 MALDI
mass spectra of poly(styrene) cationized by Ag+ and Na+
(M+PSn) are shown at right. Both metal cations yield similar
molecular-weight distributions, indicating that unimolecular loss of the
metal cation is not a significant problem for either metal or their M+-PS
binding energies are comparable enough that loss of metal cation is a similar
problem for both metals.
Arrival time distributions (ATDs) for the PS 3-mer,
5-mer, and 7-mer cationized by Li+, Na+,
Cu+, and Ag+ obtained at a drift cell temperature
of 300 K are shown below. Single peaks are present for all M+PSn
oligomers at all temperatures (100 K - 500 K) suggesting that the PS oligomers
have single conformations. The average arrival time increases with n,
consistent with an increase in size and cross-section.
Experimental collision cross-sections of M+PSn (at 300
K), obtained from a series of ATDs measured at different drift voltages,
are given in the table at left. The cross-sections for each n-mer
are similar for all 4 metal cations, suggesting that the conformations of
M+PSn may also be similar for all 4 metal cations. There
is a slightly larger difference in cross-section for the smallest PS oligomers.
The cross-sections for the Ag+ and Na+ cationized
3-mers and 4-mers are ~3% larger than the corresponding Li+
and Cu+ cationized species. For the 5-mer to 7-mer,
the cross-sections fall within 2% of each other (within experimental error).
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