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A new perspective in the lipophilicity evaluation through RP-HPLC is permitted by analysis of the retention factor (k) obtained by injecting large volumes of test samples prepared in solvents immiscible with mobile phase. The experiment is carried out on representative groups of compounds with increased toxicity (mycotoxins and alkaloids) and amines with important biological activity (naturally occurring monoamine compounds and related drugs), which are covering a large interval of lipophilicity. The stock solution of each compound was prepared in hexane and the used mobile phases were mixtures of methanol or acetonitrile and water, in suited volume ratio. The injected volume was between 10 and 100 µL, while the used stationary phases were RP-18 and RP-8. On both reverse stationary phases the retention factors were linearly decreasing while the injection volume was increasing. In all cases, the linear models were highly statistically significant. On the basis of the obtained results new lipophilicity indices were purposed and discussed. The developed lipophilicity indices and the computationally expressed ones are correlated at a high level of statistical significance.

ABSTRACT

The characterization and classification of some natural toxins (mycotoxins and alkaloids) is established by high-performance thin-layer chromatography (HPTLC) using chemically bonded stationary phases of RP-18, RP-18W, RP-8, RP-2, RP-NH2, RP-CN and RP-Diol. The used mobile phases are mixtures of methanol–water in different proportions of volume, chosen to create a suitable migration during the chromatographic process. The lipophilicity is described through different chromatographic descriptors, such as RM0, mean of RM(mRM), and scores of RM values corresponding to the first principal component (PC1/RM). The investigated compounds are characterized also by a series of computed lipophilicity descriptors (logP and logD values). The chromatographic behaviour of toxins is evidenced by graphical profiles of the lipophilicity descriptors. In addition, scores and loadings resulting from covariance matrix of retention data enable new information about similarity and differences observed between the investigated compounds. The experimental lipophilicity indices estimated from retention data are directly correlated with the computed values, via computer software and Internet module, at a high significant statistical level.

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The retention behavior of some flavonoids in reversed phase liquid chromatography (RPLC) was investigated using different chemistries of the modified silicagel based stationary phases. Highly end-capped octadecyl silicagel (ODS), polar embedded linker octadecyl silicagel (SB-18 Aqua), phenyl silicagel and pentafluorophenyl modified silicagel (PFP) were used as stationary phases. The mobile phase consisted in acetonitrile/acidified water mixtures, at different fractions of volume. The lipophilicity was estimated through different chromatographic descriptors, as it follows: log kw, m log k, S, f0 and PC1/log k. The chromatographic behavior observed on the mentioned stationary phases was evaluated by means of various graphical profiles and correlation matrices. Additionally, new information about the characteristics of the stationary phases and their (dis)-similarities were provided through lipophilicity charts and by scatterplots of loadings obtained by applying principal component analysis (PCA) to retention data. Furthermore, the experimental lipophilicity indices estimated from retention data were correlated with the computed descriptors, at a high level of statistical significance

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The fingerprinting capacity of two analytical techniques, HPLC and UV–Vis spectroscopy in the case of fruits samples (kiwi and pomelo) has been investigated. The multivariate exploratory techniques were used for sample discrimination according to the fruit species and subspecies. The combination of principal component analysis with linear discriminant analysis is opening new directions in the fingerprinting analysis. The classifications obtained were independent by the analytical techniques, which signalise that both of them may be successfully employed in the fingerprinting methodologies if they are combined with appropriate chemometric methods. One of the biggest advantages of the proposed chemometric method is the ability to discriminate different types and species and subspecies of fruits in just one analysis, which indicates that it is one of the simplest and less time consuming methods. It is strongly sustained by the good results obtained in the case of kiwi and pomelo fruit samples that were simultaneously analysed.

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The use of image analysis software for the detection and quantitative evaluation of fluorescent compounds in thin layer chromatography is investigated. Four different image analysis software packages (Sorbfil TLC, Biodit, JustTLC, and Melanie) were applied and compared. The image analysis methods were developed and validated for the simultaneous determination of quercetin and kaempferol in food supplements. The chromatographic separation used Silica gel 60 TLC plates as the stationary phase and carbon tetrachloride:acetone:formic acid (35:11:3, v/v/v) as the mobile phase. The plate images were recorded by a digital camera and imported in the image analysis software. The final results were validated by evaluating the linearity, precision, and accuracy of the methods used to quantify synthetic and real samples. All the results suggest that the image analysis software packages are proper to investigate the fluorescent compounds in quantitative thin layer chromatography

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The lipophilicity of some hazardous substances (emerging pesticides and some PAHs) was investigated by high performance liquid chromatography, on four chromatographic columns of RP-18, RP-8, phenyl and CN, with two types of mobile phases based on acetonitrile and methanol. The investigated lipophilicity indices were both experimentally (log kw, S and 0) and theoretically expressed. In order to find an objective manner of quantitative comparison of different chemically bonded stationary phases and evaluate the reliability of the obtained results some comparison procedures based on correlation diagrams and matrices were performed. The results indicated that all the stationary phases were useful for the lipophilicity investigation and that the experimentally and theoretically lipophilicity indices were highly correlated. Moreover, it was suggested that methanol used as an organic modifier led to more significant lipophilicity indices

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The optimization of the green tea flavonoid extraction conditions was investigated. The experiments were carried out with two extraction methods: ultrasound assisted extraction (UAE) and reflux extraction (RE). The parameters that were varied in this study were: the extraction solvent system composition, the type of organic modifier of the extraction mixture, temperature, and time. The highest efficiency was obtained with an extraction mixture of ethanol: water, 80:20, v/v. An extraction performed at temperature of 45°C in 50–60 minutes led to optimum results. Moreover, a new fingerprinting procedure based on thin layer chromatography (TLC) image analysis was employed in order to compare the chemical composition of green tea in comparison with white and black tea.

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Silica gel plates impregnated with a variety of oils including vegetable oils (olive, sunflower and corn oil) and synthetic oils (trioctylamine and paraffin oil) were evaluated and compared with the commercially available reversed-phases TLC plates (RP-18, RP-18W, and CN). A series of selected lipophilic vitamins was employed to evaluate the suitability of oils as reversed-phases for TLC and to provide different lipophilicity indices: R M0, scores corresponding to the first principal component of R F and/or R M, the arithmetic mean of R F and R M values obtained with solvent mixture containing various concentrations of methanol in water. The retention results were excellent (r > 0.98) and allowed accurate estimation of lipophilicity of selected vitamins and to ranking the lipophilicity of oils when comparing with chemically bonded phases. Concerning the lipophilicity scale of vegetable oils, it is worth noting that corn oil presents the highest lipophilicity, closely followed by the olive and sunflower oils.

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The lipophilicity of some emerging pesticides is investigated by reversed-phase high performance thin-layer chromatography (RP-HPTLC) on RP-18, RP-8 and CN stationary phases. The mobile phases were mixtures of methanol-water in different proportions of volume. The lipophilicity indices taken in consideration during this study are: RM0, mean of RF and RM, b, f0, scores corresponding to the first principal components of RM and RF. The obtained results are compared with the computed lipophilicity indices (Log P) in order to evaluate the suitability of the involved method in the lipophilicity estimation for the pesticides. The comparison is performed through correlation matrices and profiles. The obtained correlations are indicating a high statistical significance.

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Silica gel plates impregnated with a variety of oils (olive oil, sunflower oil, corn oil, trioctylamine, and paraffin oil) and fats (margarine, butter, cod liver fat, pig fat, sheep fat, pullet fat, and human fat) were evaluated and compared with the commercially available reversed-phases TLC plates (RP-18, RP-18 W, and CN). A representative series of flavonoids is employed to evaluate the suitability of oils and fats as reversed-phases for TLC and to provide different lipophilicity indices: RM0, scores corresponding to first principal component of RF and/or RM, arithmetic mean of RF and RM values obtained with solvent mixture containing various concentrations of methanol in water. The retention results were excellent (r > 0.96) and allowed for accurate estimation of lipophilicity of selected flavonoids and to ranking the lipophilicity of oils and fats when comparing with chemically bonded phases. The human fat-impregnated plates provided lipophilicity values closely associated with those obtained for margarine and butter. Moreover, the human fat lipophilic character seems to be placed between pullet and cod fats. Concerning the lipophilicity scale of vegetable oils, it is worth noting that the corn oil presents the highest lipophilicity, closely followed by the sunflower and olive oils

ABSTRACT

A variety of oils (paraffin, olive, sunflower, corn, castor, cod liver) and fats (margarine, butter, pig, sheep, pullet, human) impregnated TLC-plates were indirectly evaluated and characterized from the lipophilicity point of view by employing a series of experimental lipophilicity parameters estimated for a representative group of natural sweeteners from retention data. The relevance of the results was evaluated by a critical comparison of the lipophilicity parameters with a series of theoretical lipophilicity and solubility indices. The ALOGPs descriptor offers the best correlation coefficients, higher than 0.9. The principal component analysis applied to the retention data and the matrices formed by each distinct group of experimental lipophilicity indices allowed a realistic classification of the fats and oils, through the 3D graphs (“lipophilicity spaces”) and gave new insights into the retention mechanism involved in the chromatographic process

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The chromatographic behavior of some artificial and natural sweeteners was established by reverse phase high performance thin-layer chromatography (RP-HPTLC) on RP-18, RP-18W, RP-8, CN and NH2 stationary phases. The mobile phases were mixtures of acetonitrile–water in different proportions of volume, chosen to create a suitable migration during the chromatographic process. The lipophilicity was described through different chromatographic descriptors such as RM0, mean of RM (mRM), and scores of RM values corresponding to the first principal component (PC1/RM). In addition, scores and loadings resulting from covariance matrix of retention data enable new information about similarity and differences of investigated compounds and between both the stationary and mobile phases. The experimental lipophilicity indices estimated from retention data are directly correlated with the computed values, via computer software and internet module, at a high significant statistical level.

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The chromatographic behavior of some flavonoids was established by RP-HPLC on RP-18 (LiChroCART, LiChrosphere RP-18e), RP-8 (Zorbax, Eclipse XDB-C8), CN (Sâulentechnik, LiChrosphere CN100) columns. The mobile phases were mixtures of methanol-water in different volume proportions from 70 to 80% v/v for RP-18 and RP-8, while for the CN column the proportions were between 66 and 70% v/v. The lipophilicity was expressed through different lipophilicity descriptors such as mean of k (mk), mean of log k (mlog k), log k_W, S, f₀, and scores of k and log k corresponding to the first principal component. The experimental lipophilicity indices are directly correlated with the computed values, via computer software and internet module, at a high analytical level. Furthermore, the results obtained applying principal component analysis to k and/or log k values allow the prediction and explanation of the interaction involved in the retention mechanism which takes place between the compounds and the employed stationary phases during the development.

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Lipophilicity indices for vitamins A and E, and for some precursors of vitamin A, have been determined for the first time by reversed-phase high-performance liquid chromatography (RPHPLC) on C ₁₈ and C ₈ columns. For each column the mobile phases were methanol-water mixtures with methanol in volume proportions from 86 to 90% ( u/u ) in 1% steps. The regression correlation coefficients obtained for both stationary phases were excellent (usually >0.999). To compare the experimental lipophilicity estimated for the compounds by use of log k' _w , S , teta ₀ , the means of k' and log k' , and the scores of k' and log k' corresponding to the first principal component, and log P values calculated by use of different computer software a correlation matrix was constructed. Better correlations were obtained in both cases between the mean of k' and the mean of log k' , and scores corresponding to the first principal component obtained by applying principal-components analysis to the matrix of retention factors and computed log P values. The best correlations were found between the mean of k' and scores corresponding to the first principal component determined on C ₈ and most of the computed log P values.

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Estrogens have been shown to be present in the water compartment, mainly due to the inefficient removal in wastewater treatment plants (WWTP). The concentrations of these compounds, although very low (low ng/L), are sufficient to induce estrogenic responses and alter the normal reproduction and development of wildlife organisms. The compounds have been determined, by a variety of analytical procedures, in the influents and effluents of WWTP, fresh waters, rivers, and even drinking waters. Determination of natural and synthetic estrogens and progestogens in natural water is, however, a difficult analytical task, because of the very low detection limits required and the complexity of the matrix. Thus, in general, complicated, time-consuming extraction and purification processes, usually based on the application of solid–liquid extraction, are performed before final determination by immunoassay, high-performance liquid chromatography, or gas chromatography, very often coupled with mass spectrometry. This paper reviews the analytical methods so far described for the analysis of estrogens, which are currently important environmental pollutants presented in natural and wastewaters. Discuss of the main steps, from sampling up to analysis, and the techniques most commonly used in the determination is presented.

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A study of quantitative analysis of some flavonoids in Satureja hortensis L. extracts is presented. The HPTLC analyses were performed in a normal chromatographic chamber on silica gel plates, with an appropriate mobile phase. Photodensitometric evaluation of the chromatographic plates was performed by UV-visible absorbance at 320 nm for rosmarinic acid and 349 nm for luteoline, after pulverizing with NTS reagent (diphenylboryloxyethylamine). Quantitative analyses of flavonoids were performed by use of calibration curves. The quantity of compounds extracted depends on the composition of the extraction solvent and on the extraction technique. The best results were obtained by heating under reflux with systems that contained 60–70% ethanol. Under these conditions it was found that this plant contained approximately 34 mg g ^-1 rosmarinic acid and 30 mg g ^-1 luteoline. The results obtained were compared and correlated with extraction method and confirm this plant contains important amounts of flavonoids and phenolic acids.

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A simple and reliable thin layer chromatography (TLC) method for simultaneous separation of some carotenoids (ß-carotene, lycopene, lutein, astaxanthin and zeaxanthin), retinoids (retinol, retinoic acid, 9-cisretinal and all-trans-retinal) and tocopherols (a-tocopherol, ?-tocopherol and d-tocopherol) was described. For a proper separation of all compounds three different mobile phases (Benzene: Petroleum Ether, 10:90, v/v; Methanol: Benzene: Ethyl acetate, 5:75:20, v/v/v; Benzene: Petroleum Ether, 90:10, v/v) were tested, using silica gel F254 as stationary phase. The visualization was performed under UV light (254 and 365 nm). The presented method is simple and adequate for the separation and identification of these compounds from different matrices, such as pharmaceuticals and foods.

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Rapid separation of 18 synthetic preservatives on the silica gel chemically modified HPTLC plates (RP-18F254s, RP-18wF254s, CN F254s and Nano-SIL Diol/UV254) has been achieved with methanol-water as mobile phase. The development distance was 8 cm in all cases. Identification of the separated preservatives was performed by UV light at l=254 nm. Potassium sorbate, sodium benzoate and ascorbic acid were identified in some soft drinks after sample preparation by solid phase extraction on C18 column.

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The flavonoids are a group of strongly natural antioxidants that present high biological activity. Their chromatographic behavior may suggest the in vivo interactions that take place between them and the NH2 groups existed at cellular level. The NH2 high performance thin-layer chromatography (HPTLC) plates provide a useful tool that allows the prediction of the biological interactions, which are mostly influenced by the compounds particularities. For eluting the studied compounds different methanol: water mixtures are used as mobile phases. The range of methanol in mobile phase was increased with 5% in each step starting from 20 to 40%. The computational analysis of chromatographic results leads the lipophilicity estimation at a high analytical level. Moreover, the experimental lipophilicity of investigated compounds expressed by RM0, b, teta0, mean of R_F (mR_F) and R_M (mR_M), and scores of R_F and R_M corresponding to the first principal component are correlated with log P values calculated by different computer software. High correlations were observed between the experimental and theoretically estimated lipophilicity indices.

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Lipophilicity of parabens (methyl-, ethyl-, propyl-, butyl-paraben)was determined by reverse phase high performance thin layer chromatography on RP-18F_254s, RP-18WF_254s, RP-CN F_254s, and Nano-Sil Diol/UV₂₅₄ HPTLC plates. The mobile phase was a mixture of methanol, water in different volume proportion. The RM values of the compound decreased linearly with increasing concentration of methanol in the mobile phase in all cases. Retention indices corresponding to pure water (R_M0) were determined using five isocratic R_M values. The regression correlation coefficients obtained for all stationary phases were excellent (higher than 0.98 for the majority of the compounds). In order to compare the experimental lipophilicity of investigated compounds estimated by RM0 and b and the different computed logp values, a correlation matrix was performed. Highly significant correlations were obtained between different experimental indices of lipophilicity (RM0, b) and computed log P values. All types of stationary phases (RP-18F_254s, RP-18WF_254s, RP-CN F_254s, and Nano-Sil Diol/UV254) appear to be suitable for estimating the lipophilicity of the investigated compounds.

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The color pigments from different sorts of red wine (Cabernet Sauvignon, Merlot, and Burgundy) produced in different years, purchased from the Recas and Minis Romanian wineries, were separated using a new reversed-phase thin-layer chromatographic (RP-TLC) method. Chromatographic separation of the pigments was performed on silica gel RP-18F ₂₅₄ with acetonitrile-water-formic acid 40:58:2 ( v/v ) as mobile phase. Most of the natural pigments are phenolic compounds with antioxidant activity that can be evaluated by use of a stable free radical, for example DPPH (2,2-diphenyl-1-picrylhydrazyl). The proposed RP-TLC method can be used in wine monitoring to identify the origin of wine and to detect adulteration.

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