H.C.
Michelle Byrd and Sheng Lin-Gibson
Matrix-assisted
laser desorption/ionization time of flight mass spectrometry (MALDI-TOF
MS) generally uses metal salts to cationize synthetic polymers, such as
polystyrene. However, reduced analyte signal often results from complications
during the metal ionization processes in the gas phase including competition
between the analyte and matrix for cationization, self-clustering of the
metal salts, and clustering of metal salts with matrix. One approach to
increase the polymer ion signal is to apply more aggressive laser power;
however, this may result in fragmentation of the polymer leading to molecular
mass distribution (MMD) unrepresentative of the true distribution. Our
laboratory has developed a covalent cationization method in which a phosphonium
or an ammonium salt is covalently attached to one of the chain ends. This
will assure singly charged analytes and the competition associated with
metal ionization will be eliminated. Better spectra can be generated since
the undesirable background noise can also be reduced. Furthermore, polymers,
such as polyolefins, that cannot be cationized using traditional metal
approach can be cationized using covalent cationization to produce successful
MALDI spectra.
We
demonstrate the covalent cationization method used to characterize polyolefins
and polystyrenes. Furthermore, a comparison between covalent cationization
method and traditional metal cationization for polybutadiene and polystyrene
is made to gain a better understanding of the mechanisms that govern the
desorption/ionization processes.