Thin-layer chromatography--postsource-decay matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of small drug molecules

The structural analysis of small drug molecules by directly coupling thin-layer chromatography (TLC) with postsource-decay (PSD) matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is reported. The applicability of this technique is shown using two examples: the TLC-PSD MALDI analysis of two representatives of nonsteroidal antiinflammatory drugs (tenoxicam and piroxicam) and the analysis of the pharmaceutically active compound UK-137,457 and one of its related substances UK-124,912. The matrices alpha-cyano-4-hydroxycinnamic acid (alpha-CHCA) and graphite are used to investigate the effect of the precursor ion selection on the TLC-PSD MALDI spectra of the drug molecules studied. Although alpha-CHCA enhances the M+H]+ ion formation graphite produces in general only sodium adducts. Structural differentiation of tenoxicam and piroxicam is possible only by selecting the sodium adduct of both drug molecules as precursor ions. In the case of the TLC-PSD MALDI analysis of UK-137,457 and its related substance UK-124,912 at the 1% level, the PSD spectra obtained in alpha-CHCA by selecting the protonated adduct of the small molecules as precursor ions shows distinguishable dissociation patterns containing structurally significant information.