Tuesday, August 4, 2015
Told you!!! When it comes to targeted quan, a Q Exactive can hang with the QQQs!
I catch some flak once in a while for this assertion that I will now restate: Depending on what you want to quantify, the Q Exactive (family of instruments, so...also the Fusion and Lumos) can be as sensitive, if not more, than any other mass spec on earth. Don't quote me on this, but I think I could go with more sensitive, but there are caveats.
To support this statement, I bring to the court the evidence proposed in this brand new paper from Graziella Ronsein et. al., which is titled: "Parallel reaction monitoring (PRM) and selected reaction monitoring (SRM) exhibit comparable linearity, dynamic range and precision for targeted quantitative HDL proteomics". Should I go on?
Here is the thing. Sure, the QQQ is killer fast and sensitive. I've gotten to mess around here and there with the next gen QQQs like the Quantiva. If I need to accurately quantify 2k things that I have already characterized, its my pick. But when do I have 2,000 fully characterized things to quan? If I'm validating something, its the 3 cool things from my discovery experiment that I'm iffy about.
If I've got a limited number of targets, I can set the quad on the Q-exactive to filter for my ion of interest and fill the C-trap for just about as long as I want (upper limit is 6 seconds, I think). If that isn't enough to collect your ion...well...it probably doesn't exist. The sensitivity you would get from that would be orders of magnitude higher than what you could get from a straight beam quadrupole transmission. Add in PRM so you can select your high resolution fragment ions, and you've got the selectivity of your SRM (MRMs, or whatever) beat completely.
Very cool paper that proves something I've been saying for years! Yes, I feel really smart right now.