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Experiment and theory combine to produce a practical negative ion calibration set for collision cross‐section determinations by travelling‐wave ion‐mobility mass spectrometry
Author(s) -
Hamilton Jenna V.,
Renaud Justin B.,
Mayer Paul M.
Publication year - 2012
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6266
Subject(s) - chemistry , ion , mass spectrometry , ion mobility spectrometry , analytical chemistry (journal) , molecular dynamics , range (aeronautics) , calibration curve , calibration , atomic physics , computational chemistry , chromatography , physics , materials science , organic chemistry , detection limit , quantum mechanics , composite material
RATIONALE There are relatively few cross‐section measurements for negatively charged ions. Available calibrants provide sufficient cross‐section coverage for the 390 Å 2 to 641 Å 2 and 1174 Å 2 to 3395 Å 2 ranges. This is not particularly well suited for determining the collision cross‐sections of smaller ions, such as small peptides. METHODS Molecular mechanics/molecular dynamics (MM/MD) simulations, coupled with simulated annealing, were used to find the low‐energy molecular conformations of polystyrene (PS) oligomers of length 3–9 (singly deprotonated) and 5–13 (doubly deprotonated). The trajectory method in MOBCAL was employed to derive their respective collision cross‐sections, Ω. A calibration plot relating corrected Ω values to drift times in a Waters Synapt G2 mass spectrometer was used to predict the Ω values for the −2 to −6 charge states of dT 10 DNA. RESULTS The in silico design of a reliable negative ion calibration set for ion mobility spectrometry successfully resulted in the use of α,ω‐carboxy‐terminated PS oligomers to determine the collision cross‐sections of negatively charged ions in the range 132–388 Å 2 . All charge states of dT 10 DNA were predicted to within 3% of the referenced values for these ions. CONCLUSIONS α,ω‐Carboxy‐terminated PS oligomers were found to be an excellent choice to calibrate ion mobility spectrometers to obtain cross‐sections for moderately sized ions. Oligomers with fewer, or weaker, interactions among the internal side chains (like poly(ethylene glycol) oligomers) tend to have a wide range of low‐energy molecular conformations resulting in large standard deviations in their theoretically predicted collision cross‐sections. Copyright © 2012 John Wiley & Sons, Ltd.