Matrix-assisted laser desorption/ionisation time-of-flight thin layer chromatography mass spectrometry - A rapid method for impurity testing

Thin layer chromatography/matrix-assisted laser desorption/ionisation mass spectrometry (TLC/MALDI-MS) has been previously used to obtain mass spectra from a variety of compounds, principally peptides, For pharmaceutical comp ounds, which are often of relatively low molecular weight, it is important that any matrix materials employed do not interfere with the mass spectra o btained, The key step to successful TLC/ MALDI-MS is hence the preparation of the TLC plate prior to mass spectrometry. Crucial to this is the deposit ion of matrix material into the plate to promote co-crystallisation with th e analyte, In this work we have examined the literature methods for plate p reparation and developed two new approaches. The first involves brushing th e TLC plate with a supersaturated solution of matrix and the second involve s electrospraying the TLC plate with a matrix solution. Data are presented from the direct analysis of tetracycline and its impurities. Using the elec trospray method the limit of detection for tetracycline is 1 ng from a TLC plate. A commercial MALDI-TOF mass spectrometer has been modified to allow the acquisition of chromatographic data from TLC plates. Chromatograms from replicate spats of 100 and 1 mu g of tetracycline are shown. Copyright (C) 1999 John Wiley & Sons, Ltd.