Determination of the lipophilicity of some aniline derivatives by reversed-phase thin-layer chromatography. The effect of the organic phase in the eluent

Summary The lipophilicity of aniline and 36 ring-substituted aniline derivatives was determined by reversed-phase thin-layer chromatography using methanol, acetone and acetonitrile as the organic phase. The R_M value of each compound linearly decreased with increasing concentration of the organic solvent, Acetonitrile showed the highest and methanol the lowest solvent strength, however, the difference between the solvent strength of methanol and acetone was negligible. The site of the substitution considerably influenced the lipophilicity particularly in the case of –NO₂ groups. Good correlation was found between the R_M value extrapolated to zero organic phase concentration and the partition coefficient between n-octanol:water. The change in the R_M value caused by a 1% increase of the organic phase concentration also correlated with the partition coefficient, however, it was of secondary importance. The lipophilicity parameters determined by reversed-phase thin-layer chromatography correlated to a lesser extent with the calculated lipophilicity values of aniline derivatives.     

Lipophilicity determination of some new crown ethers by reversed-phase thin-layer chromatography

Summary The lipophilicity of 28 modified crown ether derivatives was determined by reversed-phase thin-layer chromatography (RPTLC) using various organic phases and supports. The lipophilicity values determined in different RPTLC systems showed good correlations, however the quality of the organic phase (methanol, acetone, acetonitrile) and the support characteristics influenced to a small extent the determination.     

Effect of nature of support and impregnating agent on lipophilicity determination for nonionic surfactants by reversed-phase thin-layer chromatography

Summary The retention of 9 nonylphenyl ethylene oxide oligomers was determined in 15 reversed-phase chromatographic systems using silicone oils of various molecular mass as impregnating agents and silica, cellulose and alumina supports. The data were evaluated with principal component analysis carried out on the covariance and the correlation matrices. The R_M values did not follow the additivity rule and they did not change linearly with increasing length of the ethylene oxide chain. This is probably due to the folded state of the chain in the eluent. The molecular mass of the silicone oils had a negligible effect on the retention whereas the retention increased with increasing level of impregnation. The support considerably influenced the lipophilicity values of these nonionic surfactants and cellulose seemed to be the most appropriate support. Calculations proved that the application of a correlation matrix may cause data distortion; therefore, the use of a covariance matrix is strongly proposed.     

Parameters influencing theoretical determination of RM-values of naphthalene derivatives in thin-layer chromatography by using binary mobile phase

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 (A_z), 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 A_z 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 A_z 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 A_z and the surface of adsorbed molecules (A_s) was also possible.     

Study of dispersive and inductive electrostatic interactions in reversed-phase thin-layer chromatography

Summary The retention behaviour of a group of polycyclic aromatic hydrocarbons having nearly equal ionization potentials but different molecular polarizability values was investigated using reversed-phase HPTLC. Normal alcohols were applied as the mobile phase. The relationships between the retention parameters and molecular polarizabilities of the solutes and solvents are discussed.     

Electrostatic interactions in normal and reversed-phase high-performance thin-layer chromatography. Preliminary experiments

Summary The retention behaviour of five polycyclic aromatic hydrocarbons having nearly equal ionization potentials but different molecular polarizability values was investigated using normal and reversed-phase high-performance TLC systems. Homologous series of hydrocarbons and n-alcohols were applied as the mobile phases. The electrostatic interactions operating in these chromatographic systems were analysed by studying the relationship between the log 1/R_F values and the molecular polarizabilities of solutes and solvents.     

Separation and fluorodensitometric determination of some purine derivative drugs by thin-layer chromatography on starch and cellulose

Summary Purine derivative drugs, aminophylline, theophylline, xantinolnicotinate, 6-mercaptopurine, 6-thyoguanine, azathioprine, 1-methylxantine, 3-methylxantine, 1-methyluric acid, 1,3-dimethyluric acid, 6-thioxantine, 2-amino-6-methylmercaptopurine, were separated by thin-layer chromatography on rice starch and cellulose by three different solvent systems. Conditions for quantitative fluorodensitometric determination of purine derivatives drugs were investigated.     

Determination of the lipophilicity of some aniline derivatives by reversed-phase thin-layer chromatography. The effect of salts

Summary The lipophilicity of aniline and 36 ring-substituted aniline derivatives was determined by reversed-phase thin-layer chromatography using NaCl, KCl, MgCl₂, CaCl₂, AlCl₃ and tetramethyl-ammoniumhydroxide, either adsorbed on the silica surface before impregnation or added to the eluent. In most cases the salts decreased the retention power of silica resulting in enhanced mobility of the aniline derivatives. The monovalent cations had the lowest, while AlCl₃ and tetramethylammoniumhydroxide had the highest impact on selectivity. This phenomenon can be explained by the different ion charges. The correlation between the R_M values and the partition coefficient between n-octanol: water were in all cases inferior to those obtained in salt-free systems this means that the presence of salts modifies differently the lipophilicity of aniline derivatives.     

固相萃取-高效液相色谱法检测食品中的非食用色素

采用超声波提取,固相萃取柱净化,液相色谱定量检测可能在食品中非法添加的5种色素。方法对样品溶液的pH、洗脱溶剂以及洗脱体积等条件进行了优化。方法对5种色素的检出限低于81ng/mL,回收率均在87%以上,相对标准偏差(n=6)在0.65%~5.1%范围内,在0.1~100μg/mL范围内有良好的线性关系,相关系数大于0.9998。本方法可以用于食品中非食用色素的同时快速检测。     

Influence of chamber saturation in thin-layer chromatography on theoretical and experimental parameters of mixture separations

The influence of chamber saturation in thin-layer chromatography on theoretical and experimental parameters of mixture separations were examined. Five different types of chambers for development of chromatograms were taken into consideration. The relation found experimentally differed widely from that calculated using O?cik's equation for different method of carrying out of the chromatographic process. The investigations presented here show the possibility of choosing chromatographic chambers which are optimum for theoretical studies on the process of thin-layer chromatography.     

Retention parameters of some isomeric 2-benzoylbenzoic acids in reversed-phase ion-pair high performance thin-layer and column chromatography

Summary The 2-benzoylbenzoic acid series was investigated by reversed-phase, high-performance, thin-layer and column chromatography using various alkylammonium salts and di(2-ethylhexyl)orthophosphoric acid as polar associating reagents. The effects of the individual substituents on retention were quantified by log k and R_M values. The compounds investigated differing in molecular structure (hydrophilic and hydrophobic substituents) commonly occurring groups in drugs and biologically active substances provide information on molecular interaction in these ion-pair systems. The combined effects on retention of organic modifier and ion-pair reagent concentration were investigated.     

Theoretical determination of optimum composition of the binary mobile phase for distribution of substances in thin-layer chromatography

The measure of the distribution of a mixture of substances in TLC with a binary mobile phase is expressed as ΔRM which represents the difference between the R_M values of substances i and j on use of the binary solvent 1 + 2 as the mobile phase. The possibility of determining its maximum value at an optimum composition of the binary mobile phase is demonstrated in this paper. This value can calculated from experimental and theoretical functions R_M1,2 = f(Φ₁) of substance i and j. More simply, ΔRM can be calculated theoretically from easily measurable adsorption parameters of excess adsorption isotherms and from chromatographic parameters obtained for pure solvents. The ΔRM value calculated theoretically can be utilized in a pilot technique for determination of the optimum composition of the mobile phase in gradient liquid chromatography.     

Improvement of separation in zonal preparative thin-layer chromatography by gradient elution

Summary Complex extracts of the plants Azulan and Hemorigen were separated by zonal micropreparative thin-layer chromatography in sandwich chambers of the ES and DS type which permitted zonal application of large volumes of sample, without auxiliary equipment. Application from the edge of the layer, in the frontal chromatography mode, markedly improved the separation efficiency and capacity owing to displacement effects which narrow the initially broad zones. Further improvement of separation efficiency and purity of fractions, revealed by densitometry, was observed using stepwise gradient elution. This was confirmed by extraction of some of the separated fractions from the layer and rechromatography; the composition of these fractions were generally simpler than for the corresponding isocratic chromatograms.     

Optimization of reversed-phase ion-pair chromatography by over-pressurized thin-layer chromatography III. Over-pressurized thin-layer chromatography using 10-camphor sulfonic acid as ion-pair reagent

Summary The use of over-pressurized thin-layer chromatography in ion pair system using acidic type pairing reagent has been studied. The most important aspect when reversed phase ion-pair TLC system is used to apply a suitable procedure for pre-treatment of the sorbents. Because of the acidic type of ion pair reagents cannot be bounded to the surface of the layer by immersion or pre-development with the reagent solution, double coating technique was used for the pre-treatment, the plate was firstly immersed in an ethanolic solution of cetrimide, then the immersion has been repeated by an ethanolic solution of acidic ion pair reagent. The necessary coating of the sorbents can be achieved by this technique. To find the optimal conditions for reversed phase ion pair TLC separation of organic amines, 10-camphor sulfonic acid as reagent, different aliphatic, aromatic amines and diamines and heterocyclic nitrogen compounds, respectively as model compounds were selected. The dependence of the selectivity and efficiency of the separation on the sorbents, on the concentrations of reagents (cetrimide and camphor sulfonic acid) applied for both immersion and in the eluent were investigated in detail. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

RM values of some colchicines and colchiceinamides determined by reversed-phase thin-layer chromatography.

The RM values of twelve colchicines and eight colchiceinamides were measured using reversed-phase thin-layer chromatography. The RM values were calculated by extrapolation from the linear range of a plot of RM values versus the composition of the mobile phase. The results showed that in the colchicine series substitution at the nitrogen in position C7 decreases the lipophilicity, whereas in the colchiceinamide series substitution at the nitrogen in position C10 increases lipophilicity. The influence of other substituent groups on the RM values are considered.     

Support matrix effects in the reversed-phase thin-layer chromatography of some peptides.

The retentions of 28 peptides in reversed-phase thin-layer chromatography (RPTLC) were determined on cellulose and on impregnated cellulose and alumina layers with 1-propanol as the organic component of the mobile phase. Each peptide showed a support matrix effect: their RM values first decreased to a minimum, then increased with increasing 1-propanol concentration. On cellulose layers only the increasing phase was observed. The retention behaviour of peptides was adequately described with a quadratic or linear function, but the slope value of the linear function had a positive value. The results demonstrate that the support matrix effect can be observed on non-silica supports and it may occur in reversed-phase chromatography in the case of polar solutes and supports with free adsorptive centres on their surfaces. Both the intercept and slope values of the function are needed to describe the lipophilicity of peptides, but the correlation is not strong enough for the determination of the lipophilicity of peptides by RPTLC. Principal component analysis showed that the peptides form distinct clusters on the basis of their retention characteristics: peptides containing a basic amino acid, peptides with a ring structure in the amino acid side-chain and peptides containing uncharged amino acids.     

反相高效液相色谱法同时测定化妆品中7种萘二酚类物质

建立了反相高效液相色谱((RP-HPLC))同时测定化妆品中7种萘二酚类物质的分析方法。膏霜类、乳液类和水类样品用95%(v/v)乙醇提取,粉类样品用95%乙醇-0.1%乙酸(3:2, v/v)溶液提取,经离心、过滤后,用C18柱,以甲醇-0.1%乙酸溶液为流动相梯度洗脱分离,使用二极管阵列检测器检测,以保留时间定性,并以紫外吸收光谱图辅助定性,外标法定量。结果表明,萘二酚类物质在线性范围内线性关系良好,相关系数均不低于0.999 0,方法的定量限(以信噪比为10计)为0.5～1.2 mg/kg,添加水平为5.0～50 mg/kg时回收率为84.0%～102%,相对标准偏差(n=6)为1.3%～5.7%。该法前处理简单、回收率高、精密度好,适用于非蜡基类化妆品中萘二酚类物质的测定。     

Determination of 1-nitropyrene by thin-layer chromatography in a diesel exhaust particulate extract

A method is described for the determination of 1-nitropyrene in a diesel exhaust particulate extract by thin-layer chromatography. 1-Nitropyrene is determined as 1-aminopyrene after prechromatographic reduction and isolation by solvent partition. The fluorescence response of 1-aminopyrene is approximately 1000-fold greater than that of 1-nitropyrene. The poor fluorescence stability of 1-aminopyrene on silica gel plates prevents in situ detection by scanning densitometry unless the plates are impregnated with a mixture of 2,6-di-tert-butyl-4-methylphenol and Fomblin H-Vac. A linear response from 1 to 150 ng of 1-aminopyrene and a detection limit of 1.0 ng were obtained using the impregnated plates. For fourteen samples of a diesel exhaust particulate extract the concentration of 1-nitropyrene was determined to be 165 μg/g with an RSD = 9.0%. No significant interferences were observed from other nitro- or aminopolycyclic aromatic compounds present in the extract.