[lochnessmonster]

For my a-level chemistry coursework I am looking at the purity of aspirin tablets.
At the moment I am looking at the affect of ingredients on my results from a forwards, back titration and colorimetry.

My tablets contain Maize Starch. Of what ive researched it seems to be modified to contain a carboxymethyl group to help disintergration.

I was wondering if anyone knew if the use of this bulking agent would affect my results?

Thanks in advance

[Rabn]

for acid/base titrations pKa/pKb are your best friend. Compare all the species pKa's, also consider any potential redox reactions you may encounter. Let me know if you need anything else.

[ARGOS++]

Dear LochNessMonster;

Titration/Back-Titration is a very unspecific method, and so you don’t know what all will influence this method of determination, but the Carboxymethyl group on its own will not have an effect.

The Carboxymethyl group will also have nearly no influence on the UV/Vis “Colorimetry” as long as you take care to have your measuring solution pH-adjusted with a “Buffer”!
Disadvantage of UV/Vis Spectroscopy:     You need a “Reference Sample” with a good and known purity.
Advantage of UV/Vis Spectroscopy:         You are specific, especial if you use the Spectrum instead of only a “Single-Wavelength”-Measurement. It means that you have at the same time also an identification (easily done with MCA, but mostly not implemented).
The Spectrum of Acetylsalicylic Acid you can see on NIST:"Acetylsalicylic Acid”
But think about this Spectrum will for sure not be pH-adjusted!

I hope it may be of help to you.

Good Luck!
                   ARGOS⁺⁺