Chromatography Forum

Hi,

Looking for a little help with this as it's not something I've come across before.

A certified reference standard we use for one of our methods is being discontinued. The supplier provides a CoA with this and the concentration is meant to be 100ug/ml. The CoA states an absolute value e.g. 99.5ug/ml or 100.3ug/ml etc. This allows us to do a correction factor for our standard and calibration points after analysis.

The replacement part number comes with a CoA that just says 100 +/- 6.6 ug/ml. There is no absolute value given.

Does anybody have experience with dealing with such a CoA?

Thanks.

That's a specification, not a value for a specific lot.
I'd try looking up the lot mark on the vendors website.
If that fails, reach out to their customer service department.

Another possibility is that the material delivered is not RS grade (wrong product sku either ordered or sent) - but that does not mean that the vendor has no idea what the assay is - again, reach out to them.

DR wrote:
That's a specification, not a value for a specific lot.
I'd try looking up the lot mark on the vendors website.
If that fails, reach out to their customer service department.

Another possibility is that the material delivered is not RS grade (wrong product sku either ordered or sent) - but that does not mean that the vendor has no idea what the assay is - again, reach out to them.

Hi DR, thanks for the reply.

This is the CoA sent directly from the vendor for a certified reference material - 100ug/ml formaldehyde-DNPH

COAs I get from SPEX and DIONEX have labeled values and certified values. It looks like the functional value is the labeled value and the derivative value is the measured value. i would think the measured value is the real certified value.

just ask the supplier.

Also have a look at the next pages of the CoA, especially on the "Associated uncertainty section".
So, for me, Supelco prepares the solution in a way, that its concentration is 100.0 mg/l but also states the combined analytical uncertainty on the 95% confidence level. Thats what the +/- value is.

So you could use the 100.0 mg/l value, but when you calculate your uncertainty of your result, the +/- 6.6 comes into account.

Btw: what was the uncertainty on the CoA of your previous supplier?