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A sensitive and specific HPLC method was developed and validated for the simultaneous determination of vincamine and its potential degradant (metabolite), vincaminic acid. Chromatographic separation was achieved on a Spheri-5 RP-C8 (5 μm) (220×4.6 mm i.d.) column using a mobile phase composed of acetonitrile and 0.05 M sodium acetate, pH 4.0 (30:70, v/v) at a flow rate of 1 mL/min. The UV detector was set at 270 nm and the quantitation of the analytes was based on the peak areas. The method was proven to be accurate and precise with linearity ranges of 0.1-50 and 0.4-50 μg/mL for vincamine and vincaminic acid, respectively. The limits of detection were 0.03 and 0.08 μg/mL for vincamine and vincaminic acid, respectively. The method was applied to serve two goals. First; stability-indicating assay of vincamine in its pharmaceutical formulations, in addition, the determination of vincaminic acid down to a level of 0.07% in presence of excess of the parent drug. Second; drug monitoring of vincamine and its main metabolite, vincaminic acid in human plasma/urine samples taken from a healthy volunteer treated with 60 mg oral dose of vincamine. The accuracy of the method was satisfactory (recovery ＞ 97%). The overall standard deviation ranged from 1.4 to 2.3%.

The article handles two related subjects. First, it's the study of forced-acid/heat degradation of phenazopyridine HCl (PAP). The reaction pathway was evidenced with different criteria. A three wavelengths-based reversed phase HPLC method with an isocratic mobile phase system (acetonitrile: acetate buffer of pH 4, 1:1, v/v) was developed as a stability-indicating assay of particular application for simultaneous determination of PAP and its related degradation products/impurity. The analysis time was less than 8 min at a flow rate of 1 mL min^(-1). The detection and quantification limits of degradation products/impurity were in the ranges of 0.02-0.1 and 0.06-0.3 μg mL^(-1), respectively. The impurity profile of PAP in drug substance and tablets was investigated and could be determined down to a level between 0.03% and 0.005%. The second subject deals with establishment of spectrofluorimetric method for quantification of phenol (PH) and 2,6-diaminopyridine (DAP), as degradant/impurity in PAP, at trace concentrations. The method is based on measurement of the native fluorescence in acidic ethanol solution (DAP) or in aqueous acidic solution (PH). The method was applied to check the purity/stability of PAP in drug substance and in tablets dosage form.

A simple, rapid and sensitive kinetic spectrophotometric method is described for the analysis of naftidrofuryl oxalate (NF) and vincamine (VN) in pure form and in their pharmaceutical preparations. The procedure was based on the kinetic investigation of the oxidation of the studied drugs with alkaline potassium permanganate and the absorbance of the produced manganate species was measured at 610 nm. Variables affecting the color development were investigated and the conditions were optimized. The concentration of the studied drugs was calculated using the regression equations for the fixed-time method. The determination of the two drugs by fixed absorbance and rate constant methods was possible but the fixed time method was more applicable. The reliability and analytical performance of the proposed method including linearity, ranges, precision, accuracy, detection and quantification limits were statistically validated. Calibration graphs are linear over the concentration ranges of 3-15 μg/mL and 4-14 μg/mL for NF and VN, respectively. The proposed method was satisfactorily applied for analysis of pharmaceutical preparations containing the studied drugs. A proposal of the reaction pathway was postulated.

Summary This work deals with the development, validation and application of an HPLC-DAD method for the determination of a ternary mixture containing amoxicillin (AX), metronidazole (MZ) and the proton pump inhibitor rabeprazole sodium (RB). This triple therapy is used for treatment of Helicobacter pylori infection. Effective chromatographic separation between the three drugs was achieved using Thermo Hypersil BDS-C8 (4.6 × 250 mm, 5 μm particle size) column and a mobile phase composed of phosphate buffer pH 7 and acetonitrile (70: 30, by volume). The mobile phase was pumped isocratically at a flow rate of 1 mL/min. Quantification of the analytes was based on measuring their peak areas at 230 nm for both AX and RB, and at 319 nm for MZ. AX, MZ and RB eluted at retention times 2.36, 3.55 and 8.72 min respectively. The reliability and analytical performance of the proposed HPLC procedure were statistically validated with respect to linearity, ranges, precision, accuracy, selectivity, robustness, detection and quantification limits. The linear dynamic ranges were 25–250, 25–250 and 5–50 μg/mL for AX, MZ and RB respectively with correlation coefficients > 0.9998. The validated method was successfully applied to the analysis of several laboratory-prepared mixtures as well as simulated intestinal fluid samples spiked with the three drugs.

This work describes the stability-indicating determination of the H2-receptor antagonist nizatidine in its bulk and capsules dosage form using high performance liquid chromatography coupled with diode array detector (HPLC-DAD). The developed method involved the use of Thermo Hypersil BDS-C8 (4.6 × 250 mm, 5 μm particle size) column and a mobile phase composed of 0.05 M phosphoric acid and acetonitrile (50:50, v/v). The mobile phase was pumped at a flow rate of 1 mL/min. Quantification of nizatidine was based on measuring its peak area at 320 nm. The retention time for nizatidine was about 3.61 min. The reliability and analytical performance of the proposed HPLC procedure were statistically validated with respect to linearity, range, precision, accuracy, specificity, robustness, detection and quantification limits. Calibration curve of nizatidine was linear in the range of 5–50 μg/mL with correlation coefficient >0.9999. The drug was subjected to forced-degradation conditions of acidic and basic hydrolysis, oxidation, dry heat and UV photolysis where it showed considerable degradation in basic and oxidative conditions. The proposed method proved to be specific and stability-indicating by resolution of the drug from its forced-degradation products. The validated HPLC method was applied to the analysis of nizatidine in capsules dosage form where it was quantified with recoveries not less than 98.2%. Assay results were statistically compared to USP 2011 pharmacopeial method where no significant difference was observed between the proposed and reference methods.

A simple, sensitive, and selective reverse phase-high performance liquid chromatography (RP-HPLC) method was developed and validated for the simultaneous determination of naftidrofuryl oxalate (NF) and its hydrolytic degradation product (metabolite), naftidrofuryl acid (NFA). Chromatographic separation was achieved on Spheri-5 RP-C8 (5 µm) (220 × 4.6 mm i.d.) column using a mobile phase composed of acetonitrile, 0.05 M sodium acetate and triethylamine (40 : 60 : 0.1, by volume) adjusted to pH 5.5 using glacial acetic acid. The mobile phase was pumped at flow rate 1.5 ml/min. The UV detector was set at 225 nm and quantification of the analytes was based on measuring the peak areas. The method was proved to be accurate and precise with linearity ranges of 0.1–25 and 0.2–25 µg ml-1 for NF and NFA, respectively. The limits of detection were 0.03 and 0.04 µg ml-1 for NF and NFA, respectively. The method was applied to serve three goals: (1) stability-indicating assay of the parent drug NF in its pharmaceutical formulation, (2) determination of the degradation product NFA down to a level of 0.005% in the presence of large excess of the parent drug, and (3) drug monitoring of naftidrofuryl and its metabolite, naftidrofuryl acid, in human plasma/urine samples taken from a healthy volunteer treated with 200 mg oral dose of naftidrofuryl oxalate. The proposed method proved to be accurate, precise, and reliable in all these application fields. Copyright © 2012 John Wiley & Sons, Ltd.

2‐Acetylbutyrolactone was characterized as a novel reagent of analytical potential in polarographic and voltammetric analyses. It forms α‐oxo‐γ‐butyrolactone arylhydrazones through Japp‐Klingemann coupling reaction with primary arylamines. α‐Oxo‐γ‐butyrolactone arylhydrazones possess an electro‐active site (azomethine center) that displays a cathodic activity at the mercury electrode. The protonated azomethine center of α‐oxo‐γ‐butyrolactone arylhydrazones is reduced by 2e/2H+ reaction to the hydrazo form. The differential pulse polarographic behavior of α‐oxo‐γ‐butyrolactone arylhydrazones was investigated in aqueous media ranging from pH 2 to 10.5. In aqueous acidic solution, α‐oxo‐γ‐butyrolactone arylhydrazones were shown to adsorb on a hanging mercury drop electrode and to be amenable to determination by adsorptive stripping voltammetry. Procedures for applying the polarographic and voltammetric methods to determination of sulfadiazine and sulfamethoxazole in pharmaceutical preparations have ...

2‐Acetylbutyrolactone (ABL) has been characterized as a novel coupling reagent for the spectrophotometric analysis of primary arylamines. 2‐Acetylbutyrolactone is a cyclic β‐keto ester that forms colored α‐oxo‐γ‐butyrolactone arylhydrazones with primary arylamines through the Japp‐Klingemann reaction. The arylhydrazones can be measured spectrophotometrically in alkaline (A532) and acidic solutions (1D349). A similar study on ethyl acetoacetate (EAA), as a coupling carbanion, was carried out. Ethyl acetoacetate is the acyclic β‐keto ester analog of ABL that forms colored azo derivatives with primary arylamines. The azo derivatives can be measured spectrophotometrically in alkaline solution (A416). Four model sulfa drugs namely, sulfadiazine (SD), sulfamethoxazole (SMX), sulfamoxole (SMO), and sulfametrole (SMR), were evaluated throughout the work. The chemistry and the pathway of the reactions of the two β‐keto esters (ABL and EAA) were discussed. Beer's law validation, accuracy, precision, limits...

Simple spectrophotometric methods are described for the assay of bisacodyl (BIS) and piribedil (PIR) based on charge‐transfer and ion‐pair complexation reactions. The first method is based on the reaction of the cited drugs with p‐chloranilic acid (p‐CA) in acetonitrile. The purple colored chromogen formed shows maximum absorbance at 518 nm. The second method is concerned with the reaction of the investigated drugs with picric acid (PA) and four sulphonphthalein acid dyes, namely; bromocresol green (BCG), bromocresol purple (BCP), bromophenol blue (BPB) and thymol blue (TB). The yellow ion‐pair complexes formed show absorption spectra with maxima within the range from 400 to 415 nm. The stoichiometric ratio was found to be 1:1, for all complexation reactions examined, as calculated by the continuous variations method. Beer's law validation, accuracy, precision, limits of detection, limits of quantification, and other aspects of analytical merit are presented in the text. The proposed methods were...

Two sensitive and selective spectrophotometric and spectrofluoimetric procedures were developed for the determination of thonzylamine hydrochloride (THAH) in tablets and nasal drops. The methods are based on König reaction which resulted in an orange-yellow fluorescent product. The orange-yellow product of the interaction between the dicyclohexylcarbodiimide (DCC), THAH and dimethylbarbituric acid (DMBA) showed an absorption maximum at 492 nm, a first-derivative signal at 494 nm and a fluorescence emission peak at 518 nm (lambda(ex)=492 nm). The orange-yellow color was found to be stable for at least 2 h. The reaction conditions were studied and optimized. The reaction obeys Beer's law over the ranges 8-20 and 0.2-2.0 microg ml(-1) for the derivative spectrophotometric and fluorimetric measurements, respectively. The detection limits were found to be 0.29 and 0.018 microg ml(-1) for the spectrophotometric and fluorimetric measurements, respectively. The proposed methods were applied to the analysis of pharmaceutical formulations containing THAH, either alone or in combination with naphazoline nitrate.

Simple, rapid and sensitive voltammetric, spectrofluorimetric and spectrophotometric methods for determination of flufenamic acid (FF) in bulk powder and capsule dosage form are presented. The methods are based on the cyclisation reaction of FF with concentrated sulphuric acid to produce the corresponding acridone derivative. The voltammetric method is based on the adsorptive stripping differential pulse (DP) technique. The acridone derivative is determined over the concentration range of 8-60 ng ml(-1) using adsorptive preconcentration at the hanging mercury drop electrode (HMDE). The lower detection limit was found to be 1.02 ng ml(-1). The fluorimetric and spectrophotometric methods are based on the measurement of the fluorescence intensity at 450 nm (lambda(ex) = 400 nm)and peak-to-peak measurements of the first- (D1) and second-derivative (D2) curves, respectively. Beer's law is obeyed over the concentration ranges of 2-20 ng ml(-1) and 0.2-8.0 microg ml(-1) for the fluorimetric and spectrophotometric measurements, respectively. The three methods were proved to be accurate and reproducible as indicated by a relative standard deviation of

The application of two-component analysis methods, differentiation of signals and orthogonal function, to the resolution of partially overlapping differential pulse voltammetric (DPV) peaks is demonstrated. The study was extended to differential pulse cathodic stripping voltammetry (DPCSV). A binary system of tin(II) and lead(II), having 72 mV of DPV peaks separation in 0.04 M acetic/ o -phosphoric/boric acids’ mixture, was used as a model throughout the work. The stripping voltammetric analysis data processed by orthogonal functions and the first-derivative ( 1 D) methods, were successfully applied to the simultaneous determination of both metals in canned soft drinks. Moreover, the applicability of the methods were demonstrated by the recovery of lead in a drinking water sample.

A sensitive method for the measurement of phenazopyridine hydrochloride (PAP) by differential pulse polarography (DPP) based on adsorptive stripping technique, using a hanging mercury drop electrode (HMDE) is described. The voltammetric peak is obtained at -0.760 V, which corresponds to the reduction of the azo group in Britton-Robinson buffer. The redox behaviour is reversible. Optimum conditions were found to be: accumulation potential -50 mV (vs. Ag/AgCl), accumulation time 60 s, scan rate 5 mV s(-1), pulse amplitude -100 mV and supporting electrolyte Britton-Robinson buffer (0.04 M, pH=11). The relative standard deviation (at 20 ng ml(-1) level) was +/-0.6% for six measurements. The calculated detection limit was 0.0299 ng ml(-1) with a 60-s accumulation time. The applicability of such a method was evaluated through the assay of PAP in human plasma and urine samples after a simple extraction procedure and in pharmaceutical preparation. The mean recovery was 97+/-2 (100 ng ml(-1) plasma).

The fluorescence properties of flufenamic (FF) and mefenamic (MF) acids were obtained in aqueous and binary aqueous–organic solvents with and without α- and β-cyclodextrins (CDs). In addition, the spectral behaviour of the model compounds in aqueous micellar systems of ionic and non-ionic surfactants were investigated. It was shown that, in aqueous acidic solutions, the investigated analytes were better incorporated in CDs (FF) and micelles (FF and MF). The luminescence emissions from the analytes were found to be greatly enhanced by surfactants. The fluorescence of analyte–surfactant system was quenched by increasing amounts of organic solvents. The changes in the dissociation constants of FF and MF in solutions of anionic and non-ionic surfactants (sodium dodecyl sulfate (SDS) and Triton X-100, respectively) were studied spectrofluorimetrically. The fluorescence intensity enhancements in CDs media relative to aqueous solution ranged from 1.3 to 1.6. Sensitive micellar-enhanced spectrofluorimetric methods for the determination of FF and MF were developed, with ranges of application down to ng ml −1 level. The linear dynamic ranges and relative standard deviations were reported. The methods were applied satisfactorily to the determination of both compounds in pharmaceutical preparations with recoveries of 98–101%.

A compensation derivative synchronous spectrofluorimetric method has been developed for the simultaneous determination of floctafenine (F) and its major metabolite floctafenic acid (FA) in plasma samples. A study of the solvent effects and wavelength scanning intervals on the fluorescence spectra was carried out. The spectra of F and FA were partially resolved by synchronous spectrofluorimetry, in combination with the first-derivative measurements. Data manipulation was performed with a computer BASIC program to evaluate the so-called compensation balance point. Plasma samples were purified by deproteinization using a selected organic solvent prior to instrumental determination. The range of application was between 0.4 – 2.0 and 3 – 10 μg ml−1 plasma for F and FA, respectively. The overall recoveries of both compounds and the standard deviation data were reported. Day-to-day precision studies were carried out.

Two easy to handle, sensitive and specific fluorimetric methods for the detection and determination of morphine in codeine are described. In method A the codeine sample investigated is treated with alkaline potassium ferricyanide, whereby morphine when present will produce the fluorescent dimer pseudomorphine. In method B, the codeine sample is thermally treated with gaseous ammonia on a chromatographic plate where morphine, if present, is converted to a highly fluorescent derivative. The limits of detection were 10 ng and 20 ng for methods A and B respectively.

A simple, sensitive, and selective reverse phase-high performance liquid chromatography (RP-HPLC) method was developed and validated for the simultaneous determination of naftidrofuryl oxalate (NF) and its hydrolytic degradation product (metabolite), naftidrofuryl acid (NFA). Chromatographic separation was achieved on Spheri-5 RP-C8 (5 µm) (220 × 4.6 mm i.d.) column using a mobile phase composed of acetonitrile, 0.05 M sodium acetate and triethylamine (40 : 60 : 0.1, by volume) adjusted to pH 5.5 using glacial acetic acid. The mobile phase was pumped at flow rate 1.5 ml/min. The UV detector was set at 225 nm and quantification of the analytes was based on measuring the peak areas. The method was proved to be accurate and precise with linearity ranges of 0.1-25 and 0.2-25 µg ml(-1) for NF and NFA, respectively. The limits of detection were 0.03 and 0.04 µg ml(-1) for NF and NFA, respectively. The method was applied to serve three goals: (1) stability-indicating assay of the parent drug NF in its pharmaceutical formulation, (2) determination of the degradation product NFA down to a level of 0.005% in the presence of large excess of the parent drug, and (3) drug monitoring of naftidrofuryl and its metabolite, naftidrofuryl acid, in human plasma/urine samples taken from a healthy volunteer treated with 200 mg oral dose of naftidrofuryl oxalate. The proposed method proved to be accurate, precise, and reliable in all these application fields.

2-Acetylbutyrolactone (ABL) has been characterized for use as a fluorogenic reagent for the spectrofluorimetric determination of primary amines. The reagent forms strongly fluorescent Schiff bases upon the reaction with primary amines in acid-catalized aqueous solutions or in dimethylformamide (DMF). Sulfamethoxazole (SMX) and ampicillin sodium (AMP Na) were used as model amines of type ArNH 2 and RNH 2 , respectively. The reaction conditions, fluorescence spectral properties and the stability of the derivatives have been investigated. The chemistry and the pathway of the reaction have been discussed. Calibration data, accuracy, precision, limits of detection, limits of quantification and other aspects of analytical merit were presented in the text. The utility of ABL for the analysis of the model drugs in pharmaceutical preparations was demonstrated. The results indicated that the proposed methods are equally accurate and precise as the official or other reported methods.

The stripping voltammetric behaviour of buspirone hydrochloride (BUS) and piribedil (PIR), as models of pyrimidine-containing compounds, was studied using a hanging mercury drop electrode (HMDE). A sensitive adsorptive stripping voltammetric method for determination of such drugs is described. The voltammetric peaks were obtained at −1.23 and −1.22 V for BUS and PIR, respectively, which correspond to the reduction of the azomethine group of pyrimidine ring in Britton–Robinson buffer (pH 7). Factors such as pH of supporting electrolyte, accumulation potential and time and instrumental parameters were optimized. Calibration plots and regression data validation, accuracy, precision, limits of detection, limits of quantification, and other aspects of analytical merit are presented. The applicability of the method was evaluated through determination of BUS and PIR in tablet dosage forms. A preliminary study of the analysis of plasma samples, spiked with the investigated drug, after a simple extraction procedure is described.

The British Pharmacopoeia defines 2-aminopyridine (2-AP) as a potential impurity in piroxicam (PX) and tenoxicam (TX). Selective spectrofluorimetric determination of 2-AP in PX and TX, within or near the pharmacopoeial level, 0.2%, was developed, based on the measurement of the native fluorescence either in aqueous 0.1N sulfuric acid or in dioxane. Accordingly, this approach was followed for confirming purity of PX and TX in bulk and pharmaceutical preparations. The study was also extended to include simultaneous determinations of PX/2-AP and TX/2-AP systems based on selective fluorescence measurements in the cited solvents.

Study of the degradation reaction of methotrexate (MTX) in acidic solution was carried out. Optimization of the experimental parameters of MTX acid hydrolysis was investigated. Spectrofluorimetric method for determination of MTX through measurement of its acid-degradation product, 4-amino-4-deoxy-10-methylpteroic acid (AMP), was developed. Stability of the standard solution of MTX prepared in sulfuric acid was discussed in the view of accelerated stability analysis. Two other comparative spectroflourimetric methods based on measuring the fluorescence intensities from either a condensation reaction with acetylacetone-formaldehyde (Hantzsch reaction) or a reaction with fluorescamine were also described. Beer's law validation, accuracy, precision, limits of detection, limits of quantification, and other aspects of analytical merit are presented in the text. The proposed methods were successfully applied for the analysis of MTX in pure drug and tablets dosage form. The sensitivity of the developed methods was favorable, so it was possible to be adopted for determination of MTX in plasma samples for routine use in high-dose MTX therapy.

H-point standard additions method (HPSAM), based on spectrophotometric and spectrofluorimetric measurements, was proposed for simultaneous determination of glafenine (G) and glafenic acid (GA). A study of the absorption spectra of G and GA in various pH media has been carried out. Reasonably resolved UV-absorption spectra were obtained with a solution adjusted at pH 4.5 with citric acid–phosphate buffer. Additionally, the fluorescence properties in aqueous micellar systems of anionic, cationic and non-ionic surfactants were investigated. Well resolved fluorescence spectra were established in aqueous Triton X-100 solution at pH 7.8 (citric acid–phosphate buffer). As a comparative method, UV-derivative spectrophotometry (based on zero-crossing technique) was suggested. First-derivative value at 352 nm (1D352) and second-derivative value at 366 nm (2D366) were selected for the quantification of G and GA, respectively. The relative standard deviations of the proposed methods approximate 2%. The proposed methods were evaluated through the analysis of commercial tablets. The results were accurate and precise.

Summary A rapid, simple spectrophotometric method for the detection and determination of benzene in ethanol is described. Thus, using 1 cm cuvettes and applying the first and/or the second derivative methods, benzene can be determined in ethanol over the concentration range of 5–25 p.p.m. with a CV% less than 1 % and with a detection limit of 2 p.p.m. This is considered to be an improvement over the method currently given in the British Pharmacopoeia.