24 hour lock mass protection
Nov. 22nd, 2011 09:22 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
beige_alertSure, sometimes science is dull. Scientific papers tend to be specifically written to be dull. But sometimes someone gets the chance to write a more unusual paper.
The Thermo LTQ Velos Orbitrap mass spectrometer is an amazing piece of hardware. If you've been in the instrumental analysis business you may have used equipment that gave amazing results on the rare occasions that it worked at all. The Orbitrap not only produces great data, it actually works most of the time. In our lab we just can't get over how well this thing actually works in practice. You can go from vented to sub-10-7-torr in literally a few minutes and down to operating pressure in the 10-10 torr range with a single overnight bake-out. A month after calibration it can still be within four or five ppm. It easily delivers resolution better than the promised 100,000 FWHM at 400 m/z.
If you really want maximum mass accuracy, better than 1 ppm, you really need a lock mass, an internal mass standard. I'm just amazed at how stable the external calibration is over days and weeks-it's vastly better than our Q-TOF-but nothing beats an internal standard for maximum accuracy. The question always is, though, what to use and how to introduce it into the system.
It turns out that there are some background contaminants right in the air that you can use if you can figure out exactly what they are and can get a reliable signal. Polydimethylcyclosiloxanes work great. They are in all sorts of ordinary household products, and thus in the air, and so you'll always see at least a little signal. If you need a stronger signal, all you need to do is set a supply of the calibration compound near the mass spectrometer source and you'll get a higher concentration. For example, see this article, "24 Hour Lock Mass Protection". "We devised a strategy to improve its performance by increasing the external abundance of calibrant molecules in laboratory air." "This method involves a simple laboratory setup using common laboratory hardware and truly off-the-shelf reagents." Yes, they set a tube of "Lady Speed Stick" deoderant by the mass spectrometer source, as a supply of calibration compound. Really. I have not personally tried this yet, but somehow I think I will.
The Thermo LTQ Velos Orbitrap mass spectrometer is an amazing piece of hardware. If you've been in the instrumental analysis business you may have used equipment that gave amazing results on the rare occasions that it worked at all. The Orbitrap not only produces great data, it actually works most of the time. In our lab we just can't get over how well this thing actually works in practice. You can go from vented to sub-10-7-torr in literally a few minutes and down to operating pressure in the 10-10 torr range with a single overnight bake-out. A month after calibration it can still be within four or five ppm. It easily delivers resolution better than the promised 100,000 FWHM at 400 m/z.
If you really want maximum mass accuracy, better than 1 ppm, you really need a lock mass, an internal mass standard. I'm just amazed at how stable the external calibration is over days and weeks-it's vastly better than our Q-TOF-but nothing beats an internal standard for maximum accuracy. The question always is, though, what to use and how to introduce it into the system.
It turns out that there are some background contaminants right in the air that you can use if you can figure out exactly what they are and can get a reliable signal. Polydimethylcyclosiloxanes work great. They are in all sorts of ordinary household products, and thus in the air, and so you'll always see at least a little signal. If you need a stronger signal, all you need to do is set a supply of the calibration compound near the mass spectrometer source and you'll get a higher concentration. For example, see this article, "24 Hour Lock Mass Protection". "We devised a strategy to improve its performance by increasing the external abundance of calibrant molecules in laboratory air." "This method involves a simple laboratory setup using common laboratory hardware and truly off-the-shelf reagents." Yes, they set a tube of "Lady Speed Stick" deoderant by the mass spectrometer source, as a supply of calibration compound. Really. I have not personally tried this yet, but somehow I think I will.
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Date: 2011-11-23 05:45 pm (UTC)no subject
Date: 2011-11-24 03:17 am (UTC)