34: What is collisionally activated dissociation? At what points in a mass spectrometer does it occur?

Collision-induced dissociation (CID), also known as collisionally activated dissociation (CAD), is a mass spectrometry technique to induce fragmentation of selected ions in the gas phase.

After the eluent is ionized by the electrospray, positive ions are attracted by the glass capillary, making its way to the detector.

Before it gets to the detector, however, it passes through the mass spectrometer. Right after passing through the glass capillary, before it goes into the skimmer cone, it undergoes collisionally activated dissociation.

Being accelerated by 60 V potential difference between the glass capillary and its metal coating, the positive ions collide with the N₂ molecules in the region between the glass capillary and the skimmer cone. The collision’s energy is enough for the ions to break into fragments. To control the degree of fragmentation, the skimmer cone voltage would be weakened.