Genowefa Misztal

Chromatographic analysis of new antidepressant drugs by normal- and reversed-phase TLC

The selectivity of the TLC separation of six new antidepressant substances has been investigated on silanized silica gel C18 and on silica gel GF254. Optimization of the retention and selectivity of these compounds on reversed-phase plates (RP C18) 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 GF254 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.

Determination of Citalopram in Tablets by HPLC, Densitometric HPTLC, and Videodensitometric HPTLC Methods

Abstract Three simple, rapid, and accurate analytical methods for the determination of citalopram in tablets were developed. The high performance liquid chromatography method was carried out using Waters Nova‐Pak C18 column with a mobile phase composed of methanol–0.067 M phosphate buffer pH 2.00 (55:45, v/v), UV‐VIS detector at 239 nm, and moclobemide as the internal standard. High performance thin layer chromatography was performed on silica gel 60F254 HPTLC plates with a mixture of benzene–acetone–ethanol–25% aqueous ammonia (45:40:10:5, v/v/v/v) as a mobile phase. The detection and quantification were carried out at 226 nm (densitometry) and 254 nm (videodensitometry). The linearity range for the HPLC method was 5–50 µg/mL and for both HPTLC methods was 0.2–3.2 µg per spot. The RSD values obtained for the standard solutions were <2.0% for HPLC, <2.4% for densitometry, and <2.9% for videodensitometry. The recovery values obtained for the model mixtures were between 99.47% and 102.70%, between 102.17% and 104.44%, and between 100.74% and 104.01%, respectively.

Determination of fluoxetine and paroxetine in pharmaceutical formulations by densitometric and videodensitometric TLC

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 F254 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; videodensitometric 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 videodensitometry. 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.

LC determination of moclobemide and three metabolites in plasma.

Moclobemide and three metabolites were quantified using 1 ml of plasma and solid-phase extraction with Bakerbond CN column after the addition of nadolol as the internal standard (I.S.). Separation and detection the analysed substances were achieved isocratically with acetonitrile-methanol-0.067 M phosphate buffer pH 2.65-0.4% triethylamine (12.7:1.9:85:0.4, v/v/v/v), a Nova-pak C(8) column and UV detection at 230 nm. The lower limits of quantitation for moclobemide was 10 ng ml(-1), for M1 (Ro 16-3177)-8 ng ml(-1), for M2 (Ro 12-5637)-10 ng ml(-1) and for M3 (Ro 12-8095)-15 ng ml(-1) (as the metabolites). Accuracies calculated of three concentrations in each of three separate runs were between 84.55 and 93.68 for moclobemide, 83.28 and 92.30 for M1, 86.31 and 92.66 for M2 and 88.42 and 93.40 for M3. Precision data within day were between 5.71 and 7.50 for moclobemide, 2.91 and 6.58 for M1, 4.98 and 6.40 for M2 and 0.94 and 4.73 for M3.

The Retention Behavior of Some Atypical Antipsychotic Drugs in Normal-Phase TLC

Chromatographic behavior in normal-phase thin-layer chromatog-raphy has been investigated for six atypical antipsychotic drugs (amisulpride, clozapine, olanzapine, quetiapine, risperidone, and ziprasidone). The drugs were separated on silica gel, alumina, NH2, CN, diol, and polyamide plates with mixtures of n-hexane and six polar modifiers (acetone, dioxane, diethylamine, ethanol, iso-propanol, and tetrahydrofuran) as mobile phases. The linearity of relationships between RM and volume fraction of modifier, the logarithm of the volume fraction, the molar fraction, and the logarithm of the molar fraction was tested. The results usually fitted the Sny-der-Soczewiński equation, with r > 0.9. The best separation was achieved on silica gel plates with ethanol-n-hexane, 1 + 1 (v/v), containing 1.5% aqueous ammonia, as mobile phase.

Determination of bezafibrate and ciprofibrate in pharmaceutical formulations by densitometric and videodensitometric TLC

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 F254 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 = axm + b for densitometry; R2 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.

Determination of fluvoxamine and moclobemide in tablets by densitometric and videodensitometric TLC

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 F254 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 flu-voxamine 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 videodensit-ometry; recovery of moclobemide from tablets was 101.15% and 98.81% respectively.

A Proposal for New R F Equal-Spread Criteria with Stable Distribution as a Random Variable

The retention factor RF 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: RU (retention uniformity) and RD (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 MonteCarlo simulations. An example is given of their use in the separation of fibrate-type antihyperlipidemic drugs by normal and reversedphase TLC (114 systems).

The reversed-phase retention behavior of some atypical antipsychotic drugs

As discussed elsewhere [3], the literature on the TLC analysis of these drugs is not extensive. The purpose of the research discussed in this paper was to investigate retention data of atypical neuroleptics – amisulpride, clozapine, olanzapine, quetiapine, risperidone, and ziprasidone (Figure 1) – on RP18, RP8, RP2, CN, diol, and NH2 plates with mixtures of phosphate buffer and six modifiers (acetone, acetonitrile, dioxane, ethanol, methanol, and tetrahydrofuran) as mobile phases. For RP18 and RP8 plates the linearity of relationships between RM and the volume fraction of the modifier, the logarithm of the volume fraction of the modifier, the molar fraction of the modifier, and the logarithm of the molar fraction of the modifier was tested. The results usually fitted the Snyder–Soczewinski equation with r > 0.95. The best separation was achieved on RP8 plates with 40 + 60 (v/v) dioxane–pH 3.51 phosphate buffer as mobile phase. This work is a continuation of our previous research on the normal-phase TLC of these drugs.

The normal-phase retention behavior of some angiotensin-II receptor antagonists

Angiotensin II is the principal mediator of the renin–angiotensin system (RAS) which plays an important role in regulating blood pressure and maintaining fluid and electrolyte balance. Angiotensin II-AT1 receptor antagonists inhibit the RAS by selectively blocking the AT1 receptor. This receptor subtype is believed to mediate all known physiological effects of angiotensin II. Therefore, sartans have therapeutic promise as antihypertensive agents [1].