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Tuning pass but EQ bead CV high?

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jimbomahoney

Master

Posts: 73

Joined: Wed Feb 27, 2019 11:21 am

Post Wed Nov 27, 2019 8:33 am

Tuning pass but EQ bead CV high?

Hi all,

I recently experienced my first "failure" for EQ beads - the CV should be <12%, and I normally see ~8%.

On this occassion, tuning passed and there was nothing unusual about it, but the bead CV was 17%!

Strangely, running it for a third time finally produced a "pass" of ~10%.

What could cause this without showing anything in the tuning results? I'm guessing cones? (The cone current was fairly low - certainly where it normally is).

Many thanks!

(If it matters, I'm using a Helios with WB injector).
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roexx078

Participant

Posts: 3

Joined: Thu Feb 08, 2018 6:21 pm

Location: Nashville, TN, USA

Post Wed Nov 27, 2019 1:28 pm

Re: Tuning pass but EQ bead CV high?

Yup, I'd say one or both of your cones is too old. My understanding is that, over time, the tiny aperture each cone gets larger and larger as the metal wears away. This eventually this leads to higher CVs and poor doublet discrimination. This can also happen if, say, you touch the tip of the skimmer/reducer cone and bend it. I don't think either of these cases (age or abuse) necessarily affects Tb counts, etc. during tune because you aren't measuring 'events'.

I'd inspect your cones, and/or order new ones. A pair of cones typically last us ~6 months, on a Helios that is using the HT injector and is run ~40 hours a week.

Hope this helps!
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mleipold

Guru

Posts: 2095

Joined: Fri Nov 01, 2013 5:30 pm

Location: Stanford HIMC, CA, USA

Post Wed Nov 27, 2019 3:13 pm

Re: Tuning pass but EQ bead CV high?

In my experience, both the sampler cone and the skimmer/reducer cone can affect CVs. As Caroline said, it's usually due to the orifice widening or becoming non-circular.

Since you said that the Tuning current and signal seemed fine, I might suggest swapping out the Sampler first. Current (and signal intensity in general) has to do with the Skimmer...the Sampler is just a pinhole orifice.

Also, at least on my two Helios instruments, the main signs to change the Skimmer have to do with the Tb signal decreasing, the Current staying high, and oddly the Oxide going below 1% and staying there (no idea why).

Also, the Sampler is cheaper. :)
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AdeebR

Grand master

Posts: 169

Joined: Thu Mar 13, 2014 5:58 pm

Location: NYC

Post Wed Dec 18, 2019 2:17 am

Re: Tuning pass but EQ bead CV high?

While I agree that aging cones can impact bead CVs, I think it's important to note that brand new cones can also show pretty significant differences in performance. We recently ordered 3 new skimmer/reducer cones and tested them on all three of our instruments:

As you can see from the attachment we observed quite a bit of variation, with overall Eu153 signal intensity seeming to be more related to the instrument and largely correlating with the Tb(159) DC at tuning, while bead CVs were more of an attribute of the cone itself, independent of the instrument. The third cone in this case was showing high enough CVs that we returned it to Fluidigm and requested a replacement.

Cone_testing.tif
Adeeb Rahman
Icahn School of Medicine at Mount Sinai, NYC

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