Structure and TLC Mobility Relationships for Tebuthiuron and Related Thiadiazoles

Abstract

Tebuthiuron and structurally-related thiadiazoles are separated by thin-layer chromatography on silica gel plates in two developing solvent systems. Relationships between chemical constitution and chromatographic mobility are discussed.     

Separation and preparative isolation of phenolic dialdehydes by on-line overpressured layer chromatography

The Reimer-Tiemann reaction carried out in a heterogeneous solid-liquid medium was found to give the isomeric dialdehydes 2-hydroxy-1,3-benzenedicarboxaldehyde and 4-hydroxy-1,3-benzenedicarboxaldehyde. The PRISMA model was employed to optimize the eluent mixture, and with careful choice of silica gel high-performance thin-layer chromatographic plates, the two isomers could be isolated and purified by on-line overpressured layer chromatography.     

Unconventional TLC systems in lipophilicity determination: A review

ABSTRACT

This review focuses on four unusual thin-layer chromatography (TLC) approaches for the determination of lipophilicity: (1) the use of medium-polar stationary phases: CN, NH₂, and DIOL instead of RP plates, together with water-based mobile phase; (2) the use of silica gel in a typical normal-phase manner and treating extrapolated retention indices as the “reversed lipophilicity”; (3) the use of oil impregnated silica gel in the reversed-phase manner; and (4) the use of salting-out mobile phases. The chromatographic indices obtained in these systems are numerously reported as well correlated with lipophilicity and they are an interesting alternative to classical RP systems approaches.     

4-Acetylpyridine 2-Benzothiazolylhydrazone as a Chromogenic Reagent for Common Epoxides

Abstract

A simple and sensitive color reaction of common epoxides as well as other some alkylating agents with 4-acetylpyrldine 2-benzothiazolylhydrazone (ABH) is described. These compounds gave a purpllsh red color after reaction with ABH for 2 hrs at 110°C in methyl cellosolve or for 20 min at 120°C followed by treatment with plperazlne on silica gel thin-layer plates. Four aliphatic terminal epoxides could be determined spectrophotometrically in the range from 20 to 125 nmol/ml. The limits of detection of these epoxides on silica gel thin-layer plates were 10 pmol/spot order by the visual inspection. The reaction mechanism is also discussed based on the chemical structure of the isolated chromophore.     

Chitin as Stationary Phase in Thin-Layer Chromatography–Application of Chromatographic Process Optimization Theory for Chitin Layers

Abstract

This paper describes initial of two basic theories of adsorption thin-layer chromatography potimization namely thermodynamic adsorption theory and theory based on mass action law, so called Snyder s theory in chromatographic systems containing chitin as stationary phase on wchich various amino acids were chromatographed. The results obtained were comparable to those obtained for analogous chromatographic systems containing silica gel as stationary phase. Comparison of applicability of these theories for well investigated silica gel and for not enough investigate chitin will permit to draw introductory conclusions about the processes carrying in the chromatographic systems containing chitin as stationary phase.     

Ion-pair reversed-phase thin-layer chromatography of basic drugs using sulphonic acids

The use of sulphonic acid ion-pair reagents in the thin-layer chromatography of four basic drugs (all secondary amines) on C18-bonded silica gel, paraffin coated silica gel and silica gel itself has been investigated. Effects of the ion-pair reagents were only obtained on C18-bonded silica gel, and only then when the reagents were pre-coated onto the stationary phase. In general the largest reductions in the RF values of the test compounds occurred when sodium dodecylsulphate was coated onto the plates.     

Thin-layer chromatographic separation of dicrotophos,ethion (or phorate), fensulfothion,oxydemeton-methyl,phosmet, phospholan,and trichlorfon from each other

A thin-layer chromatography method is reported for the separation of dicrotophos, ethion (or phorate), fensulfothion, oxydemeton-methyl, phosmet, phospholan, and trichlorfon. The procedure involves the use of commercially prepared silica gel 1B Baker-flex plates and developing with 2,2,4-trimethylpentane:methyl cyclohexane:n-hexyl alcohol:acetone (18:9:9:9). The pesticides are located by spraying with ammoniacal silver nitrate solution in acetone follwed by exposure to longwave UV light. The method does not separate ethion and phorate from each other. A method is also reported for the thin-layer chromatographic separation of ethion from phorate in the presence of the other six pesticides using solvent system 2,2,4-trimethylpentane:n-hexane:chloroform (18:18:12) on silica gel 1B Baker-flex plates.     

Isotopic fractionation in thin-layer chromatography.

The thin-layer chromatography of imipramine on silica gel plates was studied in fifteen solvent systems. The mobility of imipramine labeled with deuterium in the methyl groups of the dimethylaminopropyl side chain differs markedly from that of unlabeled imipramine. Partial or complete separations between unlabeled and deuterated imipramine were observed in all basic and neutral solvent systems investigated, but not in weakly acidic solvents. Isotopic fractionations of imipramine were also found on alumina thin-layer plates, but were not detected in cellulose chromatography. In all thin-layer isotopic separations, the unlabeled compound migrates more rapidly than the deuterated molecule. These results can be explained by a stronger basicity of deuterated imipramine relative to its unlabeled counterpart.     

The Role of Spacers in Displacement Thin-Layer Chromatography

Abstract

Displacement chromatography generates highly concentrated bands which migrate closely to each other along the stationary phase bed.

Spacer-displacement thin-layer chromatography is a planar method improving the observable resolution by inserting odd compounds (spacers) among the members of displacement train to be separated.

Substances were chromatographed by displacement mode of development using silica plates, chloroform carrier and triethanolamine displacer.

Resolution formula valid for elution chromatography has been adapted to the displacement type of developments. Explanation for the numerical value of required separation is given for various cases of displacement thin-layer chromatography.

Equations are suggested in order to calculate yield, loss and efficiency of displacement chromatography.     

Identification of subnanomole amounts of PTH-amino acids by high performance thin-layer chromatography

Summary High performance thin-layer chromatography (HPTLC) of PTH-amino acids on 5×5 cm silica gel plates precoated with a fluorescence marker gives 10–20 fold increase in sensitivity compared to ordinary silica gel plates. Separation of PTH-Leu from PTH-Ile is easily achieved in contrast to chromatography on polyamide sheets. Only two solvent systems are required and as many as 12 samples can be chromatographed on each plate. However, if the sample is contaminated with N-phenylthiourea a third solvent system is necessary.     

Argentation Thin-Layer Chromatography of the p-Nitrobenzyl Esters of Gibberellins and Their Precursors

Abstract

Thirteen p-nitrobenzyl esters of gibberellins and their precursors have been separated by thin-layer chromatography on silver nitrate-impregnated silica gel. The fluorescence produced by sulfuric acid was used for their detection.     

Application of Thin-Layer Chromatography to High-Performance Liquid Chromatographic Separation of Steroidal Hormones and Cephalosporin Antibiotics

Abstract

High-performance liquid chromatographic (HPLC) separation of steroidal hormones and cephalosporin antibiotics was investigated by adsorption chromatography and reversed-phase chromatography, respectively.

Prior to the HPLC separation of these pharmaceuticals, silica gel thin-layer adsorption chromatography of steroidal hormones and reversed-phase thin-layer partition chromatography of cephalosporin antibiotics with chemically bonded dimethylsilyl silica gel were performed in order to obtain suitable HPLC separation systems.

In the separation of steroidal hormones, the same binary mobile phase ratios of TLC did not give satisfactory results in HPLC. For the sharp separation in HPLC, solvent strength in the binary solvent mixture used for TLC had to be decreased.

The difference in solvent strength for efficient separation between TLC and HPLC might be attributed to the fact that in HPLC the solvent elution power acts in an isocratic manner while in TLC it acts in a gradient manner.

On the other hand, a correlation of mobility between TLC and HPLC separation for cephalosporin antibiotics was obtained, and the possibility of direct transfer of chromatographic systems from TLC to HPLC for separation of these antibiotics was confirmed.     

Evaluation of phenyldimethylethoxysilane treated high-performance thin-layer chromatographic plates. Application to analysis of flavonoids inScutellariae radix

Summary The retention and selectivity of flavonoids (baicalin, baicalein, wogonin, oroxylin A) inScutellariae radix have been studies by high-performance thin-layer chromatography on phenyldimethylethoxysilane-treated silica plates. The silica plates treated with phenyl groups were used for physical and chemical analysis. From elemental carbon analysis, the maximum number of bonded phenyl surface groups per gram was calculated to be 0.467×10²¹ (Oginal silica plate: Merck Art. 15109, Silica gel 100 F₂₅₄). With methanol-1/15 M phosphate buffer (pH 6.2) mixtures as mobile phase, baicalin, baicalein, wogonin, and oroxylin A inScutellariae radix were separated. It has been shown that phenyl-treated plates are more suitable for selective separation of baicalin, baicalein, wogonin, and oroxylin A than octadecyl-treated plates.     

Separation of androsterone from epiandrosterone, and dehydroepiandrosterone from its 3-hydroxy epimer by thin-layer chromatography.

The application of thin-layer chromatography to the separation of 13 steroids, including androstanes, 4-androstenes and 5-androstenes, using silica gel and 1,2-propanediol-impregnated cellulose is described. After group-wise separation of various C19 steroids on silica gel, the 3-hydroxy epimers of 5alpha-androstanes and 5-androstenes can be separated by thin-layer chromatography on impregnated cellulose plates. The chromatographic procedure is rapid and makes the prior formation of steroid derivatives unnecessary.     

Correlation of TLC,HPTLIC and PMD Results and Their Transfer to HPLC Systems

Abstract

The correlation of the results of five thin-layer chromatographic techniques and their transfer to high performance liquid chromatography are reported. The data obtained indicate that high performance thin-layer chromatographic results are faithfully reproduced by high performance liquid chromatography. Although plates were not activated, and mixed solvents were used, no major differences were observed between thin layer and high performance liquid chromatography.     

Triangular Thin-Layer Chromatography

Abstract

This study illustrates the use of triangular plates in thin-layer chromatographic separations. A comparison between triangular, conventional and circular thin-layer chromatography clearly indicates the superiority of triangular plates in terms of sensitivity, detection limits and savings in plates and solvent.     

Impregnated silica-based layers in thin layer chromatography

Abstract

Impregnated thin-layer chromatography (TLC) layers based on silica gel are presented. Impregnating agents such as metal cations, inorganic ions, chelating agents, chiral selectors, surfactants, ion-pairing reagents, and ionic liquids are discussed. The role of impregnated TLC layers in medicinal chemistry is highlighted. The historical overview of TLC separations on physically coated layers is given and some future prospects ahead of this technique are discussed.     

Use of High Pressure Liquid Chromatography and Thin Layer Chromatography for the Separation and Detection of Testosterone and its Metabolites from in vitro Incubation Mixtures

Abstract

Testosterone and its 6β-, 7α-, and 16α-hydroxylated metabolites were resolved by high pressure liquid chromatography and thin layer chromatography. Separation by HPLC was achieved in less than 45 min on a microparticulate silica gel column using isocratic elution with isopro-panol:tetrahydrofuran:hexane (5:15:80) as the mobile phase. TLC systems utilizing silica gel on glass and plastic plates, and polysilicic acid on glass fiber sheets are presented. The monohydroxylated metabolites of testosterone formed during incubation of (¹⁴C)-testosterone with liver postmitochondrial preparations from adult male rats pre-treated with phenobarbital or Aroclor 1254 were separated and quantitated by both HPLC and TLC. The results using both techniques are compared with those obtained by paper chromatography.     

Characterization of Liquid-Solid Adsorption Systems by Using TLC Data

Abstract

The thin-layer chromatography (TLC) method is used to measure the excess adsorption isotherms for different binary liquid mixtures on silica gel. These isotherms are interpreted by means of the Langmuir-Freundlich equation, which involves the adsorbent heterogeneity and the difference in the molecular sizes of the components. This equation makes possible the evaluation of the surface phase capacity, equilibrium constant and heterogeneity parameter, which characterize liquid-solid adsorption systems.