Has anyone ever heard of a method of Gravimetric Analysis of Pt in an Aqua Regia solution? I have never heard of one. This "method" supposedly involves adding some super secret ingredient to the aqua regia to get it to drop out in a powder. My preferred method of analysis for this type of material would be to run it on an ICP, or an AAS (with a La adjunct), since it is already in an aqueous form. Any thoughts?
I would be highly suspect of any method using a "secret" component. You could check it by running a standard (and a blank!), and then seeing if it returns the proper result. Even if it did work you would have to develop a factor to convert the weight of the precipitate to platinum weight.
Platinum is not a very strong element on AA, so ICP would definitely be a better choice, but you would have to ensure there were no interelement interferences (which there almost certainly would be).
The better method would be to run a fire assay preconcentration (either by lead collection or nickel sulfide), and then digest the bead in aqua regia and read that on the ICP. Again, be sure and check ANY method with standards and blanks.