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  • Author or Editor: Dorota Kowalczuk x
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A sensitive, selective, precise, and stability-indicating high-performance thin-layer chromatographic method coupled with densitometric analysis has been developed for determination of nitrendipine both as the bulk drug and in pharmaceutical dosage forms. The active substance was extracted from tablets with methanol (recovery from 97 to 105%) and chromatographed on silica gel 60 F 254 HPTLC plates in horizontal chambers with n -hexane-ethyl acetate-acetone, 6 + 3 + 2 ( v/v ), as mobile phase. UV densitometric analysis of nitrendipine was performed in absorbance mode at λ = 335 nm. The calibration plot was constructed in the range 0.025 to 0.150 μg μL −1 (corresponding to 0.5–3.0 μg spot −1 ) with good correlation ( r ≥ 0.990) and expressed as a second-order calibration function. Determination of nitrendipine in tablets was characterized by good precision (1.94% < RSD < 6.62%) and accuracy (−3.0 < RSE < 5.12). The HPTLC-densitometric method was successfully used for identification of nitrendipine in the presence of its induced degradation products. Pure drug and tablet extract were subjected to acid and alkali hydrolysis, oxidation, UV degradation, and photodegradation. The degraded products were well resolved from the nitrendipine with different R F values.

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Separation of the fluoroquinolone antibiotics has been examined using numerous mobile phases and commercially available TLC plates precoated with silica gel, cellulose, and chemically bonded silica gel (RP-C18). The best separation of the antibiotic standards was achieved on silica gel with methanol-acetone-1 mol L −1 citric acid-triethylamine, 2.8 + 2 + 0.2 + 0.5 ( v / v ) as mobile phase, on cellulose with dichloromethane-isopropanol-THF-25% ammonia, 4 + 6 + 3 + 3 ( v / v ), as mobile phase, and on silanized silica gel RP-C18 with methanol-0.07 mol L −1 phosphate buffer, pH 6–10 mmol L −1 benzyldimethyltetradecylammonium chloride, 6 + 3 + 1 ( v / v ), as mobile phase. The separated compounds were detected under UV irradiation at λ = 254 nm or by treatment of the plate surface with different dyeing agents.

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A new, simple, and rapid high-performance thin layer chromatographic method coupled with densitometry has been developed and validated for the determination of enoxacin, ofloxacin, and pefloxacin in tablets. HPTLC analysis was performed on silica gel 60F 254 plates in horizontal chambers with dichloromethane-methanol-25% NH 3 , 7 + 5 + 1.5, as mobile phase. Detection and quantification were performed by videodensitometry at λ = 254 nm and by classical densitometry at the wavelength of maximum absorption of the drugs determined. The active substances were extracted from tablets with a 0.05% solution of ammonia in methanol (enoxacin, ofloxacin) or with methanol (pefloxacin). Calibration plots were constructed in the range 0.1 to 0.6 μg μL −1 and were linear for all analytes with good correlation coefficients ( r from 0.992 to 0.9998). The precision of the proposed chromatographic methods, expressed as RSD , were between 7.56 and 10.08. The mean recoveries of the three antibiotics from tablets ranged from 97.46 to 102.87%.

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The chromatographic behavior of some antiarrhythmic compounds has been studied on commercially available TLC plates coated with octylsilane and octadecylsilane silica gel (RP-C8 and RP-C18, respectively) with organic-aqueous mobile phases containing citrate or acetate buffers at different pH. The best separations of individual and mixed drug standards were achieved on both RP-C8 and RPC18 with 3:7 ( v/v ) tetrahydrofuran-citrate buffer pH 4.45 as mobile phase. To determine the usefulness of these chromatographic systems for analysis of tablet samples, flecainide acetate was identified and quantified by UV densitometry at two wavelengths, 225 and 310 nm. Linear relationships were obtained between peak height or peak area and amount in the range 6.0 to 12.0 μg per spot, the correlation coefficient, r , was ∼0.990. The method was successfully applied to the analysis of flecainide in a pharmaceutical preparation, with satisfactory precision (RSD 1.14–5.93%) and accuracy (96.19–103.59%).

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A new, simple, and accurate TLC method, using normal- and reversed-phase techniques and densitometric detection, has been developed for measurement of quinapril and hydrochlorothiazide in combination tablets. UV detection at λ = 210 nm was used to quantify the analytes. The drugs were chromatographed on silica gel 60 F 254 HPTLC plates and on octadecilsilane (RP-18) TLC plates, in horizontal chambers, with ethyl acetate-acetone-acetic acid, 8 + 2 + 0.5 ( v/v ) and methanol-0.07 m phosphate buffer, pH 2.5, 6 + 4 ( v/v ), respectively, as mobile phases. The active substances were extracted from tablets with methanol (96% < mean recovery < 104%). Calibration curves were constructed in the range 0.4 to 2.4 μg μL −1 for quinapril and 0.25 to 1.5 μg μL −1 for hydrochlorothiazide, with good correlation ( r ≥ 0.998). The precision ( RSD < 4.4%) and accuracy (2.91 < RE < 3.92) were satisfactory for TLC-densitometric determination of quinapril in combination with hydrochlorothiazide in commercial tablets.

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A normal-phase (NP) TLC method has been established for separation of the five antiarrhythmics — disopyramide, flecainide, mexiletine, tocainide, and verapamil. The analysis was performed in horizontal chambers on aluminum oxide 60 F 254 and silica gel 60 F 254 TLC plates. The best mobile phases for separation of the compounds were tetrahydrofuran-hexane-25% ammonia, 5 + 4.8 + 0.2 ( v/v ), on the alumina plates and chloroform-tetrahydrofuran-ethanol-25% ammonia, 8.1 + 1.9 + 2 + 0.1 ( v/v ), on the silica plates. The substances were identified by use of different reagents and under UV irradiation at λ = 254 nm. Quantification of mexiletine hydrochloride in Mexicord capsules was performed densitometrically at λ = 210 nm. A good correlation coefficient ( r = 0.9974) was obtained for the calibration plot constructed in the concentration range 20–45 μg per band. The active substance was extracted from the formulation with methanol (recovery 97.01 ± 2.39%, mean ± SD ). The RSD expressing the precision of the proposed method was 5.23%. The procedure was simple and rapid and the results were reliable.

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The chromatographic behavior of seven oral antidiabetic drugs — chlorpropamide, tolbutamide, glibenclamide, metformin, pioglitazone, rosiglitazone, and repaglinide — has been investigated. Normal-phase chromatography was performed on silica gel and alumina layers with mixtures of chloroform, diethyl ether, and ethyl acetate as mobile phases. For more effective resolution aqueous ammonia or acetic acid was added to the mobile phases. Silica gel enabled better separation than alumina. Reversed-phase chromatography was performed on octadecyl-bonded silica gel (RP-18) with mixtures of acetonitrile or 2-propanol with phosphate buffer as mobile phases. The effect of pH on the separation of the drugs was also examined. For separation of these drugs reversed-phase chromatography was more effective than use of normal-phase mode.

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