Thin Layer Chromatography-Laser Mass Spectrometry (TLC-LMS) of Triphenylmethane Dyes: Initial Results

Lab-on-a-plate: extending the functionality of MALDI-MS and LDI-MS targets

We review the literature that describes how (matrix-assisted) laser desorption/ionization (MA)LDI target plates can be used not only as sample supports, but beyond that: as functional parts of analytical protocols that incorporate detection by MALDI-MS or matrix-free LDI-MS. Numerous steps of analytical procedures can be performed directly on the (MA)LDI target plates prior to the ionization of analytes in the ion source of a mass spectrometer. These include homogenization, preconcentration, amplification, purification, extraction, digestion, derivatization, synthesis, separation, detection with complementary techniques, data storage, or other steps. Therefore, we consider it helpful to define the "lab-on-a-plate" as a format for carrying out extensive sample treatment as well as bioassays directly on (MA)LDI target plates. This review introduces the lab-on-plate approach and illustrates it with the aid of relevant examples from the scientific and patent literature.

Direct TLC-MALDI coupling using a hybrid plate

A new TLC-MALDI direct coupling method which recovers approximately 100% of the analyte is presented. The method makes use of a hybrid TLC-MALDI plate in which a silica layer and a MALDI layer are configured adjacently on a common backing. After TLC separation, the plate is rotated 90 degrees and the separated analyte spots are eluted from the silica layer to the MALDI layer via capillary action of the MALDI layer. Signal-to-noise ratios are significantly improved over previously reported coupling methods. Low-femtomole detection limits have been demonstrated for small cyclic peptides, which are comparable to detection limits for standard MALDI measurements.

Thin-layer chromatography-mass spectrometry using activated carbon, surface-assisted laser desorption/ionization

The analysis of compounds separated by thin-layer chromatography (TLC) by surface-assisted laser desorption ionization (SALDI) mass spectrometry has been demonstrated. The compounds are analyzed from the surface of the intact TLC plate, and the preparation of the TLC plate is rapid and robust: the gel surface is covered with 2 microns activated carbon particles, and glycerol is added. Analytes diffuse from the interior of the gel to the surface where they are adsorbed onto the activated carbon. A nitrogen laser is used to desorb analyte ions from the carbon particles in a time-of-flight mass spectrometer. A wide range of organic compounds, including peptides, can be detected, either as protonated or as cationized molecules. Interference with "matrix peaks" is limited since background TLC-SALDI mass spectra typically show only a few intense peaks at low mass. The detection limit for bradykinin from a developed plate is approximately 25 ng (calculated for S/N = 3). The mass resolution (FWHM) varied from a high of about 500 to a low of about 100. This variability was likely due to surface charging. Methods to improve both mass resolution and sensitivity of TLC-SALDI are suggested.

Particle beam liquid chromatography-mass spectrometry of triphenylmethane dyes: application to confirmation of malachite green in incurred catfish tissue

Eight triphenylmethane dyes (malachite green, leucomalachite green, gentian violet, leucogentian violet, brilliant green, pentamethyl gentian violet, N',N'-tetramethyl gentian violet and N',N"-tetramethyl gentian violet) have been characterized by particle beam liquid chromatography-mass spectrometry. The electron ionization spectra obtained of these dyes by this technique exhibit similar fragmentation, with the formation of phenyl and substituted phenyl radicals, and loss of alkyl groups from the amines. It was observed that the six cationic dyes are reduced in the mass spectrometer source to form the corresponding leuco compounds. This technique was evaluated for the confirmation of malachite green and leucomalachite green in incurred catfish (Ictalurus punctatus) muscle tissue.

Mass spectrometric detectors for samples separated by planar electrophoresis

Mass spectrometric detection for samples separated by planar chromatography (high-performance thin-layer chromatography and planar electrophoresis) has evolved over the past 10 years from concept to feasibility and to commercial availability. This review concentrates on the interface between planar electrophoresis and mass spectrometry. Although hardware aspects of the interface have been developed and refined over the past few years, and there are impressive demonstrations of feasibility, we are only beginning to exploit new methods in sample storage, preparation and reaction in conjunction with planar chromatographic separation, and new uses of complex multi-dimensional imaging data.

High-performance thin-layer chromatography/fast atom bombardment (tandem) mass spectrometry of Pseudomonas rhamnolipids

Several rhamnolipid preparations from Pseudomonas strains were studied by thin-layer chromatography/fast atom bombardment (TLC/FAB) mass spectrometry and TLC/FAB tandem mass spectrometry (MS/MS). The preparations were separated with normal-phase (Silica 60) and reversed-phase (RP-8) chromatography. Silica 60 plates appeared to be very useful in the separation of rhamnolipids according to the number of monosaccharide residues present. Spectra which show characteristic fragment ions could be obtained from components of mixtures with a total sample size of less than 200 ng. Chromatography on RP-8 plates gave a good separation of the rhamnolipids based on the length of the fatty acid alkyl chain. MS/MS of the sodium cationized molecules gave information about the sequence of the building blocks. Particularly, heterogeneity in beta-hydroxy fatty acid composition was determined for the principal as well as minor components present in natural rhamnolipid mixtures.

Importance of enantiomeric purity and its control by thin-layer chromatography

Methods for the direct resolution of enantiomers are important and are necessary for pharmaceutical and biomedical analysis, synthetic and mechanistic studies and various other fields. The present paper deals with the results of recent approaches, such as ligand exchange, ion exchange and steric interactions, providing direct resolution of enantiomers of a variety of compounds by thin-layer chromatography. General aspects of various methods for analysis of enantiomeric purity and resolution have been compared.

T.l.c. enantiomeric separation of amino acids

Resolution of enantiomers is very important particularly in the fields of asymmetric synthesis, mechanistic studies, geochronology, studies of structure-function relationship of proteins, pharmacology, and medicine. Various chromatographic methods have replaced the classical fractional crystallization, seeding and enzymatic procedures. Of these, t.l.c. provides a direct, simple, and inexpensive method for resolution of enantiomers of amino acids and their derivatives. Ligand exchange, ion exchange, and molecular inclusion complexation have been the basis of t.l.c. resolution of enantiomers of amino acids and their derivatives. The innovation of new plate types, and methods of development and detection have renewed interest in the direct resolution of enantiomers of amino acids, their derivatives and a variety of other compounds by t.l.c. The present report provides an overview of some of the more recent approaches to the direct t.l.c. resolution of amino acids and their derivatives together with special advantages and scope of t.l.c.

Progress in densitometry for quantitation in planar chromatography

The principal methods for obtaining quantitative information from separations performed by planar chromatographic techniques are reviewed. Recent advances in obtaining structural information for sample identification of separated components are also discussed. Reasonable expectations concerning future developments in densitometry are made.