New substrates for polymer cationization with time-of-flight secondary ionmass spectrometry

Cationization of large polymers and their fragments on novel self-assembled monolayer substrates has been studied with time-of-flight secondary ion ma ss spectrometry (ToF-SIMS). Low (1 kDa) and high (400 kDa) molecular weight poly(ethylene oxide) (PEO) were spin-coated on metal ion substituted, carb oxylic terminated, self-assembled monolayers on gold. Both cationized fragm ents and additional whole molecular species were observed for the 1 kDa PEO , while for 400 kDa PEO, only chain fragments of up to 30 monomer units wer e detected. Fragmentation pattern dependence on polymer molecular weight an d the nature of the substrate is discussed. The intensity of the cationized fragments was found to depend on the metal ion used. Complementary experim ents carried out on methyl terminated self-assembled monolayers suggested t hat metal ions that are desorbed from the gold surface, and therefore not i n close proximity to the polymer, do not cationize polymers and their fragm ents. The substrates used in this work are simple to prepare, reproducible, and provide a model system for studies on the cationization of both polyme rs and proteins. Also, these ionically terminated self-assembled monolayer substrates open up new analytical possibilities for static SIMS.