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New Ion Trap Ensures Utmost Resolving Power in Ultra-Strong Magnetic Fields

Mass spectrometers are extensively used for the analysis of highly complex biological and chemical mixtures. Scientists from Skoltech have now created a novel mass spectrometer that measures masses with higher accuracy (FT ICR) by using rotation frequencies of ionized molecules in strong magnetic fields.

Analytical Chemistry magazine. Image Credit: Skolkovo Institute of Science and Technology.

The researchers have developed an ion trap that enables the maximum possible resolving power in ultra-strong magnetic fields. The study was reported recently in the Analytical Chemistry journal.

The team shaped the ion trap in the form of a cylinder composed of electrodes, where electric and magnetic fields are produced from within. The accurate masses of the ions of a sample to be tested can be measured by using their rotation frequencies.

A crucial aspect is that the electrodes must generate a harmonized field of a specific shape such that the ions rotate predictably. A trap with such a field is termed as a Dynamically Harmonized Cell (DHC).

Evgeny Nikolaev, a Professor at the Skoltech Center for Computational and Data-Intensive Science and Engineering (CDISE), invented the DHC in 2011. In reality, the field of the cell is highly complex in nature and not harmonized, but for rapidly rotating ions in the magnetic field, it still seems harmonized because of the averaging effect, and thus the cell’s name.

The DHC has been the most ideal trap to date with respect to spectrum measurement accuracy, and thus has been used extensively in research and commercial mass spectrometers that demand high accuracy and combined with the strongest magnetic field mass spectrometer at the National High Magnetic Field Laboratory in Tallahassee, FL.

The cost of super-strong magnets could reach tens of millions of dollars. Although the accuracy of mass measurement is expected to increase linearly with the strength of the magnetic field, it does not act so: the pattern is non-linear in reality, and the increase in accuracy is considerably slower than anticipated.

The researchers presumed that non-linearity emerges since the vacuum level in the cell is not adequate, irrespective of how advanced the pumps are. They created a trap with both ends open for the simple evacuation of residual gases and called it the “Zig-Zag Cell.”

Right now, our lab is manufacturing the new cell which we will use for experiments to check whether our assumptions and theoretical predictions are correct, and if they are, the trap will put the linear relationship between mass spectrum measurement accuracy and magnetic field strength back in place, thus ensuring higher accuracy at very high values of magnetic field strength.

Anton Lioznov, PhD Student, Skolkovo Institute of Science and Technology

The fact that the accuracy increases with an increase in magnetic field strength means that the trap will potentially help create the most accurate mass spectrometer of all,” added Lioznov.

Professor Evgeny Nikolaev, who is the lead author of the study, explained that mass spectrometers with a new kind of cell will enable higher accuracy for complex mixtures, such as oil, and biological samples, where even current mass spectrometers of this kind with the DHC can detect nearly 400,000 compounds.

Journal Reference:

Nikolaev, E & Lioznov, A (2021) How to Increase Further the Resolving Power of the Ultrahigh Magnetic Field FT ICR Instruments? The New Concept of the FT ICR Cell–the Open Dynamically Harmonized Cell as a Part of the Vacuum System Wall. Analytical Chemistry.

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