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  • Author or Editor: Rafał Pietraś x
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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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The retention (R M) values of nine one-point adsorption model compounds: diphenylamine, indol, 2-naphtol, 1-naphtol, 1-naphtylamine, 4-toluidine, carbazole, 4-chloraniline, and thymol were investigated on silica gel using six modifiers: acetone, dioxane, hexane, isopropanol, methylethylketone, ethyl acetate, and tetrahydrofurane (in hexane). These compounds showed small but visible curvilinearity of dependence of R M vs. modifier concentration. This curvilinearity is very similar among the investigated compounds, so relative differences of extrapolated R M are almost the same (strictly intercorrelated) regardless of the regression technique used. We have compared several robust and weighted regression methods and investigated their impact on extrapolated values. It can be concluded that one should primarily consider weighted regression with 1/x weights during retention extrapolation. It seems to be a better alternative than classical regression (better extrapolation) and also better than polynomial approaches (better stability).

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Thin-layer chromatography (TLC) on two adsorbents (RP18 and CN) and with six modifiers (acetonitrile, acetone, dioxane, propan 2-ol, methanol, and tetrahydrofurane), followed by classical R M value extrapolation (previous results), was chemometrically compared with new one-run gradient high-performance liquid chromatography (HPLC) (C18, C18e, CN, and DIOL columns, acetonitrile, and methanol as modifiers) and, additionally, with seven computational algorithms (ALOGPs, AClogP, ALOGP, MLOGP, KOWWIN, XLOGP2, and XLOGP3) as a lipophilicity assessment tool on 35 model compounds with known lipophilicity. The statistical significance of intercepts and slopes of Collander equation (log P — retention dependence) and their values were compared. Whole results data set was subjected to scaled principal component analysis, which allowed exploring two main trends in these data. It can be concluded that one-run gradient HPLC does not outperform TLC in lipophilicity determination. Very good correlations were obtained between real log P and computational approaches; however, this is not a surprise for such simple molecules.

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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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