共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary Ten pesticides have been completely separated by two-dimensional (2D) development on TLC plates coated with coupled layers
of octadecyl silica (reversed-phase, RP) and plain silica (normal-phase, NP). The binary mobile phases, aqueous-organic for
RP chromatography and nonaqueous for NP chromatography, were chosen from plots ofR
F against mobile-phase composition and graphicalR
F(RP)-R
F(NP) correlations. The different selectivity of the RP and NP systems enabled dispersion of spots over the plate area and good
separation. 相似文献
2.
Summary Relationships betweenR
F values and mobile-phase composition have been determined for moderately polar pesticides in normal-phase systems (NP) of
the type silica-non-polar diluent (heptane)-polar modifier (ethyl acetate, tetrahydrofuran, or dioxane) and in reversed-phase
systems (RP) of the type octadecyl silica-water-polar modifier (acetonitrile, methanol, or tetrahydrofuran). These relationships
constitute a retention database which has enabled choice of the optimum conditions for preparative column chromatographic
separation of pesticides into fractions; these were then applied to a silica plate and chromatographed. The plate was videoscanned,
furnishing a real picture of the plate showing complete separation of the pesticide fractions. 相似文献
3.
Summary An equation describing RM values in TLC with a binary mobile phase has been derived and examined by using TLC data. Two different methods have been proposed to determine the chromatographic parameters characterizing energetic heterogeneity of the adsorption system and solute-solvent interactions. These methods differ in the estimation of the mole fractions of solvents in the surface phase. In method I an analytical equation for evaluating these mole fractions is assumeda priori. Method II utilized the excess adsorption isotherm measured for the mobile phae-adsorbent system. 相似文献
4.
Summary To characterize the retention and selectivity of separations of 23 flavonoids (aglycones and glycosides) relationships betweenR
F and modifier concentration were determined for silica and diol adsorbents (with mixtures of ethyl acetate and methanol as
mobile phases), for cyanopropyl silica (with mixtures of ethyl acetate and dichloromethane as mobile phases), for aminopropyl
silica (with mixtures of ethyl acetate, methanol and water as mobile phases) and for octadecyl silica (with mixtures of methanol
and water as mobile phases). Owing to large polarity differences between aglycones and glycosides, these groups of compounds
cannot be separated other than by use of reversed-phase systems, for which the selectivity is lower. It follows from correlation
plots ofR
F1 againstR
F2 that for some pairs of adsorbents (e. g. silica and diol) selectivity differences are small; for others the points in the
plot are widely dispersed, indicating selectivity differences. The chemometric database obtained can be used to choose optimum
chromatographic systems for the separation of given sets of flavonoids and for planning gradient elution programs for separation
of flavonoid aglycones and glycosides in a single TLC experiment. 相似文献
5.
6.
Relationships between R
F
values and mobile-phase composition have been determined for urea herbicides and fungicides in normal-phase systems (NP) of the type silica-nonpolar or weakly polar diluent (heptane, toluene, diisopropyl ether) – polar modifier (ethyl acetate, tetrahydrofuran, dioxane, ethyl-methyl ketone and 2-propanol). These relationships constitute a retention database which has enabled to choose optimum systems for preliminary fractionation of a multicomponent mixture of pesticides by zonal micropreparative TLC. The mixture was applied from the edge of the layer in the frontal + elution mode which increased the separation efficiency because or displacement effects. The separated simpler fractions were applied to a silica plate and rechromatographed. The plate was videoscanned, furnishing a real picture of the plate showing preliminary separation of the simpler pesticide fractions. Complete separation of the fractions was carried out by two-dimensional thin-layer chromatography on plates with chemically bonded-cyanopropyl silica stationary phase using non-aqueous eluent in the first direction and aqueous reversed-phase eluent in the second direction. 相似文献
7.
A study has been undertaken on the effect of temperature on retention characteristics in thin-layer chromatography (TLC) with low-volatility mobile phases (MP). It is shown that temperature variations in TLC in melts bring about variations in both the relative retention values and, in some cases, in the order of migration of the chromatographic zones across the layer. The variation in the capacity factor k' with temperature agrees well with Martin's equation. To explain the temperature dependence of Rf one must, in general, take into account the variations with temperature in both the partition coefficient and the phase ratio. To describe the variation in Rf with temperature in TLC with low-volatile MP one can use an approximate equation in which In Rf is a linear function of 1/T. The experiments indicate that temperature is a major factor in TLC in melts. 相似文献
8.
J. K. Rzyo M. Jaroniec J. A. Jaroniec H. Kolodziejczyk 《Journal of separation science》1979,2(8):524-526
In the Part 1 of this series a new equation for determining the Rm values in TLC with mixed mobile phases was proposed and examined by using the parameter m, which is a measure of energetic heterogeneity of the adsorbent surface with regard to the adsorbing molecules (admolecules). The numerical values of m, evaluated for 13 chromatographic systems, have been compared with that of the O?cik's parameter A, which characterizes solute-solvent interactions. 相似文献
9.
Summary A TLC-densitometric method for flavonoid analysis is described. Results are comparable to those obtained with classical methods. As the isolation step can be avoided results can be observed with 100 ng samples. 相似文献
10.
11.
J. K. Rzyo M. Jaroniec H. Kolodziejczyk J. A. Jaroniec J. Gross 《Journal of separation science》1980,3(4):180-182
TLC experimental data have been measured for polycyclic hydrocarbons in binary and ternary mobile phases on silica gel. These data have been interpretated using the equation discussed by us in Part 1 of this series [HRC & CC 2 (1979) 236]. The heterogeneity parameter appearing in this equation has been evaluated and compared for different ternary and binary mobile phases. 相似文献
12.
Summary The effects of some factors important in ion-pair, high-performance liquid chromatography were studied in ion-pair, thin-layer
chromatography. Tetramethyl and cetyltrimethylammonium salts were used as ion-pairing reagents. As stationary phases, silica
gel and chemically bonded reversed-layers (C18) were used. Layers were impregnated with ion-pairing reagent prior to chromatography. In some cases the stationary phase
was treated with buffer at different concentrations. The mobile phase contained methanol and water, in one set of experiments
buffer, salt for adjustment of ionic strength and ion-pairing reagent were added. The migration behaviour of different benzoic
acids was studied. Several problems of ion-pair thin-layer chromatography are discussed.
Passed away on 13th of April, 1998
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997. 相似文献
13.
The retention of a solute in RP chromatography is a very complex process which depends on many factors. Therefore, the study of the influence of a mobile phase modifier concentration on the retention in different reversed phase chromatographic systems is very important for understanding the rules governing retention and mechanisms of substance separation in a chromatographic process. Composition changes and the nature of mobile phases enable tuning of the separated analytes' retention over a wide range of retention parameters and optimization of the chromatographic process as well. Optimization of the chromatographic process can be achieved by several different methods; one of them is the so-called interpretative strategy. The key approach adopted in this strategy is the implementation of adequate retention models that couple the retention of solute with the composition of a mixed mobile phase. The use of chemically bonded stationary phases composed of partially non-bonded silica matrix and organic ligands bonded to its surface in everyday chromatography practice leads to questions of the correct definition of the retention model and the dominant retention mechanism in such chromatographic systems. The retention model for an accurate prediction of retention factor as a function of modifier concentration and the heterogeneity of the adsorbent surface should be taken into consideration. In this work the influence of mobile-phase composition on the retention of sixteen model substances such as phenols, quinolines, and anilines used as test analytes in different RP-TLC systems with CN-, NH2-, and Diol-silica polar bonded stationary phases has been studied. The aim of this study is to compare the performance of three valuable retention models assumed as the partition, adsorption/partition, and adsorption mechanism of retention. All the models were verified for different RP-TLC systems by three statistical criteria. The results of investigations presented in this work demonstrate that the best agreement between the experimental and calculated Rf values was obtained by the use of new-generation retention models, which assume heterogeneity of adsorbent surface. The results reported here show that heterogeneity of the adsorbent surface may be important in analysis of the elution process in liquid chromatography. Consideration of the goodness of fit for the experimental data to the examined retention models is in conformity with the adsorption mechanism of retention on all polar bonded stationary phases in most eluent systems for most investigated compounds. 相似文献
14.
Summary Direct, simple and reliable means for characterization of the common amino acids, using mixtures of structural analogues of amino acids and combinations of low-voltage electrophoresis (1.04 mol dm–3 formic acid) and chromatography (tert-butanol/methanol/pyridine/formic acid/water, 33:43:9.6:0.4:20, v/v, methanol/pyridine/formic acid/water, 70:9.6:0.4:20, v/v, or tertpentanol/methylethylketone/pyridine/water, 37.5:37.5:5:20, v/v) on amorphous cellulose thin-layer are given. The efficiency of the procedures is evaluated in various examples.Abbreviations used: TLC = thin-layer chromatography, TLE = thin-layer electrophoresis, TLP = thin-layer plate; other abbreviations: see Table I and end of text.for structural analogues of amino acids and glucosamine, see Table I. 相似文献
15.
J. K. Ryo J. A. Jaroniec H. Koodziejczyk M. Jaroniec 《Journal of separation science》1979,2(5):236-242
Thin-layer adsorption chromatography with a multicomponent mobile phase is discussed. A new equation for predicting RM-values in TLC with mixed mobile phases using the RM-ValUeS obtained for pure solvents is proposed. This equation takes into account effects of energetic heterogeneity of the adsorbent surface with regard to adsorbed molecules of solvents and solutes. Experimental verification of this equation is presented for RM-data obtained by TLC using a binary mobile phase. 相似文献
16.
17.
The purpose of the studies being carried out is to find some regularities of a general character which determine the relationship between the structures of the chromatographed substances and the composition of the mobile phase, i.e., between the log of the partition coefficient of the sample (Az), the K1-values which characterize the adsorption equilibrium of component “1” in a given chromatographic system, the structures of the mobile phase components and the structures of the substances being chromatographed. This paper deals with the relationship between the Az and K1 parameters and the structure of naphthalene and a number of its derivatives. It has been shown that there is a close relationship between the kind, size, frequency and site of the substituent on the one hand and the Az and K1 values on the other. In order to eliminate the possibility of unwanted side effects, the investigations were carried exclusively using non-active binary mobile phases of the type N + N or N + /B/. From these investigations, a comparison between the parameter Az and the surface of adsorbed molecules (As) was also possible. 相似文献
18.
Javier Gotta Sonia Keunchkarian Cecilia Castells Mario Reta 《Journal of separation science》2012,35(20):2699-2709
The prediction capability of the solvation parameter model in reverse‐phase liquid chromatography at different methanol‐water mobile phase compositions and temperatures was investigated. By using a carefully selected set of solutes, the training set, linear relationships were established through regression equations between the logarithm of the solute retention factor, logk, and different solute parameters. The coefficients obtained in the regressions were used to create a general retention model able to predict retention in an octadecylsilica stationary phase at any temperature and methanol‐water composition. The validity of the model was evaluated by using a different set (the test set) of 30 solutes of very diverse chemical nature. Predictions of logk values were obtained at two different combinations of temperature and mobile phase composition by using two different procedures: (i) by calculating the coefficients through a mathematical linear relationship in which the mobile phase composition and temperature are involved; (ii) by using a general equation, obtained by considering the previous results, in which only the experimental values of temperature and mobile phase composition are required. Predicted logk values were critically compared with the experimental values. Excellent results were obtained considering the diversity of the test set. 相似文献
19.
An overview is given of the literature publisned in the field of thin-layer chromatography on chemically bonded phases. Aspects which merit further attention are: quantitative analysis, organic solvent selection, stationary phase characteristics, surface modification of precoated silica plates, ion-pair chromatography and correlation of thin-layer and column chromatographic data. 相似文献
20.
Summary Dansyl derivatives of four long-chain primary aliphatic amines and five secondary aliphatic amines were chromatographed in two adsorption systems: heptane+diisopropyl ether — silica and water+methanol — octadecyl cilica. In the normal-phase system RM (log k) values were approximately linearly dependent on the log concentration of diisopropyl ether in the eluent; the separation selectivity of dansyl C8–C12 primary amines was poor. For the reversed-phase system the derivatives of both primary and secondary amines were well separated, the log k values being linearly dependent on per cent concentration of methanol in the eluent. 相似文献