Mobile Phase Ethyl Acetate Research Articles

Chromatographic determination of volatile compounds of Achillea micranthoides Klok. et Krytzka

The processes of free radical oxidation are known to play a crucial role in the pathogenesis of many diseases. Therefore, the use of antioxidants is considered both pathogenetically justified and rational. Plants belonging to the genus Achillea L. are noted for their diverse content of biologically active substances, which contributes to their antioxidant activity. Given the availability of raw materials and the high biological activity of volatile compounds, it is particularly advisable to explore promising species within the genus Achillea L., such as yarrow (Achillea micrantoides Klok. et Krytzka). Yarrow is widespread in Ukraine, characterized by a long vegetation period, and holds promise for further pharmacognostic study. Aim. The purpose of the work is to study the volatile compounds of the yarrow extract (Achillea micrantoides Klok. et Krytzka) and to establish their component composition. Materials and methods. The Thin-Layer Chromatography (TLC) method and Gas Chromatography-Mass Spectrometry (GC/MS) on an Agilent Technology 7890 B chromatograph were employed to determine the component composition of volatile compounds in Achillea micranthoides Klok. et Krytzka. The NIST14 mass spectral library was utilized for identifying the components of the samples. Results. Identification of volatile compound components was carried out by chromatography of ethyl acetate extracts from the leaves and inflorescences of the subject TLC in the mobile phase ethyl acetate – toluene (5:95). By the gas method Chromatography-mass spectrometry determined the presence of 30 volatile compounds of grass A. micranthoides Klok. et Krytzka, 26 of the compounds were identified, which accounted for 86.76 % of the total number of compounds.

HPTLC Quantification of α-Glucosidase Inhibitor Mangiferin in Hydro-alcoholic extract of Salacia Species and Antidiabetic Poly-herbal Formulation

Salacia oblonga Wall. and Salacia reticulata Wight. (Family Celastraceae) are commonly known as Saptarangi and used in Ayurvedic medicine as potent antidiabetic agent. It is a woody climber, mainly habitat in Sri Lanka and Southern India. A large number of chemical constituents such as salacinol, neosalacinol, kotalanol, neokotalanol, and mangiferin were isolated from stem and root of saptarangi which shows various therapeutics activities. Chemical constituent presents in both species of Salacia are working as α-glucosidase inhibitor for diabetes management. Among them mangiferin is a plant natural polyphenol of C-glycosylxanthone structure and found in many plant species. Many chromatography techniques like LC-MS, HPLC are available to quantify mangiferin but no proper data available for simple, rapid, precise, economic HPTLC method. So, HPTLC method was developed with mobile phase ethyl acetate: formic acid: water (4:0.5:0.5 v/v/v) which confirmed the presence of mangiferin at 0.38±0.01 Rf value observed under 254nm. Mangiferin was present in 1.02% in Salacia oblonga root extract, 0.94% in Salacia reticulata stem extract and 0.42% in polyherbal formulation. The validated HPTLC method will be useful in standardization of different Ayurvedic formulations using mangiferin as a marker.

Eco friendly stability indicating HPTLC method for simultaneous determination of sofosbuvir and ledipasvir in pharmaceutical tablets and HPTLC-MS characterization of their degradation products

Recently, the analytical community has shown increasing interest in developing more environment-friendly practices by eliminating or reducing the use of hazardous chemicals and solvents which are extremely dangerous to human health and the environment. Thus in this study, a simple, rapid, inexpensive and eco-friendly HPTLC method with densitometric detection was designed, optimized and validated for the simultaneous quantitation of the antiviral drugs sofosbuvir (SOF) and ledipasvir (LED) in pure powder, synthetic mixtures, combined pharmaceutical formulation and in the presence of their stressed degradation products with high sensitivity and no interference. The separation was carried out on silica gel F254 plates, using green mobile phase ethyl acetate: water: ethanol (94:5:1v/v/v) for development followed by densitometric detection of SOF and LED at 250 and 320 nm, respectively. Both drugs had second order polynomial calibration curves within ranges 100–5000 ng/spot and 100–3000 ng/spot for SOF and LED, respectively, with correlation coefficients >0.9998 and the limits of detection were 30 and 29 ng/spot and the limits of quantification were 90 and 88 ng/spot for SOF and LED, respectively. The method was validated in terms of linearity, accuracy, precision, selectivity, and robustness. The drugs were subjected to acidic and basic hydrolysis, oxidation and photolytic conditions as per ICH guidelines, followed by detection of the degradation products and structure elucidation of their fragments with the aid of the HPTLC-ESI- MS technique. The greenness of the proposed method was assessed using the analytical Eco-Scale as an assessment tool with a 93-point score. So, it is considered excellent green.

Nonnegative principal component analysis in thin layer fingerprint screening: A case of Gentiana extracts from in vitro cultures

Twenty-one species of Gentiana L. were successfully grown in vitro in the same conditions and 72 samples of various cultures of these species (root, shoots, cotyledon callus, hypocotyl callus, and root callus) were obtained. The investigated species were as follows: G. affinis, G. andrewsii, G. bhutanica, G. burseri, G. cachemirica, G. capitata, G. crassicaulis, G. dahurica, G. decumbens, G. freyniana, G. frigida, G. gelida, G. grossheimii, G. kurroo, G. macrophylla, G. paradoxa, G. robusta, G. scabra, G. septemfida, G. siphonantha, and G. tianschanica. The obtained samples were extracted with methanol–acetone–water (3:1:1) mixture, evaporated to dryness, and subjected to TLC on silica gel with mobile phase ethyl acetate–methanol–water (8:2:2) in sandwich mode. Data fusion of two densitometric modes: extinction at 254 nm and fluorescence at 312 nm (emission above 370 nm) were used as a fingerprint of each sample. Densitograms were denoised, subjected to baseline removal, warped, and analyzed with principal component analysis (PCA), hierarchical cluster analysis and—the novel proposal—nonnegative PCA. This allowed to split negatively intercorrelated fingerprint features to subsequent principal components (PCs), which increases the number of PCs required to see the same information, but these PCs are much more informative.

Isolation of Catechins from Roscoea purpurea

Background: Roscoea purpurea also known as Kakoli is an endangered species of “Ashtawarga” group which faces immense identification and authentication crisis in Ayurvedic literature. Due to less availability and high medicinal value of Kakoli plant, adulteration and substitution was done by drug manufacturers. Objectives: This scientific investigation was carried out to isolate discrete and specific chemical compounds from Kakoli using chromatographic and spectral analysis techniques for quality standardization and identification of Kakoli containing herbal formulations. Materials and Methods: The methanol root extract of plant was used for phytochemical screening and isolation of marker compounds. Two compounds with Rf values 0.51 and 0.73 respectively were isolated and purified by using mobile phase ethyl acetate: n-hexane: formic acid (07: 03: 0.1 v/v/v). Characterization of isolated compounds was done with help of melting point and spectral analysis. Results: The blackish brown methanol extract showed the presence of flavonoids, alkaloids, terpenoids, phenolic phytosterols and amino acid. The final isolated compounds were of off white and yellowish white with melting point range of 217-220°C and 239- 242°C respectively and molecular ion peak at m/z 329 (M+Na) and at 291 (M+H) being according to the proposed structure of Epigallocatechin and Epicatechin respectively. Conclusion: In present study Epigallocatechin and Epicatechin were isolated for the first time and may prove potential tools for differentiation and accurate identification of the authentic plant from its official substitutes and cheap common adulterants.

Standardization of some plants of the Cucurbitaceae family by a validated high-performance thin-layer chromatography method

Medicinal plants of the Cucurbitaceae family are widely consumed as foods in human diet. In the present study, a simple, rapid, quantitative, and validated high-performance thin-layer chromatographic (HPTLC) method has been developed for the estimation of chlorogenic acid (CA) in the hydroalcoholic fruit extracts of Luffa acutangula (sponge gourd), Sechium edule (chayote squash), Trichosanthes cucumerina (snake gourd) and Trichosanthes dioica (pointed gourd) belonging to the Cucurbitaceae family. Densitometric analysis of CA was carried out in the absorbance mode at 254 nm. The method gave spot at RF = 0.55 ± 0.04, corresponding to CA in different samples. The limit of detection and limit of quantification per spot were confirmed with the mobile phase ethyl acetate‒chloroform‒formic acid (6:4:0.5, V/V). Linear regression analysis data for the calibration plot for CA showed a good linear relationship with a correlation coefficient (r) of 0.9997 in the concentration range of 200–1000 ng per spot. The method was validated for sensitivity, linearity, accuracy, precision and specificity as per the international conference on harmonization guidelines. The proposed validated HPTLC method provides a novel approach for the quality control and standardization of some selected medicinal food plants of the Cucurbitaceae family.

Eco-friendly HPTLC method for simultaneous analysis of sofosbuvir and ledipasvir in biological and pharmaceutical samples: Stability indicating study

Recently, many single-pill combinations are used as a promising choice in hepatitis C treatment. However, this trend made a serious challenge to drug analysts due to difficulty of analysis of two or more drugs simultaneously. In this study, sofosbuvir (SF) and ledipasvir (LD) were simultaneously analyzed by developing a simple, inexpensive, rapid and eco-friendly high-performance thin layer chromatographic (HPTLC) method with densitometric detection. Separation was carried out using aluminum HPTLC plates silica gel 60 F254 as the stationary phase developed using the mobile phase ethyl acetate: methanol: water: glacial acetic acid (30: 1.5: 1: 0.2% v/v). Development was done in a twin-trough chamber followed by densitometric detection of SF and LD at 260 and 320 nm, respectively. The calibration curves for standard solutions showed a rectilinear relationship for SF and LD in the range of 2 –12 and 0.45–6.0 μg band−1, respectively with correlation coefficients > 0.9995 and limits of detection of 0.6 and 0.1 μg band−1 for SF and LD, respectively. While, calibration curves for biological samples showed linear relationships for SF and LD in the range of 1.0–20 and 0.2–6.0 μg mL−1, respectively with correlation coefficients > 0.99 and limits of detection of 0.21 and 0.27 μg mL−1 for SF in plasma and urine samples, respectively and 0.05 and 0.03 μg mL−1 for LD in plasma and urine samples, respectively. Also, it was effectively used in the analysis of the investigated drugs within their pharmaceutical form and biological fluids without any matrix interference with high precision (% RSD < 2%) and good accuracy with% Er value < 2%. Moreover, SF and LD were analyzed along with their degradation products after performing forced degradation studies.

Development of quantitative HPTLC methods for dolutegravir, lamivudine, and tenofovir disproxil fumarate in a combination pharmaceutical product using a model process published earlier for transfer of minilab TLC screening methods to HPTLC-densitometry

High-performance thin-layer chromatography (HPLTC)–densitometry methods are described for the analysis of the anti(retro)virals dolutegravir (D), lamivudine (L), and tenofovir disoproxil fumarate (TDF) in a pharmaceutical tablet product. To the best of our knowledge, no previous quantitative planar chromatography method has been reported in the literature for this combination formulation. The method for L was transferred from a thin-layer chromatography (TLC) screening method published in the Global Pharma Health Fund (GPHF) Minilab Manual designed for identification of counterfeit and substandard drug products using a model process published earlier. D and TDF are not included in the list of drugs for which TLC screening methods are published for the Minilab, but HPTLC–densitometry procedures were developed for them using the transfer process guidelines. L was analyzed simultaneously with TDF on Merck Premium Purity silica gel 60 F plates using the mobile phase ethyl acetate–methanol–acetone–concentrated ammonium hydroxide (30:7:3:1) and densitometric scanning at 254 nm. D was analyzed on a second plate by scanning at 366 nm after chromatography with the chloroform–methanol–formic acid (32:8:2) mobile phase. Data for all three drugs are shown to meet the requirements of the model transfer process for calibration curve r values, assay of tablets relative to their label values, peak purity/peak identity tests, and validation by standard addition analysis of samples spiked at 50%, 100%, and 150% of the label value of active ingredients. A TLC screening method for TDF in the combination product was developed and published online with open access.

PHYTOCHEMICAL EVALUATION AND HIGH-PERFORMANCE THIN LAYER CHROMATOGRAPHY PROFILING: SAPINDUS EMARGINATUS VAHL. AND MORINDA PUBESCENS J.E.SM. BARKS EXTRACTS

ABSTRACTObjective: To identify the flavonoids high-performance thin layer chromatography (HPTLC) profiles from barks of Sapindus emarginatus Vahl.(Sapindaceae) and Morinda pubescens J.E.Sm. (Rubiaceae) by ethanol extracts.Methods: The barks of S. emarginatus Vahl. and M. pubescens J.E.Sm. extracted each separately with ethanol. Both these ethanol extracts weresubjected to preliminary phytochemical analysis. Based on phytochemical studies, the extracts obtained were subjected to HPTLC profiles for identifyand confirmation flavonoids, both these samples were compared with standard (Rutin). HPTLC analysis performed with silica gel G 60 F254 plateswith mobile phase ethyl acetate:n-butanol:formic acid:water (5:3:1:1). Detection of flavonoid compound was performed by scanning the developedplate at 254 nm.Results: Result of these both extracts shows positive tests for flavonoids. Ethanol extracts barks of S. emarginatus Vahl. and M. pubescens J.E.Sm eachwere showed bands of different Rf values with range 0.50-0.90 and standard showed bands of 0.50 Rf values.Conclusion: It can be concluded that rutin constituents of each bark extract are presents and have effective components which can be utilized as auseful herb for alleviation of various illness and disorders.Keywords: Sapindus emarginatus Vahl., Morinda pubescens J.E.Sm. Ethanol extracts, High-performance thin layer chromatography, Rutin.

Comparative study of the resolution efficiency of HPLC and HPTLC-densitometric methods for the analysis of mebeverine hydrochloride and chlordiazepoxide in their binary mixture

Accurate, rapid, and selective reversed phase HPLC and HPTLC-densitometric methods with UV detection have been developed and validated for simultaneous determination of a binary mixture of mebeverine hydrochloride (MVH) and chlordiazepoxide (CDZ) in their Co-formulation. For the HPLC method, ACE-126-2546 AQ C-18 column, (250×4.6 mm i.d., 5 μm particle size) in isocratic mode, with mobile phase containing 25 mM ammonium acetate buffer: acetonitrile in the ratio of (60:40, v : v ), pH adjusted to 3±0.2 by using hydrochloric acid, the flow rate of 1.0 mL/min and detection was performed at 260 nm. The retention times were 7.23±0.01 and 3.85±0.01 min for MVH and CDZ, respectively. For the HPTLC-densitometric method, the separation was performed using stationary phase pre-coated silica gel 60F 254 and mobile phase ethyl acetate: methanol (8:4, v : v ) were used and scanned at 222 nm with Camag TLC scanner controlled by Wincats Software. The R f values were 0.26±0.02 and 0.73±0.01 for MVH and CDZ, respectively. The linearity graphs for MVH and CDZ, respectively, were found to be linear over 1-50 μg/mL and 0.5-40.0 μg/mL with mean percentage recoveries 100.14±0.354 and 99.70±0.764 for HPLC method and 0.5-30.0 μg/band and 1-14 μg/band with mean percentage recoveries 100.29±0.665 and 99.68±0.987 for HPTLC-densitometric method. A comparative study of different analytical validation parameters such as accuracy, precision, specificity, robustness was conducted. The obtained results were statistically compared with those of the official methods; using student t -test, F-test, and one way ANOVA, showing no significant difference with respect to accuracy and precision.

Quantification of gallic acid in fruit and leaves of Careya arborea by High performance thin layer chromatography (HPTLC)

Objective: The present study was aimed to quantification of Gallic acid in Careya arborea (Lecythidaceae). Method: High performance thin layer chromatography (HPTLC) quantification was carried out for various extract of leaf and fruits of C. arborea. The thin layer chromatography (TLC) plate was spotted with gallic acid and fruits and leaves extract of Careya arborea. The extract of fruit and leaves shows the Gallic acid spot at Rf: value 0.68 using mobile phase ethyl acetate: toluene: formic acid (8:2:0.3, v/v). So, the gallic acid was selected as marker. The gallic acid was quantified using HPTLC technique in CFE (C. arborea fruit ethyl acetate extract), CFA (C. arborea fruit alcoholic extract), CLE (C. arborea leave ethyl acetate extract) and CLA (C. arborea alcoholic extract of leaves) of Careya arborea. Result: The percentage (w/w) amount of gallic acid was found to 2.11%, 1.2 %, 0.54% and 0.48% in CFE, CFA, CLE and CLA of C. arborea respectively. Conclusion: This HPTLC quantification method useful for standardization of fruits and leaf Careya arborea.

HPTLC Method for Simultaneous Analysis of Stevioside and Rebaudioside-A in Stevia rebaudiana

An HPTLC method was developed and validated for simultaneous determination of stevioside (STE) and rebaudioside-A (REB-A) in Stevia rebaudiana leaves. The HPTLC separation was performed on precoated silica gel 60F254 HPTLC plates with the mobile phase ethyl acetate-ethanol-acetone-water (15 + 3 + 6 + 6, v/v/v/v). The densitometric quantification of steviol glycosides was carried out at Amax 580 nm in the reflection-absorption mode after spraying with anisaldehyde-sulfuric acid reagent. Rf values were 0.34 and 0.28 for STE and REB-A, respectively. The content of STE and REB-A in leaf extract was found to be 6.94 and 6.35%, respectively. The method was validated in terms of precision, accuracy, specificity, and robustness. The method can be useful for routine analysis of the sweeteners.

ANTIISCHEMIC PROPERTIES OF THE NEW ANTIOXIDANT DRUG VALEOKOR-Q10 (EXPERIMENTAL STUDY)

s. PHYTOPHARM 2012 M 96 Obzory po kliniceskoj farmacologii i lekarstvennoj terapii [Reviews of clinical pharmacology and drug therapy] ТОМ 10/2012/2 ANTIISCHEMIC PROPERTIES OF THE NEW ANTIOXIDANT DRUG VALEOKOR-Q10 (EXPERIMENTAL STUDY) © Selezneva A. I. , Makarov V. G. , Djachuk G. I. , Makarova M. N. , Zabozlaev A. A. , Khodko S. V. , Kovaleva M. A. 1 Saint-Petersburg Institute of Pharmacy, Russia Northwestern State Medical University n. a. I. I. Mechnikov, Saint-Petersburg, Russia NPK “PHARMASoFT”, Moscow, Russia The aim was an experimental study of antiischemic effect of the new antioxidant drug Valeokor-q10 on the model of acute myocardial infarction. Acute experimental myocardial infarction was modulated by the method of h. Selye (1960) — occlusion of the descending branch of left coronary artery in Wistar rats. The drug Valeokorq10 was administered in forms of injection at doses of 1,6, 2,5, 7,4, 22,2 mg/kg intravenously, and suspension of the tablets at doses of 0,2, 1,6, 7,4 mg/kg intraperitoneally. Mildronate (JSC Grindeks, latvia) was used as reference. The amplitude of the ST complex on the ECG, enzymes aspartate aminotransferase and creatine kinase and neovascularization of damaged myocardium were controlled. Positive effect of Valeokor-q10 on the dynamics of the complex amplitude of the ST on ECG was observed. Valeokor-q10 at a dose of 1,6 mg/kg introperitoneally and doses of 1,6, 2,5 mg/kg intravenously reduced activity of creatine kinase. intraperitoneal administration of Valeokor-q10 in doses of 1,6 and 7,4 mg/kg reduced the level of aspartate aminotransferase. The drug increased the neovascularization of ischemic myocardium area and accelerated differentiation of blood vessels in arterioles and venules. The maximum effect was observed at a dose of 1,6 mg/kg. New drug has antiischemic effect and can be successfully used in the treatment of coronary heart disease. DEVELOPMENT AND VALIDATION OF TLC METHOD FOR THE IDENTIFICATION OF AERVA LANATA HERB © Semionova M. V., Obukhova V. V., Kuzminova L. V. JSC “Krasnogorskleksredstva”, Krasnogorsk, Moscow region, Russia in order to ensure quality and efficacy of herbal medicinal products the national quality standards must contain the modern quality control methods. The purpose of our study was to develop and validate the identification method for Aerva lanata herb. The study object was Aerva lanata herb; TlC was chosen as an analytical method for identification of phenolic compounds profile in the samples. Ethanol (80 %) appeared to be the best extraction agent and the best Aerva lanata herb phenolic compounds resolution was achieved using mobile phase ethyl acetate — anhydrous formic acid — water (12:2.5:3) in the plates TlC Silica gel 60 f254 (aluminium sheets, Merck, Germany). Solutions of rutin and quercetin were used as reference solutions. After developing the plate was heated at 100–105 °С for 3–5 minutes. Then the plate was sequentially sprayed with 1 % diphenylboryloxyethylamin solution and 5 % polyethyleneglycol solution (both in 96 % ethanol) and dried at room temperature for 30 minutes. The following zones of reference compounds present: detection at 365 nm with the reference solutions: the zone with yellow, yelloworange or orange color (R f approx. 0.4–0.5 that was accepted as R s = 1.0, due to rutin) and the zone with yellow, yellow-orange or orange color (R s approx. 1.9–2.5, due to quercetin). The following zones of phenolic compounds present in the plate with the test solution: the zone with yellow, green-yellow, yellow-orange or orange color (R s (by rutin) approx. 0.3–0.4), 2 zones with green or green-yellow color (R s approx. 0.4–0.5 and 1.8–2.2), the zone with light blue color (R s approx. 0.8–1.0); others zones could be present. The method validation was performed on 6 industrial batches (from 2009 to 2012 production years) by workers of 2 laboratories (Research & development department and quality Control department). The method specificity was evaluated by coincidence of the different batches chromatographic profiles by the main zones and by compliance of abovementioned profiles with the test solution chromatogram description. Chromatographic profiles of the different batches have coincided and been compliant with the test solution chromatogram description. The resolution between zones of rutin (R s approx. 1.0) and quercetin (R s approx. 1.9–2.5) in the chromatogram obtained with the reference solutions has been chosen as a chromatographic system suitability index. The resolution value between the

ISOLATION AND IDENTIFICATION OF FLAVONOIDS FROM WATER FRACTION OF SECANG WOOD (CAESALPINIA SAPPAN. L) WITH THIN LAYER CHROMATOGRAPHY AND UV-VIS SPECTROPHOTOMETRY METHODS

Aim of this research was to determine chemical structure of flavonoid from water fraction ofSappan wood. The flavonoid was isolated by Soxhlet xtraction using methanol and infundation.First, the detection of flavonoid was done using Thin Layer Chromatography (TLC) with statioramphase silica gel GF 254 and mobile phase ethyl acetate : acetyc acid 15 % (9:1 v/v) smoked byNH3, and detected under UV 366 nm, showed 5 spots with hRf 7, 50, 61, 68, and 80. PreparatifTLC was done to water fraction, disolveed in methanol and detected with UV-Visspectrophotometry using diagnostic reagents NaOH, NaOAc, NaOAc+H3BO3, AlCl3, ACl3+HCl andcompared with references. In fraction 1, 2, and 5 showed isoflavon with 7-OH, substitution oxygenin position six. In fraction 3 showed isoflavon with 7-OH, substitution oxygen in position six, 6,7diOH in A ring, and o-diOH in 6,7 or 7,8. In fraction 4 showed isoflavon with 7-OH, substitutionoxygen in 6, o-diOH in 6,7 or 7,8 and 5-OH.Key Words: Caesalpinia Sappan. L, Flavonoid, TLC, UV-Vis Spectrophotometry

Chromatographic behaviour of some porphyrins and their complexes with Zn, Pd(II) and Cu(II)

In this work the influence of the porphyrin structure and of the nature of the mobile phase upon retention parameters is examined by means of reversed phase high-performance liquid chromatography (HPLC). Acetonitrile–ethyl acetate and other mixtures were used as eluents. An increase in the retention of azo- and benzosubstituted porphyrins as well as of those containing a large number of carbon atoms as substituents of macrocycles may be noted. A variation in the polarity of the mobile phase affects the retention of the ligands more than that of their zinc complexes. The retention of the most hydrophobic compounds may be well described in coordinates lg k'– lg M. For less hydrophobic porphyrins these dependences are close to linear only within limited intervals of mobile phase ethyl acetate concentration. The best separation of zinc complexes was achieved with acetonitrile as the eluent. The detection limit of porphyrin ligands and complexes with metals is n × 10-8 M.

Simultaneous determination of some multicomponent dosage forms by quantitative thin layer chromatography densitometric method

In this study, simultaneous determination of naproxen with diflunisal (mixture I), paracetamol with chlorzoxazone (mixture II) and chlorphenoxamine hydrochloride with 8–chlorotheophylline and caffeine (mixture III) in multicomponent mixtures was conducted by a thin layer chromatography–densitometric method. The mobile phase ethyl acetate: methanol: ammonia 25% (85:15:5 v/v) was used for the separation of the components of mixtures (I) and (II) with Rf values of 0.16 for naproxen, 0.4 for diflunisal, 0.77 for paracetamol and 0.32 for chlorzoxazone. Efficient separation of the components of mixture (III) was attained using ethyl acetate as mobile phase with Rf values of 0.12, 0.62 and 0.42 for chlorphenoxamine hydrochloride, 8–chlorotheophylline and caffeine, respectively. Linearity ranges, mean recoveries and relative standard deviations in calibration graphs of the proposed method were calculated. The method has been successfully applied to pharmaceutical formulations, sugar-coated tablets, capsules and suppositories. The results obtained were statistically compared with those obtained by applying the reported alternate methods.

Adsorption isotherms of ethyl acetate modifier on silica from supercritical carbon dioxide

Adsorption isotherms were determined for ethyl acetate on silica in supercritical carbon dioxide using the peak maxima method. Langmuir equation fits of the isotherm data suggest monolayer adsorption, and plots of inverse stationary phase coverage versus mobile phase density were found to be linear. Stationary phase coverage was plotted as a function of both pressure and mobile phase ethyl acetate concentration. Under the conditions examined, stationary phase saturation coverage by ethyl acetate occurs at approximately 1% (g/ml) ethyl acetate in the mobile phase, with a maximum stationary phase coverage of approximately 0.031 (g/g).