Ionization source for mass spectrometry needs no external power supply

Ionization in mass spectrometry usually requires an external power supply. Thalappil Pradeep of the Indian Institute of Technology Madras and coworkers have developed a new ionization method that doesn’t require energy input to generate ions. In the new method, called streaming ionization, the researchers flow an organic alcohol—methanol works best—over filter paper coated with layers of 2D molybdenum disulfide (ACS Nano 2021, DOI: 10.1021/acsnano.0c09985). When an alcohol flows over the surface, the device generates a detectable current, which is produced by the dissociation of solvent molecules and the movement of anions. Analyte molecules get ionized in the flow. To make an ionization source, the researchers cut the MoS₂-coated paper into a triangle so that the tip could generate charged microdroplets containing the analyte. The researchers used the coated paper to ionize molecules such as fullerenes, iodine, and small organic molecules and biomolecules before detection by mass spectrometry. They detected uric acid in a 5 µL raw urine sample and less than 3% ethanol in simulated breath. Eliminating the need for a power supply for the ion source simplifies the instrument design, which could lead to applications in portable mass spec, says Facundo M. Fernandez, a mass spectrometrist at the Georgia Institute of Technology, who has designed other low-power ion sources.