Fri May 23, 2014 9:49 pm by ErinSimonds
Mike is right about the Nolan lab's experience -- we found samarium in 2 lots of the PFA from EMS. This led to a search for alternative PFA from other vendors and several conversations with EMS, the upshot of which was actually that EMS prepares the PFA for several other vendors. Since it turned out to be a lot-to-lot issue, and quite rare overall, we now simply test each new lot.
Interestingly, it was not simply ionic samarium in solution, it was actual chunks of precipitated samarium. These showed up as cell-like "events" on the CyTOF, rather than simply a constant background of metal in solution. We never figured out why there were chunks samarium in the PFA, but I love the BIC lighter theory. That could very well be it. Our best guess at the time was that it came from a magnetic stir bar.
The artifactual events tended to be iridium-negative and they had the isotopic abundance profile of naturally-occurring samarium:
144: 3.1%
147: 15.1%
148: 11.3%
149: 13.9%
150: 7.4%
152: 26.6%
154: 22.6%
It's easy enough to test each new lot of PFA and make sure this isn't an issue. It's good practice to test each new reagent you bring into your CyTOF workflow by either checking them in solution-mode, or running some unstained cells in each experiment to check for background.
- Erin