Based On The Measurement And Analysis Of Molecular Collision Cross Section Within FTICR-Cells

With the development of proteomics, it is important to know both its composition and structure. In this paper, a mass spectrometric based approach has been proposed and applied to demonstrate that collision cross sections and high-resolution mass spectra of biomolecule ions may be obtained simultaneously by Fourier transform ion cyclotron resonance mass spectrometry. This approach maintains the potentially high resolution of Fourier transform ion cyclotron resonance mass spectrometry(FTICR MS), and enables collision cross section(CCS) measurements for high-mass biomolecules. In the present approach, we conduct the experiment in a 9.4 Telsa FTICR-cells unit with a pulsed leak valve controlled N2 buffer gas pressure in the ICR cell. Image current signal collected from the ICR cell were fed into a data processing system, in which frequency, phase, decay profile and CCS of selected ion(or mass peak) were extracted. A multi-step low pass filtering(finite impulse response(FIR) filter with decreased bandwidth) and down-sampling process(13 rounds in this case) were then carried out to carefully remove other mass peaks and noises inside the transient signal. Two major factors affect accuracy: electrical noise and chemical noise. Over 8 million data points were handled.This approach can measure the structure and function of biological molecules. To achieve that purpose, cell pressure,total ion number, signal transient length, number of data point,cell diameter, and ion excitation radius were carefully controlled:pressure in the ultrahigh vacuum region of the instrument was maintained between 10-10 and 5.9 × 10-9 Torr;total number of ions in the cell was controlled by external accumulation(40 ms) in an octopole ion trap; transient signal length was set at 6.115 s(8388608 data points); inner diameter(ID) of the ICR cell is 94 mm; ions were excited to 40% of the cell radius for image current detection.With the current instrument setup, a ubiquitin ion(10+ charge state, m/z ～857)has a kinetic energy of ～17.5 keV after excitation, and the maximum exchange energy available during a single ion-neutral collision is ～114 eV. Therefore, a single collision should dephase a ubiquitin ion from the spatially coherent ion packet. Thus, an energetic hard-sphere ion-neutral collision model was used to calculate CCSs from the decay factors.Therefore,a fast fourier transform method based on time signal can be used to measure the structure of biological molecules with maintaining high resolution mass spectrometry.