Total carbohydrate content

Remco Viëtor remco at
Tue Oct 28 13:53:28 EST 1997

Ian McFarlane wrote:
> I've used this assay [Dubois, phenol sulphuric acid, RV] as well. 
> I did the assay in plastic LP4 tubes (they
> are polycarbonate I think), they melt a bit but don't seem to affect the
> reaction. The most important thing we have found is to squirt the conc.
> sulphuric directly onto the sample or the colour development isn't very
> strong.

That is because the heat developed by the mixing of acid and water
the reaction. You can also heat the tubes for a while in a boiling water 
bath, though normally that is not required.
I would stick to pyrex glass tubes though, and indeed be very carefull
with both the phenol solution (poisonous) and especially the sulfuric
acid. The latter can be _very_ nasty, even when dilute. I have holed 
several labcoats while washing tubes that contained sulphuric acid:
the dilute acid gets on the coat, the water evaporates => concentrated
acid => holes.
Also, a collegue of mine got acid on his shoe. He rinsed it of
and neutralised the surface, then carried on as usual. That is, until
foot started itching after a while: the acid had penetrated into the
and continued working its way inwards, until it reached flesh...


Remco Vietor				Department of Chemistry
remco at			J. Black Building
					University of Glasgow
					Glasgow G12 8QQ

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