Question about lock-mass option

Whether you are building your own mass spec, modifying an existing one, or just need help with instrument settings post about it in here.
Pippuri
Phosphoserine Member
Phosphoserine Member
Posts: 10
Joined: Sun Oct 23, 2011 10:28 am

Question about lock-mass option

Postby Pippuri » Wed May 02, 2012 8:35 am

Dear All,

I have a question about this lock-mass option on an LTQ OrbitrapXL, especially after reading Oslen et al (MCP, 2005, 4:2010-2021, from Mann's group)...

So, in the paper, the authors stated that "for accurate mass measurement the lock mass option was enabled.........and the PCM ions generated in the electrospray process from ambient air...... m/z 455.120025"

-- My question is, to apply this method to a LC-MS/MS run, one only need to turn on the lock mass option with the specified m/z without having to add/do anything? OR, is there any prerequisite for the instrument front?

Many thanks!!

arledvina
Phosphoserine Member
Phosphoserine Member
Posts: 14
Joined: Wed Jun 29, 2011 6:09 am

Postby arledvina » Wed May 02, 2012 8:55 am

My advice would be to try running the method on something you infuse (like calibration mix) and try to figure out if the instrument is doing what you think it is.

Alternatively, what is your application? With calibration every week or so, you shouldn't have much more that 2-3 ppm mass error; you might be OK without lock mass.

Leadazide
Serine Member
Posts: 8
Joined: Wed May 02, 2012 10:51 am

Postby Leadazide » Wed May 02, 2012 10:54 am

From my experience at various users all they do is add this lock mass and run.. Nothing is added.

Craig
E. Coli Lysate Member
E. Coli Lysate Member
Posts: 220
Joined: Sun Jun 26, 2011 6:49 pm

Postby Craig » Wed May 02, 2012 12:01 pm

Lock masses are chosen because they are typically abundant enough without being manually added. If that's not the case you could always try this approach.


lockmass.jpg
You do not have the required permissions to view the files attached to this post.

arledvina
Phosphoserine Member
Phosphoserine Member
Posts: 14
Joined: Wed Jun 29, 2011 6:09 am

Postby arledvina » Wed May 02, 2012 12:51 pm

Nice Craig.

Leadazide: I should clarify; one might try running an instrument method with and without lockmass selected and compare the resulting data to determine whether or not the lockmass works as (s)he might suppose; for the sake of brevity, this could easily be accomplished by infusing calibration mix and running the instrument methods on the cal mix itself.

Pippuri
Phosphoserine Member
Phosphoserine Member
Posts: 10
Joined: Sun Oct 23, 2011 10:28 am

Postby Pippuri » Wed May 02, 2012 2:18 pm

Hey Guys, thanks very much for all the replies.

The instrument that I am using is calibrated once every 4 to 5 weeks. Since I am not authorized to do any calibration, I thought using the lock-mass option might help me with the mass accuracy while trying to map PTM sites. Special thank to Craig for pointing out the neat trick!

ajbureta
Proton Member
Proton Member
Posts: 1
Joined: Mon Jul 18, 2011 10:25 am

Postby ajbureta » Thu May 03, 2012 7:36 pm

If Craig's deodorant idea doesn't work, I'd recommend trying this instead:

LockMass.jpg
You do not have the required permissions to view the files attached to this post.


Return to “Instrumentation”

Who is online

Users browsing this forum: No registered users and 1 guest