Mass Selection in Mass Spectrometry - (Feb/19/2009 )

Hello all,

I am looking at isolating a particular m/z protein in a mixture of protein for collision induced dissociation. What are some methods that are used to mass select for a particular protein?

Thanks,

Hey

We setup a threshold here and everything above a particular m/z is picked up for MS/MS analysis. If you have prior knowledge of the protein sequence, you can goto expasy tools or any other online database and theoretically digest yr protein and pick only these peaks for MS/MS analysis.

Hope it helps.

TC

wildcat on Feb 19 2009, 11:31 PM said:

How is the protein selected for? Is it by passing current through a quadropole, and everything below a certain threshold is absorbed so a larger complex can be used is MS/MS. I am trying to understand how just one is selected.

Thanks,

Oh thats electronics.

A quadrupole has 4 rods, where the polarity of two opposite rods keeps changing, this leads to a circular motion of the ions. A voltage at the far end leads to translational motion. When you tell the machine to choose a particular ion, it adjusts the voltages on the rods in a way that only ions in a particular window (includes the ion u choose) oscillates within the rods and other ion either collide with the rods or are thrown out. Its a very smart way of doing it.

Hope i was able to explain it or else tell me and would write in details.

best
TC