Preliminary results for 2‐D separation with high‐performance thin‐layer chromatography and pressurized planar electrochromatography

Preliminary results of 2‐D separation of test dye mixture using high‐performance thin‐layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC) are demonstrated. The advantage of 2‐D HPTLC/PPEC separation is based on different separation selectivities obtained in both HPTLC and PPEC systems. HPTLC RP18 W plates of 5×20 cm from Merck were used in the investigations. In the first dimension, a HPTLC process was performed using 5 cm length of the plate and in the second dimension PPEC separation was obtained applying plate of 20 cm length. PPEC process followed prewetting the chromatographic plate with sample zones on it, which were partly separated after first dimensional (HPTLC) separation. In the experiments, the modified version of PPEC device for 20 cm long chromatographic plate and the reservoir for prewetting the adsorbent layer were applied.     

Pressurized planar electrochromatography,high-performance thin-layer chromatography and high-performance liquid chromatography—Comparison of performance

Kinetic performance, measured by plate height, of High-Performance Thin-Layer Chromatography (HPTLC), High-Performance Liquid Chromatography (HPLC) and Pressurized Planar Electrochromatography (PPEC) was compared for the systems with adsorbent of the HPTLC RP18W plate from Merck as the stationary phase and the mobile phase composed of acetonitrile and buffer solution. The HPLC column was packed with the adsorbent, which was scrapped from the chromatographic plate mentioned. An additional HPLC column was also packed with adsorbent of 5 μm particle diameter, C18 type silica based (LiChrosorb RP-18 from Merck). The dependence of plate height of both HPLC and PPEC separating systems on flow velocity of the mobile phase and on migration distance of the mobile phase in TLC system was presented applying test solute (prednisolone succinate). The highest performance, amongst systems investigated, was obtained for the PPEC system. The separation efficiency of the systems investigated in the paper was additionally confirmed by the separation of test component mixture composed of six hormones.     

A Modified Device for Pressurized Planar Electrochromatography and Preliminary Results with On-Line Sample Application

Pressurized planar electrochromatography (PPEC) is a separating technique in which an electric field is applied to force the mobile phase movement through a porous media (electroosmotic effect). High separation efficiency, fast separations and changes in separation selectivity in comparison to liquid chromatography, especially thin layer chromatography (planar chromatography, TLC), are features of this technique. Constructional methodological challenges to PPEC are obstacles to its development and application in laboratory practice. In this article, an attempt to overcome the challenges related to device construction and sample application/injection is described. The introduced device enables both prewetting of the adsorbent layer and electrochromatogram development with a single PPEC device. It also enables simultaneous application/injection of six samples on a chromatographic plate in a stream of the mobile phase (on-line application/injection). In addition, the PPEC chamber was equipped with a thermostat. The device is characterized by an impressive throughput in comparison to the other planar technique, TLC/HPTLC. Although the developed device still needs improvement, it is, in our opinion, a considerable step toward possible automation of this planar separation technique.     

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.     

Influence of the Modifier Type and its Concentration on Electroosmotic Flow of the Mobile Phase in Pressurized Planar Electrochromatography

The aim of this work was to find a relationship between electroosmotic flow (EOF) velocity of the mobile phase in pressurized planar electrochromatography (PPEC) and physicochemical properties like zeta potential, dielectric constant, and viscosity of the mobile phase as well as its composition. The study included different types of organic modifiers (acetonitrile, methanol, ethanol, acetone, formamide, N-methylformamide and N,N-dimethylformamide) in the full concentration range. In all experiments, chromatographic glass plates HPTLC RP-18 W from Merck (Darmstadt) were used as a stationary phase. During the study we found that there is no linear correlation between EOF velocity of the mobile phase and single variables such as zeta potential or dielectric constant or viscosity. However, there is quite strong linear correlation between EOF velocity of the mobile phase and variable obtained by multiplying zeta potential of the stationary phase–mobile phase interface, by dielectric constant of the mobile phase solution and dividing by viscosity of the mobile phase. Therefore, it could be concluded that the PPEC system fulfilled the Helmholtz–Smoluchowski equation.     

Pressurized planar electrochromatography

Theoretical backgrounds, development, examples of separations, constructional details and principle of action of devices of pressurized planar electrochromatography (PPEC) are presented. Development of the mode is described in respect of operating variables (composition of the mobile phase, pressure exerted on adsorbent layer, mobile phase flow velocity, temperature of separating system, etc.) influencing separation efficiency (kinetic performance, repeatability, separation time). Advantages of PPEC such as high kinetic performance, short separation time and different separation selectivities, especially relative to conventional thin-layer chromatography, are described. Examples of two-dimensional separations are demonstrated to show high separation potential of the mode when combined with conventional thin-layer chromatography (TLC). The PPEC mode is in infancy stage of development, so its challenges are presented as well.     

Comparison of Overpressured-Layer Chromatography and High-Performance/High-Pressure Layer Electrochromatography Using the New Prototype Equipment in Various Operational Modes

In our previous paper we have presented the new prototype equipment and introduced a new analytical technique—high-performance/high-pressure layer electrochromatography (HPLEC), a combination of overpressured-layer chromatography (OPLC) and pressurized planar electrochromatography (PPEC). In this paper, the work of the equipment in various operational modes is investigated. Some difficulties and challenges related to various aspects of separation are discussed. The OPLC and HPLEC techniques are compared in terms of selectivity and performance. The results show that our equipment can be successfully used for singe- and multichannel OPLC and HPLEC separations in various sample application and detection modes. It includes the high-throughput, multichannel, and fully automated online separation of multiple samples simultaneously. The equipment allows for the independent optimization of various operational parameters. HPLEC combines the advantages of column/capillary and planar separation techniques while overcoming their limitations. It also combines the advantages and overcomes the drawbacks of OPLC and PPEC. It provides hydrodynamic flow of the mobile phase, irrespective of the voltage used and/or the mobile phase composition. Thus, any optimization of the composition and the voltage can be used independently. Both can be used to obtain the required selectivity of separation. The voltage can be used to facilitate the mobile phase flow and accelerate the analysis.     

Separation of Some Aromatic Amino Acid Enantiomers with Pressurized Planar Electrochromatography and TLC

Influence of buffer pH, buffer concentration and ratio of methanol to acetonitrile in ternary mobile phase on migration distance of enantiomers of phenylalanine, tyrosine and DOPA in pressurized planar electrochromatography (PPEC) and thin-layer chromatography (TLC) systems is presented and compared. The applied operating variables in PPEC system more strongly influence on separation selectivity of investigated solutes than those in TLC one. Higher separation efficiency of PPEC system relative to TLC one is also demonstrated.     

Emerging materials for sample preparation

This review provides an update on the implementation of emerging materials as sorbents for sample preparation in combination with chromatographic separation. We have focused on recent applications of metal–organic frameworks, layered double hydroxides, porous carbons obtained from polymers or biomass precursors, and silicates (clays and zeolites). The review is directed toward the strategies followed by the authors to engineer suitable supports enabling the application of materials with unconventional size and shape as high‐performance sorbents to explore new boundaries in sample pretreatment in manual or automated modes.     

Correlation of Migration Distance of Peptides in High-Performance Thin-Layer Chromatography and Pressurized Planar Electrochromatography Systems

In a series of our previous papers we have investigated the influence of various variables on retention/migration of peptides in various high-performance thin-layer chromatography (HPTLC) and pressurized planar electrochromatography (PPEC) systems. Here we present a correlation of the selectivity of peptide separation in similar, as well as in various HPTLC and PPEC systems investigated before. Our results show that the selectivity in similar HPTLC and PPEC systems is quite different. This results from the share of electrophoresis in separation of solutes by PPEC. The results suggest that combination of HPTLC and PPEC, with properly selected separation conditions (the same, or even better—different for each technique), may be used for efficient two-dimensional separation of peptides. The best separation can be obtained if PPEC is carried out in two opposite directions (toward the cathode and the anode) simultaneously.     

An off-line two-dimensional analytical procedure for determination of polycyclic aromatic hydrocarbons in smoke aerosol

Smoke aerosol from stoves consists of a wide variety of chemical substances of which a number have toxic properties. To study the impact of aerosol emissions on health and environment reliable analytical procedures must be available for these samples. An off-line two-dimensional HPLC method is described for the determination of a number of polycyclic aromatic hydrocarbons (PAH). The method consists of a HPLC clean-up step yielding distinct fractions on activated silica and followed by analysis of each of the fractions by isocratic reversed phase HPLC. Detection is by UV and fluorescence monitors in series. Combination of the chromatographic data obtained from both the clean-up and analytical step provides additional qualitative information.     

Progress in planar electrochromatography

Developments in planar electrochromatography in open (PEC) and closed (PPEC) systems are reviewed. The discussion focuses on progress in chamber construction for planar electrochromatography, separating system performance, equilibration of the PPEC process, separation time and selectivity, and the general advantages, disadvantages and prospects of this separation mode. Presented at the 11th International Conference on Chemistry and the Environment, 9–12 September 2007, Torum, Poland.     

Comparison of two aerosol-based detectors for the analysis of gabapentin in pharmaceutical formulations by hydrophilic interaction chromatography

Comparison of hydrophilic interaction chromatography (HILIC) columns coupled with an evaporative light scattering detector (ELSD) or charged aerosol detector (CAD) was done for the detection of gabapentin in pharmaceutical formulations. The chromatographic separations were achieved on four HILIC columns: ZIC HILIC, ZIC pHILIC, Luna HILIC, and Atlantis HILIC. Experimental factors such as mobile phase composition, acetonitrile content, and mobile phase pH were evaluated. Validation of method was done in terms of linearity, sensitivity, accuracy, and precision. The performance of ELSD detection method is comparable to that of CAD. The intra-day and inter-day variations were below 1.7% and 3.2% for CAD and 2.8%, and 3.4% for ELSD, respectively. In addition, detection sensitivities of ELSD, CAD, and UV detectors were also compared for HILIC and reversed phase (RP) modes and the highest sensitivities were obtained in the HILIC mode when connected with CAD and ELSD. The developed HILIC aerosol based detection methods were successfully applied to the analysis of gabapentin in commercial tablets and capsules.     

Pressurized planar electrochromatography as a supporting tool for qualitative toxicological chemical analysis with thin-layer chromatography and UV–Vis spectrometry

ABSTRACT

Pressurized planar electrochromatography (PPEC) was applied to support qualitative toxicological chemical analysis performed with thin-layer chromatography (TLC) and UV–Vis spectrometry. Based on retention/migration distance data of substances obtained in TLC and PPEC systems and database of their wavelength maxima of remission UV–Vis spectra as well, a combined fit factor was calculated for substance identification. The involvement of PPEC, TLC, and UV–Vis spectral data together in calculation of the combined fit factor lead to its lower values for substances, which were not identical with reference, in comparison with those when the combined fit factor was calculated using TLC and spectral data only. The results evidence that involvement of PPEC data in qualitative toxicological chemical analysis performed with TLC and UV–Vis spectrometry enhances reliability of it.     

食品中有机酸的高效液相色谱分析法

对离子交换色谱法、离子排斥色谱法和反相高效液相色谱法分析食品中有机酸的特色和近几年的研究与应用状况作一综述。     

A comparative study of large volume injection techniques for microbore columns in HPLC

Summary This paper focuses attention on the potentially larger signal-to-noise ratios produced by microbore columns in comparison with conventional columns. The increased chromatographic signals by the application of microbore columns are due to the lower chromatographic dilution of elution profiles which are proportional to the square of the column inner radius. Generally less than 1μl sample should be injected into microbore systems to obtain the full benefit of the column performance. However, since more sample can be loaded on conventional columns compared to microbore columns the advantage of improved signal-to-noise ratio can only be realised in situations where very little sample is available. To inject more than 1μl sample, at the same time avoiding extra band-broadening effects, suitable injection techniques must be available. In this study three injection methods for microbore systems that meet this condition, are studied and compared.     

Determination of adsorption isotherms of proteins by H-root method: comparison between open micro-channels and conventional packed columns

This communication compares the accuracy of a micro open parallel plate system (microOPPS) with a conventional packed column for predicting isotherm data by using the H-root method (HRM). HRM is restricted to compounds obeying the Langmuir isotherm model. The performance of the two chromatographic systems was simulated by using comprehensive mathematical models. Operating conditions were varied and their effects on the accuracy of predictions was evaluated. Better accuracy in the isotherm predictions was obtained with the packed column due to its higher efficiency. However, good predictions can be obtained with the microOPPS with the advantage of significantly lower sample consumption.     

Precise and Sensitive Water Soluble Ion Extraction Method for Aerosol Samples Collected on Polytetrafluoroethylene Filters

Abstract

The widely used aerosol collection filters composed of polytetrafluoroethylene (Teflon) present a problem in the extraction of water soluble ions from the collection surface due to the hydrophobic nature of the Teflon. A method is presented for the extraction and analysis of water soluble ions from Teflon aerosol filters which is efficient and sensitive. This method uses a direct application of ethanol to the filter surface to decrease the surface tension of the filter and allow a dilute HC10, solution to contact the collection surface and extract any water soluble ions. This study compares this extraction method with other extraction methods currently being used. The results obtained from the extraction of water soluble ions from the Teflon filters were also compared to the results obtained from quartz filters collected on a colocated high volume sampler. From these studies, it is concluded that the hydrophobic nature of the Teflon filters makes the complete dissolution of water soluble ions exceptionally difficult and that the prewetting of the Teflon filters with ethanol minimizes dissolution and extraction problems.     

Solvent generated liquid-liquid systems on unmodified silica

Summary The liquid-liquid distribution properties of three liquid-liquid systems, solvent generated on silicagel, were investigated by correlating retention volumes of solutes with their statically determined partition coefficients. The application of these phase systems for the prediction of partition coefficients from chromatographic data and the performance of solvent generated liquid-liquid columns were studied. The results show that liquid-liquid distribution is by far the dominating retention process for the investigated binary liquid-liquid systems. This allows the determination of liquid-liquid partition coefficients with an accuracy of about 5% from chromatographic data. Further the solvent generated liquid-liquid systems show a surprisingly good column performance with theoretical plate heights of 2 times the particle diameter at the minimum of the H/〈v〉 curve. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

侧链含氨基的聚(对亚苯基亚乙炔基-对亚苯基-咔唑)三元共聚物的合成及其聚集态下荧光特性

通过Sonogashira偶联反应制备了含有4-[2-(对苯胺)乙烯基]苯(M1)、2,5-二戊烷氧基-1,4-二乙炔基苯(M2)和9-辛基咔唑(M3)3种结构单元的三元共轭聚合物PPEC,并通过核磁共振氢谱确定了3种结构单元的比例为0.54∶1.00∶0.46(M1∶M2∶M3).由于在PPEC的侧链中含有氨基基团,通过在PPEC的THF溶液中分别加入水、甲醇和正己烷,诱导其产生聚集,其聚集后的荧光性质表现出明显的不同,在THF与水的混合溶剂中,PPEC发光强度会随着水含量的增加先是急剧降低,而后在高水含量时发光强度又显著增强;在THF与甲醇的混合溶剂中,PPEC发光强度随着甲醇的加入只是逐渐降低;在THF与正己烷的混合溶剂中,PPEC的发光强度则会随着正己烷的增加而增强.该结果表明氨基通过与水,或者自身所形成氢键作用,改变了PPEC分子链之间的聚集态结构,降低了分子内旋转非辐射能量效率,从而有效改善共轭聚合物的主链发光性质,这为设计聚集态下(或固态下)高性能的荧光共轭聚合物提供了一种新思路.