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Hello my name is Taina Matos. I am a Ph.D. candidate at Norfolk State University and
today I'm going to guide you through the usage of FTIR spectroscopy or better known as Fourier
Transform Infrared Spectroscopy. The reason why we tend to use this is to identify
functional groups by their different vibrational modes.
So these transparent discs are salt plates used for FTIR and they are made from sodium
chloride and they're very fragile, so the first thing that we want to do is to sandwich
them together and place them on the salt plate holder. And carefully we are going to put
the top on it applying a little bit of pressure without cracking the actual plates.
So this is how they look. So in order to place our sample in the FTIR
instrument cavity we are going to open it and we're going to slide our sample holder
making sure that the laser is going through the sample and you can do that easily by either
putting a piece of paper or by placing your hand and seeing the laser beam.
Then we close it- make sure it’s securely closed- and we start running our sample.
And note this FTIR when you're using a purge system keep in mind that when you open the
cavity box you are letting atmospheric carbon dioxide and water vapor in. So once you close
it you're going to have to let it purge for about fifteen minutes or so, so you will not
longer half carbon dioxide and water vapor signals.
In order to bring up the software that we use for FTIR we’re going click on the Opus
icon and we're going to enter the password. The first window that pops up is “About
OPUS” so we click ok. And the first thing in the screen you are
going to have a variety of different buttons on the top of your page. And the first thing
they want to do is we want to go to measure and from measure we go to advanced measurement.
Once the measurement window opens with we’re going go into to “basic” we're going to
make sure that the experiment is MIR.EPN we going to enter the operator’s name, the
sample name, in this case octadecylphosphonic acid and after that we're going to click on
advanced. So we already went to the experiment which
is already “load” we went to the filename which is the file name that you want your
sample to be called so I will put ODPA, the path that you would like to select, and then
we'll move on to the resolution box which we want to have a 4 centimeters inverse.
The sample scan time this normally run sixteen scans and the background scan time should
be the same or higher than the sample scan time. Then we go to the “save data” box
and he's pretty much the range of the spectrum that you want to scan. So we want to scan
from 4000 to 500 centimeters inverse. Then we'll move onto the “results spectrum”
and we want to make sure it’s on transmittance then we move on to the “data block's to
be saved” box in which we want “transmittance, single-channel, and background” to be checked.
And after that we moved back to the basics tab.
In the basic stuff the first thing that we're going to deal before we load our sample is
still run a background scan of the salt plates they we are going to use.
So now we are ready finished running our background and we're going to remove the salt plates
out of the sample holder. We are going to put our sample in between the salt plates
and we're going to use of a little amount of sample just a little drop.
And we're going sandwich the sample in between, carefully placing it again in the sample holder.
And now we are ready to run our sample. After the background signal is completed now
we're going to move on to run our actual sample and we do that by clicking on “sample single-channel”.
After our data is collected we pretty much obtain a signal or a spectrum in the front
page as soon as the experiment is completed. On the y axis we have the transmittance and
on the x-axis we have the range of the spectrum or the wave number and centimeters inverse.
These peaks are characteristics of different vibrational modes on molecules or vibrational
modes of the bonds. And specifically in this area and here it is between 2900 and 2800
pretty much this is characteristic of the CH2 stretching of symmetric and asymmetric
vibrational modes of carbon bonded to hydrogen.