bcr2-g sulphur composition

[Ben Buse]

Hi,
I was looking for standard values for sulphur in bcr2-g

Any ideas?

GeoRem quote 3 papers - 20-40ppm, one of which ICPMS, the others EPMA with large errors.

Whereas Agnès Michel and Benoît Villemant have 158-165, although this may be the rock rather than the glass
https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1751-908X.2003.tb00643.x

And Xu-Jie Shu and Cin-Ty A. Lee have 159 ppm for the glass



Thanks

Ben

[DavidAdams]

Hi Ben,

I performed 935 microprobe analyses across 5 different grains on BCR-2G in May 2019. My detection limits for S were 70 ppm. Of the 935 analysis points only 30 were above detection and ranging from 70 to 100 ppm. The average value was 78 ppm and 13%RSD.

Hope this helps!
Dave

[Ben Buse]

Thanks Dave,

That's very useful, although I'm slightly confused, if 905 points were below the detection limit of 70ppm, how is the average value 78 ppm.

[Probeman]

Just as an aside to this discussion, I have found that it's also worth keeping in mind that just because something wasn't detected at the 99% confidence level (3 sigma), does *not* mean that it wasn't detected at say, the 95% confidence level (2 sigma).

Yes, we in EPMA generally utilize the 99% confidence interval to proclaim "detection", but we may also discuss the statistics of lower levels of confidence...

[jon_wade]

quant S by laser ablation?  We've found BCR2 somewhat variable as a LA-ICPMS elemental standard - its typically glassed in air and may have variable Fe contents depending how it was glassed (Pt crucible etc), all of which doesn't bode well for its S content.

[DavidAdams]

Thanks Dave,

That's very useful, although I'm slightly confused, if 905 points were below the detection limit of 70ppm, how is the average value 78 ppm.

The average of the 30 points above detection was 78 ppm

[DavidAdams]

quant S by laser ablation?  We've found BCR2 somewhat variable as a LA-ICPMS elemental standard - its typically glassed in air and may have variable Fe contents depending how it was glassed (Pt crucible etc), all of which doesn't bode well for its S content.

Hi Jon,

BCR glassed at the USGS in Denver is always glassed in air and in Pt crucibles. I spent years trying to get Steve to glass his reference materials in  controlled atmospheres but he never saw the value of doing so.

[jon_wade]

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...)