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A protocol for the preparation of polymeric samples for time-of-flight matrix-assisted laser desorption ionization mass spectrometry (TOF-MALDI-MS) analysis was developed. Dithranol was identified as a good matrix for polystyrene (PS), and the addition of silver for cationization of molecules was determined to be necessary. Based on this preparative method, low molecular weight samples of other polymers [polyisoprene, polybutadiene, poly(ethylene oxide), poly(methyl methacrylate), and polydimethylsiloxane] were analyzed with molecular weights up to 49 ku. The effects of laser intensity were determined to influence the molecular weight distribution of intact oligomers, most significantly for low molecular weight polymers. Linear and reflectron modes of analysis were evaluated; better signal intensity and resolution were obtained in the reflectron mode. The TOF-MALDI-MS measurements are compared with time-of-flight secondary ion mass spectrometry (TOF-SIMS) and gel permeation chromatography (GPC) for the same polymers. The M n values calculated by TOF-MALDI-MS consistently are higher than values calculated by TOF-SIMS for all classes of polymers with molecular weights up to 8 ku. The molecular weights of the PS calculated from TOF-MALDI-MS are in good agreement with GPC (±10%). The composition of the terminal group on a polymer chain may affect the ion yields. The ion yields of intact oligomers were evaluated as a function of end group composition for both TOF-MALDI-MS and TOF-SIMS. The slight disparity of results between TOF-SIMS and TOF-MALDI-MS for the perfluoroalkyl-terminated PS suggests that the oligomers are desorbed preferentially from the surface in the TOF-SIMS analysis, rather than having an increased ionization probability.

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We report here molecular characterization of a new method derived from reactive microcontact printings microstamping on an activated polymer surface (MAPS)swhich enables biological ligands and proteins to be patterned on a polymer surface with a spatial resolution of at least 5 µm and good reproducibility. MAPS is a multistep procedure: first, the surface of a polymer is modified, in one or more steps, to introduce a reactive group of interest. In a subsequent step, an elastomeric stamp, inked with a biological ligand containing a complementary terminal reactive group, is brought into contact with the activated surface of the polymer. This results in spatially resolved transfer and coupling of the biological ligand to the reactive surface of the polymer. We used MAPS to pattern biotin on carboxylic acid derivatized poly-(ethylene terephthalate) (PET), and subsequently with streptavidin, mediated by the high affinity streptavidin-biotin interaction. X-ray photoelectron spectroscopy of biotin-derivatized PET showed that approximately one in five PET repeat units in the top 50-100 Å were functionalized with biotin. Timeof-flight secondary ion mass spectrometry (TOF-SIMS) suggested an increased concentration of PET oligomers in the top 10 Å due to chain scission during modification and clearly identified the derivatization of PET with biotin. TOF-SIMS imaging mapped biotin and streptavidin to the stamped regions. TOF-SIMS also imaged the spatial distribution of residual reagents from the multistep derivatization in MAPS, such as pentafluorophenol, Tween 20 surfactant, as well as poly(dimethylsiloxane) (PDMS), which was transferred from the elastomeric PDMS stamp to the surface during MAPS.