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  • Author or Editor: Genowefa Misztal x
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The selectivity of the TLC separation of six new antidepressant substances has been investigated on silanized silica gel C 18 and on silica gel GF 254 . Optimization of the retention and selectivity of these compounds on reversed-phase plates (RP C 18 ) was performed by changing the pH and the concentration of organic solvent (methanol, acetonitrile, tetrahydrofuran) in the aqueous mobile phases. The substances were separated in horizontal chambers and the drugs were detected by use of a videoscanning system and illumination of the plates at λ = 254 nm. The drugs were also separated on silica gel GF 254 after solid phase extraction (SPE) from plasma. The best separation was achieved with benzene-acetone-ethanol-ammonia, 9 + 7 + 2 + 1 ( v/v ) as mobile phase.

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New, simple, rapid, and accurate thin-layer chromatographic methods have been established for determination of fluvoxamine and moclobemide in tablets. The drugs were chromatographed on silica gel 60 F 254 plates in horizontal chambers with benzene-acetone-ethanol-25% aqueous ammonia, 9 + 7 + 2 + 1 ( v/v ), as mobile phase. Densitometric detection and quantification were performed at λ = 249 nm and λ = 236 nm, respectively, for fluvoxamine and moclobe-mide; videodensitometric detection was performed at λ = 254 nm for both drugs. The range of linearity was 1–10 μg per spot for fluvoxamine and moclobemide for both methods. The relative standard deviation for determination of these antidepressants in pharmaceuticals was less than 2.5% for densitometry and less than 5.1% for videodensitometry. Recovery of fluvoxamine from tablets was 101.20% by use of densitometry and 98.96% by use of videodensitometry; recovery of moclobemide from tablets was 101.15% and 98.81% respectively.

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New simple TLC methods with densitometry and videoscanning have been developed for the quantitation of bezafibrate in Bezamidin tablets and ciprofibrate in Lipanor capsules. Analysis was performed on HPTLC Diol F 254 plates with hexane-tetrahydrofuran, 8 + 2, as mobile phase. Detection was performed by densitometry at λ = 227 nm and videoscanning at λ = 254 nm. Calibration plots were constructed in the range 5–30 µg per spot for both drugs. The calibration data were tested using several regression models and the optimum models were selected (quadratic for videoscanning and nonlinear y = ax m + b for densitometry; R 2 was always >0.995). The active substances were extracted from tablets with methanol. The linearity of the method was tested by spotting different amounts of extracted solution (15–30 mg). The recovery function was always sufficiently linear, with an insignificant intercept and slope very close to unity. Accuracy was tested by quantitating three fortified samples (50, 100, and 150%); this resulted in homogeneous results without significant differences. Recovery measured by use of densitometry was 100.3% ( RSD 7.84%) for bezafibrate and 98.01% ( RSD 6.12%) for ciprofibrate. Videodensitometry resulted in recovery of 96.16% ( RSD 9.8%) and 97.8% ( RSD 11.2%), respectively. The F-Snedecor test and t -test for two means showed there was no significant difference between the precision and accuracy of the methods.

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Relationships between R M values and mobile phase composition have been determined for the six antihyperlipidemic agents-bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil. The drugs were separated on silica gel, CN, and Diol plates using mobile phases containing n -hexane as weakly polar diluent and five polar modifiers: acetone, dioxane, ethyl methyl ketone, ethyl acetate, and tetrahydrofuran. The optimum mobile phases were also investigated on alumina, NH 2 , and polyamide phases for comparison. The linearity of relationships between R M and modifier volume fraction, molar fraction, and logarithm of molar fraction was calculated. Plates were developed in horizontal chambers, visualized under UV irradiation at λ = 254 nm, and scanned with a densitometer in the multi-wavelength scan mode. Most results fitted the Snyder-Soczewinski equation with r > 0.9; for approximately half r > 0.99. Separation of all the drugs was achieved on Diol plates with mobile phases containing 20–30% of each modifier in n -hexane, and with hexane-acetone, 9 + 1, on CN plates. Five drugs were separated using the same mobile phases on silica gel. The best separation was obtained on Diol plates with tetrahydrofuran-hexane, 2 + 8, as mobile phase.

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The retention factor R F is used in several criteria generally known as chromatographic response functions (CRF). In TLC and HPTLC most of these are based on differences between the retention factors of two substances, which are summed or multiplied. There are also other functions, for example the multispot response function ( MRF ) which enables the quality of a separation to be estimated. Although good CRF criteria should have well-defined distribution and range, current criteria based on the differences do not satisfy this requirement. Only MRF has a clearly defined range (0 to 1), but its distribution is unstable. In this paper two new independent coefficients: R U (retention uniformity) and R D (retention distance) are proposed; these always have values within the range 0 to 1 and stable density, irrespective of the number of compounds separated. Their reliable mathematical properties have been tested in wide range by Monte-Carlo simulations. An example is given of their use in the separation of fibrate-type antihyperlipidemic drugs by normal and reversed-phase TLC (114 systems).

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Relationships between R M values and mobile phase composition have been examined for six fibrate-type drugs — bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil. They were separated in horizontal chambers on RP18 plates by use of mobile phases containing phosphate buffer and different amounts of six modifiers — acetone, acetonitrile, dioxane, isopropanol, methanol, and tetrahydrofuran. Plates were visualized under UV irradiation at λ = 254 nm, and scanned with a densitometer in multi-wavelength scan mode. Optimum modifier concentrations were also investigated on RP8 and CN plates for comparison. The linearity of relationships between R M and modifier volume fraction, molar fraction, and the logarithm of the molar fraction was calculated. Most results fitted the Snyder-Soczewiński equation with r > 0.95; for almost half r > 0.99. Separation of all the drugs was achieved on RP18 plates with mobile phase containing 70% dioxane in pH 7.60 phosphate buffer.

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Two new, simple, rapid, and accurate thin-layer chromatographic methods have been developed for determination of fluoxetine in capsules and paroxetine in tablets. The drugs were chromatographed on silica gel 60 F 254 plates in horizontal chambers with benzene-acetone-ethanol-25% aqueous ammonia, 9 + 7 + 2 + 1 ( v/v ) as mobile phase. Densitometric detection was performed at λ = 218 nm and 293 nm for fluoxetine and paroxetine, respectively; video-densitometric detection was performed at λ = 254 nm for both drugs. The range of linearity was 2–10 μg per spot for fluoxetine and 0.5–8 μg per spot for paroxetine. The relative standard deviation for determination of these antidepressants in pharmaceuticals was less than 4.3% for densitometry and less than 4.9% for video-densitometry. Recovery of fluoxetine from capsules was 105.1% by use of densitometry and 104.3% by use of videodensitometry; recovery of paroxetine from tablets was 99.15% and 98.2%, respectively.

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Authors: Łukasz Komsta, Robert Skibiński, Anita Iwańczyk and Genowefa Misztal

The normal-phase thin-layer chromatographic behavior of five statin-like drugs — atorvastatin, cerivastatin, fluvastatin, lovastatin, and simvastatin — has been investigated. Chromatograms on silica gel, diol, and CN layers were developed with binary mobile phases containing hexane and a polar modifier in different proportions. The R F values obtained with all the mobile phases were then used to calculate Snyder-Soczewinski equations, assuming linear dependence of R M on the volume fraction of the mobile phase modifier, on the mole fraction of the modifier, and on their logarithms. The correlation between regression coefficients within and between models were investigated in depth. The coincidence between regression coefficients were also investigated by calculating Spearman’s rank correlation, and the similarity between modifiers was also checked by use of dendrograms.

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