[curiouscat]

I have an analyte for which I cannot seem to obtain a 100% pure standard solution.

The best I can get is a 95% solution.

http://www.sigmaaldrich.com/catalog/product/aldrich/w287407?lang=en&region=IN&cm_sp=Insite-_-prodRecCold_xviews-_-prodRecCold10-1

Is it possible to quantitate such a substance on a GC. If not with high accuracy with some, known, reproducible margin of error?

Alternatively, any ideas how I might obtain a pure sample of this standard?

[Arkcon]

A quick Google search for "phenylacetaldehyde reference standard usp didn't give me an easy answer, but it may be buried in the results.  Check if the USP will sell you a reference standard, or check if you want a custom standard.  USP standards generally cost $300-400 USD, custom made standards likely much more.

Once you have a reference standard, your 95% standard (you can also buy 98% standard) can be standardized against your reference standard. 

[curiouscat]

A quick Google search for "phenylacetaldehyde reference standard usp didn't give me an easy answer, but it may be buried in the results.  Check if the USP will sell you a reference standard, or check if you want a custom standard.  USP standards generally cost $300-400 USD, custom made standards likely much more.

Once you have a reference standard, your 95% standard (you can also buy 98% standard) can be standardized against your reference standard.

Thanks Arkcon.

I think the issue here may be that 100% Phenylacetaldehyde is labile. It either isomerizes or polymerizes.

Commercial quantities are, in fact, shipped as only a 50% conc.

In the light of this, are there any quantitation workarounds I can use? Aren't there other GC analyses where a 100% pure reference is not accessible?

[Arkcon]

Well, yeah.  Pretty much all of them.  The purity is given, say 99.98%, and you calculate based on that.  The reference standard could be 50%, but its actual purity will be recorded, say as 49.87%.  Reference standards just have carefully defined purity, they don't have to be more pure than any other source.

[curiouscat]

Well, yeah.  Pretty much all of them.  The purity is given, say 99.98%, and you calculate based on that.  The reference standard could be 50%, but its actual purity will be recorded, say as 49.87%.  Reference standards just have carefully defined purity, they don't have to be more pure than any other source.

Right. Understood.

But then there always has to be *some* standard around that's 100%? i.e. To record a purity of 49.87% what's the original reference & so on ad infinitum.

Just wondering how the whole thing works. Or is the master reference a non-GC standard or something else. i.e. Are there analtical methods allowing absolute quantitation without a reference that one can bootstrap everything from?

[Arkcon]

The more you look into it, the more it seems like a house of cards, but that's just what the definition of "analysis" is.

A standard is just a batch of substance, rigorously analyzed, sometimes by orthogonal methods, sometimes by classical methods, at a laboratory that is certified by a reporting body as having done the work well.  If the material is very rare, the manufacturer itself may be called upon to make a standard, and provide the standard.  Such was the case with a previous boss -- she provided the USP with the USP standard for her companies manufactured pharmaceutical.  She characterized it, and gave it to the USP, and that was the standard, for anyone, worldwide, who wanted to claim their product was traceable to the USP.

We don't have to esoteric here.  Most everyone has a pH meter.  How does it work?  Its essentially worthless if not standardized, but how?  To what?  What are those standardization buffers?  What does it mean when we use them?