Answer 9.5

a) What advantages do triple quadrupole mass spectrometers offer in addition to single quadrupole instruments?

In triple quadrupole instruments (QqQ), Q1 and Q3 are operated independently as MS1 and MS2, respectively, making MS/MS a straightforward matter.

b) Often, the “second quadrupole” of a triple quadrupole instrument is not a quadrupole. What is used instead and why?

RF-only quadrupoles were used in the first-generation triple quadrupole instruments to serve as ion-guiding collision cells – hence the name. RF-only multipoles of higher order, i.e., hexapoles (h) or octopoles (o) have stronger ion-guiding capabilities (deeper potential wells). Modern triple quadrupole instruments are therefore built QhQ or QoQ.

c) Enumerate three tandem MS modes of triple quadrupole instruments.

  1. Product ion scan
  2. Precursor ion scan
  3. Constant neutral loss scan

d) The three tandem MS modes of the triple quadrupole instrument call for different settings to achieve them. Which part of the instrument is set to SCAN, SELECT, TRANSMIT?

Along the sequence Q q (h, o) Q we have to operate the building blocks as follows to realize either of the three tandem MS modes.

Product ion scan:

Precursor ion scan:

Constant neutral loss scan: