Dear Forum Members,

I am facing a problem with the Absorbance Ratio values between a Monomer and a Dimer of Pharmaceutical Drug. The Absorbance Ratio of the Dimer of that particular compound is almost half that of the Monomer. Is it same with all the Dimer compounds. If yes, why is it so, any theory behind it. I have taken well standardized Dimer compound and well standardized Monomer compound, prepared the same concentration solution for both and injected. I am getting almost half the response for Dimer when compared against its monomer. Even the same solutions I have checked in the UV-Vis Spectrophotometer, and the case is same. The spectrums of both the compounds are exactly same with same UV max values. I feel theoretically the Absorbance ratio of Monomer and Dimer shall be 1 when we take the molar concentrations and calculate.
I am waiting for your valuable responses.

what are the chemical structures? What wavelenght did you use?

is there one more double bond (or other absorbing group) in the monomer?

Thanks for the response.

The Monomer contains one conjugated double bond (two double bonds),and two -C=O groups where as,

the dimer consists of two conjugated double bonds (four double bonds), three -C=O groups and one -COOH group.

These are the only chromophores available in the molecule. The compounds are showing a wavelength maxima of 238 nm, and was analyzed at the same wavelength.