Tarek S. Belal

Simultaneous spectrofluorimetric determination of amlodipine besylate and valsartan in their combined tablets

Amlodipine, a dihydropyridine calcium channel blocker, and valsartan, an angiotensin II receptor blocker, are co-formulated in a single-dose combination for the treatment of hypertension. The combination is used by patients whose blood pressure is not adequately controlled on either component monotherapy. This work describes a simple, sensitive, and reliable spectrofluorimetric method for the simultaneous determination of the two antihypertensive drugs; amlodipine besylate (AML) and valsartan (VAL) in their combined tablets. The method involved measurement of the native fluorescence at 455 nm (λ(Ex) 360 nm) and 378 nm (λ(Ex) 245 nm) for AML and VAL, respectively. Analytical performance of the proposed spectrofluorimetric procedure was statistically validated with respect to linearity, ranges, precision, accuracy, selectivity, robustness, detection, and quantification limits. Regression analysis showed good correlation between fluorescence intensity and concentration over the concentration ranges 0.2-3.6 and 0.008-0.080 µg mL⁻¹ for AML and VAL, respectively. The limits of detection were 0.025 and 0.0012 µg mL⁻¹ for AML and VAL, respectively. The proposed method was successfully applied for the assay of the two drugs in their combined pharmaceutical tablets with recoveries not less than 98.85%. No interference was observed from common pharmaceutical additives. The results were favourably compared with those obtained by a reference spectrophotometric method.

GC-IRD methods for the identification of isomeric ethoxyphenethylamines and methoxymethcathinones

A series of 12 isomeric phenethylamines were evaluated by gas chromatography using vapor phase infrared spectrophotometric detection. The major mass spectral fragments for each of these unique isomers occur at equivalent mass and all have equal molecular weight. The infrared spectra for these compounds allow for identification of any one of these amines to the exclusion of all other isomers. This differentiation is accomplished without the need for chemical derivatization. The methoxymethcathinones show unique infrared absorption bands in the 1690-1700 cm(-1) range for the carbonyl group and the ring substitution pattern in the ethoxymethamphetamines can be differentiated by several bands in the 700-1610 cm(-1) region. Side chain and degree of nitrogen substitution can be evaluated in the 2770-3000 cm(-1) region of the infrared range. All the studied regioisomers could be differentiated from 3,4-MDMA via their vapor phase IR spectra. Capillary gas chromatography on an Rxi-50 stationary phase successfully resolved the side chain regioisomers, the substituted methamphetamines and the methoxymethcathinones.

New simple spectrophotometric method for determination of the binary mixtures（atorvastatin calcium and ezetimibe;candesartan cilexetil and hydrochlorothiazide） in tablets

A new simple spectrophotometric method was developed for the determination of binary mixtures without prior separation. The method is based on the generation of ratio spectra of compound X by using a standard spectrum of compound Y as a divisor. The peak to trough amplitudes between two selected wavelengths in the ratio spectra are proportional to concentration of X without interference from Y. The method was demonstrated by determination of two drug combinations. The first consists of the two antihyperlipidemics: atorvastatin calcium (ATV) and ezetimibe (EZE), and the second comprises the antihypertensives: candesartan cilexetil (CAN) and hydrochlorothiazide (HCT). For mixture 1, ATV was determined using 10 μg/mL EZE as the divisor to generate the ratio spectra, and the peak to trough amplitudes between 231 and 276 nm were plotted against ATV concentration. Similarly, by using 10 μg/mL ATV as divisor, the peak to trough amplitudes between 231 and 276 nm were found proportional to EZE concentration. Calibration curves were linear in the range 2.5–40 μg/mL for both drugs. For mixture 2, divisor concentration was 7.5 μg/mL for both drugs. CAN was determined using its peak to trough amplitudes at 251 and 277 nm, while HCT was estimated using the amplitudes between 251 and 276 nm. The measured amplitudes were linearly correlated to concentration in the ranges 2.5–50 and 1–30 μg/mL for CAN and HCT, respectively. The proposed spectrophotometric method was validated and successfully applied for the assay of both drug combinations in several laboratory-prepared mixtures and commercial tablets.

GC–MS studies on acylated derivatives of 3-methoxy-4-methyl- and 4-methoxy-3-methyl-phenethylamines: Regioisomers related to 3,4-MDMA

A series of side chain regioisomers of 3-methoxy-4-methyl- and 4-methoxy-4-methyl-phenethylamines have mass spectra essentially equivalent to the controlled drug substance 3,4-methylenedioxymethamphetamine (3,4-MDMA), all have molecular weight of 193 and major fragment ions in their electron ionization mass spectra at m/z 58 and 135/136. The acetyl, propionyl and trifluoroacetyl derivatives of the primary and secondary regioisomeric amines were prepared and evaluated in GC-MS studies. The mass spectra for these derivatives were significantly individualized and the resulting unique fragment ions allowed for specific side chain identification. The trifluoroacetyl derivatives provided more fragment ions for molecular individualization among these regioisomeric substances. These trifluoroacetyl derivatives showed excellent resolution on a non-polar stationary phase such as Rtx-1.

Comparison of GC–MS and GC–IRD methods for the differentiation of methamphetamine and regioisomeric substances

Gas chromatography-mass spectrometry (GC-MS) and gas chromatography-infrared detection (GC-IRD) methods were developed and compared for the differentiation of regioisomeric phenethylamines related to methamphetamine. There are a total of five regioisomeric phenethylamines (methamphetamine and four regioisomers) that produce essentially equivalent mass spectra. This unique set of five phenethylamines having the same molecular weight and elemental composition yield major mass spectral fragments at equivalent mass. The trifluoroacetyl derivatives of the primary and secondary amines yield characteristic individual fragment ions allowing structural differentiation among these regioisomers. The vapor phase infrared spectra generated via capillary gas chromatography differentiated among these compounds without the need for derivatization. The regioisomeric phenethylamines are well resolved by GC with the elution order generally determined by the degree of molecular linearity.

Adsorptive stripping voltammetric behaviour of azomethine group in pyrimidine-containing drugs.

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.

Gradient HPLC-DAD stability indicating determination of miconazole nitrate and lidocaine hydrochloride in their combined oral gel dosage form.

The pharmaceutical combination of miconazole nitrate (MZ) and lidocaine hydrochloride (LD) is used in the curative and prophylactic therapy of the oral and gastro-intestinal infections caused by Candida albicans. To the best of our knowledge, no attempts have yet been made to assay this combination by any analytical method. A simple and selective high-performance liquid chromatography-diode array detection (HPLC-DAD) stability-indicating method was developed for the simultaneous determination of MZ and LD in their combined formulation. Effective chromatographic separation was achieved using a Zorbax SB-C8 column with gradient elution of the mobile phase composed of 0.05 M phosphoric acid and acetonitrile. The gradient elution started with 25% (by volume) acetonitrile, ramped up linearly to 65% in 6 min, then kept constant until the end of the run. The mobile phase was pumped at a flow rate of 1 mL/min. The multiple wavelength detector was set at 215 nm and analytes were quantified by measuring their peak areas. The retention times for LD and MZ were approximately 4.1 and 8.4 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. Calibration curves were linear in the ranges of 5-100 µg/ml for both drugs with correlation coefficients > 0.999. Both drugs were subjected to stress conditions of hydrolysis, oxidation, photolysis and thermal degradation. The proposed method proved to be stability-indicating by the resolution of the two analytes from the related substance and potential impurity (2,6-dimethylaniline) and from the forced-degradation products. The validated HPLC method was applied to the analysis of MZ and LD in the combined oral gel preparation, in which the two analytes were successfully quantified and resolved from the pharmaceutical additives. The proposed method made use of DAD as a tool for peak identity and purity confirmation.

Spectrophotometric Determination of Bisacodyl and Piribedil

ABSTRACT 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. Beers 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 applied for the determination of the analytes in their pure forms and in pharmaceutical preparations. The results were in good agreement with those obtained by the official and reported methods.

Mass spectral studies on 1‐n‐pentyl‐3‐(1‐naphthoyl)indole (JWH‐018), three deuterium‐labeled analogues and the inverse isomer 1‐naphthoyl‐3‐n‐pentylindole

RATIONALE A number of synthetic cannabinoids such as the 1-alkyl-3-acylindoles are the target of significant designer drug activity. One of the first waves of these compounds identified in clandestine samples was 1-n-pentyl-3-(1-naphthoyl)indole, JWH-018. These totally synthetic molecules can be prepared in a number of regioisomeric forms. METHODS The electron ionization mass spectrometric (EI-MS) fragmentation of the 1-n-pentyl-3-(1-naphthoyl)indole is compared to its inverse isomer 1-naphthoyl-3-n-pentylindole. These two substances are directly available from indole using identical precursor reagents and similar reaction conditions. Stable isotope deuterium labeling of the three major regions of the JWH-018 molecule allows confirmation of the structures of the major fragment ions. The spectra for the 1-n-pentyl-3-(1-naphthoyl)-d(5) -indole, 1-n-pentyl-3-(1-d(7) -naphthoyl)indole and 1-d(11) -n-pentyl-3-(1-naphthoyl)indole provide significant assistance in elucidating the structures for the major fragment ions in JWH-018. RESULTS The EI mass spectra for these isomers show a number of unique ions which allow for the differentiation of the 1-alkyl-3-acylindole compounds from the inverse regioisomeric 1-acyl-3-alkylindoles. The fragment ion [M-17](+) at m/z 324 for JWH-018 was formed by the elimination of a hydroxyl radical and the spectra of the three deuterium-labeled derivatives indicated the loss of hydrogen from the naphthalene ring. Further structural analogues suggest the hydrogen to come from the 8-position of the naphthalene ring. CONCLUSIONS The three deuterium-labeled analogues provide significant assistance in confirming the structures for the major fragment ions in the mass spectrum of the traditional synthetic cannabinoid compound, 1-n-pentyl-3-(1-naphthoyl)indole, JWH-018. The 1-naphthoyl-3-n-pentylindole inverse regioisomer can be easily differentiated from the traditional synthetic cannabinoid compound.

Validated Stability-Indicating HPLC-DAD Method for the Simultaneous Determination of Diclofenac Sodium and Diflunisal in Their Combined Dosage Form

A simple, rapid, and highly selective HPLC-DAD method was developed for the simultaneous determination of diclofenac sodium (DIC) and diflunisal (DIF) in pure form and in their combined formulation. Effective chromatographic separation was achieved using a Zorbax SB-C8 (4.6×250 mm, 5 μm particle size) column with a mobile phase composed of 0.05 M phosphoric acid, acetonitrile, and methanol in the ratio of 40:48:12 (by volume). The mobile phase was pumped isocratically at a flow rate of 1 mL/min, and quantification of the analytes was based on measuring their peak areas at 228 nm. The retention times for diflunisal and diclofenac were about 7.9 and 9.5 min, respectively. The reliability and analytical performance of the proposed HPLC procedure were statistically validated with respect to system suitability, linearity, ranges, precision, accuracy, specificity, robustness, detection, and quantification limits. Calibration curves were linear in the ranges of 5–100 μg/mL for both drugs with correlation coefficients >0.9998. The proposed method proved to be selective and stability-indicating by the resolution of the two analytes from four of their related substances and potential impurities as well as from forced-degradation (hydrolysis, oxidation, photolysis, and dry heat) products. The validated HPLC method was successfully applied to the analysis of DIC and DIF in their combined dosage form (suppositories). The proposed method made use of the diode array detector (DAD) as a tool for peak identity and purity confirmation.