Analytical Chemistry
ARTICLE
the diagnostic fragment peak, while the Rel. Int. value did not
change much (Table 1).
ChemistryDepartmentandWarwickCentre for AnalyticalScience
(EPSRC funded EP/F034210/1) are gratefully acknowledged.
A direct comparison of the results acquired on different
instruments is not possible because of the difference in multiple
operating parameters, energetics of the reactions, and the mass
analyzers. When comparing spectra obtained using the same
instrument, the results suggest that supplemental activation gen-
erally leads to higher S/N ratios for diagnostic ions. The effect of
additional energy input on fragmentation depends on the peptide
sequence, particularly on the presence of basic residues and side-
chain interactions. An example is shown on the ETD data acquired
on an Orbitrap instrument with or without SA for the modified
Ang II peptide (Figure 5). Similar to the ETD results acquired
on an amaZon instrument mentioned earlier, the S/N ratio of
the diagnostic ion became 4 times greater when SA was applied
(Figure 5b).
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’ CONCLUSIONS
The N-terminal isoAsp residue was differentiated from Asp
using ECD, hotECD, and ETD. On the basis of the detection
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(isoAsp7), and [M + 2H À 60]+• (Asp1, Asp7) it was possible to
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S
Supporting Information. ECD spectra of chromato-
b
graphic peaks I, IVÀVII from the partially deamidated Aβ1À10
(N1N7) peptide mixture. Spectra for fractions II and III are not
shown because they consist of unrelated peptides. This material is
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’ AUTHOR INFORMATION
(28) Krokhin, O. V.; Antonovici, M.; Ens, W.; Wilkins, J. A.; Stand-
ing, K. G. Anal. Chem. 2006, 78, 6645–6650.
(29) Winter, D.; Pipkorn, R.; Lehmann, W. D. J. Sep. Sci. 2009,
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Corresponding Author
*Phone: +44 024 7615 1008. Fax: +44 7615 1009. E-mail: p.
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’ ACKNOWLEDGMENT
The authors acknowledge Eugene Moskovets and Alexander
Cherkassky for helpful discussions. This work was supported by
the NIH/NCRR-P41 RR10888, NIH/NIGMS-R01GM078293,
and NIH/NCRR-S10 RR025082 grants. The Warwick University
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dx.doi.org/10.1021/ac201223d |Anal. Chem. 2011, 83, 6675–6682