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  • Author or Editor: Hanna Hopkała x
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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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The chromatographic separation of fenbufen, ibuprofen, ketoprofen, diclofenac sodium, mefenamic acid, and tiaprofenic acid has been investigated. Normal-phase chromatography on silica gel by the ascending and horizontal techniques, and reversed-phase chromatography on octadecyl-bonded silica gel (RP-18) in horizontal chambers, were performed with suitable mobile phases. The substances were identified by UV illumination at λ = 254 nm and by use of dyeing reagents. Reversed phase chromatography with phosphate buffer, pH 5.73–10% CTMA-Br in methanol, 3.5 + 6.5 ( v/v ), as mobile phase enabled better separation of the six drugs than normal-phase mode. A simple videodensitometric TLC method on silica gel RP-18 was developed and validated for quantitative determination of fenbufen in tablets. The limits of detection and quantification were determined by videodensitometry at λ = 254 nm. A calibration plot was constructed in the range 2.0–12.0 μg/5-μL spot and was linear with a good correlation coefficient (0.9926). RSD for quantitation of fenbufen were from 2.44 to 3.10%. The method was applied satisfactorily to pharmaceutical preparations.

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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 cyclooxygenase inhibitors lornoxicam, meloxicam, piroxicam, and tiaprofenic acid have been separated by normal- and reversed-phase TLC by ascending and horizontal development with suitable mobile phases on silica gel and silanized gel. The substances were identified by UV illumination at λ = 254 nm and by use of dyeing reagents. Meloxicam and tiaprofenic acid were determined in pharmaceutical preparations by videodensitometric TLC on silica gel and ascending development with toluene-acetic acid-methanol, 11 + 1 + 0.5 ( v/v ), as mobile phase. The range of linearity was 0.5–5.0 μg per spot for both drugs. The method was applied satisfactorily to pharmaceutical preparations. Results from quantitative analysis were assessed statistically by determination of the correlation coefficient for the calibration equation obtained from the calibration procedure. The RSD for quantitation of meloxicam and tiaprofenic acid were 5.8 and 5.9%, respectively.

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The thin-layer chromatographic behavior of three of the newest oral antidiabetic agents, pioglitazone, rosiglitazone, and repaglinide, has been studied in reversed-phase systems. Chromatography was performed on RP-8 as adsorbent with buffer-organic modifier binary mobile phases of widely different composition. Phosphate buffers of pH 2.4, 4.4, 6.0 and 7.9 were used with three organic mobile-phase modifiers, acetonitrile, 2-propanol, and methanol; the concentration of organic modifier was varied between 20 and 80% ( v/v ). Plates were developed in horizontal chambers, visualized by UV illumination at λ = 254 nm, and scanned with a densitometer. The effect of the mobile phase on retention was studied. The selectivity of the chromatographic systems is discussed. The linearity of relationships between R M and modifier volume fraction, molar fraction, and logarithm of the molar fraction was calculated.

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A simple, rapid, and stability-indicating thin-layer chromatographic method has been developed for quantitative determination of repaglinide in tablets. Analysis was performed on RP-8 TLC plates with acetonitrile-pH 6.0 phosphate buffer, 60 + 40 (% v/v ), as mobile phase. Detection and quantification were performed by classical densitometry at the wavelength of maximum absorption of repaglinide, 225 nm. A calibration plot constructed in the range 0.6–3.6 μg/10 μL was linear with a good correlation coefficient ( r = 0.998 ± 0.001, mean ± SD , n = 5). Limits of quantitation and detection of repaglinide were 0.27 μg/10 μL and 0.08 μg/10 μL, respectively. Instrumental precision established at three concentrations of the drug ranged from 3.92 to 0.97% for the lowest and highest concentrations of repaglinide, respectively. The mean intra-day and inter-day variability, including three concentrations of repaglinide, were 1.93 and 2.25% ( n = 9), respectively. Recovery from model mixtures, at three levels of addition, ranged from 103.06 to 102.49% for the lowest and highest levels, respectively. Total mean ± SD recovery was 102.71 ± 2.04% ( n = 15). The mean ± SD recovery from commercially available tablets was 101.85 ± 1.83% ( n = 10). The effect of pH, temperature, and UV light on degradation of repaglinide was also investigated. The analytical method presented was found to be simple, reliable, and convenient for routine pharmaceutical analysis. Its analytical performance fulfilled acceptance criteria established for TLC methods in the official literature.

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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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Five anti-diabetic thiazolidinediones have been chromatographed on C 18 TLC plates with binary mobile phases containing water and the organic modifiers acetone, 1,4-dioxane, or methanol. Linear relationships were obtained between the R M values of the compounds and the concentration of organic modifier in the mobile phase. These R M values enabled calculation of R M0 values by extrapolation. Calibration equations were then obtained for nine standards of known lipophilicity in the range 0.83–6.04. From these equations the partition coefficients log P EXP were calculated for the drugs. Lipophilicity values were also calculated by use of computational methods. Finally, interesting relationships were obtained between experimental and theoretical log P values and pharmacological data from the literature.

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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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