Posted by **mary** on Wednesday, March 23, 2011 at 6:02pm.

Hello, can someone please help me? I'm stuck on a question:

I'm doing an analysis of the absorbance of FeSCN2+ at it's max wavelength (i.e. 450nm where abs=0.154)The species I used to make the solution tested were Fe(NO3)3, HNO3, and KSCN.

Now, the question is: Suppose there are one or more interfering species in the solution, which also absorb more or less strongly at this same wavelength. How could/should you deal with such a situation of overlapping absorbances?

I've scanned all my notes and I'm still stuck. I think it may have something to do with finding the equilibrium concentrations and then converting values using a ratio formula using the absorbance and concentration values...

A/A = C/C? I think i may be wrong, can someone please explain this theory question to me?

- chemistry abs spectrum and wavelength analysis -
**DrBob222**, Wednesday, March 23, 2011 at 6:32pm
One thing you can do is to use a wavelength other than 450 nm and one which the contaminant doesn't absorb. A second thing you can do, if the contaminant an be identified, is to determine how much of the other material is there and subtract the A due to that material. A third thing you can do is to determine, by successive approximations, the amount of FeSCN+2, a procedure which I simply can't explain on this board. If there is more than one contaminant and the interference is bad, I would go with the first suggestion first.

- chemistry abs spectrum and wavelength analysis -
**mary**, Wednesday, March 23, 2011 at 6:56pm
Wow! Thank you, that makes a lot of sense! I know what you mean by successive approximations, I didn't think of it like that before..

Thank you so much again :)

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