Optimization of sample deposition for plasma‐desorption mass spectrometry of peptidoglycan monomers

Three selected peptidogycan monomers isolated from muramidase‐digested Escherichia coli‐sacculus were characterized by positive‐ and negative‐ion 252 Cf plasma‐desorption mass spectrometry (PDMS). Dut to the high affinity of sugar moieties towards alkali cations multiple alkali attachment in PDMS can be a problem. Electrospray, nitrocellulose, nitrocellulose sandwich anthracene‐9‐carboxylic acid 3‐(3‐Pyridyl)acrylic acid deposition techniques were evaluated for the degree of (de)proltonation and cationization of the molecular species by sodium and/or potassium. Electrosprayed and nitrocellulose‐deposited samples mainly exhibited intense cationized molecular ion species whereas anthracene‐9‐caboxylic acid‐deposition sample show a similar pattern but with much lower intensity. An extension of the nitrocellulose deposition technique, the so‐called nitrocellulose sandwich sample preparation reduced the aallkali attachment problem for these hydrophilic compounds. Application of the small molecule matrix 3‐(3‐pyridyl)acrylic acid yielded mass spectra with abundant [M+H] + and [MH] − ions in the positive‐ and in the negative‐ion modes, respectively.