RP-18 Plates Research Articles

Comparative validation of quetiapine Determination in tablets by NP-HPTLC and RP-HPTLC with densitometric and videodensitometric detection

Two new simple and accurate methods for determination of quetiapine in tablets-normal phase (NP) and reversed-phase (RP) high performance thin layer chromatography (HPTLC), each with densitometric and videodensitometric detection, were developed and validated. NP-HPTLC was developed with HPTLC silica F 254 plates and hexane-dioxane-propylamine 1:9:0.4 ( v/v ) as mobile phase. RPHPTLC was carried out using HPTLC RP8 F 254 plates with tetrahydrofuran-phosphate buffer, pH 9.0, 5:5 ( v/v ) as mobile phase. The silica gel plates were developed to a distance of 9 cm and RP8 plates to a distance of 4.5 cm. Both analyses were performed in horizontal chambers and scanned with a densitometer at 243 nm and a video-densitometer at 254 nm. Calibration plots were linear in the range 0.2–1.2 μg quetiapine per spot for NP-HPTLC and in the range 0.1–1.1 μg for RP-HPTLC. The precision and accuracy of the four methods were fully compared and no significant differences were observed. The methods can be used in routine pharma...

Analysis of Selected Anti-Depressive Drugs by High Performance Thin-Layer Chromatography

The retention behavior of 11 anti-depressive basic drugs was investigated on silica layers with non-aqueous mobile phases containing polar modifier – methanol, medium polar diluent – diisopropyl ether and aqueous ammonia or diethyl amine. The effect of ammonia or amine concentration and modifier concentration on retention, separation selectivity, and efficiency was examined. Investigated compounds were also chromatographed in RP systems on RP18 and CN-silica layers by use of aqueous eluents with various additives. The best results were obtained with addition of ammonia, playing the role of silanol blocker, which causes elimination of ion-exchange interaction of basic analytes with surface residual silanols. On the basis of these investigations, systems for extraction from human serum and quantitative determination of amitriptiline and doxepin were selected. Cyano SPE columns conditioned and pre-eluted with methanol-water (1:1) and eluted with methanol-water (8:2) containing 5% of formic acid were used for sample preparation with high recoveries of both drugs. RP-18 plates eluted with 70% methanol in water + 1% ammonia were used for quantitative analysis by a calibration curve method.

TLC of Alkaloids on Cyanopropyl Bonded Stationary Phases. Part II. Connection with RP18 and Silica Plates

Some standards of the alkaloids and synthetic or natural mixtures are separated by two-dimensional thin-layer chromatography (TLC) on different adsorbent layers. Normal- and reversed-phase systems are used to obtain significant differences in the separation selectivity. Optimization of the one-dimensional TLC separation of the alkaloids' standards is performed on cyanopropyl-silica, RP18W, and silica layers in various eluents containing (besides diluent and modifier) silanol blockers, such as diethyl amine or ammonia. The most selective systems are used for the separation of the alkaloids' mixtures by two-dimensional TLC with an adsorbent gradient method. The mixtures of alkaloids or plant extracts (Chelidonium majus, Fumaria officinalis, or Glaucium flavum) are chromatographed in system I; the plates are connected with the plate pre-coated with various adsorbent, and partly separated fractions are transferred to the second layer and developed in system II. CN-silica-RP18W and CN-silica-silica are used as the connected layers. The alkaloids are identified by R(F) values of standards, and the components of plant extracts are identified in both systems, and by the comparison of UV spectra obtained in diode array detector densitometry.

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.

Investigation of homologous series of fatty acids by TLC. Part IV. Separation on RP18 plates with ternary mobile phases

Fatty acids from heptanoic to eicosanoic have been separated on RP-18 HPTLC plates, with and without concentrating zone, with methanol-ethanol-water, methanol- n -propanol-water, and ethanol- n -propanol-water mixtures as mobile phases. The best chromatographic conditions for separation of the fatty acids were RP-18 plates without concentrating zone and methanol-ethanol-water, 45 + 45 + 10 ( v/v as mobile phase, and RP-18 plates with concentrating zone and methanol-ethanol-water or methanol- n -propanol-water, 45 + 45 + 10 ( v/v ), as mobile phases. Taking into consideration previous results of our research we can state that the best RP HPTLC separations of fatty acids have been obtained on RP-18 plates without concentrating zone and with methanol-water, 95 + 5 ( v/v ), as mobile phase, and on RP-18 plates with concentrating zone with methanol-water, 90 + 10 or 95 + 5, 100% methanol, ethanol-water, 95 + 5 or 90 + 10 ( v/v ), or methanol-ethanol-water or methanol- n -propanol-water, 45 + 45 + 10 ( v/v ), a...

Reversed-phase chromatographic retention behavior of some fibrate-type antihyperlipidemic drugs

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-Soczewinski 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.

Analysis of non-selective calcium-channel blockers by reversed-phase TLC

The selectivity of TLC separation of non-selective calcium-channel blockers prenylamine, lidoflazine, bepridil, and fendiline has been investigated silanized silica gel RP8 and RP18 plates. Optimization of retention and selectivity for these compounds was achieved by altering the pH and the concentration of organic modifier (methanol, ethanol, tetrahydrofuran, acetonitrile) in the aqueous mobile phases. The substances were separated in horizontal chambers and the drugs were detected by videoscanning and illumination of the plates at λ = 254 nm. On RP8 plates the best separation was achieved with 50% acetonitrile in pH 2.06 phosphate buffer as mobile phase. On RP18 the best separation was achieved with 50% ethanol in pH 2.06 phosphate buffer.

Investigation of a homologous series of fatty acids by TLC. Part III. Application of terms describing the separation of homologous series of saturated fatty acids in TLC

Fatty acids from pentanoic to tricosanoic have been separated on RP-18 HPTLC plates, with and without concentrating zone, with methanol-water, ethanol-water, and n -propanol-water mobile phases. Separation factors (α), resolution ( R S ), and Δ R F values were calculated for all the chromatograms. Analysis showed that the most useful measures of the quality of the chromatographic separation of these fatty acids were the resolution, R S , and Δ R F . The best chromatographic conditions for separation of the fatty acids were RP-18 plates without concentrating zone and methanol-water, 90 + 10 ( v/v ), methanol-water, 95 + 5 ( v/v ), and ethanol-water, 90 + 10 ( v/v ), as mobile phases, and RP-18 plates with concentrating zone and methanol-water, 90 + 10 and 95 + 5 ( v/v ), 100% methanol, and ethanol-water, 90 + 10 and 95 + 5 ( v/v ), as mobile phases.

Quantitative structure-retention relationships (QSRR) of biogenic amine neurotransmitters and their metabolites on RP-18 plates in thin-layer chromatography

The possibility of using molecular descriptors to predict both the retention behavior and the mechanism of retention of biogenic amine neurotransmitters and some of their metabolites in TLC has been examined. QSRR analysis was achieved by simultaneous solution of a set of linear equations. Basic correlations were found between retention and molecular descriptors calculated by means of semi-empirical methods of quantum chemistry. The functions obtained provided insight into the mechanism of chromatographic retention on a molecular level. Experimentally obtained retention data for biogenic amine neurotransmitters and their derivatives also served as a basis for cluster analysis of these TLC systems.

Investigation of homologous series of fatty acids by TLC. Part I. Comparison of separations of fatty acids on RP-18 plates with and without a concentrating zone

Fatty acids from pentanoic acid to tricosanoic acid have been separated on RP-18 plates with and without a concentrating zone. Although similar separation factors, α , were obtained for the acids on both types of plate, visual inspection of the chromatograms revealed that better separation of the acids was obtained on RP-18 plates with concentrating zone, because compact chromatographic bands were obtained. The resolution, R S , values calculated confirmed these observations. Topological indexes based on the distance matrix, the adjacency matrix, information theory, and electrotopological states were calculated for the acids. It was found that R M values were related to topological indexes by linear or quadratic functions.

Densitometric thin-layer chromatography of polycyclic aromatic sulfur compounds

Thin-layer chromatography has been used to separate a mixture of sulfur polynuclear aromatic hydrocarbons (S-PAH), heterocyclic compounds with mutagenic and carcinogenic properties. S-PAH were oxidized to give the sulfone derivatives and then S-PAH standards, their oxidized forms, and PAH were applied to silica gel and RP-18 plates and developed in a horizontal chamber with different mobile phases. After chromatography the plates were observed in UV light at λ = 254 nm and scanned densitometrically at the same wavelength. R F values were determined for the compounds.

Ultrasonic solvent extraction of pesticides from soil

Ultrasonic solvent extraction of the pesticides atrazine, propham, chlorpropham, diflubenzuron, α-cypermethrin and tetramethrin from soil is reported. The extraction procedure was optimized with regard to the amount of solvent, the duration of sonication and the number of extraction steps. Ultrasonic solvent extraction was compared with traditional extraction methods, shake-flask and Soxhlet extraction. The recovery of pesticides was determined by quantitative thin-layer chromatography on RP-18 plates. Ultrasonic extraction using acetone showed satisfactory extraction efficiencies combined with simplicity of use and low solvent consumption.

Solute effects on reversed-phase thin-layer chromatography a linear free energy relationship analysis

RM w values determined by Dross et al. using RP-18 precoated TLC plates and aqueous methanol mobile phases have been analysed using our general LFER to give the equation, RM w = 0.259 + 0.239 R 2 − 0.662 π 2 H − 0.666 α 2 H − 3.006 Σβ 2 O + 3.603V x n = 76, ϱ = 0.9891, S.D. = 0.206, F = 635 The solute descriptors are, R 2 an excess molar refraction, π 2 H the dipolarity/polarizability, Σα 2 H and Σβ 2 O the overall or effective hydrogen-bond acidity and basicity, and V x the McGowan characteristic volume. The coefficients in (i) are very similar to those for the correlation of water-octanol partition coefficients, confirming the suggestion that RP-TLC extrapolated RM values can be used as a measure of lipophilicity. However, for a number of solutes, particularly aromatic and heterocyclic nitrogen bases, RM w values do not correlate either with i, or with log P oct, and hence care should be taken in the application of the RP-TLC method to these compounds. More limited data by Podgorny and Kowalska on RP-18 plates with aqueous tetrahydrofuran (THF) mobile phases suggests that it is not always necessary to use extrapolated RM w values, but that RM values with 80% water-20% THF can be used to estimate log P oct.

High-performance thin-layer chromatography/fast atom bombardment (tandem) mass spectrometry ofPseudomonas rhamnolipids

Several rhamnolipid preparations from Pseudomonas strains were studied by thin-layer chromatography/fast atom bombardment (TLC/FAB) mass spectrometry and TLC/FAB tandem mass spectrometry (MS/MS). The preparations were separated with normal-phase (Silica 60) and reversed-phase (RP-8) chromatography. Silica 60 plates appeared to be very useful in the separation of rhamnolipids according to the number of monosaccharide residues present. Spectra which show characteristic fragment ions could be obtained from components of mixtures with a total sample size of less than 200 ng. Chromatography on RP-8 plates gave a good separation of the rhamnolipids based on the length of the fatty acid alkyl chain. MS/MS of the sodium cationized molecules gave information about the sequence of the building blocks. Particularly, heterogeneity in beta-hydroxy fatty acid composition was determined for the principal as well as minor components present in natural rhamnolipid mixtures.

Isolation of chlorinated dibenzothiophenes by high-performance thin-layer chromatography

Chlorinated dibenzothiophenes can cause environmental problems analogous to chlorinated dibenzodioxins and dibenzofurans. In the analysis of chlorinated dibenzodioxins by gas chromatography—mass spectrometry some unknown chlorinated compounds have been found. The chlorinated dibenzothiophenes have the same m/z values as the corresponding dioxins in low-resolution mass spectrometry and they are found in same planar aromatic compound fraction in alumina and carbon column chromatography. Some chlorinated dibenzothiophenes were synthesized to serve as model compounds in analytical work. High-performance thin-layer chromatography (TLC) with different plates and several eluents was tried to find a separation method for the chlorinated dibenzothiophenes. The experiments showed that reversed-phase TLC with RP-18 plates and acetonitrile—water eluents could separate the chlorinated dibenzothiophenes from many interfering compounds but not completely from complex environmental samples.

Combined Use of Normal and Reversed Phase Thin Layer Chromatography in the Screening for Basic and Quaternary Drugs

Abstract The combined use of normal and reversed phase thin layer chromatography in drug screening is evaluated by the mean list length method. A reversed phase system, involving RP-18 plates and aqueous hydrochloric acid - methanol as a mobile phase, is shown to be an effective complementary pair to basic medium-polar normal phase systems. With a set of 140 basic and quaternary drugs, a mean list length of 1.8 is obtained for a TLC/RPTLC pair. The combination is also applicable to hydrophilic drugs extracted as bis(2-ethyl-hexyl)phosphate ion-pairs.

Thin-layer chromatography of chlorinated anisoles and veratroles

The thin-layer chromatography of chlorinated anisoles (methoxybenzenes) and veratroles (1,2-dimethoxybenzenes) has been examined on silica gel G60 and RP-18 thin-layer plates. More than fifty solvent systems were screened and some of them recommended for particular separations. Acetone was shown to be suitable for group separation of both chlorinated anisoles and veratroles on a silica gel G60 stationary phase having a very narrow range of RF values. On the other hand, benzene, dichloromethane and the various mixtures of light petroleum (b.p. 40–60°C) and a more polar eluent (such as diethyl ether, acetone or ethyl acetate) were recommended for separation of certain individual isomers. The best separation of chloroanisoles was achieved using RP-18 plates and methanol-water (90∶10) as the solvent system.

High-performance thin-layer chromatography of 2,4-dinitrophenyl-amino acids on layers of RP-a8, RP-18 and ammonium tungstophosphate

The chromatographic characteristics of eighteen DNP-amino acids, of dinitrophenol and dinitroaniline were studied on RP-18 and RP-18 plates eluted with aqueous—organic solutions and with mixtures of organic solvents. The optimum conditions for the separation of the highest number of compounds were studied and a two-dimensional chromatogram is reported. On home-made layers of ammonium tungstophosphate, water, aqueous solutions of ammonium nitrate and nitric acid and water—methanol mixtures were used as eluents to separate the pairs of DNP-amino acids which exhibit the same chromatographic behaviour on RP-8 and RP-18 plates.

Separations in Thin Layer and High Performance Liquid Chromatography Using Alkyl Silica Gel Bonded Phases

Abstract Separations in thin layer (TLC) and high performance liquid chromatography (HPLC) using alkyl bonded phases were carried out under optimum solvent conditions for each of three phases, RP-2, RP-8 and RP-18. The phases were tested for their efficiency and resolving power using three groups of compounds in three binary organic-water mobile phases. The organic solvents were acetonitrile, methanol and tetrahydrofuran, which are widely used as solvent modifiers in reversed phase liquid chromatography. The results showed that, unlike HPLC, TLC using RP-18 plates was the most, and RP-2 plates the least, efficient. A naphthalene and biphenyl mixture which was resolved by HPLC using any of the three solvents and columns was not resolved by TLC using any plate or solvent combination, unless the plate was prewashed with an organic modifier. The addition of NaCl (1–2% wt/vol) to the solvent for TLC speeded development unless an alcohol was used, but did not greatly affect the separation.

TLC as a pilot technique for the optimization of gradient HPLC II. Use of data obtained from RP-18 plates for the prediction of gradient programs in reversed-phase liquid chromatography

A method is described and experimentally verified permitting the determination of the optimal gradient programs in HPLC on the basis of isocratic TLC data. The proposed method has many advantages and can also be used in reversed-phase systems. A satisfactory agreement between the theoretical and experimental of VR/VO values has been confirmed. Some discrepancies for more strongly retained solutes are, probably due to the respective equilibrium and nonequilibrium state of the column in isocratic and gradient elution.