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polynomial filters are useful if no other option, such as ensemble averaging, exists but should be applied with care and will not generally perform as well as symmetric polynomial filters.
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(9) Beckwlth, P. M.; Crouch, S. R. Anal. Chem. 1972, 4 4 , 221-227.
Peter D. Wentzell Thomas P. Doherty S. R. Crouch* Department of Chemistry Michigan State University East Lansing, Michigan 48824 RECEIVED for review July 29, 1986. Accepted September 23, 1986. The authors gratefully acknowledge the financial support of the National Science Foundation through NSF Grant No. CHE 8320620 and the Natural Sciences and Engineering Research Council of Canada through an NSERC Graduate Fellowship (P.D.W.).
Polymer Investigations with the Laser Microprobe Sir: The laser microprobe is gaining a place in organic microspot analysis. It has been used with good results where it has been necessary to identify low molecular weight substances with high spatial resolution ( I , 2). In contrast, the investigation of polymers by this method is just beginning. The reason for this is that too few systematic investigations of the fragmentation behavior of polymers under laser bombardment have been undertaken. Most of the published investigations have been restricted to comparing spectra by the fingerprint method or have merely attempted to interpret the spectra in the mass range mle 400. Sometimes, we found that the mass differences corresponded to the monomer unit. The effects were not reproducible, however. It could be that the investigated polymers contained a certain amount of oligomers in the mass range concerned. This was undoubtedly the case with the aforementioned polyamide 6 sample. A methanol extract was prepared and
washed with water to remove most of the lactam and the dimer and to enrich the higher oligomers. The residual white powder constituted about 0.05% of the original material. The molecular weight distribution as determined by HPLC is given in Figure 1. The laser microprobe spectrum (Figure 2) shows reproducibly multiples of the monomer unit (up to 7-fold) cationized with Na. The intensities even reflect approximately the quantities from the molecular weight distribution. We therefore started to investigate spectra of other oligomers. In each case it was found that two types of ions are formed: (a) fragment ions of mle
