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.
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.
Authors: Hui Ouyang; Carlos Larriba-Andaluz; Derek R Oberreit; Christopher J Hogan Journal: J Am Soc Mass Spectrom Date: 2013-09-12 Impact factor: 3.109
Authors: Ailin Li; Christopher R Conant; Xueyun Zheng; Kent J Bloodsworth; Daniel J Orton; Sandilya V B Garimella; Isaac K Attah; Gabe Nagy; Richard D Smith; Yehia M Ibrahim Journal: Anal Chem Date: 2020-11-02 Impact factor: 6.986