Hi @tara_unicorn
I think the issue here is that you need two types of ratio for UCPb:
- Pb/Pb ratios for your primary reference material to model the downhole fractionation (quite often the same mineral as your unknowns, eg apatite, etc), and
- one 7/6 ratio for correcting Pb bias (quite often a NIST glass) and
For the downhole correction setup, your RM will likely have common Pb ratios listed with the "C". This is because that composition might not actually exist in your sample, but rather is a calculated value to tie one end of the data through the common Pb intercept.
For the Pb bias correction, you need Pb ratios without the "C" in it. That's because these materials pretty much only contain common Pb, and materials for this correction (e.g. NIST glasses) mostly only have the Pb ratios listed without the C by convention.
So, in summary: Add "C" to the Pb ratios of your primary RM, and leave it out for the mass bias material.
I hope that makes sense. Please let me know if you have any questions.
Kind regards,
Bence
