Are double spike isotopic standards suitable for quantification by isotope dilution mass spectrometry?

I would like to apply isotope dilution mass spectrometry (IDMS)\* to quantify lead at trace levels. A good spike solution for the process would be the [NIST SRM 991](https://www-s.nist.gov/srmors/view_detail.cfm?srm=991) which is an enriched material of almost only lead-206, but this material is now discontinued and the replacement is a radioactive material [NIST SRM 983](https://www-s.nist.gov/srmors/view_detail.cfm?srm=983), which I think, will be a little difficult to import.


The NRC of Canada has produced the lead-204 and lead-207 double spike isotopic standard [BLED-1](https://nrc.canada.ca/en/certifications-evaluations-standards/certified-reference-materials/list/145/html) which contains 49% and 33% the two isotopes, respectively, and I was wondering if it could be suitable for IDMS considering that the natural relative abundance of those isotopes is low. I have only performed IDMS using the (single spike) [NIST SRM 991](https://www-s.nist.gov/srmors/view_detail.cfm?srm=991), and although I think the same IDMS equations will apply to each pair of isotopes, would like to know please if there is something I am not taking into account.


\*) An overview about this technique is provided by Vogel, J.; Prizkow, W. Isotope dilution mass spectrometry — A primary method of measurement and its role for RM certification. *MAPAN* **25**, *2010*, 135–164, [doi 10.1007/s12647-010-0017-7](https://doi.org/10.1007/s12647-010-0017-7). The author's copy on [ResearchGate](https://www.researchgate.net/publication/225942041_Isotope_Dilution_Mass_Spectrometry_-_A_Primary_Method_of_Measurement_and_Its_Role_for_RM_Certification).




Yes, I think it would be suitable, although I am not an expert in IDMS either. It seems like the new standard contains two stable isotopes. This should give you a built-in check on the data you collect: if you treat Pb-204 as the spike isotope, and calculate the concentration of Pb in your sample from it, you should get the same (or very similar) answer as if you treat Pb-207 as the spike isotope.


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