FTIR Cary 630 - Simethicone Identification

Hi Scharf welcome to the Community!

I moved your question to the Molecular Spectroscopy Forum for better visibility.

Cheers,

Kristen

Hi Scharf,

The % transmittance is very very low across the entire spectrum (normally the signal varies from 100% down to 0% rather than 1% to 0%), and in some places it seems the signal is saturating the detector (the areas illustrating flat lines at zero). There is also some strange behaviour / "spikes" on either side of most peaks. Without additional information it will be difficult to comment, but I would be interested in knowing:

- What sampling interface / sample cell is being used to collect the data?

- What solvent is the background spectrum taken on?

- Does the Cary 630 FTIR currently pass its performance tests?

Hello David, first of all, thank you for your reply.

The sample cell used is the dialpath 0.5µm. The background solvent is the analysis blank, which is toluene.

The equipment is new and have passes all the performance tests.

I have made a few more tests, but I am still having problems with signal saturating the detector. Could it be that the background could not compensate these signals? (because they saturate the detector). For example, after collecting the background I read the same sample (blank) and get the current spectrum:

In my interpretation, there are a lot of problems. First, the scalling, which includes signal with transmittance higher than 100. Second, the flat lines. Also, normally in literature, the scale is reversed (0 being on top). 

I have also read the sample the same way as described before but using absorbance. 

The spectra here is overall better, but i get some signal with 5 Abs, which i think is the limit of my detector (5 Abs equals 10^-5 transmittance).

The problem is: these signal with higher absorbance do not maintain their wave number, and so I can´t properly use the spectra for identification.

Do you have any suggestion on what I could do to avoid those signal that saturate the detector?

The Dialpath accessory usually comes with one of two sets of pathlengths:

- 30, 50, 100 um

- 50, 100, 200 um

As far as I know, 0.5 um is not a support pathlength (minimum is 30 um). If the signal is saturating the detector (which seems to be the case, from what I can see above), then I recommend using a shorter pathlength than whichever one is being used, especially given that toluene has fairly intense absorbance bands.

I *think* this might solve the issue? Please let me know how you get on when you have a moment to try it out.

Hi, thanks again for the reply.

The cell I am using is 500 microns, not 0.5 µm, sorry, that was a typo.

My Dialpath apparatus contains the following sets of pathlenghts:

- 100, 500, 1000 microns

I have made some tests with the 100 microns cell, but there is still signal saturating the detector. The following image is the blank (toluene) spectrum using the 100 microns cell.

I have also made some tests with the ATR module (0.02 mm pathlength) but in this case It is not possible to properly identify the signal, because the band intensity is very low compared to the rest of the spectra. The following image shows overlay spectra, red being standard solution and blue being blank (toluene). The circled area shows the band of interest.

I have concluded that to proper identify the sample I would need a dialpath with pathlength 30 or 50 microns. The problem is that I am using an USP method as reference and It states that the cell must have 0.5 mm pathlength. My question is: using the current cell (0.5mm), is there a way of reading the sample without saturating the detector?