Temperature, Azo Dyes and Spectrophotometers? :S

[GreyScott20]

 

Hey everyone,

 

Just did an experiment spectrophotometer looking at the effects of high temperatures and found something rather unusual.

 

Its with the secondary azo dye; congo red with beta-glucans in the form of brewers yeast and oyster mushroom tablets BUT at temperatures of 50 and 70 degrees celsius.

 

Repeated tries over 3 times and found that the higher the concentration of the tablets, the lower the absorbance read by the spectrophotoemeter. Essentially saying the presence of these dye complexes actually decrease absorbance.

 

Can anyone help me out and give me a hypothetical or actual reason on why this happens please? Literature and Journals aren't really explaining this. But if more details are needed ont he experiemnt protocol or certain conditions, I'd be happy to co-operate.

 

Thank you very much all,
Scott.

[hypervalent_iodine]

Do you know how stable congo red is to higher temperatures? It could be that it is decomposing, though I am not 100% sure on that (it seems like it should be fairly stable at those temperatures). Were you using something to create a standard curve? Perhaps try and look at how your standards change in absorbance with temperature if so.

[John Cuthber]

I think congo red is probably pretty stable.

On the other hand the Merck index says it's colour changes with the solvent.

So you might be looking at something like a solvatochromic effect.

A much simpler explanation would be a pH effect.

Is the mixture buffered to keep the pH constant?