Applying a dynamic method to the measurement of ion mobility

Abstract

A dynamic method is applied to measure the mobility of gas-phase ions in the dual ion funnel interface of the electrospray source of a quadrupole orthogonal time-of-flight mass spectrometer. In a new operational mode, a potential barrier was formed in the second ion funnel of the mass spectrometer and then progressively increased. In this region, a flow of gas drags the ions into the mass spectrometer while the electric force applied by the potential barrier decelerates them. Ions with lower mobility can be carried by the gas flow more easily than those with high mobility. Thus, electrical forces can block the more mobile ions more easily. Hence, the electric barrier formed in the ion funnel permits only ions below a certain mobility threshold to enter the mass spectrometer. When the barrier voltage is increased, this threshold moves from high to low mobilities. Ions with mobilities above the threshold cannot enter the mass spectrometer, and their signal decreases to zero. Thus, in a barrier voltage scan, mass spectrometric signals of ions sequentially disappear. Differentiation of these decreasing ion signal curves produces peaks from which an ion mobility spectrum can be reconstructed. Blocking voltages, i.e., the positions of the peaks on the barrier voltage scale are directly related to the mobility of these ions. An internal calibration using ions with known mobility values helps determine the unknown ion mobilities and allows calculation of ionic cross sections. (J Am Soc Mass

High Resolution Trapped Ion Mobility Spectrometery of Peptides

“…The experimentally measured Ω values are in agreement (≤2% error) with previous drift tube IMS measurements (Ω = 332 and 340 Å 2 ). 24 However, not all peptide ions display expansive conformational heterogeneity in the gas phase. For example, the TIMS distribution of [AT + 3H] 3+ shown in Figure 1c contains only a single feature at Ω = 480 Å 2 .…”

“…Using this calibration procedure, the voltage axis was converted to K 0 (and subsequently Ω) using values for [BK + 3H] 3+ previously measured by drift tube IMS in nitrogen gas. 24 All resolving power values reported herein were determined from peak fitting features in the TIMS distributions using the expression…”

The pH Dependent Cu(II) and Zn(II) Binding Behavior of an Analog Methanobactin Peptide

“…A calibration method was used to determine the collision cross-sections of amb and amb complexes using previously published collision cross-section values of the polymer a,w,-dicarboxy-terminated polystyrene 23 for negative ion analysis and angiotensin I, angiotensin II, tetraglycine and pentaglycine for positive ion analysis. [24][25][26] Cross-sections were extracted from the drift time measurements using the method previously described 27 which uses the following relationships.…”

Ion Mobility-Mass Spectrometry with a Radial Opposed Migration Ion and Aerosol Classifier (ROMIAC)

“…# Indicates peak was also used as a mobility calibrant. References: b [9] c [20] d [8]. Labeled peaks are product ions specific to each isomer used for identification during separation by the ROMIAC; other peaks common to both isomers are not labeled for clarity.…”