Spectrométrie de masse à résonance cyclonique ionique

La spectrométrie de masse à résonance cyclotronique ionique (FT-ICR-MS) est un instrument possédant un haut pouvoir de résolution et une bonne exactitude sur la masse très important pour l’analyse des protéines. C’est une technique basée sur le piégeage et l’excitation des ions dans une cellule ICR (résonance cyclotronique des ions) sous l’action d’un champ électromagnétique. Le spectre de masse est obtenu via la transformée de Fourier qui convertit le signal temporel acquis en spectre de fréquence proportionnel à la masse. FT-ICR-MS a été développée pour la première fois par Comisarow et Marshall en 1974, et l’utilisation du principe d’ICR dans un spectre de masse par Sommer. Cette technique d’analyse est très appliquée dans le domaine pharmaceutique, biologique par exemple pour l’identification des protéines. Mouvement cyclotronique des ions dans la cellule ICR Les ions sont piégés dans la cellule ICR par un champ magnétique. Un ion, sous l’action d’un

Fourier transform mass spectrometry at the uncertainty principle limit for improved qualitative and quantitative molecular analyses

Anton Kozhinov

Nowadays, among the instrumentation park of mass spectrometry, Fourier transform mass spectrometers (FTMS), including ion cyclotron resonance (ICR) and Orbitrap FTMS, provide the highest analytical performance for accurate measurements and mass resolution. Nevertheless, molecular analysis in currently challenging research areas, such as life and environmental sciences, necessitates further improvement of these analytical characteristics. In recent decades, a regular approach to address the problem behind the analytical performance was using increased electromagnetic fields. However, per a given increase of their magnitudes, that approach is currently requiring more and more resources, hence demonstrating its limited feasibility for tomorrow. Therefore, only a qualitative breakthrough in the underlying methodology may then lead to the next series of developments enabling improved molecular analysis. The present research is dedicated to the fundamental question behind the analytical performance in FTMS. Specifically, this thesis represents an interdisciplinary study aimed at improved molecular analysis in FTMS-based applications, achieved via better comprehension of the uncertainty principle in FTMS, viz. its dependence on the measurement scheme, including ion traps, signal processing, and data analysis, as well as its influence on achievable analytical characteristics in FTMS. To start, the uncertainty principle for measurements in FTMS has been investigated, asserting a limit to the precision with which complementary physical quantities in FTMS, e.g. detection period and scale of frequency details to resolve, can be measured. Specifically, two corollaries of the uncertainty principle are considered, viz. resolution performance and performance for accurate measurements in FTMS. Importantly, the uncertainty principle shows dependence on the particular measurement scheme employed. For instance, signal detection, signal processing, and data analysis of the standard measurement scheme impose their own restrictions to the resulting uncertainty principle, thus leading to the current limitations. However, the ultimate limitations in the analytical characteristics in question are defined by the uncertainty principle limit due to physics of ion motion in the mass analyzer. Hence, with corresponding developments in data analysis methods, methods for signal processing, and designs of ion traps, novel measurement schemes have been implemented, where the quantitative form of the uncertainty principle is modified towards the ultimate limit. Finally, the implemented solutions have been evaluated in the context of FTMS-based analysis of crude oil fractions, protein identification and characterization, quantitative proteomics, and analysis of isotopic fine structures of peptides. To conclude, the achieved success of this work should considerably contribute to the currently challenging analytical applications of FTMS.

EPFL2015

High-Resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry with Increased Throughput for Biomolecular Analysis

Anton Kozhinov, Konstantin Nagornov, Yury Tsybin

A multielectrode ion cyclotron resonance (ICR) cell, herein referred to as the 4X cell, for signal detection at the quadruple frequency multiple was implemented and characterized on a commercial 10 T Fourier transform ICR mass spectrometer (FT-ICR MS). Notably, with the 4X cell operating at a 10 T magnetic field we achieved a 4-fold increase in MS acquisition rate per unit of resolving power for signal detection periods typically employed in FTMS, viz., shorter than 6 s. Effectively, the obtained resolution performance represents the limit of the standard measurement principle with dipolar signal detection and FT signal processing at an equivalent magnetic field of 40 T. In other words, the achieved resolving powers are 4 times higher than those provided by 10 T FT-ICR MS with a standard ICR cell. For example, resolving powers of 170 000 and 70 000 were obtained in magnitude-mode Fourier spectra of 768 and 192 ms apodized transient signals acquired for a singly charged fluorinated phosphazine (m/z 1422) and a 19-fold charged myoglobin (MW 16.9 kDa), respectively. In peptide analysis, the baseline-resolved isotopic fine structures were obtained with as short as 768 ms transients. In intact protein analysis, the average resolving power of 340 000 across the baseline-resolved 13C isotopic pattern of multiply charged ions of bovine serum albumin was obtained with 1.5 s transients. The dynamic range and the mass measurement accuracy of the 4X cell were found to be comparable to the ones obtained for the standard ICR cell on the same mass spectrometer. Overall, the reported results validate the advantages of signal detection at frequency multiples for increased throughput in FT-ICR MS, essential for numerous applications with time constraints, including proteomics.

Amer Chemical Soc2014

Device and Method for Ion Cyclotron Resonance Mass Spectrometry

Anton Kozhinov, Konstantin Nagornov, Yury Tsybin

The present invention relates to a method and device for measuring m/z ratios of ions in ion cyclotron resonance (ICR) mass spectrometry. The described ion traps for ICR mass spectrometry are distinct from the previous configurations by having one or many narrow aperture (flat) detection electrodes that could be moved radially inward the ICR trap, for example on the plane where radiofrequency excitation potential is minimal, closer to the post-excitation ion trajectories.

2017

Fourier transform mass spectrometry at the uncertainty principle limit for improved qualitative and quantitative molecular analyses

Anton Kozhinov

EPFL2015