Effect of Traveling Waveform Profiles on Collision Cross Section Measurements in Structures for Lossless Ion Manipulations

Abstract

We evaluated the effect of four different waveform profiles (Square, Sine, Triangle, and asymmetric Sawtooth) on the accuracy of collision cross section (CCS) measurements using traveling wave ion mobility spectrometry (TWIMS) separations in structures for lossless ion manipulations (SLIM). The effects of the waveform profiles on the accuracy of the CCS measurements were evaluated for four classes of compounds (lipids, peptides, steroids, and nucleosides) at different TW speeds (126-206 m/s) and amplitudes (15-89 V). For the lipids and peptides, the TWIMS-based CCS (^TWCCS) deviations from the corresponding drift-tube-based CCS (^DTCCS) measurements were significantly lower in experiments conducted using the Sawtooth waveform compared to the square waveform. This observation can be rationalized by the lower maximum electric field experienced by ions with a Sawtooth waveform, as compared to the other waveforms, resulting in a lower probability for significant ion heating. We also observed that given approximately comparable resolution for all four waveforms, the Sawtooth waveform resulted in lower ^TWCCS error and a better agreement with ^DTCCS values than the Square waveform. In addition, for the steroids and nucleosides, an opposite ^TWCCS trend was observed, with higher errors with the Sawtooth waveform and lower with the Square waveform, suggesting that these molecules tend to become slightly more compact under ion heating conditions. Under optimum conditions, all ^TWCCS measurements on the SLIM platform were within 0.5% of those measured in the drift tube ion mobility spectrometry.

Figure 1.

Schematic diagram of SLIM-TWIMS-MS platform utilized in this work.

Figure 2.

The shapes of the Square, Sine, Triangle, and Sawtooth traveling waveform profiles applied to TW electrode arrays.The waveforms applied to each 8-electrode set are sequentially shifted by 45 degrees between each electrode to create the TWs (see text).

Figure 3.

The ^TWCCS errors for a mixture of Avanti Lipid standard at a TW speed 206 m/s and different TW amplitudes for (A) Sawtooth, (B) Triangle (TRI), (C) Sine, and (D) Square waveforms.

Figure 4.

(A) Histograms of the electric fields experienced by ions using different waveform profiles extracted from ion trajectory simulations at a TW speed of 206 m/s and 40 Vp-p amplitude and for PC14:1 (m/z 674.47). (B) The calculated rise in ion temperature due to motion in the TW. The shaded area represents that for typical fields in DTIMS (see text).

Figure 5.

CCS errors for a 9-peptide mixture at a TW speed of 206 m/s and different TW amplitudes for (A) Sawtooth, (B) Triangle (TRI), (C) Sine, and (D) Square waveforms.

Figure 6.

(A) Arrival time distribution and (B) CCS error plot of Kemptide (+2), Angiotensin1 (+3), Angiotensin2 (+2), and Melittin (+4) from 9-peptide mixture at a TW speed of 166 m/s and amplitudes of 35 V, 45 V, 50 V and 65 V for Square, Sine, Triangle, and Sawtooth waveform profiles, respectively.

Figure 7.

Histograms of the electric fields experienced by ions extracted from ion trajectory simulations at a TW speed of 166 m/s for m/z 432 (Angiotensin1 (3+)). Field distributions for each waveform were chosen based on wave amplitudes exhibiting an approximate resolution among all four waveforms.

Figure 8.

CCS errors for a set of Steroids at a TW speed 206 m/s at different TW amplitudes for the (A) Sawtooth, (B) Triangle (TRI), (C) Sine, and (D) Square waveforms.