yeah, I've never though of using it as a Sulfur standard, but folk often use Pt crucibles for glassing bcr2 as its easy to remove. However, this leaves the final glass often inhomogeneous and low in Fe as it happily alloys with the Pt. Although its a common LA-ICPMS standard, I've found it highly variable from lab to lab and tend to avoid it. At a push, I'll use it only as a secondary standard, or just to check drift just because its available. (saying all that, I've a piece of NIST 610 that has swirl marks apparent in the BSE...)