I know right! SMDH the original video was useless. This video rules.

Alejandra, Quadrupole acts as a filter, so only certain precursor ions, let’s say 500+-0.5 m/z, could pass, while other ions become unstable, hit the wall, turn into neutrals, and cannot move forward. Thus, only packets of 500+-0.5 m/z are proceeding for fragmentation. Also note that one MS1 scan is followed by 10 or more MS2 scans. During the MS1 full scan, the software determines top 10 most intense precursor ions at that point in time. In the subsequent 10 MS/MS scans, the software tells quadrupole to open for 500+-0.5 m/z, fragment that top 1 packet of ions by HCD, and measure fragments in the Orbitrap. Following that, it then tells quadrupole to open for the top 2 precursor, let’s say 600+-0.5 m/z, fragment that packet, and measure. After completion of all top 10, the next cycle of MS1-10 MS/MS starts.

@@andreidrabovich3921 There's still something I don't understand. I have had spectra measured in an Orbitrap, and I see that the software shows the fragments for a precursor ion of exact mass. How can one select a precursor ion of exact mass using a quadrupole analyzer? Thank you.

@@felipevasquez8393 Precursor ions (MS1) are indeed measured with Orbi, while quadrupole is nearly fully open. The fast quadrupole analyzer is then used to select the first narrow pack of MS1 ions (for example, 500+-0.5 m/z) for the subsequent fragmentation and measurement of MS2 fragments with Orbi. The quadrupole then goes for the second narrow pack of MS1 ions (for example, 600+-0.5m/z). And so on, to complete the Top20 cycle.

@@andreidrabovich3921 Oh, I see. Thank you for your response!