separation. In this method, no reagent was used for enhancement of the fluorescence signal of albumin in the solution. Effects of some parameters, such as energy difference between excitation and emission monochromators (ΔE), emission and excitation slit widths and scan rate of wavelength were studied and the optimum conditions were established. For this purpose factorial design and response surface method were employed for optimization of the effective parameters on the fluorescence signal. The results showed that the scan rate of the wavelength has no significant effect on the analytical signal. The calibration curve was linear in the range 0.1–220.0 µg mL^–1 of albumin with a detection limit of 7.0 × 10^–3 µg mL^–1. The relative standard deviations (RSD) for six replicate measurements of albumin were calculated as 2.2%, 1.7% and 1.3% for 0.5, 10.0 and 100.0 µg mL^–1 albumin, respectively. Furthermore the proposed method has been employed for the determination of albumin in human serum and urine samples. Copyright © 2014 John Wiley & Sons, Ltd.     

Trace analysis of N‐acetyl‐L‐cysteine using luminol–H2O2 chemiluminescence system catalyzed by silver nanoparticles

N‐Acetyl‐L‐cysteine (NAC) can inhibit the luminol–H₂O₂, reaction, which is catalyzed by silver nanoparticles. Based on this phenomenon a new method was developed for NAC determination. Under optimum conditions, a linear relationship between chemiluminescence intensity and NAC concentration was found in the range 0.034–0.98 µg/mL. The detection limit was 0.010 µg/mL (S/N =3), and the relative standard deviation (RSD) was <5% for 0.480 µg/mL NAC (n =5). This simple, sensitive and inexpensive method has been applied to measure the concentration of NAC in pharmaceutical tablets. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimizing the spectrofluorimetric determination of cefdinir through a Taguchi experimental design approach

The aim of this work is to optimize a spectrofluorimetric method for the determination of cefdinir (CFN) using the Taguchi method. The proposed method is based on the oxidative coupling reaction of CFN and cerium(IV) sulfate. The quenching effect of CFN on the fluorescence of the produced cerous ions is measured at an emission wavelength (λ_em) of 358 nm after excitation (λ_ex) at 301 nm. The Taguchi orthogonal array L₉ (3⁴) was designed to determine the optimum reaction conditions. The results were analyzed using the signal‐to‐noise (S/N) ratio and analysis of variance (ANOVA). The optimal experimental conditions obtained from this study were 1 mL of 0.2% MBTH, 0.4 mL of 0.25% Ce(IV), a reaction time of 10 min and methanol as the diluting solvent. The calibration plot displayed a good linear relationship over a range of 0.5–10.0 µg/mL. The proposed method was successfully applied to the determination of CFN in bulk powder and pharmaceutical dosage forms. The results are in good agreement with those obtained using the comparison method. Finally, the Taguchi method provided a systematic and efficient methodology for this optimization, with considerably less effort than would be required for other optimizations techniques. Copyright © 2015 John Wiley & Sons, Ltd.     

Development of sensitive spectrofluorimetric and spectrophotometric methods for the determination of duloxetine in capsule and spiked human plasma

A new, sensitive and selective spectrofluorimetric method has been developed for the determination of duloxetine (DLX) in capsule and spiked human plasma. DLX, as a secondary amine compound, reacts with 7‐chloro‐4‐nitrobenzofurazon (NBD‐Cl), a highly sensitive fluorogenic and chromogenic reagent used in many investigations. The method is based on the reaction between the drug and NBD‐Cl in borate buffer at pH 8.5 to yield a highly fluorescent derivative that is measured at 523 nm after excitation at 478 nm. The fluorescence intensity was directly proportional to the concentration over the range 50–250 ng/mL. The reaction product was also measured spectrophotometrically. The relation between the absorbance at 478 nm and the concentration is rectilinear over the range 1.0–12.0 µg/mL. The methods were successfully applied for the determination of this drug in pharmaceutical dosage form. The spectrofluorimetric method was also successfully applied to the determination of duloxetine in spiked human plasma. The suggested procedures could be used for the determination of DLX in pure form, capsules and human plasma being sensitive, simple and selective. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of the anti‐viral drug Ribavirin in dosage forms via micelle‐enhanced spectrofluorimetric method

A simple and sensitive spectrofluorimetric method was developed for the determination of Ribavirin in pharmaceutical formulations. The proposed method was based on the fluorescence spectral behaviour of Ribavirin in a sodium dodecyl sulfate (SDS) micellar system. In an aqueous acetate buffer solution of pH 4.0, the fluorescence intensity of Ribavirin was significantly enhanced by about 217% in the presence of SDS. Fluorescence intensity was measured at 396 nm after excitation at 270 nm for Ribavirin. The fluorescence‐concentration plot was rectilinear over the range of 0.01‐3.0 µg/mL for Ribavirin with a lower detection limit of 5.02 x 10^‐3 µg/mL. The method was successfully applied to the analysis of the drug in its commercial capsules. Results were in good agreement with those obtained with the official method. The application of the proposed method was extended to stability studies of Ribavirin after exposure to different forced degradation conditions such as acidic, alkaline, photo and oxidative conditions according to ICH guidelines. Copyright © 2012 John Wiley & Sons, Ltd.     

Novel high-performance liquid chromatographic and solid-phase extraction methods for quantitating methadone and its metabolite in spiked human urine

A novel solid-phase extraction (SPE) method and HPLC method were developed for the determination of methadone and its metabolite from spiked human urine. For sample cleanup, a spiked urine sample was pretreated with phosphoric acid followed by a well-thought-out SPE method using a 10-mg Oasis HLB 96-well extraction plate. In this SPE method, the concentration of methanol as well as the pH are optimized to preferentially isolate the analytes of interest from the sample matrix. Low elution volumes (200 μl) are achieved; this eliminates evaporation and reconstitution of the sample solution. Recoveries from human urine matrix were greater than 91% with RSD values less than 4.5%. For the HPLC analysis, the separation was obtained using a SymmetryShield RP₁₈ column with a mobile phase of 0.1% TFA–methanol (60:40, v/v). Good peak shapes were obtained without the need of addition of any competing reagent to the mobile phase. Additionally, significant signal-to-noise enrichment was achieved by diluting the final SPE eluates four-fold with water.     

Determination of puerarin in biological samples and its application to a pharmacokinetic study by flow‐injection chemiluminescence

A simple and sensitive flow injection–chemiluminescence (FI–CL) method has been developed for the determination of puerarin, based on the fact that puerarin can greatly inhibit CL of the luminol–H₂O₂–haemoglobin system. The inhibition of CL intensity was linear to the logarithm of the concentration of puerarin in the range 0.08–10.0 μg/mL (r² = 0.9912). The limit of detection was 0.05 μg/mL (3σ) and the relative standard deviation (RSD) for 1.0 μg/mL (n = 11) of puerarin solution was 1.4%. Coupled with solid‐phase extraction (SPE) as the sample pretreatment, the determination of puerarin in biological samples and a preliminary pharmocokinetic study of puerarin in rats were performed. The recoveries for plasma and urine at three different concentrations were 89.2–110.0% and 91.4–104.8%, respectively. The pharmacokinetics of puerarin in plasma of rat coincides with the two‐compartment open model. The T_1/2α, T_1/2β, CL/F, V_Z/F, AUC_{(0 – t)}, MRT_{(0 – ∞)}, T_max and C_max were 0.77 ± 0.21 h, 7.55 ± 2.64 h, 2.43 ± 1.02 L/kg/h, 11.40 ± 3.45 L/kg, 56.67 ± 10.65 mg/h/L, 5.04 ± 2.78 h, 1.00 ± 0.35 h and 19.70 ± 4.67 μg/mL, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Spectrofluorimetric method for the determination of sulpiride in pharmaceutical preparations and human plasma through derivatization with 2‐cyanoacetamide

A sensitive and accurate spectrofluorimetric method has been developed for the determination of sulpiride in pharmaceutical preparations and human plasma. The developed method is based on the derivatization reaction of 2‐cyanoacetamide with sulpiride in 30% ammonical solution. The fluorescent derivatized reaction product exhibited maximum fluorescence intensity at 379 nm after excitation at 330 nm. The optimum conditions for derivatization reactions were studied and the fluorescence intensity versus concentration plot was found to be linear over the concentration range 0.2–20.0 µg/mL with a correlation coefficient of 0.9985. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.82 and 2.73 ng/mL, respectively. The proposed method was validated according to ICH guidelines. The effects of common excipients and co‐administered drugs were also studied. The accuracy of the method was checked using the standard addition method and percent recoveries were found to be in the range of 99.00–101.25% for pharmaceutical preparations and 97.00–97.80% for spiked human plasma. The method was successfully applied to commercial formulations and the results obtained for the proposed method were compared with a high‐performance liquid chromatography reference method and statistically evaluated using the Student's t‐test for accuracy and the variance ratio F‐test for precision. A reaction pathway was also proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Derivative emission spectrofluorimetry for the simultaneous determination of guaifenesin and phenylephrine hydrochloride in pharmaceutical tablets

Rapid, simple and sensitive derivative emission spectrofluorimetric methods have been developed for the simultaneous analysis of binary mixtures of guaifenesin (GUA) and phenylephrine hydrochloride (PHE). The methods are based upon measurement of the native fluorescence intensity of the two drugs at λ_ex = 275 nm in methanolic solutions, followed by differentiation using first (D1) and second (D2) derivative techniques. The derivative fluorescence intensity–concentration plots were rectilinear over a range of 0.1–2 µg/mL for both GUA and PHE. The limits of detection were 0.027 (D1, GUA), 0.025 (D2, GUA), 0.031 (D1, PHE) and 0.033 (D2, PHE) µg/mL and limits of quantitation were 0.089 (D1, GUA), 0.083 (D2, GUA), 0.095 (D1, PHE) and 0.097 (D2, PHE) µg/mL. The proposed derivative emission spectrofluorimetric methods (D1 and D2) were successfully applied for the determination of the two compounds in binary mixtures and tablets with high precision and accuracy. The proposed methods were fully validated as per ICH guidelines. Copyright © 2014 John Wiley & Sons, Ltd.     

Derivative emission spectrofluorimetry: Application to the analysis of newly approved FDA combination of ibuprofen and famotidine in tablets

A new combination of ibuprofen (NSAID) and famotidine (H₂ receptor antagonist) was recently approved by the FDA. It was formulated to relief pain while decreasing the risk of ulceration, which is a common problem for patients receiving NSAID. A rapid and simple derivative emission spectrofluorimetric method is proposed for the simultaneous analysis of this combination in their pharmaceutical preparation. The method is based upon measurement of the native fluorescence intensity of the two drugs at λ_ex = 233 nm in acetonitrile. The emission data were differentiated using the first (D1) derivative technique. The plots of derivative fluorescence intensity versus concentration were rectilinear over a range of 2–35 and 0.4–8 µg/mL for both ibuprofen (IBU) and famotidine (FAM), respectively. The method was sensitive as the limits of detection were 0.51 and 0.12 µg/mL and limits of quantitation were 1.70 and 0.39 µg/mL, for IBU and FAM respectively. The proposed derivative emission spectrofluorimetric method was successfully applied for the determination of the two drugs in their synthetic mixtures and tablets with good accuracy and precision. The proposed method was validated as per ICH guidelines. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimization of ASE and SPE conditions for the HPLC‐FLD detection of piperazine in chicken tissues and pork

Accelerated solvent extraction (ASE) and solid‐phase extraction (SPE) conditions were optimized by a high‐performance liquid chromatography‐fluorescence detector (HPLC‐FLD) method for the detection of piperazine in chicken tissues and pork. Piperazine residues were determined by precolumn derivatization with trimethylamine and dansyl chloride. Samples were extracted with 2% formic acid in acetonitrile using an ASE apparatus and purified using a Strata‐X‐C SPE column. The monosubstituted product of the reaction of piperazine with dansyl chloride was 1‐dansyl piperazine (1‐DNS‐piperazine). Chromatographic separations were performed on an Athena C₁₈ column (250 × 4.6 mm, id: 5 μm) with gradient elution using ultrapure water and acetonitrile (5:95, V/V) as the mobile phase. The calibration curves showed good linearity over a concentration range of LOQ‐200.0 μg/kg with a coefficient of determination (R²) ≥ .9992. The recoveries and relative standard deviations (RSD values) ranged from 78.49% to 97.56% and 1.19% to 5.32%, respectively, across the limit of quantification (LOQ) and 0.5, 1, and 2.0 times the maximum residue limit (MRL; μg/kg). The limits of detection (LODs) and LOQs were 0.96 to 1.85 μg/kg and 3.20 to 5.50 μg/kg, respectively. The method was successfully applied for the validation of animal products in the laboratory.     

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.