World record in mass spectrometry

Scientists at ETH Zurich have set a world record in mass spectrometry by observing the largest ever mass-to-charge ratio of over 1 Mio Dalton (MDa) using a special mass spectrometer. The researchers in the team of Prof. Renato Zenobi had to overcome two obstacles, the intact vaporization and ionization of the sample, as well as the detection of the very large ions. Modern soft ionization methods allow giant molecules such as proteins or DNA to be brought into the gas phase. The ETH researchers employed desorption and ionization using a pulsed UV laser.

For mass separation, they used a time-of-flight mass spectrometer, which separates ions of different mass-to-charge ratio by their drift time through an evacuated fligh tube. The largest ions take the longest time, and are difficult or impossible to detect with conventional detectors, due to their small drift velocity. One possibility would be to produce multiply charged ions and detect them in a more accessible mass-to-charge ratio range. The ETH researchers chose a more direct and elegant way, by carrying out their measurements on an instrument developed by Comet AG of Switzerland equipped with a superconducting tunnel junction detector. In this way, simple and directly interpretable mass spectra were obtained from immunoglobuline M (ca. 1 MDa) and from von Willebrand factor, a group of proteins that play an important role in coagulation of blood (signals at 0.5, 1, 1.5 and 2 MDa).