Ultraviolet laser desorption ionisation mass spectrometry of selected calixarenes with and without matrix assistance

Ultraviolet (UV) matrix-assisted laser desorption/ionisation (MALDI) and laser desorption/ionisation (LDI) mass spectrometry have been applied to study the macrocyclic, basket-like compound class of calixarenes for rapid characterisation, Three different types of cyclic oligomeric alkyl phenols-underivatised calixarenes and calixarenes carrying one or several acyl moieties as additional functional groups, as well as so-called resorcinarenes-have been investigated, It is shown that relative molecular mass determination of nitrogen-free calixarenes Is possible by detecting alkali adduct ions in the positive-ion mode and sometimes deprotonated molecular ions in the negative-ion mode by both MALDI and LDI, Best results with the MALDI technique have been obtained with the matrices alpha-cyano-4-hydroxy-cinnamic acid and 3-hydroxy picolinic acid, Depending on the applied laser energy, fragmentation can be induced to some degree in MALDI as well as LDI, Since positive-ion MALDI mass spectrometry gave mainly sodiated molecular ions for the selected calixarenes, post source decay (PSD) experiments were carried out applying a coaxial curved-field reflectron in order to generate fragment ions, The positive-ion PSD spectra contained diagnostic fragment ions, which enabled, to some extent, the kind and number of ester or ether groups on the hydrophilic rim of the bowl-shaped macrocyclic compound to be established unambiguously.