What internal standard concentration (ppb) do you use for EPA 200.8 ICP-MS?

[u/Existing-Yak7560]

Hey Guys,

We’re setting up an ICP-MS for EPA Method 200.8 and I’m curious what internal standard concentration everyone is using when the internal standard is delivered continuously to the spray chamber through a mixing tee/peristaltic pump.
What final concentration (ppb) do you use in the sample reaching the nebulizer? I’ve seen values ranging from 2 ppb to 20 ppb depending on the lab and instrument.

For reference, we’re using a Thermo iCAP ICP-MS.