Stability-indicating chromatographic methods for the determination of some oxicams

Two sensitive and selective methods were developed for the determination of some oxicams, namely, lornoxicam (LOX), tenoxicam (TEX), and meloxicam (MEX), in the presence of their alkaline degradation products. The first method is based on the thin-layer chromatographic separation of the 3 drugs from their alkaline degradation products, followed by densitometric measurement of the intact drug spots for LOX, TEX, and MEX at 380, 370, and 364 nm, respectively. The developing systems used for separation are ethyl acetate-methanol-26% ammonia (17 + 3 + 0.35, v/v/v) for LOX and TEX and chloroform-n-hexane-96.0% acetic acid (18 + 1 + 1, v/v/v) for MEX. The linear ranges were 0.25-6.0 microg/spot for LOX and TEX and 0.5-10 microg/spot for MEX, with mean recoveries of 99.80 +/- 1.32, 100.57 +/- 1.34, and 100.71 +/- 1.57%, respectively. The second method is based on the liquid chromatographic separation of the 3 drugs from their alkaline degradation products on a reversed-phase C18 column, using mobile phases of methanol-acetonitrile-acetate buffer, pH 4.6 (4.5 + 0.5 + 5.0, v/v/v) for LOX and MEX and methanol-acetonitrile-acetate buffer, pH 4.6 (1.9 + 0.1 + 3.0, v/v/v) for TEX at ambient temperature. Quantification is achieved by UV detection at 280 nm, based on peak area. The linear ranges were 0.5-20 microg/mL for LOX and TEX and 1.25-50 microg/mL for MEX, with mean recoveries of 99.81 +/- 1.01, 98.90 +/- 1.61, and 100.86 +/- 1.55%, respectively. The methods were validated according to guidelines of the International Conference on Harmonization. The developed methods were successfully applied to the determination of LOX, TEX, and MEX in bulk powder, laboratory-prepared mixtures containing different percentages of degradation products, and pharmaceutical dosage forms.     

Stability-indicating methods for the determination of linezolid in the presence of its alkaline-induced degradation products

Three methods are presented for the determination of linezolid in the presence of its alkaline-induced degradation products. The first method was based on separation of linezolid from its alkaline degradation product by TLC followed by densitometric measurement of the spots of intact drug at 244 nm. The separation was carried out on silica gel 60 F₂₅₄ using isobutanol:ammonia (9:1 v/v) as a mobile phase. The second method was based on first derivative ¹D ultraviolet spectrophotometry with zero crossing point and peak to base measurement. The ¹D value at 251.4 nm was selected for the assay of linezolid in the presence of degradation product. The third method was depended on the first derivative of the ratio spectra ¹DD by measurement of the value at 263.6 nm. The proposed methods were successfully applied to the determination of the drug in bulk powder, in laboratory prepared mixtures with its degradation product and in commercial tablets.     

Stability-indicating methods for determination of tiapride in pure form, pharmaceutical preparation, and human plasma

Four different stability-indicating procedures are described for determination of tiapride in pure form, dosage form, and human plasma. Second derivative (D2), first derivative of ratio spectra (1DD), spectrofluorimetric, and high-performance column liquid chromatographic (LC) methods are proposed for determination of tiapride in presence of its acid-induced degradation products, namely 2-methoxy-5-(methylsulfonyl) benzoic acid and 2-diethylaminoethylamine. These approaches were successfully applied to quantify tiapride using the information included in the absorption, excitation, and emission spectra of the appropriate solutions. In the D2 method, Beer's law was obeyed in the concentration range of 1.5-9 microg/mL with a mean recovery of 99.94 +/- 1.38% at 253.4 nm using absolute ethanol as a solvent. In 1DD, which is based on the simultaneous use of the first derivative of ratio spectra and measurement at 245 nm in absolute ethanolic solution, Beer's law was obeyed over a concentration range of 1.5-9 microg/mL with mean recovery 99.64 +/- 1.08%. The spectrofluorimetric method is based on the determination of tiapride native fluorescence at 339 nm emission wavelength and 230 nm excitation wavelength using water-methanol (8 + 2, v/v). The calibration curve was linear over the range of 0.2-3 microg/mL with mean recovery of 99.66 +/- 1.46%. This method was also applied for determination of tiapride in human plasma. A reversed-phase LC method performed at ambient temperature was validated for determination of tiapride using methanol-deionized water-triethylamine (107 + 93 + 0.16, v/v/v) as the mobile phase. Sulpiride was used as an internal standard at a flow rate of 1 mL/min with ultraviolet detection at 214 nm. A linear relation was obtained over a concentration range of 2-30 microg/mL with mean recovery of 99.66 +/- 0.9%. Results were statistically analyzed and compared with those obtained by applying the reference method. They proved both accuracy and precision.     

Stability-indicating thin-layer chromatographic method for quantitative determination of ribavirin

A simple and accurate stability-indicating thin-layer chromatographic (TLC) method is developed and validated for the quantitative determination of ribavirin (RBV) in its bulk and with used for development consists of chloroform-methanol-acetic acid (60:15:15, v/v/v). The separated spots are visualized as bluish green spots after being sprayed with anisaldehyde reagent. RBV is subjected to different accelerated stress conditions. The drug is found to undergo degradation under all stress conditions, and the degradation products are well resolved from the pure drug with significantly different Rf values. The optical densities of the separated spots are found to be linear with the amount of RBV in the range of 5-40 microg/spot with a good correlation coefficient (r=0.9980). The limit of detection and limit of quantitation values are 1.40 and 4.67 microg/spot, respectively. Statistical analysis proves that the method is repeatable and accurate for the determination of RBV in the presence of its degradation products. The method meets the International Conference on Harmonisation/Food and Drug Administration regulatory requirements. The proposed TLC method is successfully applied for the determination of RBV, pure and in capsules, with good accuracy and precision; the label claim percentages are 98.8%+/-1.5%. The results obtained by the proposed TLC method are comparable with those obtained by the official method.     

Stability-indicating methods for determination of pyritinol dihydrochloride in the presence of its precursor and degradation product by derivative spectrophotometry

A first-derivative spectrophotometric (1D) method and a derivative-ratio zero-crossing spectrophotometric (1DD) method were used to determine pyritinol dihydrochloride (I) in the presence of its precursor (II) and its degradation product (III) with 0.1N hydrochloric acid as a solvent. Linear relationships were obtained in the ranges of 6-22 microg/mL for the (1D) method and 6-20 microg/mL for the (1DD) method. By applying the proposed methods, it was possible to determine pyritinol dihydrochloride in its pure powdered form with an accuracy of 100.36 +/- 1.497% (n = 9) for the (1D) method and an accuracy of 99.92 +/- 1.172% (n = 8) for the (1DD) method. Laboratory-prepared mixtures containing different ratios of (I), (II), and (III) were analyzed, and the proposed methods were valid for concentrations of < or = 10% (II) and < or = 50% (III). The proposed methods were validated and found to be suitable as stability-indicating assay methods for pyritinol in pharmaceutical formulations.     

Stability-indicating high-performance column liquid chromatography and high-performance thin-layer chromatography methods for the determination of olopatadine hydrochloride in tablet dosage form

This paper describes two simple, specific, accurate, and precise methods for estimation of olopatadine hydrochloride (OLO) in tablet dosage form. The first method is a stability-indicating isocratic RP-HPLC method. The analysis is performed on an RP-18 column using 0.1% orthophosphoric acid (adjusted to pH 4.5 with triethylamine)-acetonitrile (75 + 25, v/v) mobile phase at a flow rate of 1 mL/min. Paracetamol (PAR) was selected as the internal standard. Retention times of OLO and PAR were 11.30 +/- 0.02 and 4.70 +/- 0.03 min, respectively. For the HPTLC method, precoated silica gel 60 F254 aluminum sheets were used as the stationary phase; the mobile phase was methanol-chloroform-ammonia (8 + 2 + 0.1, v/v/v). The detection of the analyte band was carried out at 301 nm, and its Rf value was 0.46 +/- 0.03. The analytical methods were validated according to International Conference on Harmonization guidelines. Linear regression analysis data for the calibration plots showed a good linear relationship between response and concentration in the range of 0.1-1 microg/mL and 0.1-0.9 microg/band for HPLC and HPTLC, respectively.     

Stability-indicating method for the determination of clorazepate dipotassium-II. Via N-desmethyldiazepam and determination of its degradation products

A spectrophotometric method for the determination of the intact clorazepate dipotassium in the presence of its degradation products is developed. It depends upon preliminary hydrolysis of clorazepate dipotassium-thus liberating its equivalent of N-desmethyldiazepam which is extracted, with benzene-methylene chloride (9:1). The extract is evaporated, the residue dissolved in methanol and its absorbance measured at about 315 nm. The procedure determines 0.4-1.6 mg of clorazepate dipotassium with an accuracy of 100.2+/-0.7%. The procedure is applied successfully for the determination of clorazepate dipotassium in bulk powder and in capsules; retaining its accuracy in the presence of up to 80% degradation. Determination of the different degradation products is also possible. Thus, N-desmethyl diazepam is determined after preliminary extraction with benzene-methylene chloride mixture, followed by TLC separation, 2-amino-5-chlorobenzophenone by directly applying the first derivative spectrophotometric technique, and glycine in the aqueous layer determined colorimetrically with ninhydrin reagent in the presence of pyridine.     

Stability-indicating method for the determination of clorazepate dipotassium-I. Via its final degradation products

A sensitive spectrophotometric procedure is described for the determination of 1,4-benzodiazepine (clorazepate dipotassium) in the presence of its degradation products. The procedure is based on acid hydrolysis of clorazepate dipotassium to yield its final degradation products viz., 2-amino-5-chlorobenzophenone and glycine. The amino-chlorobenzophrenone is extracted from the neutralized hydrolysate with diethyl ether, the extract is evaporated, the residue is dissolved in methanol and its absorbance measured at about 240 nm or 380 nm. Glycine, left in the aqueous layer after etherial extraction of aminochlorobenzophenone, is treated with ninhydrin reagent in the presence of pyridine and the bluish violet colour formed is measured at about 560 nm. The suggested procedures determine 20–100 mg of clorazepate dipotassium via its degradation products aminochlorobenzophenone and glycine with mean accuracies of 100.0 ± 0.5% at 560 nm, 100.2 ± 0.6% at 380 nm and 99.8 ± 0.5%. The suggested procedures are suitable for stability-testing of clorazepate dipotassium in bulk powder and in pharmaceutical preparations.     

Stability-indicating determination of meropenem in presence of its degradation product

Stability-indicative determination of meropenem (MERM) in the presence of its open-ring degradation product, the metabolite, is investigated. The degradation product has been isolated, via acid-degradation, characterized and confirmed. Selective quantification of MERM, singly in bulk form, pharmaceutical formulations and/or in the presence of its major degradate is demonstrated. The indication of stability has been undertaken under conditions likely to be expected at normal storage. Among the analytical techniques adopted for quantification are spectrophotometry [first-derivative (¹D), first-derivative of ratio spectra (¹DD) and bivariate analysis], as well as chromatography [coupled TLC-densitometry and HPLC].     

Stability-indicating high-performance liquid chromatographic assay for the determination of metoclopramide hydrochloride in pharmaceutical dosage forms

A simple, reliable and selective high-performance liquid chromatographic method for the determination of metoclopramide hydrochloride in pharmaceutical dosage forms has been developed and evaluated. The drug and the internal standard (phenobarbitone) were eluted from a 5-micron C8 reversed-phase column at ambient temperature with a mobile phase consisting of phosphate buffer (10 mM)-methanol-acetonitrile (50 + 28 + 22) adjusted to pH 4.8 with orthophosphoric acid. The mobile phase was pumped at a flow-rate of 1.5 ml min-1 and the effluent was monitored spectrophotometrically at 214 nm. The retention times of the internal standard and metoclopramide hydrochloride were 3.0 and 7.5 min, respectively. Quantification was achieved by measuring the peak-height ratio of the drug to the internal standard. A linear relationship was found over the range 1-10 micrograms ml-1. Within-day coefficients of variation (CVs) ranged from 0.50 to 1.70% and between-day CVs from 0.68 to 4.07% at three different concentrations. The developed procedure was compared with the current BP method for the assay of metoclopramide hydrochloride in tablets. The proposed method was also used to study the stability of metoclopramide hydrochloride.     

Stability-indicating derivative spectrophotometry method for the determination of biapenem in the presence of its degradation products

A first-derivative UV spectrophotometric method, with or without the subtraction technique, was developed for the determination of biapenem in pharmaceutical dosage form in the presence of its degradation products. The method was based on the measurement of first-derivative amplitudes at zero crossing point (λ = 312 nm) and the peak-to-zero technique and validated with regard to linearity, limits of detection and quantitation, selectivity and precision. The observed rate constants for the degradation of biapenem were comparable to those obtained in the stability-indicating HPLC method.      

Stability-indicating RP-LC method for the determination of vildagliptin and mass spectrometry detection for a main degradation product

A simple, precise and stability-indicating reversed-phase liquid chromatography method was developed and validated for the determination of vildagliptin (VLG) in pharmaceutical dosage form. The chromatographic separation was obtained within 6 min and was linear in the range of 20-80 μg/mL (r(2) = 0.9999). Limit of detection and limit of quantitation were 0.63 and 2.82 μg/mL, respectively. The method was validated in accordance with International Conference on Harmonization acceptance criteria for specificity, linearity, precision, accuracy, robustness and system suitability. Stress studies were carried out and no interference of the degradation products was observed. The excipients did not interfere in the determination of VLG. Furthermore, the main degradation product obtained from the stress studies (thermal, oxidative and alkaline hydrolysis) was evaluated for mass spectrometry and its molecular structure was predicted. The proposed method was successfully applied for the quantitative analysis of VLG in tablet dosage form, which will help to improve quality control and contribute to stability studies of pharmaceutical tablets containing this drug.     

Stability-indicating methods for determining omeprazole and octylonium bromide in the presence of their degradation products.

Four stability-indicating assays were developed for determining omeprazole and octylonium bromide. Omeprazole is photodegraded and estimated in the presence of its degradation products sulphenamide (I) and benzimidazole sulphide (II) by 2 methods. The first method depends on use of first-, second-, and third-derivative spectrophotometry at 290.4, 320.6, and 311.6 nm, respectively. The second method is based on applying the charge-transfer technique with chloranil as pi acceptor to form a complex with omeprazole, the absorbance of which is measured at 377 nm. These methods determine omeprazole in concentration ranges of 5-20 micrograms/mL by first-, second-, and third-derivative spectrophotometry and 10-50 micrograms/mL by charge-transfer complexation with mean accuracies of 99.92 +/- 0.73, 99.71 +/- 1.02, 99.64 +/- 0.66, and 100.24 +/- 0.81%, respectively. Octylonium bromide is determined by a densitometric method using thin-layer chromatography in the presence of its degradation products p-[2-(n-octyoxy)benzoyl]-aminobenzoic acid (III) and diethyl-(2-hydroxyethyl)-methyl ammonium bromide (IV) without any interferences. Alternatively, octylonium bromide is evaluated by a colorimetric method using the acid dye rose bengal. The ion pair formed is extracted in chloroform at pH 4, and its absorbance is measured at 562 nm. These methods determine octylonium bromide in the presence of its degradation products in concentration ranges of 0.1-0.5 microgram/microL by densitometry and 4.5-22.5 micrograms/mL by colorimetry, with mean accuracies of 100.21 +/- 0.93 and 99.73 +/- 0.89%, respectively. The suggested methods were used to determine drugs in bulk powder, laboratory-prepared mixtures, and pharmaceutical dosage forms. Results were compared statistically with those obtained with reference methods.     

Stability-indicating method for determination of oxyphenonium bromide and its degradation product by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method was developed for determination of oxyphenonium bromide (OX) and its degradation product. The method was based on the HPLC separation of OX from its degradation product, using a cyanopropyl column at ambient temperature with mobile phase of acetonitrile-25 mM potassium dihydrogen phosphate, pH 3.4 (50 + 50, v/v). UV detection at 222 nm was used for quantitation based on peak area. The method was applied to the determination of OX and its degradation product in tablets. The proposed method was also used to investigate the kinetics of the acidic and alkaline degradation of OX at different temperatures, and the apparent pseudo first-order rate constant, half-life, and activation energy were calculated. The pH-rate profile of the degradation of OX in Britton-Robinson buffer solutions within the pH range 2-12 was studied.     

Fast,selective and sensitive methods for the determination of lead-210 in phosphogypsum and phosphate ore

Two methods are presented for a fast, accurate and precise determination of²¹⁰Pb in industrial samples with a calcium-phosphate and-sulphate matrix. One method combinessolid-liquid extraction on a Pb-selective column Sr^*Spec (Eichrom) with gamma-ray spectrometry of²¹⁰Pb and can be applied to samples >10 g for aselective ²¹⁰Pb determination. The yield is determined gravimetrically. The detection limit is 380 mBq for a 24 h counting period. The other method combineschromatography on Sr^*Spec with liquid scintillation counting of²¹⁰Pb for asensitive ²¹⁰Pb determination and can be applied to samples of up to 1 g. The yield is determined on-line by the UV signal of PbEDTA. The detection limit is 70 mBq for a 2 h counting period. Aspects of accuracy, precision, selectivity, sensitivity and the application of both methods to phosphogypsum and phosphate ores are presented.     

Stability-indicating high performance thin layer chromatographic determination of sulfanilamide in human urine

A simple, sensitive, selective, precise and stability-indicating high-performance thin-layer chromatographic (HPTLC) method was developed and applied to human urine for the densitometric determination of sulfanilamide. A mixture of chloroform-ethyl acetate-xylene (2.5: 4.0: 1.0, v/v/v) was used as a mobile phase. The system was found to give compact spots for sulfanilamide (retardation factor, R _f = 0.21±0.02). The linear regression analysis data for the calibration plots showed good linear relationship with r ² = 0.9970 ± 0.0003 and r ² = 0.9947 ± 0.020 within the concentration range of 50–250 ng per spot and 100–1000 ng per spot with respect to peak area, respectively. The limit of detection (LOD) and quantification (LOQ) were 8 and 25 ng per spot, respectively. Sulfanilamide was subjected to acid and alkali hydrolysis, oxidation, dry heat and wet heat treatment. According to the International Conference on Harmonization (ICH) guidelines the method was validated for precision, recovery and robustness. The ultraviolet (UV) spectra of the degradation products which had different spectra from sulfanilamide were also recorded. The article is published in the original.     

The accurate determination of cobalt: Gravimetric methods and in particular the phosphate method

Some gravimetric methods for determining cobalt have been examined in order to assess their value for the accurate determination of the metal. The electrolytic method was found to give high results (about 1.4%), and the anthranilate method slightly high results (0.2 – 0.3%). A modification of the phosphate method has been developed in which a former drawback, the solubility of CoNH₄PO₄·H₂O, has been overcome using a rapid spectrophotometric determination of residual cobalt. The final procedure developed has been found to give accurate results ( ±0.1 – 0.2%) and its use is recommended where this degree of accuracy is required.     

Extractive-spectrophotometric determination of disopyramide and irbesartan in their pharmaceutical formulation

Picric acid, bromocresol green, bromothymol blue, cobalt thiocyanate and molybdenum(V) thiocyanate have been tested as spectrophotometric reagents for the determination of disopyramide and irbesartan. Reaction conditions have been optimized to obtain coloured comoplexes of higher sensitivity and longer stability. The absorbance of ion-pair complexes formed were found to increases linearity with increases in concentrations of disopyramide and irbesartan which were corroborated by correction coefficient values. The developed methods have been successfully applied for the determination of disopyramide and irbesartan in bulk drugs and pharmaceutical formulations. The common excipients and additives did not interfere in their determination. The results obtained by the proposed methods have been statistically compared by means of student t-test and by the variance ratio F-test. The validity was assessed by applying the standard addition technique. The results were compared statistically with the official or reference methods showing a good agreement with high precision and accuracy.     

Stability-indicating liquid chromatography for determination of clopidogrel bisulfate in tablets: Application to content uniformity testing

The present study describes a simple stability-indicating reversed-phase HPLC assay for antiplatelet drug, clopidogrel bisulfate. Separation of the drug and the degradation products, under stress conditions was successfully achieved on a C-18 column utilizing 0.01 M Na₂HPO₄ (pH 4): acetonitrile in the ratio 80:20 v/v, pumped at a flow rate of 0.5 ml min^?1 with UV detection at 235 nm. The retention time of clopidogrel was 6.84 min. The method was satisfactorily validated with respect to linearity, precision, accuracy, selectivity, sensitivity and ruggedness. The response was linear in the range of 0.2–3.5 μg ml^?1 with detection limit 0.079 μg ml^?1. The suggested method was successfully applied for the analysis of clopidogrel in bulk and in commercial tablets. The results were favorably compared to those obtained by a reference method. The proposed method was successfully applied to the content uniformity testing of tablets and for determination of clopidogrel in presence of its co-administered drug, acetyl salicylic acid.     

Solid-state ion-selective electrodes for the potentiometric determination of phosphate

A number of solid-state ion-selective electrodes for the potentiometric determination of phosphate have been made and their properties investigated. The most successful of these electrodes, which had a membrane comprising silver sulphide, lead sulphide and lead hydrogen phosphate, had a theoretical Nernstian response to orthophosphate ion at concentrations down to 5 mug/ml total phosphate at pH 8.3. The electrode had a slow response and its standard potential changed with time. Anions such as sulphate, bicarbonate and nitrate did not interfere; chloride had a transient effect, but even at its worst the interference was less serious than with other phosphate electrodes. The electrode was used as an indicator in the potentiometric precipitation titration of phosphate and lanthanum.