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How Long can the CyTOF be run?

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BostonJohn

Participant

Posts: 1

Joined: Mon Dec 02, 2013 6:23 pm

Post Wed Mar 12, 2014 12:36 am

How Long can the CyTOF be run?

Hi All,
Our user base is starting to ramp up and I was wondering if there was a limit on how many hours a CyTOF can be in "work mode" before things become sub standard. I have heard conflicting reports where it can run round the clock for two weeks and other reports that it needs a rest "every six hours or so". I assume it could be a factor of wear and tear but was wondering if there is a consensus.
any opinions?
Thanks
john
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Ofir

Master

Posts: 75

Joined: Thu Nov 07, 2013 12:46 pm

Location: US, CA

Post Wed Mar 12, 2014 8:59 am

Re: How Long can the CyTOF be run?

Hi John,
We typically run 10 hour days consecutively. Sometimes longer.
You do want to monitor your sensitivity as it can drop precipitously when sample introduction elements get dirty. Best way to do that is by monitoring the intensity (MFI equivalent) of EQ Four Element Calibration Beads.
Do make sure that your are running water through the nebulizer when the heater / plasma is on so it doesn't overheat.
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mleipold

Guru

Posts: 5796

Joined: Fri Nov 01, 2013 5:30 pm

Location: Stanford HIMC, CA, USA

Post Wed Mar 12, 2014 3:50 pm

Re: How Long can the CyTOF be run?

Hi John,

There is some loss of sensitivity of the machine over very long runtimes (5-6+ hr). But we at the HIMC regularly run longer than that. In most cases, this slight drop is not sufficient to cause problems in your analysis. However, if you are running very large samples (several mL) due to particularly rare events, or barcoded samples, where you would combine several FCS files, this would be more of an issue than just running a lot of samples that are of comparatively short (<30min) acquisition time each.

1. Cleanliness of your samples is important. You will get less tuning drift if you do the water washes and then water resuspension to remove all possible free metal/antibody/buffer salts. Buildup of salts usually affects the Current parameter the most: you should have less than 1 Current unit drift over even very long runtimes (10+ hr) if you do the water washes, and this should basically keep you "on-peak". If you do not do the washes, or if you still have a dirty sample, then yes, you can shift yourself "off-peak" even in one day's runtime.

2. The 4 element calibration beads can allow you to renormalize your data to remove most of the decrease in sensitivity, before you combine FCS files.

3. In addition to Current-related salt build-up, according to DVS, the decrease in signal intensity supposedly comes from temperature-related changes in the TOF performance. Basically, your TOF start and Integration Time stay the same, but the actual ion peak shifts slightly to higher TOF. Therefore, you effectively lose some ion intensity because you're now missing part of your peak. As the machine gets hot, it will shift. However, when you shut down, it cools back down, so that it will have returned to the initial TOF time by startup the next day.

I have recently heard that some labs basically retune after 6 hr or so of runtime, including checking the appropriateness of the Mass 1 and Mass 2 TOF start settings. So far, this is not something that the HIMC has integrated into our user workflow....partly b/c I have grave misgivings about telling the average user to mess with the TOF windows.....


I think in most cases, with well-prepared samples that are <30min each, the 4-element beads are probably all that you would truly need for rigorous comparisons. But I have not formally tested this.


Mike

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