Becoming an Expert: FTIR and Raman Spectroscopy
Introduction:
Fourier Transformation Infrared Spectroscopy (FTIR) is used for qualitative analysis of
compounds, and more recently for quantitative analysis of compounds. FTIR detects the
vibration characteristics of functional groups in an analyte. When exposed to the FTIR’s
infrared light, chemical bonds bend, contract, or stretch in a manner that is unique to each
functional group, creating a spectrum of wavelength absorbance.
Raman Spectroscopy is used for qualitative analysis of compounds and is based on the inelastic
scattering of monochromatic light, which forms a spectrum that can be analyzed, similarly to that
of the FTIR, to give the types of functional groups in an analyte.
Purpose:
The purpose of this lab was to become proficient with both the FTIR, and Raman instruments, as
well as to develop skills creating calibration curves and interpreting the data received from the
instruments.
Student Operating Procedures:
FTIR:
1. Make sure than the instrument is on.
2. Make sure that the black lever between the FT-IR and the Raman is down
3. Double click on the Varian Resolutions Pro icon in the top right of the display.
4. In the Current scan menu on the bottom of the screen select IR scan.
5. From the Collect menu at the top of the screen select Rapid scan
6. the Electronics tab parameters should be:
speed: 20 KHz
Filter: 5
UDR: 2
7. the Optics tab parameters should by:
IR Source: Mid-IR
Beam: internal
Detector: DTGS
Beamsplitter: KBr Broadband
Accessory: none
Optical filter: none
Aperture: 4 cm-1 at 2000 cm-1
8. click setup. The voltage reading should be between 1-5V. If not, change the selectivity
9. Click background to run a background scan
10. Return to rapid scan from the collect menu and click scan
The transformers menu allows you to convert to %T
11. To shut down, close Varian Resolutions Pro and LEAVE EVERYTHING ON
~~~*~~~
Raman Spectroscopy:
1. Fill the blue dewar with liquid nitrogen and wait 20 minutes then top off.
2. Make sure the FTIR is on
3. Turn on the laser power supply switch and then turn the key to the on position
4. make sure the lever between the Raman and FTIR is up, the lever between the Raman and
microscope is down, and the internal lever in the Raman should be up, meaning bypass closed
5. double click on the Varian Resolutions Pro icon to open software
DON’T USE SOFTWARE UNTIL SAMPLE IS LOADED (SEE TROUBLESHOOTING)
6. From the current scan menu select Raman scan
7. the optics parameters should be:
IR Source: off
Beam: right
Detector: Raman Ge
Beamsplitter: quartz near IR
Accessory: FT-Raman
ATR Crystal: none
Optical filter: holographic notch
Aperture: open
8. select the laser tab and click turn on diode
9. press the shutter switch on the front of the Raman (to open) and turn the power to its highest, 3
10. under the laser tab, adjust laser control current until the Raman display reads between 600700 mW
11. Click setup. If filled with noise, click autoscale (the four arrows)
12. adjust same with X, Y, and Z, knobs until the centerburst is at its maximum
13. click scan
14. to shut down: collect menu> Raman scan> Laser tab and click turn diode off. Press the
shutter button (closed), remove your sample, turn off the laser power supply and turn key to off
position, and exit Varian Resolutions Pro. Leave everything else on!
Troubleshooting:
FTIR using the HATR accessory:

If when running a background scan, only noise shows up, make sure that the trough is in
the HATR accessory

Before click scan, make sure you load your sample

Make sure to clean and dry trough thoroughly in between different samples to avoid
contamination

When installing the HATR accessory, put the immovable side against the left wall face of
the FTIR and the movable end against the right wall face of the FTIR, fully extended.
~~~*~~~
Raman:

If after clicking “setup” the signal remains around .002 V, and doesn’t change with
movement of the sample or by opening the lid/turning off the laser, then the detector is
not picking up any signal. Talk to Donna or an instructor/lab assistant.

When filling the blue dewar with liquid nitrogen, make sure that it is overflowing after
the first time you fill it, and after the 15-20 minute waiting period, top it off with more
liquid nitrogen because if the detector isn’t cool enough it won’t work.

The red dot, is not actually red, it’s more of a pale pinkish. To find it, lower the lid about
halfway and then adjust the X, Y, and Z knobs to center it.

If you are having trouble finding the center burst, play around with the knobs for a few
more minutes, but if you’re still unsuccessful, press the shutter button, open the lid, and
re-center the sample on the red dot by eye. It should work or be very close after that, so
don’t more it far in any direction. Most center bursts are not as defined as the example in
the provided SOP, but Donna’s acetaminophen(s) sample has a very good center burst.
Method:
Day one:
A compound with s known FTIR spectrum, 2-Propanol(l), was analyzed to both verify the FTIR
was properly operating, and to provide a spectrum for the known analyte.
Day two:
The blue dewar behind the Raman instrument was filled with liquid nitrogen and the laser turned
on, however the instrument’s detector was not functioning, as per Donna. FTIR spectra were
obtained for known analytes 2-Butanone(l) and Toluene(l).
The three FTIR spectra showed the characteristic peaks for each of the three known analytes: a
broad O—H peak, a sharp carbonyl peak, and the two C—C aromatic peaks for 2-Propanol, 2Butanone, and toluene, respectively.
Spectra are located in lab book.
Day three:
With the Raman working, scans of Acetaminophen (s) and Methyl Salicylate (l) were collected.
The two scans seemed very similar, so a scan of 2-Propanol was done in addition in order to
confirm that the scattering was from the compounds and not the glass in which they were held.
Spectral comparison confirmed that the scans were of different compounds with similar
structures.
Spectra are located in lab book.
With the Raman scans completed, an FTIR calibration curve was needed. FTIR scans of
solutions containing Toluene, 2-Butanone, and 2-Propanol in ratios of 1:1:1, 1:2:1, and 2:1:2,
respectively were done. The resulting spectra, located in the lab book, show the relationship
between the percent composition of the three compounds and the percent transmittance of the
peaks unique to each of the compounds. For toluene, the C=C aromatic peaks at 1500 cm-1 and
1600 cm-1 were analyzed, for 2-butanone, the C=O peak between 1650-1800 cm-1 was analyzed,
and for 2-propanol, the O—H alcohol peak, a broad peak between 3000-3300 cm-1, was
analyzed. The resulting data were regressed, resulting in the below equations for percent
composition.
NOTE: for toluene, the percent compositions calculated by the two equations should be averaged
together.
Toluene
1500 cm-1 Peak
Percent Composition (y)
100
40
33.33
25
Percent Transmittance (x)
39
74
69
76
1600 cm-1 Peak
Percent Composition (y)
100
40
33.33
25
Percent Transmittance (x)
9
35
39
54
2-Butanone
Percent Composition (y)
100
50
33.33
20
Percent Transmittance (x)
0
3
11
30
2-Propanol
Percent Composition (y)
100
40
33.33
25
Percent Transmittance (x)
19
56
61
74
Regressed Equations
% Composition Toluene = -1.75392(x) + 109.65429
= -1.94001(x) + 174.7936
(1600 cm-1)
(1500 cm-1)
% Composition 2-Butanone = -2.05128(x) + 73.3966
% Composition 2-Propanol = -1.43151(x) + 124.73693
Unfortunately, there was insufficient time to run a mixture of unknown concentrations on the
FTIR and calculate the percent composition of each component using their respective percent
transmittance per peak(s) of interest.
Day four:
A mixture of unknown proportions of Toluene, 2-Butanone, and 2-Propanol was scanned using
the FTIR. The resulting spectrum is located in the lab book. To denote the presence of all three
compounds, peaks for C=C aromatic at 1500 cm-1 and 1600 cm-1, C=O carbonyl at 1650-1800
cm-1, and O—H at 3000-3500 cm-1, representing Toluene, 2-Butanone, and 2-Propanol,
respectively. These peaks were present and the percent transmittance for each of the
characteristic peaks was measured, with both of the Toluene peaks being utilized, resulting in the
following data:
Bond
C=C 1500 cm-1
C=C 1600 cm-1
C=O
O—H
Percent Transmittance
48
76
5
61
In order to determine the percent composition of the three compounds, the equations derived on
day three were used, resulting in the following:
Conc. of 2-Propanol = -1.43151(61) + 124.73693
Conc. of 2-Propanol = 37.41%
Conc. of 2-Butanone = -2.05128(5) + 73.3966
Conc. of 2-Butanone = 63.15%
(1500 cm-1) Conc. of Toluene = -1.94001(48) + 174.79136
(1500 cm-1) Conc. of Toluene = 81.67%
(1600 cm-1) Conc. of Toluene = -1.7539(76) + 109.65429
(1600 cm-1) Conc. of Toluene = -23.64%
Conc. of Toluene = (81.67 -23.64)/2
Conc. or Toluene = 29.015%
Total = 37.41% + 63.15% + 29.015%
Total = 129.575%
Conclusions:
While the proficiency with both instruments dramatically increased over all four days, the results
were les than satisfactory. Good spectra of 2-Propanol, 2-Butanone, and Toluene were procured
from the FTIR and good spectra were obtained from the Raman of Acetaminophen, Methyl
Salicylate, and 2-Propanol. However, even with good spectra, the calibration curve comprised of
the data from the FTIR scans did not yield an adequate set of equations for determining the
percent composition of 2-Propanol, 2-Butanone, and Toluene, as evidenced by the total of
129.575% composition of the unknown mixture. Possible reasons for this include but are not
limited to the relative imprecise measurement of volume for the known concentration mixtures,
the imprecision of measuring the percent transmittance manually, and the apparent inaccuracy
with which the Toluene peaks’ transmittance, specifically, were measured.