CH908, Problem set 7, Tandem Mass Spectrometry
1. In a quadrupole ion trap, a m/z 660 ion is fragmented, with the
instrument running at a qz of 0.3. What is the low mass cut off for the
MS/MS data?
LMCO = qz* precursor mass, so (0.3*660) = 198 Da
2. In the pharmaceutical industry, triple quadrupole mass
spectrometers are used extensively for quality control and
measurement of pharmacokinetics. The most common experiment
used is called “Selected Reaction Monitoring”. Explain this
experiment and why it’s useful for the pharmaceutical industry.
One ion (one m/z region) is isolated (usually using a quadrupole) from
a sample stream (usually an LC or GC effluent) and fragmented. The
intensity of one fragment ion peak is then plotted over time to yield a
selected ion chromatogram.
3. For peptides, what kind of ion series is most dominant for the
following fragmentation methods: a) CAD, b) ECD/ETD, c) UVPD, d)
IRMPD. Define these acronyms.
a) collisionally activated dissociation - same as collision induced
dissociation - generates the b/y ion series.
b) electron capture dissociation or electron transfer dissociation generates c/z• ion series from peptides.
c) ultraviolet photodissociation. Generates the a/x ion series, and
some b/y ions.
d) infrared multiphoton dissociation. Generates b/y ions, just like
CAD.
4. In ECD and ETD, the bond n-terminal to proline is not cleaved.
Why?
The n-cα that is usually cleaved is within the ring, so it would require
two bond cleavages to observe a mass change.