Ham-milton said:
knowing that there's going to be some APAP left no matter what, I think the only reasonable test would have to change very slowly, or you'd too easily reach max coloration.
it is not as complicated as you suggest. in fact I can see a way of getting semiquantitative results,
dilution is the key.
A sample of the original BEFORE CWE material is dissolved say 10mg per ml in water to make the
BEFORE CWE master reference.
the same amount of the material left AFTER CWE is dissolved in water at the same weight per ml as the
BEFORE CWE master reference.[/B]
The
BEFORE CWE master is then diluted to 2 3,4, 6, 8 10 and 16, (the number of dilutions would probably need to be modified by experiment. I cannot remember how sensitive ferric chloride is)
then 1 drop of 1% ferric chloride is added to the AFTER CWE,
1 Drop of Ferric chloride is added to the BEFORE CWE master reference,
1 drop of ferric chlorde is added to each of the diluted BEFORE CWE solutions.
The intensity of colour of the AFTER CWE solution will lie between two of the Before CWE diluted solutions, easy to do with a piece of paper. from this everything else is easy...
for example,
if the intensity of the colour of the AFTER CWE sample is darker than the 4x dilution but lighter than the 4x dilution then it is pretty certain that the AFTER CWE material contains 3-4 times less Acetaminophen per gram than the BEFORE CWE material. and as the manufacturers tell you how much acetaminphen is in the starting material you know approximately how much is in the AFTER CWE material.
I personally would use a spectrophotometer as it would save pissing about diluting solutions but that is just me.
Vecktor