[Horatio]

Hi everyone,
I have some questions I need help with.
Why is it so that the uv spectrum of acetylsalicylic acid is dependent on the pH of the solution being analysed. And the molar absorption coefficient is totally different depending if you have an acidic or basic solution.
I hope I was clear enough

[Borek]

What dominates solution in low pH, what in high pH? Remember acetylsalicylic acid is a weak one.

[ARGOS++]

Dear Horatio,

What the name is telling, your substance is an ACID. As you know, an Acid has a coresponding BASE, and that means, dependend of your Solvent (if itsself a Base or an Acide) is determining which form of acetylsalicylic Acid/Base is dominating in Solution.
But two Substances MUST HAVE two different Spectra.
As a result, you will find different absorption coefficient for the identical wavelength for nearly every pH, because THE RATIO is important!

If you are more interessted in, please read:
   "How does pH affect the molar absorbtion/absorption coefficient of Beer-Lambert Law?"
    http://www.p-forster.com/english/themes/Spectroscopy/Spectroscopy_FAQ.htm#FAQ_SM01

Good Luck!
                 ARGOS⁺⁺