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?
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.
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 :)
Of course, I'd be happy to help you with your question!
When dealing with a situation where there are interfering species that also absorb at the same wavelength, there are a few strategies you can use to address this overlap:
1. Spectral Correction: One approach is to first obtain the spectrum of each individual species in the solution. This can be done by measuring the absorbance of each species at various wavelengths. Once you have the spectra, you can then use mathematical techniques, such as spectral correction, to subtract the absorbance contribution of the interfering species from the total absorbance at the desired wavelength.
2. Selective Wavelength: Another method is to choose a different wavelength where the interfering species does not absorb significantly, but the analyte of interest (FeSCN2+) still absorbs with a sufficiently high intensity. This wavelength should be as much exclusive to FeSCN2+ as possible, minimizing interference from other species. By measuring the absorbance at this selective wavelength, you can focus on the concentration of FeSCN2+ without being influenced by the interfering species.
3. Additive Color Method: If the interfering species is known and its concentration is relatively low compared to the concentration of your analyte, you can try the additive color method. This involves adding a known excess concentration of the interfering species to the sample and then measuring the absorbance. The idea here is that the increase in absorbance will be proportional to the concentration of the interfering species. By subtracting this contribution from the total absorbance, you can obtain the absorbance solely due to the analyte of interest.
Regarding your mention of the ratio formula, it seems that you might be referring to the Beer-Lambert Law, which states that the absorbance of a solution is directly proportional to the concentration of the absorbing species. Mathematically, it can be expressed as A = εbc, where A is the absorbance, ε is the molar absorptivity (a constant specific to the absorbing species and wavelength), b is the path length of the sample, and c is the molar concentration of the absorbing species. However, in the case of multiple species absorbing at the same wavelength, the direct application of the Beer-Lambert Law might not give accurate results without additional corrections or strategies.
Remember, when dealing with overlapping absorbances, it is important to first identify the interfering species and understand their spectral behavior. Based on that, you can then choose the most appropriate method to address the interference and accurately determine the concentration of FeSCN2+.