Multidimensionality in planar chromatography

Sample preparation for planar chromatography

High-performance thin-layer chromatography has favorable properties for high-throughput separations with a high matrix tolerance. Sample preparation, however, is sometimes required to control specific matrix interferences and to enhance the detectability of target compounds. Trends in contemporary applications have shifted from absorbance and fluorescence detection to methods employing bioassays and mass spectrometry. Traditional methods (shake-flask, heat at reflux, Soxhlet, and hydrodistillation) are being challenged by automated instrumental approaches (ultrasound-assisted and microwave-assisted solvent extraction, pressurized liquid extraction, and supercritical fluid extraction) and the quick, easy cheap, efficient, rugged, and safe extraction method for faster and streamlined sample processing. Liquid-liquid extraction remains the most widely used approach for sample clean-up with increasing competition from solid-phase extraction. On-layer sample, clean-up by planar solid-phase extraction is increasingly used for complex samples and in combination with heart-cut multimodal systems. The automated spray-on sample applicator, the elution head interface, biological detection of target and non-target compounds, and straightforward mass spectrometric detection are highlighted as the main factors directing current interest toward faster and simpler sample workflows, analysis of more complex samples, and the determination of minor contaminants requiring high concentration factors.

Planar chromatography - Current practice and future prospects

Planar chromatography, in the form of thin-layer or high-performance thin-layer chromatography (TLC, HPTLC), continues to provide a robust and widely used separation technique. It is unrivaled as a simple and rapid qualitative method for mixture analysis, or for finding bioactive components in mixtures. The format of TLC/HPTLC also provides a unique method for preserving the separation, enabling further investigation of components of interest (including quantification/structure determination) separated in both time and space from the original analysis. The current practice of planar chromatography and areas of development of the technology are reviewed and promising future directions in the use of TLC/HPTLC are outlined.

LE. Clasificación de extractos etanólicos de especies de la familia Lauraceae por cromatografía en capa fina bidimensional y análisis estadísticos multivariado CCD-2D/ PCA-cluster

Se caracterizaron los extractos etanólicos de hojas y cortezas de 13 especies de la familia Lauraceae mediante cromatografía en capa fina de dos dimensiones (2D-CCD). Los datos posteriores se analizaron mediante técnicas de análisis estadístico multivariado (cluster y análisis de componentes principales (PCA)). Lo anterior permitió hacer una distinción entre los extractos obtenidos de diferentes partes de la planta (hojas y cortezas). Se observó, además, que la metodología usada es capaz de diferenciar entre extractos obtenidos a partir de especies de Lauraceae y los de otras familias de plantas.

Recent trends in electrospinning of polymer nanofibers and their applications in ultra thin layer chromatography

Fabrication of polymer derived electrospun nanofibers by electrospinning as chromatographic sorbent bed for ultra-thin layer chromatography (UTLC) is a very demanding topic in analytical chemistry. This review presents an overview of recent development in the fabrication of polymer derived electrospun nanofibers and their applications to design UTLC plates as stationary phases for on-plate identification and separation of analytes from their mixture solutions. It has been reported that electrospun fiber based stationary phases in UTLC have enhanced separation efficiency to provide separation of analyte mixture in a shorter development time than those of traditional particle-based TLC stationary phases. In addition, electrospun UTLC is cost effective and can be modified for obtaining different surface selectivities by changing the polymer materials to electrospun devices. Electrospun UTLC plates are not available commercially till date and efforts are being rendered for their commercialization. The morphology and diameter of electrospun nanofibers are highly dependent on several parameters such as type of polymer, polymer molecular weight, solvent, viscosity, conductivity, surface tension, applied voltage, collector distance and flow rate of the polymer solution during electrospinning process. Among the aforementioned parameters, solution viscosity is an important parameter which is mainly influenced by polymer concentration. This review provides evidence for the fabrication of UTLC plates containing electrospun polymer nanofibers. Furthermore, the future prospects related to electrospinning and its application in obtaining of different types of electrospun nanofibers are discussed. The present communication is aimed to review the work which appeared during 2009-2014 on the application of polymer derived electrospun nanofibers in ultra thin layer chromatography.

Coupling of In Vitro Bioassays with Planar Chromatography in Effect-Directed Analysis

Modern analytical test methods increasingly detect anthropogenic organic substances and their transformation products in water samples and in the environment. The presence of these compounds might pose a risk to the aquatic environment. To determine a possible (eco)toxicological risk, aquatic samples are tested using various bioassays, including sub-organismic assays such as the luminescent bacteria inhibition test, the acetylcholinesterase inhibition test, and the umu-test. The effect-directed analysis (EDA) combines physicochemical separation methods with biological (in vitro) tests. High-performance thin-layer chromatography (HPTLC) has proved to be particularly well suited for the separation of organic compounds and the subsequent analysis of effects by the application of the biotests directly on the surface of the HPTLC plate. The advantage of using HPTLC in comparison to high-performance liquid chromatography (HPLC) for EDA is that the solvent which is used as a mobile phase during chromatography is completely evaporated after the separation and therefore can no longer influence the applied bioassays.A prioritization during the complex identification process can be achieved when observed effects are associated with the separated zones in HPTLC. This increases the probability of identifying the substance responsible for an adverse effect from the multitude of organic trace substances in environmental samples. Furthermore, by comparing the pattern of biological effects of a separated sample, it is possible to track and assess changes in biological activity over time, over space, or in the course of a process, even without identifying the substance. HPTLC has already been coupled with various bioassays.Because HPTLC is a very flexible system, various detection techniques can be used and combined. In addition to the UV/Vis absorption and fluorescence measurements, TLC can also be coupled with a mass spectrometer (MS) for compound identification. In addition, detection of functional groups by means of derivatization reagents can support this identification. It is also possible to combine derivatization and HPLC-MS.Two case studies are used to illustrate the significance of HPTLC-EDA in investigating water quality: Study on a wastewater treatment plant Possible influence of an artificial turf surface on ground water.

Aligned electrospun nanofibers for ultra-thin layer chromatography

The fabrication and implementation of aligned electrospun polyacrylonitrile (PAN) nanofibers as a stationary phase for ultra-thin layer chromatography (UTLC) is described. The aligned electrospun UTLC plates (AE-UTLC) were characterized to give an optimized electrospun mat consisting of high nanofiber alignment and a mat thickness of ~25 μm. The AE-UTLC devices were used to separate a mixture of β-blockers and steroidal compounds to illustrate the properties of AE-UTLC. The AE-UTLC plates provided shorter analysis time (~2-2.5 times faster) with improved reproducibility (as high as 2 times) as well as an improvement in efficiency (up to100 times greater) relative to non-aligned electrospun-UTLC (E-UTLC) devices.

Coupling of planar chromatography with Direct Analysis in Real Time mass spectrometry

Direct Analysis in Real Time mass spectrometry (DART-MS) is an emerging and rapidly developing area of ambient desorption ionization mass spectrometric techniques. Its coupling with planar chromatography is especially promising, as compared to other ambient desorption ionization techniques, because it does not require the use of liquids that may distort the shape of a spot by diffusion effects. In the first publications on TLC/HPTLC-DART-MS, due to the fixed, horizontally aligned supply of the gas flow from the DART ionization source to the MS inlet, the introduction of HPTLC/TLC plates as cut strips was inconvenient for quantitation, and the repeatability was very low due to the manual positioning. Recently a new version of the DART ion source was suggested, which allows adjusting the angle of the DART gas stream and the use of a motorized rail, thereby, improving highly the capabilities of TLC/HPTLC-DART-MS. This comprehensive review describes the development and analytical capabilities of TLC/HPTLC-DART-MS, and the general DART-MS perspectives for surface analysis or imaging MS.

Biosynthesis of antitumoral and bactericidal sanguinarine

A simple, rapid, and reliable TLC method for the separation and determination of sanguinarine has been established. This intensively studied biologically active alkaloid has a wide range of potentially useful medicinal properties, such as antimicrobial, antiinflammatory, and antitumoral activities. Sanguinarine has also been incorporated into expectorant mixtures and has a strong bactericidal effect upon gram-positive bacteria, particularly Bacillus anthracis and staphylococci. These medicinal properties are due to the interaction of sanguinarine with DNA. A fibre-optic-based fluorescence instrument for in situ scanning was used for quantitative measurements. The sanguinarine was determined over the range 5–40 ng and a detection limit of 1.60 ng. The method was applied to the quantification of sanguinarine in tissue culture extracts of Chelidonium majus L.

Monolithic superhydrophobic polymer layer with photopatterned virtual channel for the separation of peptides using two-dimensional thin layer chromatography-desorption electrospray ionization mass spectrometry

Superhydrophobic monolithic porous polymer layers with a photopatterned hydrophilic channel have been prepared. These layers were used for two-dimensional thin layer chromatography of peptides. The 50 microm thin poly(butyl methacrylate-co-ethylene dimethacrylate) layers supported onto 4.0 x 3.3 cm glass plates were prepared using UV-initiated polymerization in a simple glass mold. Photografting of a mixture of 2-acrylamido-2-methyl-1-propanesulfonic acid and 2-hydroxyethyl methacrylate carried out through a mask afforded a 600 microm wide virtual channel along one side of the layer. This channel, which contains ionizable functionalities, enabled the first dimension separation in ion exchange mode. The aqueous mobile phase migrates only through the channel due to the large difference in surface tension at the interface of the hydrophilic channel and the superhydrophobic monolith. The unmodified part of the layer featuring hydrophobic chemistry was then used for the reversed phase separation in the orthogonal second dimension. Practical application of our technique was demonstrated with a rapid 2D separation of a mixture of model peptides differing in hydrophobicity and isoelectric point using a combination of ion-exchange and reversed phase modes. In the former mode, the peptides migrated 11 mm in less than 1 min. Detection of fluorescently labeled peptides was achieved through UV light visualization. Separation of the native peptides was monitored directly using a desorption electrospray ionization (DESI) source coupled to a mass spectrometer. Unidirectional surface scanning with the DESI source was found suitable to determine both the location of each separated peptide and its molecular mass.

HPTLC/DESI-MS imaging of tryptic protein digests separated in two dimensions

Desorption electrospray ionization mass spectrometry (DESI-MS) was demonstrated as a method to detect and identify peptides from two-dimensional separations of cytochrome c and myoglobin tryptic digests on ProteoChrom HPTLC Cellulose sheets. Data-dependent tandem mass spectra were acquired during lane scans across the TLC plates. Peptides and the corresponding proteins were identified using a protein database search software. Two-dimensional distributions of identified peptides were mapped for each separated protein digest. Sequence coverages for cytochrome c and myoglobin were 81 and 74%, respectively. These compared well with those determined using the more standard HPLC/ESI-MS/MS approach (89 and 84%, respectively). Preliminary results show that use of more sensitive instrumentation has the potential for improved detection of peptides with low R(f) values and improvement in sequence coverage. However, less multiple charging and more sodiation were seen in HPTLC/DESI-MS spectra relative to HPLC/ESI-MS spectra, which can affect peptide identification by MS/MS. Methods to increase multiple charging and reduce the extent of sodiation are currently under investigation.

Two-Dimensional Ultra-Thin-Layer Chromatography and Atmospheric Pressure Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry in Bioanalysis

The feasibility of ultra-thin-layer chromatography (UTLC) and atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry (AP-MALDI-MS) for bioanalysis was studied with benzodiazepines as model substances in human urine. Two-dimensional (2D) UTLC was shown to be an efficient technique for the separation of benzodiazepines. Separations occurred in 4-12 min, and the separated compounds were identified by AP-MALDI-MS. The limits of detection with AP-MALDI-MS and AP-MALDI-MS/MS were in the picomole range and thus low enough for bioanalysis. The applicability of the 2D UTLC-AP-MALDI-MS was demonstrated in detection of metabolites with an authentic biological urine sample.

A multidimensional overpressured layer chromatographic method for the characterization of tetrazine libraries

The recent combinatorial approach in synthetic organic chemistry started a new age in drug discovery. The generation of compound libraries in combination with high-throughput screening has become the method of choice for the production of new pharmacological leads for chemical optimization. Characterization and separation of such pool of compounds have been lagging behind the synthetic and screening methodologies. Overpressured layer chromatography (OPLC) is an instrumentalized planar liquid chromatographic technique associated with the use of optimized layers prepared from particles of narrow particle size distribution and small diameter. On one hand, uni-directional OPLC allows the simultaneous separation of large number of samples in minutes. On the other hand, two-dimensional OPLC offers multidimensional separation on a single layer. This paper shows the complete multidimensional separation of a tetrazine library prepared by parallel combinatorial synthesis. In general, this approach may become the method of choice for the characterization of compound libraries.

Linear voltage profiles and flow homogeneity in pressurized planar electrochromatography

Planar electrochromatography (PEC) is an emerging technique for thin-layer chromatography (TLC) where electroosmosis is the driving force for the solvent, not capillary action. This allows for much faster and constant flow rates in turn yielding increased zone capacities and efficiencies. Instrumental designs have changed greatly over the last few years solving many of the initial instrumentation challenges. We have previously shown that low applied pressure (or no applied pressure) PEC instruments do not give linear voltage drops across the separation path length of a TLC plate, which in turn results in non-stable electroosmotic flow (EOF). By the use of our unique reader electrode grid we have the ability to monitor the potential at eight discrete positions throughout the 10-cm separation path length. We now show that high-pressure PEC instruments, most commonly referred to as pressurized planar electrochromatography (PPEC) do show a linear voltage drop and constant EOF. We compare plate equilibration times of PPEC and low-pressure PEC, use of increased field strengths, as well as sample application designs. In addition, we discuss the use of rhodamine B as a visual marker for reproducible migration and calculation of theoretical plates.

Characterization of flow and voltage profiles in planar electrochromatography

Planar electrochromatography (PEC) is a new technology for thin layer chromatography (TLC) where the separation is driven by electroosmotic forces, not capillary action. This allows for much faster and more efficient chromatography in a planar format. Care needs to be taken when performing these experiments because voltage and flow characteristics can change through a single run, due to buffer gradients, temperature changes (Joule heating) and localized plate heterogeneity. We have designed a PEC instrument and cover grid to allow investigation of flow and voltage characteristics as solvent moves across a TLC plate. Our unique cover grid allows monitoring voltage at eight discrete points between the positive and negative reservoirs. A linear relationship between voltage and distance should be seen, giving a constant voltage drop across a plate, but this did not occur. This non-linear function changes over time, following the plate equilibration. Once a plate is equilibrated, voltage and flow characteristics remain fairly constant. Theoretical calculations support the physical observations. Larger plate widths (5 cm) were also briefly investigated and it is concluded that large width plates could be easily implemented to maintain multiple sample capability.

Thin-layer chromatography: challenges and opportunities

The purpose of this article is to identify core technologies with the potential to influence the development of thin-layer chromatography over the next decade or so. Core technologies are identified as: (i) methods to provide a constant and optimum mobile phase velocity (forced flow and electroosmotically-driven flow), (ii) video densitometry for recording multidimensional chromatograms, (iii) in situ scanning mass spectrometry, and (iv) bioactivity monitoring for selective detection. In combination with two-dimensional, multiple development and coupled column-layer separation techniques these core technologies could dramatically increase the use of thin-layer chromatography for the characterization of complex mixtures. It is also demonstrated that thin-layer chromatography has strong potential as a surrogate chromatographic model for estimating biopartitioning properties. To convert these opportunities into practice the current state-of-the-art of the core technologies is described and the principle obstacles to progress identified.

Practitioner's guide to method development in thin-layer chromatography

The authors provide a personal perspective of method development in thin-layer chromatography for the novice and more experienced chromatographer alike. No attempt has been made at a comprehensive survey of the literature. Instead we provide an overview with insights into a smaller number of approaches that the authors have found useful in their own work and indicate the factors responsible for the variation in retention and their control. The main topics covered are the relationship between sorbent chemistry and retention, the selection of primary solvents for mobile phase optimization and mobile phase optimization using the PRISMA and solvation parameter models.

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.

Planar chromatography at the turn of the century

An overview of the state-of-the-art of modern thin-layer chromatography (planar chromatography) is presented with emphasis on the complementary features of thin-layer and column liquid chromatographic separations. The reasons for selecting thin-layer chromatography for a particular analysis are identified by its attributes: a disposable stationary phase; simultaneous parallel separations; static detection free of time constraints; storage device for chromatographic information; all sample components are observed in the chromatogram. Future prospects for improved separation performance in TLC using zone refocusing, forced flow and electroosmotic flow methods are discussed as well as increasing zone capacity by using two-dimensional development and coupling to column chromatographic methods. Advances in coupling thin-layer chromatography with spectroscopic methods for structural elucidation are also considered. Finally, some predictions are made for how thin-layer chromatography will be practiced in the future.