Severe 209-Bismuth Background Contamination

[Jahangir]

Dear CytoFers,

I hope everyone is well.

My query is about the recent background contamination in the 209-Bi channel that my lab and I are currently observing. Please see the attached file below:

Here is a list of information that may be of benefit to you:
- This has only started to occur within the last month or so. Before this, the background in the 209-Bi was not bad whatsoever.
- The attached file has no antibody used in that channel.
- The data that is shown in the attached file is DNA+.
- There is very little to no background contamination in the 208-Pb channel. So there is no spillover from that channel. 209 - 16 = 193.
- We are using the Supersampler (with the helios system) instead of the PSI.
- I've tested all the buffers and equipment and consumables in my lab and there is no 209-Bi contamination coming from any of them.
- I've thoroughly cleaned the different parts of the SuperSampler and when running MaxPar water by itself thereafter, there isn't any 209-Bi contamination whatsoever.

So my question is, where on earth is this 209-Bi background contamination coming from? It's a great channel that we've used for a long time and would be a huge shame if we lost it.

Best regards to everyone,

Jahangir Sufi

[DMcDonald]

Hi Jahangir,

As you've checked your buffers I'd be looking to the samples. Do you see it on all sample types or are you always running the same ones? If you run an unstained sample (even without Irridium) do you still see the contamination? We once had a single sample in a batch that was swamped with bismuth, with the nature of the samples our best guess was it was from peptobismol! If it was coming from your sample introduction you'd see it during your EQ bead check too.

Good luck!

David

[Jahangir]

Hi David,

Many thanks for you reply. So to update, I've had a chat with my local FAS and he also suggested:

- If the 209-Bi background contamination was coming from Peptobismol (we are using colorectal cancer organoids derived from patients) but (as I told him) by this stage, I highly doubt the pepto-bismol signal would still be in our organoids after extraction of the tumour, transforming it into an organoid and all the passages of the organoid and the wash steps of the CyTOF protocol, etc). But furthermore, I've used the same organoids a couple of months ago and I wasn't seeing this sort of background contamination in the 209-Bi at all.

- And we are currently only running the same type of sample. And when we did run a different sample, we used an antibody in the 209-Bi channel (it has quite high negative signal (10^1.5) and a positive signal of 10^4) so probably needs titrating down).

- He also suggested we perform the same test of running unstained iridium cells and seeing if there is any 209-Bi contamination through the +16 oxidation. So that's something I'm going to be checking after the xmas holidays.



And I've also checked my EQ beads - I ran them neat and there was no 209-Bi background contamination. My current thinking is that it may be coming from the iridium. But I'll keep you and everyone updated.

Many thanks again,

Jahangir