Fri Jul 20, 2018 3:36 pm by mleipold
Hi all,
We have been running 3% nitric acid through all versions of our CyTOFs for close to 7 years now. As James said, Tuning solution is 2% nitric, so it's obviously ok with the fluidics of the instrument.
We dilute concentrated nitric to 3% v/v. We used Optima Grade Nitric Acid, Fisher # A467-500; Optima grade acids are certified for trace metal assays and ICP-MS, so they're super-clean.
Yes, in our experience, Nitric does a better job removing +2 metals (Ba, Cd, Pd, Pt) and Iodine than Wash solution (HF) does. Additionally, as James mentioned, just running Tuning solution will work: not only is there 2% nitric, but also other metal ions to compete with Ba (or any other contaminant) for non-specific binding sites in the PSI, tubing, etc. This can be useful if someone overtiters an antibody or has massive specific contamination/debris like CD56 debris in brain tissue, and it streaks like a tire track. Otherwise, you'll be running Wash solution for hours to clean out everything.
Yes, assuming that most of the barium is "stuck" in the tubing, running nitric or Tuning through all the tubing and having it drip into a tube will clean it....no need for plasma to be on. However, as you know, this would not address any Ba stuck to the spray chamber, injector, or cones. I'd probably worry most about the Injector, as that's the part that I see get the most dirty from samples; Helios spray chambers don't seem to get so dirty as the old v1/v2 glass ones.
Regarding the gut samples: honestly, this is something that your lab will have to decide policy on. On rare occasions, the HIMC has refused to run samples that are too highly contaminated, on the basis that it damages the instrument (ages the detector, etc) and affects other people's runs. At the *very* least, such samples have to be run the day before you plan to fully clean the instrument, so that you're not having to do a full clean every day.
That means that you have to get your customers/researchers to tell you what the heck they did with the samples, including all the way back to where they were coming out of the body. For example, if they did an upper GI imaging series and had someone drink Barium for Xray contrast before sample biopsy, I don't know that such a sample could *ever* be run on a CyTOF. I have no idea what the timeline/kinetics of barium excretion are from the gut: Ba salts are generally insoluble in water....whether a next day or next week sample would be clean enough, I don't know.
Mike