Synopsis: Slow Down to Take a Better Spectrum

The resolution and sensitivity of mass spectrometers can be improved by laser-cooling the measured sample species.

Mass spectrometry—an analytical technique routinely found in physics, chemistry, and biology labs—is used to determine the distribution of masses in a molecular sample. Improvements in sensitivity and mass resolution of this ubiquitous technique depend on the ability to prepare samples whose constituents’ velocities and positions are not too spread out. This is often a challenge because most instruments manipulate the molecules by first ionizing them, which produces molecules with a large velocity spread. To narrow the momentum distribution, a cooling stage is required, typically involving a buffer gas at room temperature.

But the cooling ability of a buffer gas cannot be easily improved beyond current levels. Researchers in the laboratory of Eric Hudson at the University of California, Los Angeles (UCLA), have now demonstrated how laser cooling can replace buffer-gas cooling to improve the resolution and sensitivity of a conventional mass spectrometer by over an order of magnitude. To achieve this, the authors make use of a technique called “sympathetic cooling,” in which a laser ablates atoms from a target (either barium or ytterbium) and another laser cools a specific isotope of the target element. Through Coulomb interactions, these isotopes can, in turn, slow down and cool the atoms or molecules whose mass spectra have to be determined.

The UCLA team carried out their proof-of-principle experiments in a conventional time-of-flight mass spectrometer equipped with sympathetic cooling. They found that both the mass resolution and the sensitivity increase by more than an order of magnitude. Although the mass resolution achieved in this setup is far from the current state-of-the-art, the authors suggest that their method could benefit even the best mass spectrometers available.

This research is published in Physical Review Applied.

–David Voss


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Atomic and Molecular Physics

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