This cryogenic 2D linear ion trap mass spectrometer facilitates both the isolation of targeted ions and the recording of their infrared (IR) action spectra, which can aid in the identification of many unknowns, such as small molecule analytes. Mass spectrometry is an important bioanalytical technique used to explore complex biological systems on a molecular level. Commercially available mass spectrometers identify small molecules based on accurate mass measurement combined with fragmentation by collisional activation. However, researchers are limited to matching them only to analytes already contained in databases, automatically eliminating identification of unknown molecules. The detailed chemical information contained in the vibrational spectrum of a cryogenically cooled ion would, in principle, make IR ion spectroscopy a gold standard technique for molecular identification. Nonetheless, challenges, in terms of sensitivity and duty cycle, exist and need addressing before technique is deemed analytically useful. Researchers at the University of Florida have developed a cryogenic mass-selective 2D linear ion trap mass spectrometer that cools ions down to cryogenic temperatures, close to absolute 0, selects the ions of interest, ejects all other ions, and records IR spectra of the trapped ions to aid identification of even unknown analytes. Two-dimensional linear ion traps are widely regarded as the most sensitive mass spectrometers, since their ion injection efficiencies can reach close to 100 percent, and they can trap a large number of ions. The IR approach to this invention facilitates tagging multiple ions with different mass-to-charge ratios, enabling recording of the IR spectra of multiple ions in parallel, thereby increasing the duty cycle of the technique.
Cryogenic 2D linear ion trap to record and identify unknown molecules using IR mass spectroscopy
This cryogenic 2D linear ion trap mass spectrometer facilitates the mass manipulation of ions, tagging many ions with different mass-to-charge ratios in parallel. A gas pulse introduced into the trap via a pulsed valve assists trapping of externally injected ions, facilitates their cooling to cryogenic temperatures, and allows attachment of an inert gas “tag” (e.g. N2). The tagged ions then are mass selected and irradiated with a tunable IR light source, followed by a mass scan to detect the background-free photodissociation yield. Users can record the photodissociation behavior of a number of analytes in this way, provided that the masses of different analytes do not interfere. Plotting the photodissociation yield as a function of ifrared frequency provides the IR spectrum for each tagged ion. Since the tag is very weakly bound, absorption of a single IR photon detaches the tag, giving rise to sharply resolved IR spectra in a linear spectroscopy scheme, where the relative IR band intensities relate directly to absorption cross sections. The gathered IR information goes through an automated matching procedure that utilizes pattern-recognizing, machine-learning algorithms to identify unknown analytes, thereby providing the ions’ structural components with respect to their mass. The high trapping capacity and sensitive ion detection enable this cryogenic 2D linear ion trap to be a highly efficient mass analyzer for many levels of mass selection and fragmentation.
