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.