An activated carbon substrate surface for laser desorption mass spectrometry

A method to obtain laser desorption/ionization mass spectra of organic compounds by depositing sample solutions onto a carbon substrate surface is demonstrated. The substrate consists of a thin layer of activated carbon particles immobilized on an aluminum support. In common with the porous carbon suspension samples used in previous "surface-assisted laser desorption/ionization" (SALDI) work, the mass spectra contain only a few "matrix" background ion peaks, minimizing interference with analyte ion peaks. The presence of glycerol ensured that the ion signals were stable over hundreds of laser shots. In addition, the carbon substrate surface has several advantages over the suspension samples. The use of a very thin layer of carbon significantly improves the sensitivity. Detection limits range from attomoles for crystal violet to femtomoles for bradykinin. Very little sample preparation is required as the analyte solution is simply pipetted onto the substrate surface and glycerol added. When using an alternate sample deposition method, a mass resolution for bradykinin of 1800 is achieved in linear time-of-flight mode. This is close to the resolution limit set by the detector system and above instrument specification for matrix-assisted laser desorption/ionization mass spectra.