ICP lab recommendation for gold purity

[Stibnut]

My first batch of refined gold went well, but I only had it tested by XRF so I can't be totally sure what the fineness was. For my next batch, I'm going to want to see if I manage to hit 4N fine or, if not, what the contaminating element(s) are. My impression is that the way to do this is by ICP using a subtraction method. Does anyone have any recommendations for a lab in the US that can do this test, and how expensive does this tend to be?

 

[Lou]

We do routine ICP analysis by difference for silver and gold bullion for several large mints.

Typically it’s a minimum 1 g sample and a $200-300 charge to run it and certify it against the relevant ASTM standard.

Usually run at 30-300 dilution.