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Chemistry Forums for Students => Organic Chemistry Forum => Organic Spectroscopy => Topic started by: Arkcon on March 26, 2014, 02:41:58 PM

Title: A specific and general question on FTIR spectral ID
Post by: Arkcon on March 26, 2014, 02:41:58 PM

Say guys, I have a general question, and a specific one, on using an FTIR to identify what an impurity might be.  I have some peaks and I know their wavenumber, and I was hoping I could find an online reference that would tell exactly what functional group I was looking at.  Various resources (mostly online, but I did check my old org chem book,) tend to give ranges, and I don't see how these peaks exactly match.  So I was hoping someone had a resource with a more specific id for these peaks.

These two peaks are in a blown up section of a scan of potassium sorbate samples.  The black line is the USP standard.  The red and blue lines are samples I'm interested in.  The nearest guess I can make is the ATR crystal may have been contaminated by methanol or acetone used to clean it.  But the problem doesn't go away for these samples if I retake the background, and it doesn't appear in all samples, or for other chemicals.

Title: Re: A specific and general question on FTIR spectral ID
Post by: marquis on May 20, 2014, 07:44:13 PM

Perkin Elmer software for their IRs used to include PSU's (possible structural units)
as one of the search tools.  Haven't seen it on line, but a PE salesman might run it
through as a courtesy.

Title: Re: A specific and general question on FTIR spectral ID
Post by: Furanone on July 18, 2014, 10:42:39 PM

Can I ask if you have the whole ATR-FTIR spectra from 400-4000 cm-1 and are these two peaks the only peaks that are additional. Below is a whole spectra for FTIR of potassium sorbate I have run, and when I blow up the area from 1000-1160 cm-1 I do not see the peak at 1056 but I do see a very small peak at 1033 cm-1.

Another question I have concerns the two samples tested, the red and blue line, were these the same sample that was tested one after the other? The increase in the two contaminating peaks could mean they are absorbing something from atmosphere while being tested since the blue gets proportionally bigger than the red sample while the regular potassium sorbate peaks at 1008 and 1148 cm-1 remain at constant level.

I am only speculating, but it could be an anti-caking agent added to materials in very small amounts <1-2% to prevent clumping.

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fi60.tinypic.com%2F261p3kj.jpg&hash=0590df9e71327be3ea949bc4cb2fcae3666984e2)