The Absence of an Isosbestic Point on a couple of Spectra on the same Plot doesn't mean anything at all!

Without any other very relevant Information absolutely no Statement of any kind is possible!

Yes you can do it, if you do it right!

* Use a Congo Red solution of pH 6-7 and a 1.0 cm Cuvette. * Adjust the concentration that at Lambda(max) near 500nm becomes ~1.4 AU's. * Read the first Spectrum. * Use a very fine capillary (< 0.2mm) and add slowly HCl-Gas!! till you detect the smallest possible Change in color! * Read the second Spectrum. * Add a minimal amount of HCl-Gas!! And read the third Spectrum. * Repeat th last step above till the indicator becomes real blue. * If you overlay now all read Spectra you will see your Isosbestic/Isobestic Point! *

It is important to use HCl-Gas and not an aqueous solution, because the volume must be constant during the whole Experiment!! About Isosbestic/isobestic Points you may also read on: Related Link Nr. 1. below.