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.     

HPLC, TLC, and first-derivative spectrophotometry stability-indicating methods for the determination of tropisetron in the presence of its acid degradates

Three stability-indicating assay methods were developed for the determination of tropisetron in a pharmaceutical dosage form in the presence of its degradation products. The proposed techniques are HPLC, TLC, and first-derivative spectrophotometry (1D). Acid degradation was carried out, and the degradation products were separated by TLC and identified by IR, NMR, and MS techniques. The HPLC method was based on determination of tropisetron in the presence of its acid-induced degradation product on an RP Nucleosil C18 column using methanol-water-acetonitrile-trimethylamine (65 + 20 + 15 + 0.2, v/v/v/v) mobile phase and UV detection at 285 nm. The TLC method was based on the separation of tropisetron and its acid-induced degradation products, followed by densitometric measurement of the intact spot at 285 nm. The separation was carried out on silica gel 60 F254 aluminum sheets using methanol-glacial acetic acid (22 + 3, v/v) mobile phase. The 1D method was based on the measurement of first-derivative amplitudes of tropisetron in H2O at the zero-crossing point of its acid-induced degradation product at 271.9 nm. Linearity, accuracy, and precision were found to be acceptable over concentration ranges of 40-240 microg/mL, 1-10 microg/spot, and 6-36 micro/mL for the HPLC, TLC, and 1D methods, respectively. The suggested methods were successfully applied for the determination of the drug in bulk powder, laboratory-prepared mixtures, and a commercial sample.     

Development and Validation of HPLC,TLC and Derivative Spectrophotometric Methods for the Analysis of Ezetimibe in the Presence of Alkaline Induced Degradation Products

Reversed phase‐high performance liquid chromatography (RP‐HPLC), thin layer chromatography (TLC) densitometry and first derivative spectrophotometry (1D) techniques are developed and validated as a stability‐indicating assay of ezetimibe in the presence of alkaline induced degradation products. RP‐HPLC method involves an isocratic elution on a Phenomenex Luna 5μ C₁₈ column using acetonitrile: water: glacial acetic acid (50:50:0.1 v/v/v) as a mobile phase at a flow rate of 1.5 mL/min. and a UV detector at 235 nm. TLC densitometric method is based on the difference in Rf‐values between the intact drug and its degradation products on aluminum‐packed silica gel 60 F₂₅₄ TLC plates as stationary phase with isopropanol: ammonia 33% (9:1 v/v) as a developing mobile phase. On the fluorescent plates, the spots were located by fluorescence quenching and the densitometric analysis was carried out at 250 nm. Derivative spectrophotometry, the zero‐crossing method, ezetimibe was determined using first derivative at 261 nm in the presence of its degradation products. Calibration graphs of the three suggested methods are linear in the concentration ranges 1–10 mcg/mL, 0.1–1 mg/mL and 1–16 mcg/mL with a mean percentage accuracy of 99.05 ± 0.54%, 99.46 ± 0.63% and 99.24 ± 0.82% of bulk powder, respectively. The three proposed methods were successfully applied for the determination of ezetimibe in raw material and pharmaceutical dosage form; the results were statistically analyzed and compared with those obtained by the reported method. Validation parameters were determined for linearity, accuracy and precision; selectivity and robustness and were assessed by applying the standard addition technique.     

Stability-indicating methods for the determination of disopyramide phosphate

Four methods were developed for the determination of intact disopyramide phosphate in the presence of its degradation product. In the first and second methods, third-derivative spectrophotometry and first derivative of the ratio spectra were used. For the third-derivative spectrophotometric method, the peak amplitude was measured at 272 nm, while for the derivative ratio spectrophotometric method, disopyramide phosphate was determined by measuring the peak amplitude at 248 and 273 nm. Both methods were used for the determination of disopyramide phosphate in the concentration range 12.5-87.5 microg/mL, with corresponding mean recovery 100.8 +/- 0.7% for the first method and 99.9 +/- 0.7% and 99.6 +/- 0.7% for the second method at 248 and 273 nm, respectively. In the third method, an ion selective electrode (ISE) was fabricated using phosphotungstic acid as an anionic exchanger, PVC as the polymer matrix, and dibutylsebacate as a plasticizer. The ISE was used for the determination of disopyramide phosphate in pure powder form in the concentration range 10(-2)-10(-5) M. The slope was found to be 58.5 (mV/decade), and the average recovery was 99.9 +/- 1.6%. The fourth method depended on the quantitative densitometric determination of the drug in concentration range of 0.25-2.5 microg/spot using silica gel 60 F245 plates and ethyl acetate-chloroform-ammonium hydroxide (85 + 10 + 5, v/v/v) as the mobile phase, with corresponding mean accuracy of 100.3 +/- 1.1%. The 4 proposed methods were found to be specific for disopyramide phosphate in presence of up to 80% of its degradation product for the spectrophotometric methods, 90% of its degradation for the densitometric method, and 40% for the ISE method. The 4 proposed procedures were successfully applied for the determination of disopyramide phosphate in Norpace capsules. Statistical comparison between the results obtained by these methods and the official method of the drug was done, and no significant differences were found.     

Determination of trimetazidine dihydrochloride in the presence of its acid-induced degradation products

Three methods are presented for the determination of trimetazidine dihydrochloride in the presence of its acid-induced degradation products. The first method was based on measurement of first-derivative D1 value of trimetazidine dihydrochloride at 282 nm over a concentration range of 8.00-56.00 microg/mL with mean percentage accuracy of 99.80+/-1.17. The second method was based on first derivative of the ratio spectra DD1 at 282 nm over the same concentration range with the percentage accuracy of 99.14+/-0.68. The third method was based on separation of trimetazidine dihydrochloride from its acid-induced degradation products followed by densitometric measurement of the spots at 215 nm. The separation was performed on silica gel 60 F254 using methanol-ammonia (100+/-1.5, v/v) as mobile phase. This method was applicable for determination of the intact drug in the presence of its degradation products over a concentration range of 2.00-9.00 microg/spot with mean percentage accuracy of 99.86+/-0.92. The proposed methods were successfully applied for the determination of trimetazidine dihydrochloride in bulk powder, laboratory-prepared mixtures containing different percentages of degradation products, and pharmaceutical dosage forms. The validity of results was assessed by applying the standard addition technique. The results obtained agreed statistically with those obtained by the reported method.     

Validated stability-indicating methods for the determination of nizatidine in the presence of its sulfoxide derivative

Four new selective, precise, and accurate methods are described for the determination of nizatidine (NIZ) in the presence of its sulfoxide derivative in both the raw material and pharmaceutical preparations. Method A is based on zero-order (0D), first-derivative (1D), and second-derivative (2D) spectrophotometric measurement of NIZ in aqueous solution at the zero-crossing point of its sulfoxide derivative (at 314, 295-334, and 318-348 nm, respectively). Method B is a 1DD spectrophotometric method based on the simultaneous use of the first derivative of the ratio spectra and the measurement of peak amplitude at 297 nm. Method C uses a solvent-induced derivative-difference spectrophotometry with deltaD1 measurement from peak to peak at 315-345 nm. Method D involves quantitative densitometric evaluation of a mixture of the drug and its sulfoxide derivative after separation by high-performance thin-layer chromatography on silica gel plates with chloroform-methanol (9 + 1, v/v) as the mobile phase; Rf values for NIZ and its sulfoxide derivative were 0.4 and 0.2, respectively. The spot was scanned at 254 nm. The first-derivative spectrophotometric method was used to investigate the kinetics of the hydrogen peroxide degradation process at different temperatures. The apparent pseudo-first-order rate constant, half-life, and activation energy were calculated. The results obtained by the proposed methods were analyzed statistically and compared with those obtained by the official method. These methods are suitable as stability-indicating for the determination of NIZ in the presence of its oxidation-induced degradation product (sulfoxide derivative) either in the bulk powder or in pharmaceutical preparations.     

Thin Layer Chromatographic Method for Rapid Quantification and Identification of Trimethoprim and Sulfamethoxazole in Pharmaceutical Dosage Forms

Abstract

A densitometric and a spectrophotometric method for rapid but accurate determination of sulfamethoxazole (SMA) and trimethoprim (TMP) present in combined dosage forms were described. SMA and TMP were extracted with 90% acqueous methanol and the interfering and related contaminants were removed by thin layer chromatography (TLC) or high performance TLC (HPTLC) on silicagel plates using chloroform : isopropanol : diethylamine :: 10 : 6 : 1 (v/v) as mobile phase. Assay was done at the respective absorption maxima of the drugs by in situ densitometry and by spectroscopy after extracting the drugs from TLC plates with 90% acqueous ethanol. Results obtained by both the methods agreed well with those obtained by the method prescribed by the United States Pharmacopoeia XXI edition. Total time required for HPTLC and densitometric assay of 32 samples using 4 standards was 30 min. Probable source of errors in densitometric studies and their rectification was discussed.     

Determination of Sumatriptan and Zolmitriptan in Presence of Their Corresponding Degradation Products by HPTLC Methods

Accurate, sensitive, and precise high performance thin layer chromatographic (HPTLC) methods were developed and validated for the determination of sumatriptan and zolmitriptan in presence of their degradation products. Sumatriptan was separated from its degradation products and analyzed on TLC silica gel 60 F₂₅₄ plates using chloroform–ethyl acetate–methanol–ammonia (4:3:3:0.1, v/v) as a developing system followed by densitometric measurement of the bands at 228 nm. Zolmitriptan was determined using chloroform–ethyl acetate–methanol–ammonia (3:3:3:1, v/v) as a developing system followed by densitometric measurement at 222 nm. The methods were validated over a range of 0.5–4 μg/spot for sumatriptan and 0.5–3 μg/spot for zolmitriptan. The proposed methods were successfully applied for the determination of the studied drugs in bulk powder and in their pharmaceutical formulations.     

Different chromatographic methods for simultaneous determination of diloxanide furoate,metronidazole and its toxic impurity

TLC densitometric and RP-HPLC methods are innovative chromatographic methods used for determination of diloxanide furoate, metronidazole and its impurity, 4-nitroimidazole. In the developed TLC densitometric method, appropriate separation was achieved using silica gel 60 F₂₅₄ TLC plates and ethyl acetate/acetone/hexane/ammonia solution (9.5:0.5:0.3:0.3, by volume), as a developing system and the separated bands were UV-scanned at 276 nm. While the developed RP-HPLC method depended on separation of components on C8 column using deionized water containing 0.05 % TEA: methanol (40:60, v/v) as a mobile phase at constant flow rate of 1 mL/min with UV detection at 276 nm. Variables affecting performance of the developed methods were studied and optimized. Regression analysis showed acceptable correlation coefficients in the selected ranges with excellent percentage recoveries. The methods showed no significant interferences from dosage form excipients, and the validity of the proposed methods was further assessed by applying standard addition technique. In addition, results obtained by applying the proposed methods were statistically compared to those obtained by applying the reported method and no significant difference was found between them. The suggested methods were successfully applied for the determination of the cited drugs in bulk powder, laboratory prepared mixtures and commercial tablets.     

Spectrophotometric and spectrodensitometric determination of paracetamol and drotaverine HCl in combination

Thin-layer chromatography, first derivative, ratio spectra derivative spectrophotometry and Vierordt's method have been developed for the simultaneous determination of paracetamol and drotaverine HCl. TLC densitometric method depends on the difference in Rf values using ethyl acetate:methanol:ammonia (100:1:5 v/v/v) as a mobile phase. The spots of the two drugs were scanned at 249 and 308 nm over concentration ranges of 60-1200 microg/ml and 20-400 microg/ml with mean percentage recovery 100.11%+/-1.91 and 100.15%+/-1.87, respectively. The first derivative spectrophotometric method deals with the measurements at zero-crossing points 259 and 325 nm with mean percentage recovery 99.25%+/-1.08 and 99.45%+/-1.14, respectively. The ratio spectra first derivative technique was used at 246 and 305 nm with mean percentage recovery 99.75%+/-1.93 and 99.08%+/-1.22, respectively. Beer's law for first derivative and ratio spectra derivative methods was obeyed in the concentration range 0.8-12.8 and 0.4-6.4 microg/ml of paracetamol and drotaverine HCl, respectively. Vierordt's method was applied to over come the overlapping of paracetamol and drotaverine HCl in zero-order spectra in concentration range 2-26 and 2-40 microg/ml respectively. The suggested methods were successfully applied for the analysis of the two drugs in laboratory prepared mixtures and their pharmaceutical formulation. The validity of the methods was assessed by applying the standard addition technique. The obtained results were statistically agreed with those obtained by the reported method.     

A comparative study on various spectrometries with thin layer chromatography for simultaneous analysis of drotaverine and nifuroxazide in capsules

Three spectrophotometric methods including Vierordt's method, derivative, ratio spectra derivative, and thin layer chromatography (TLC)-UV densitometric method were developed for simultaneous determination of drotaverine HCl (DRT) and nifuroxazide (NIF) in presence of its impurity, 4-hydroxybenzohydrazide (4-HBH). In Vierordt's method, (E(1 cm)(1%)) values were calculated at 227 and 368 nm in the zero-order spectra of DRT and NIF. By derivative spectrophotometry, the zero-crossing method, drotaverine HCl was determined using the second derivative at 245 nm and the third derivative at 238 nm, while nifuroxazide was determined using the first derivative at 399 nm and the second derivative at 411 nm. The ratio spectra derivative spectrophotometry is basedon the measure of the amplitude at 459 nm for DRT and at 416 nm for NIF in the first derivative of the ratio spectra. Calibration graphs of the three spectrophotometric methods were plotted in the range 1-10 mug/ml of DRT and 2-20 mug/ml of NIF. TLC-UV densitometric method was achieved on silica gel plates using ethyl acetate : methanol : ammonia 33% (10 : 1 : 0.1 v/v/v) as the mobile phase. The Rf values were 0.74, 0.50, 0.30+/-0.01 for DRT, NIF and 4-HBH, respectively. On the fluorescent plates, the spots were located by fluorescence quenching and the densitometrical area were measured at 308 and 287 nm with linear range 0.2-4 mug/spot and 0.6-12 mug/spot for DRT and NIF, respectively. The proposed methods have been successfully applied to the commercial pharmaceutical formulation without any interference of excipients. Mean recoveries, relative standard deviations and the results of the proposed methods were compared with those obtained by applying the alternate methods.     

Stability indicating methods for the determination of norfloxacin in mixture with tinidazole

Three stability indicating assay methods are developed for the determination of norfloxacin (Nor) in the presence of its decarboxylated degradation product and in mixture with tinidazole (Tnd). The proposed methods are reversed phase ion pair liquid chromatography (LC), thin layer densitometry (TLC) and second derivative ratio spectra zero crossing spectrophotometry ((2)DD). Chromatographic separation was achieved on mu-Bondapack C18 column 5 microm (300 mm x 3.9 mm, I.D.) and precoated silica gel TLC stationary phases for LC and TLC methods, respectively. Mobile phases consisting of phosphate buffer pH 3.2 : methanol (3 : 1, v/v) containing 0.005 M pentane sulfonic acid sodium salt and isopropanol : butanol : concentrated ammonia : water (25 : 50 : 5 : 25, v/v/v/v) were used for resolution of Nor and Tnd by both techniques, respectively. Detection was carried at 280 nm. In the ratio spectra method, detection of Nor was carried at 282 nm. Linearity, accuracy and precision were found to be acceptable over concentration ranges of 20-225 microg/ml, 0.8-4 microg/spot and 1-7 microg/ml for Nor by LC, TLC and (2)DD methods and over concentration ranges of 37.5-375 microg/ml and 4.8-20 microg/spot for Tnd by LC and TLC methods respectively. The suggested methods were successfully applied for the determination of both drugs in bulk powder, laboratory prepared mixtures and in commercial samples. Statistical comparison between the results obtained by the proposed and the reference methods was carried out using Student t-test, F ratio and one way ANOVA.     

Utility of Derivative Spectrophotometry in the Determination of Carbochromen Hydrochloride and Dipyridamole in the Presence of Their Oxidative Degradation Products

Abstract

Direct spectrophotometric methods for the determination of carbochromen hydrochloride and dipyridamole, each in the presence of its oxidative degradation products, are presented. the methods are based on the first derivative (D₁) and second derivative (D₂) spectrophotometric measurement (absolute trough, U) at 336 nm and (Peak-trough, Y) at 309–342 nm for carbochromen hydrochloride and at 240–260 nm(U) and 246–268 nm(Y) for dipyridamole. Plots of D₁ or D₂ versus concentration were linear over the concentration range of 8.00–16.00 μg/ml for carbochromen hydrochloride and 4.00–12.00 μg/ml for dipyridamole. Oxidative degradation of these drugs has been optimized with respect to hydrogen peroxide concentration. Determining the intact in coexistence with its oxidative degradation product, the proposed derivative spectrophotometric methods proved to be of high potential in correcting the systematic error appearing in the results of the A_max method due to the latter. Assaying the commercial tablets, the proposed method gave results of high accuracy and reproducibility.     

Baclofen impurities: Facile synthesis and novel environmentally benign chromatographic method for their simultaneous determination in baclofen

An efficient, economic and high yielding method was described for the synthesis of baclofen (BAC) pharmacopoeial impurities (impurity A and impurity B) which can be used for gram‐scale synthesis. Furthermore, a novel ecofriendly thin‐layer chromatographic TLC–densitometric method was established and validated for the determination of BAC and its synthesized impurities. The developed TLC–densitometric method is based on the chromatographic separation using TLC plates (60 F₂₅₄) using a green mobile phase of ethyl acetate–methanol–ammonia solution, 33% (8:2:0.1, by volume) with UV scanning at 220 nm. The proposed method was validated with respect to International Conference on Harmonization guidelines. The validated method was successfully applied for determination of BAC in pure form and in its commercial dosage form. Additionally, the greenness profile of the developed method was evaluated and compared with those of the reported chromatographic methods. The developed method was found to be superior to the published methods, being environmentally benign.     

Stability indicating reversed-phase high-performance liquid chromatographic and thin layer densitometric methods for the determination of ziprasidone in bulk powder and in pharmaceutical formulations

Two sensitive and reproducible methods were developed and validated for the determination of ziprasidone (ZIP) in the presence of its degradation products in pure form and in pharmaceutical formulations. The fi rst method was based on reversed-phase high-performance liquid chromatography (HPLC), on a Lichrosorb RP C(18) column using water:acetonitrile:phosphoric acid (76:24:0.5 v/v/v) as the mobile phase at a fl ow rate of 1.5 mL min(-1) at ambient temperature. Quantification was achieved with UV detection at 229 nm over a concentration range of 10-500 micro g mL(-1) with mean percentage recovery of 99.71 +/- 0.55. The method retained its accuracy in presence of up to 90% of ZIP degradation products. The second method was based on TLC separation of ZIP from its degradation products followed by densitometric measurement of the intact drug spot at 247 nm. The separation was carried out on aluminium sheet of silica gel 60 F(254) using choloroform:methanol:glacial acetic acid (75:5:4.5 v/v/v) as the mobile phase, over a concentration range of 1-10 micro g per spot and mean percentage recovery of 99.26 +/- 0.39. Both methods were applied successfully to laboratory prepared mixtures and pharmaceutical capsules.     

Validated chromatographic methods for determination of hydrochlorothiazide and spironolactone in pharmaceutical formulation in presence of impurities and degradants

Two specific, sensitive, and precise stability indicating chromatographic methods have been developed, optimized, and validated for Hydrochlorothiazide (HCT) and Spironolactone (SPR) determination in their mixtures and in presence of their impurities and degradation products. The first method was based on thin layer chromatographic (TLC) combined with densitometric determination of the separated spots. The separation was achieved using silica gel 60 F(254) TLC plates and ethyl acetate-chloroform-formic acid-triethyl amine (7:3:0.1:0.1, by volume) as a developing system. Good correlations were obtained between the integrated peak area of the studied drugs and their corresponding concentrations in different ranges. The second method was based on the high-performance liquid chromatography with ultraviolet detection, by which the proposed components were separated on a reversed phase C(18) analytical column using gradient elution system with deionized water-acetonitrile (97:3, v/v) for 8 min. Then acetonitrile was successively increased to 35% in the next 2 min, and kept constant in the following 10 min, finally 3% acetonitrile was regained again to stabilize the chromatographic system. The flow rate was maintained at 2 mL/min and the detection wavelength was at 230 nm. Linear regressions were obtained in the range of 4.0-50 μg/mL and 5.0-50 μg/mL for both HCT and SPR, respectively. Different parameters affecting the suggested methods were optimized for maximum separation of the cited components. System suitability parameters of the two developed methods were also tested. The suggested methods were validated in compliance with the ICH guidelines and were successfully applied for determination of HCT and SPR in their commercial tablets. Both methods were also statistically compared to each other and to the reported method with no significant difference in performance.     

Simultaneous HPTLC and RP-HPLC methods for determination of bumadizone in the presence of its alkaline-induced degradation product

Accurate, selective, sensitive and precise HPTLC‐densitometric and RP‐HPLC methods were developed and validated for determination of bumadizone calcium semi‐hydrate in the presence of its alkaline‐induced degradation product and in pharmaceutical formulation. Method A uses HPTLC‐densitometry, depending on separation and quantitation of bumadizone and its alkaline‐induced degradation product on TLC silica gel 60 F₂₅₄ plates, using hexane–ethyl acetate–glacial acetic acid (8:2:0.2, v/v/v) as a mobile phase followed by densitometric measurement of the bands at 240 nm. Method B comprises RP‐HPLC separation of bumadizone and its alkaline‐induced degradation product using a mobile phase consisting of methanol–water–acetonitrile (20:30:50, v/v/v) on a Phenomenex C₁₈ column at a flow‐rate of 2 mL/min and UV detection at 235 nm. The proposed methods were successfully applied to the analysis of bumadizone either in bulk powder or in pharmaceutical formulation without interference from other dosage form additives, and the results were statistically compared with the established method. Copyright © 2011 John Wiley & Sons, Ltd.     

Simultaneous high-performance thin-layer chromatography densitometric assay of trandolapril and verapamil in the combination preparation

A high-performance thin-layer chromatography (TLC) method coupled with densitometric analysis has been developed for simultaneous measurement of trandolapril (TRA) and verapamil (VER) in 2-component mixtures and in their combination capsules. The active substances were extracted from capsules with methanol (mean recovery: 103.4% for TRA, 97.13% for VER) and chromatographed on TLC plates coated with silica gel 60 F254 in horizontal chambers with ethyl acetatc-ethanol-acetic acid (8 + 2 + 0.5, v/v) mobile phase. Chromatographic separation of these components was followed by ultraviolet densitometric quantification at 215 nm. The calibration graphs were constructed over the concentration range from 0.5 to 1.5 microg/microL (corresponding to 5.0-15.0 microg/spot) for both drugs with good correlation (r > or = 0.990). Detection and quantitation limits were found to be 1.25 and 3.75 microg/spot for TRA and 0.15 and 0.45 microg/spot for VER, respectively. The proposed method was used for determination of both drugs in TRA-VER capsules with satisfactory precision [0.97% < relative standard deviation (RSD) < 4.50% for TRA, 0.49% < RSD < 3.10% for VER] and accuracy [2.16% < relative error (RE) < 4.90% for TRA, 1.73% < RE < 5.68% for VER].     

Stability-Indicating Method for the Determination of Hydrochlorothiazide,Benzydamine Hydrochloride and Clonazepam in the Presence of Their Degradation Products

Abstract

Spectrophotometric, colorimetric and densitometric methods for the determination of hydrochlorothiazide, benzydamine hydrochloride and clonazepam in the presence of their degradation products are described. Hydrochlorothiazide was determined in the presence of its degradation products methoxyhydrothiazide, hydroxyhydrothiazide and 5-chloro-2,4-disulfonamidoaniline applying the first and second derivative spectrophotometer at 278.8 nm and 254.4 nm, respectively, while benzydamine hydrochloride was determined in the presence of its toxic photodegradation products 5-hydroxybenzydamine and 2-B-dimethylaminopropyl-l-benzylindalolin-3-one colorimetrically using the acid dye bromophenol red and measuring the absorbance of the chloroform solution of the ion-pair formed at 425nm. Clonazepam was determined densitometrically in the presence of its degradation products carbostyril and 2-amino-2-chloro-5-nitrobenzophenone. The suggested methods determine hydrochlorothiazide, benzydamine hydrochloride and clonazepam in the presence of degradation products with mean accuracies of 99.57±0.51%, 100.04±0.41%, 100.03±0.21% and 99.84±0.34%, respectively. The proposed methods are suitable for stability testing in bulk powder and in pharmaceutical preparations.     

Determination of fenofibrate and gemfibrozil in pharmaceuticals by densitometric and videodensitometric thin-layer chromatography

New thin-layer chromatography (TLC) methods with densitometric and videoscanning detection were elaborated for the quantitative determination of fenofibrate in Fenoratio capsules and gemfibrozil in Gemfibral tablets. Analysis was performed on high-performance TLC diol F254 plates using hexane-tetrahydrofuran (8 + 2, v/v) mobile phase in horizontal DS chambers using the sandwich technique. The active substances were extracted from tablets with methanol. Densitometric assay was performed at 227 nm and videoscanning quantitation at 254 nm. Calibration plots were constructed in range 5-30 microg/spot (20 microL of solutions in different concentrations) for both of the drugs. The calibration data were tested against 3 regression models, and the optimum model was selected (quadratic for videoscanning and nonlinear y = ax(m) + b for the densitometric method, R2 > 0.997 in all cases). Linearity of the methods was tested by spotting different amounts of extracted solution (15-30 mg/spot). The recovery function was sufficiently linear in all cases, with an insignificant intercept and a slope very close to 1. Accuracy was tested by quantitating 3 fortified samples (50,100, and 150% of theoretical), and the results were homogeneous with no significant differences. The recovery in the densitometric assay was 101.42% (total relative standard deviation 10.76%) for fenofibrate and 100.47% (9.7%) for gemfibrozil. Videodensitometry resulted in recoveries of 102.73% (12.59%) and 98.79% (8.56%), respectively. The F-Snedecor test and Student's t-test for 2 means showed no significant differences between the precision and accuracy of both methods.