Comparison of log k′ — solvent composition relationships in thinlayer and column chromatography for systems of the type: Silanized silica — water + methanol

Relationships between log k' values of polynuclear hydrocarbons and composition of water/methanol mixtures were determined for HPTLC on RP-18 silica and for HPLC using RP-2 silica. In spite of differences in the adsorbents used, a good correlation between HPLC and TLC parameters was found. In the TLC experiments, a sandwich tank with a modified solvent distributor was used. It has been reported that thin-layer chromatography is a good technique for the preliminary optimization of column chromatographic separations [1–5]. So far, the comparison of TLC and HPLC has been mainly restricted to silica as the adsorbent. Since TLC plates precoated with silanized adsorbents recently became commercially available, it seemed interesting to compare the chromatographic parameters obtained for the “reversed phase” systems with the two techniques (see also ref. 6).     

(3,5-二甲基苯基氨基甲酸酯)衍生的纤维素手性固定相

纤维素三（3,5-二甲基苯基氨基甲酸酯）是液相色谱中使用最广泛的手性柱。该文详细地研究了不同程度衍生的纤维素（3,5-二甲基苯基氨基甲酸酯）以及不同硅胶（粗制硅胶、氨丙基粗制硅胶、精制硅胶、氨丙基精制硅胶、大孔硅胶、氨丙基大孔硅胶）作为支撑体对该柱手性分离能力的影响。自制了13根手性色谱柱,分别考察了其对16种外消旋体的拆分,分离结果显示：三取代纤维素柱 > 二取代纤维素柱 > 纤维素柱;精制硅胶和大孔硅胶优于粗制硅胶,大孔硅胶的柱压更低;硅胶的氨丙基化对手性选择性有一定的影响;这些手性柱之间具有一定的互补性,尤其是纤维素柱。该文有助于人们更深刻地理解和更好地把握高效液相色谱手性柱的制备。     

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.     

Comparison of the chromatographic behavior of tricyclic neuroleptics on calixarene-bonded, monolithic and conventional RP-HPLC columns

The effect of different chromatographic conditions, such as buffer concentration and type of organic modifier, on the retention behavior of nine tricyclic neuroleptics on three different RP-HPLC columns was investigated. Two recently developed columns, calixarene-bonded (CALTREX) AIII) and monolithic (Chromolith) Performance RP-18e) columns, were compared with a conventional RP-C18 HPLC column (LiChrospher). The results showed how the mobile phase conditions had different effects on the analyte retention on these three columns. For example, the elution order of some analytes and the initiation of separation of the geometric isomers of the three analytes--which have E/Z-isomers (cis/trans-isomers)--could be altered by changing the conditions and the column type. Under identical conditions, a calixarene-bonded phase was the best for this separation, a monolithic phase gave comparable results and the conventional RP-column was the least effective. Concerning the geometric isomers separation, the Chromolith Performance RP-18e was superior.     

Thin-layer chromatography (TLC) as pilot technique for HPLC. Utilization of retention database (R F) vs. eluent composition of pesticides

Summary TLC and HPLC are frequently unjustly regarded as competitive methods. Using the advantages of both methods, a combination of TLC and HPLC leads to a considerable saving of time and expense in analysis. Experimental data are presented aslog k (HPLC) vs.R _M (TLC) correlations; high correlation coefficients indicate that TLC using octadecyl silica, wettable with water (RP-18W) can be applied as a pilot technique for HPLC (RP-18).     

Separation of coumarins from Archangelica officinalis in high-performance liquid chromatography and thin-layer chromatography systems

Complex, multicomponent mixtures are difficult to separate in a single chromatographic run. Therefore, the possibility to separate twelve coumarins from Archangelica officinalis was studied by combining a HPLC and a TLC system. HPLC optimized by the use of DryLab for Windows software was performed on RP-18 column and TLC was performed on silica plates. Fractions from the RP column were evaporated, applied on silica plate and developed in non-aqueous solvent. Possibilities of complete separation of investigated coumarins were discussed in RP and NP systems. The result of their complete separation was presented by HPLC chromatograms, DryLab simulated chromatograms and a video scan of TLC plate.     

Fast high performance liquid chromatography analysis in lipidomics: Separation of radiolabelled fatty acids and phosphatidylcholine molecular species using a monolithic C18 silica column

HPLC procedures using conventional C₁₈ columns are usually used to separate simple and complex lipid mixtures but these methods of separation remain often laborious and very slow. Here, monolithic columns were successfully applied to separate lipids - radiolabelled fatty acid mixtures and individual phosphatidylcholine (PC) molecular species. For that, isocratic elution was performed using two Chromolith™ Performance RP-18e columns connected in series. Detection was achieved by online measurement of radioactivity for radiolabelled fatty acids and by UV absorbance at 205 nm for PC molecular species. The performances of such silica rods were compared to conventional reverse-phase silica columns. Monolithic stationary phase separated radiolabelled fatty acids and PC molecular species two times and four times faster, respectively. In each analysis, monolithic columns allowed better separation efficiency per unit of time, with lower inlet pressure. The main advantages of this method for lipid separation are that, under isocratic conditions, it is simpler and much faster, while remaining accurate and selective when compared to conventional methods. Therefore, monolithic columns may represent a powerful tool for the near future in the field of lipidomics.     

Behaviour of phenols in normal and reversed-phase thin-layer chromatography

Chromatographia - Thin-layer chromatographic systems have been established for the separation of phenol mixtures on silica stationary phases (RP-8 and RP-18) with the following mixed eluents:...     

Modeling of chromatographic retention of the selected antiarrhythmics and structurally related compounds in the hydrophilic interactions under the TLC and HPLC conditions

Abstract

High-performance liquid chromatography (HPLC) plays an important role in testing the pharmaceutically active compounds. In despite of the advantages of HPLC, thin-layer chromatography (TLC) retains its applicability to the different experimental tasks. The experimental conditions which allow hydrophilic interactions in the chromatographic system were tested in the HPLC and TLC systems for ivabradine, its related compounds, diltiazem and verapamil. Under the TLC conditions, retention behavior of the investigated compounds was tested on silica gel modified with cyanopropyl ligands as stationary phase and acetonitrile?+?methanol containing 25% v/v formic acid. Under the HPLC conditions, we used silica gel modified with cyanopropyl ligands as a column packing and the acetonitrile + 0.25% aqueous solution of formic acid as mobile phase. Retention behavior of the investigated analytes depending on the changing volume fractions of the mobile phase modifier was characterized both for TLC and HPLC data sets by the Soczewiński–Wachtmeister equation. Linear relationships were established between the retention coefficients characterizing the retention mechanism (R_M⁰/m, logk₀/m) and molecular properties of the investigated compounds. The Quantitative Structure Retention Relationship (QSRR) modeling was performed with the use of the stepwise multiple linear regression, in order to select molecular properties which influence retention.     

Stability‐indicating chromatographic methods for determination of flecainide acetate in the presence of its degradation products; isolation and identification of two of its impurities

In this work, two stability‐indicating chromatographic methods have been developed and validated for determination of flecainide acetate (an antiarrhythmic drug) in the presence of its degradation products (flecainide impurities; B and D). Flecainide acetate was subjected to a stress stability study including acid, alkali, oxidative, photolytic and thermal degradation. The suggested chromatographic methods included the use of thin layer chromatography (TLC‐densitometry) and high‐performance liquid chromatography (HPLC). The TLC method employed aluminum TLC plates precoated with silica gel G.F₂₅₄ as the stationary phase and methanol–ethyl acetate–33% ammonia (3:7:0.3, by volume) as the mobile phase. The chromatograms were scanned at 290 nm and visualized in daylight by the aid of iodine vapor. The developed HPLC method used a RP‐C₁₈ column with isocratic elution. Separation was achieved using a mobile phase composed of phosphate buffer pH 3.3–acetonitrile–triethylamine (53:47:0.03, by volume) at a flow rate of 1.0 mL/min and UV detection at 292 nm. Factors affecting the efficiency of HPLC method have been studied carefully to reach the optimum conditions for separation. The developed methods were validated according to the International Conference on Harmonization guidelines and were applied for bulk powder and dosage form. Copyright © 2016 John Wiley & Sons, Ltd.     

Separations in Thin Layer and High Performance Liquid Chromatography Using Alkyl Silica Gel Bonded Phases

Abstract

Separations in thin layer (TLC) and high performance liquid chromatography (HPLC) using alkyl bonded phases were carried out under optimum solvent conditions for each of three phases, RP-2, RP-8 and RP-18. The phases were tested for their efficiency and resolving power using three groups of compounds in three binary organic-water mobile phases. The organic solvents were acetonitrile, methanol and tetrahydrofuran, which are widely used as solvent modifiers in reversed phase liquid chromatography.

The results showed that, unlike HPLC, TLC using RP-18 plates was the most, and RP-2 plates the least, efficient. A naphthalene and biphenyl mixture which was resolved by HPLC using any of the three solvents and columns was not resolved by TLC using any plate or solvent combination, unless the plate was prewashed with an organic modifier. The addition of NaCl (1–2% wt/vol) to the solvent for TLC speeded development unless an alcohol was used, but did not greatly affect the separation.     

Chromatographic identification of pesticides

The chromatographic properties of 51 common pesticides have been measured using seven different chromatographic systems involving gas-liquid chromatography (GLC), high-performance liquid chromatography (HPLC) with diode-array spectrophotometric detection and thin-layer chromatography (TLC) with different spray reagents. Correlation coefficients were calculated for combinations of all systems. The best combination of the chromatographic systems examined for the identification of an unknown compound is GLC on OV-17, HPLC on ODS-Hypersil with acetonitrile-water as eluent and TLC using an isooctane-ethyl acetate solvent system.     

Separation of drug substances by modern liquid chromatography on silver impregnated silica gels.

The use of silver halide impregnated supports for high-pressure liquid chromatographic (HPLC) and thin-layer chromatographic (TLC) analysis of drug substances has been studied. Successful separations of xanthines and mixtures containing barbiturates, xanthines, ergot alkaloids, and tropane alkaloids have been achieved with isocratic conditions or by using simple gradients. The Ag-supports show a similar behavior as many chemically bonded stationary phases, such as modification fo adsorption sites on silica gel to give lower retention but better specificity; rapid reconditioning in connection with gradient elution (3-5 minutes). Reasonable cost, simplicity of preparation and usage, and good chemical and physical stability render the silver halide phases applicable in routine analysis and quite competitive with many commercially available chemically bonded stationary phases.     

Analysis of the Cinchona alkaloids by high-performance liquid chromatography and other separation techniques

The Cinchona alkaloids, which include the pharmaceuticals quinine and quinidine, continue to have a wide variety of important uses. A number of different chromatographic procedures have been developed for the qualitative and quantitative analysis of these compounds in a variety of sample matrices. Reversed-phase HPLC using ODS columns in combination with acidic mobile phases, and UV detection, is the most widely used method. Nevertheless, precautions need to be taken due to the strong silanophilic interactions which can occur with these analytes and the column surface, which can lead to poor peak shape and resolution. Different selectivity may be achieved in HPLC separations by use of alternative stationary phases, or by varying mobile phase pH. The specificity of detection systems may be improved by use of photodiode array UV detectors, or especially mass spectrometers. Thin-layer chromatography (TLC) provides a cheap alternative analytical method, which is especially useful for qualitative analysis. High-performance TLC, gas chromatography, capillary electrophoresis and capillary electrochromatography are all methods which after some development, could prove useful for Cinchona alkaloid separations.     

Application of bromoacetate‐substituted β‐CD‐bonded silica particles as chiral stationary phase for HPLC

Bromoacetate‐substituted [3‐(2‐O‐β‐cyclodextrin)‐2‐hydroxypropoxy]propylsilyl‐appended silica particles (BACD‐HPS), an important and useful synthetic intermediate for preparation of novel types of macrocycles‐capped β‐CD‐bonded silica particles including crown ether/cyclam/calix[4]arene‐capped β‐CD‐bonded silica particles, have been prepared and used as chiral stationary phase for HPLC. This synthetic stationary phase is characterized by means of elemental analysis. For the first time, the chromatographic behavior of BACD‐HPS was systematically evaluated with several disubstituted benzenes and some chiral drug compounds under both normal and RP conditions in HPLC. The results show that BACD‐HPS has excellent selectivity for the separation of aromatic positional isomers and chiral isomers of some drug compounds when used as stationary phase in HPLC.     

Improved cleanup method for the multiresidue analysis of N-methylcarbamates in grains,fruits and vegetables by means of HPLC with postcolumn reaction and fluorescence detection

Summary An improved and quick cleanup method has been developed for the liquid chromatographic determination of 21 N-methylcarbamate pesticides and 10 of their metabolites in grains, fruits and vegetables. Various types of solid phase extraction columns have been tested for the cleanup step in order to replace the time-consuming cleanup method found in the literature. Aminopropyl-bonded silica columns proved to be superior to unbonded silica or octyl, octadecyl, cyanopropyl and diol-bonded silica. For all 16 types of matrices tested, a single column cleanup step appeared to be satisfactory. The final determination was performed by separation of the N-methylcarbamates via high-performance liquid chromatography followed by postcolumn reaction, fluorogenic labelling of the hydrolytically formed methylamine with the orthophthalaldehyde/2-mercaptoethanol reagent, and fluorescence detection. Recovery data for 256 carbamate/commodity combinations will be given. The results of the routine analysis of real samples will also be presented. Finally, possibilities for confirming positive samples by an independent, second method will be discussed.     

Thermo-responsive monolithic materials

One of the recent major improvements of HPLC was the introduction of monolithic silica columns, which have the advantage of faster separation and lower back pressure as compared to common silica beads. Here, we present an interesting alternative to such reversed-phase monolithic columns by a convenient coupling route of a thermo-responsive polymer to hydrophilic silica monoliths. Poly(N-isopropylacrylamide) (PNIPAM) was polymerized in solution via a reversible addition fragmentation chain transfer (RAFT) polymerization technique and coupled then in situ onto an amino-modified silica monolithic column. These columns were compared with RP-18 monolithic columns in the separation of steroids under isocratic condition in aqueous mobile phase. Separation is optimized just by changing the temperature, instead of changing the mobile phase composition.     

Titania-coated monolithic silica as separation medium for high performance liquid chromatography of phosphorus-containing compounds

A method of preparing titania-coated monolithic silica stationary phase has been developed to achieve liquid chromatographic separation of phosphorus-containing compounds, which have recently been attracting increasing attention in biochemical research. The titania-coated silica columns exhibited efficient separation with low pressure drop, which is a typical feature of monolithic structures, and also possessed phospho-selectivity, which is a unique property of the titania surface. The material characteristics of titania-coated monolithic silica were examined, and then resin-clad columns were applied to the HPLC analysis of phosphorylated compounds. Highly efficient separation of phosphorylated substances indicated that the novel titania-coated monolithic silica column will find applications as a useful tool in the field of biochemistry, especially in post-genomic analyses.     

Separation of four mixtures of pesticides by pressurized planar electrochromatography (PPEC)

Examples of separations of four mixtures of pesticides by pressurized planar electrochromatography (PPEC) under different operating conditions are presented. The samples were separated on a prewetted RP-18W chromatographic plate in a system with acetonitrile-buffer as the mobile phase. A potential of 2.3 kV was applied to a 10 cm long plate to create the electric field. Reproducible retention of pesticides was obtained during PPEC in the closed system when the sorbent layer of the plate was prewetted and equilibrated with the mobile phase. The reported separations of pesticides by PPEC are over 10 times faster than the corresponding separations by TLC.     

Capillary action liquid chromatography

Capillary action LC (caLC) is introduced as a technique using capillary action as the driving force to perform LC in capillary columns packed with HPLC type microparticulate materials. A dry packing method with centrifugal force was developed to prepare capillary columns in parallel (10 columns per 3 min) to support their disposable use in caLC. Using a digital microscope for real‐time imaging and recording separations of components in a dye mixture, caLC was found to have flow characteristics similar to TLC. Based on the investigation of microparticulate HPLC silica gels of different size (1.5–10 μm) and a typical TLC grade irregular medium, Merck 60G silica, the van Deemter curves suggested molecular diffusion as the major contribution to band broadening in caLC. With Waters Xbridge 2.6 μm silica, plate heights down to 8.8 μm were obtained, comparable to those achievable in HPLC. Assisted by an image‐processing method, the visual caLC separation was converted to a classical chromatogram for further data analysis and such a facility confirmed the observation of highly efficient bands.