CyTOForum

Hi James,

Yes, that is my understanding: the skimmer-reducer is what gets charged by the Current setting.

The sampler cone is basically just an orifice to reduce the ions being introduced into the instrument, as well as helping to set up the initial stage of the vaccum gradient.


Mike

Thanks Mike.

Now that I've got my hands on some Citranox, I'm going to give the standard sonication method a go and see if I can reduce the current. It's crept up from about 6 when the machine was first installed to about 9 now.

Hi James,

As you use the cones, the Current will progressively increase. Yes, generally speaking, after a cleaning, the Current will drop at least slightly, but over weeks/months, it will go from probably around I=6 to around I=10 or I=11.

With my Helios instruments, these are the signs I use to tell when to replace the skimmer-reducer:
1. if the Current goes up to 10-11 and stays there, even after a clean
2. if the oxide ratio drops below 1% and consistently stays there (days/weeks)
3. Tb and Tm values continue to decrease over days/weeks

If all 3 of the above criteria are met and it's been at least 5-6 months (fairly heavy usage), then I change the skimmer-reducer. Right now, under the fairly heavy usage of my 2 machines, we're getting about 6mo out of skimmer-reducers, so we have to budget for 2 per machine per year.


Mike

I thought lower oxide ratio was better?

The others I can understand.

Like with most things, it's a compromise.

Very low oxide (under 1% or so) usually comes with lower sensitivity (Tb/Tm signal).

However, higher oxide comes with more spillover into M+16. The upper limit to pass Tuning is 3%, which was decided to be a sufficient balance.

If the skimmer-reducer is in its healthy lifetime range and everything else is working well, the oxide ratio from the automatic Tuning is typically 1.5-2.5%.


For more information about how Current and Makeup Gas changes affect Oxide Ratios, I'd recommend going back to the CyTOF1 and CyTOF2 manuals, in the Manual Tuning section. There, you can see the Masses Per Reading rainbow graph of signal vs Current/MG.

Or, if you can't easily access those, we covered that a bit in this JoVE paper on tuning a CyTOF1: https://www.ncbi.nlm.nih.gov/pubmed/23149654

Thanks Mike.

I remember a diagram Fluidigm showed me now, with the peak Tb/Tm occurring just as the oxides start to ramp up (Dual Counts Y axis / Makeup gas X axis). It's in that link you provided too.