Cryogenic Electrospray Ionization MS With Infrared Detection: Highlights From ASMS 2018

Cryogenic electrospray ionization/mass spectrometry (CEI/MS) uses ion mobility sections in the ion optics for vacuum-induced evaporative cooling of solvated ions. This can dramatically reduce the temperature of the ion. Yes, desolvation can change the structure of ions, but the time is short. Once the cooling starts, the available energy for fragmentation or rearrangement is low.

However, mass spectrometry is often blind to isomers and to small differences in structure, such as anomers of carbohydrates. A poster by Valeriu Scutelnic and Thomas Rizzo of Ecole Polytechnique in Lausanne, Switzerland, describes the addition of an infrared spectrometer segment to a CEI/MS to obtain IR spectra associated with 16O and 18O in proteins, and conformers of carbohydrates (Scutelnic, V. and Rizzo, T.R. “Cryogenic Ion Spectroscopy for Identification of Monosaccharide Anomers,” Poster WP287, ASMS 2018). This information might be useful in the study of similarity of glycoforms of biosimilars.

Since infrared spectroscopy provides information that is often orthogonal to MS, the authors inserted a novel dual-wavelength IR spectrometer in the ion optics ahead of the mass analyzer. The spectrometer consists of an octupole ion trap to retain the analyte. The pump beam illuminates the ion trap from one end, while the probe light enters the other end.

The authors focused on the O–H segment of the IR spectrum between 3200 and 3700 cm-1. They used a tunable probe laser to focus on particular anomer-specific wavelengths to locate signature hydroxyls in the spectrum of a mixture of three chain forms.

Another study showed that the substitution of 18O for natural 16O produced a 12 cm-1 shift in the absorbance spectrum. The authors anticipate that this information will be useful in estimating conformational heterogeneity.

Robert L. Stevenson, Ph.D., is Editor Emeritus, American Laboratory/Labcompare; e-mail: [email protected]

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