Infrared Spectroscopy (FT-IR)

Infrared spectroscopy is a technique used to identify various functional groups in unknown substances through the identification of different covalent bonds that are present in the compound. By identifying the different covalent bonds that are present in a compound, you can establish the types of functional groups present. By comparing the absorptions seen in an experimental spectrum to the literature absorptions of various functional groups, you can determine a list of possible identities for the bonds present.

An interactive web tutorial Infrared Spectroscopy and Organic Functional Groups provides more specific information about how you can use IR spectroscopy to identify functional groups.

Apparatus

Procedure
FT-IR spectra may be run from 8 AM to 6 PM Monday-Friday ONLY. If you want to run one during another lab, please get the Instructor's approval.

1. Open the Spectrum Application software.

2. Select user name “Analyst” from the drop down menu.

3. Select the instrument “SpectrumA” or ”SpectrumB” from the drop down menu.

4. If the commands on the toolbar are in gray tone, then a background spectrum has not been run.  You will be prompted to do this when you set up to scan so do not put any sample on the plate yet.

5. From the “Instrument” drop done menu list, select “scan”.

6. In the “Scan Instrument Setup” display screen, type in your sample name.

7. If you need to run a background, click on “start” and the “Scan Progress Display” will open up prompting you to clean the sample plate.  Click on “scan” and the FTIR will start collecting 4 scans for the background.  When it is finished it will prompt you to place your sample on the plate and click on start.  If your sample is liquid, proceed as prompted and the system will acquire 4 scans.  There is one more additional step required for solid samples and you need to close out of the Sample progress menu to get back to the “Scan Instrument Set-up” display

8. FOR A SOLID SAMPLE:  Click on the monitor icon at the left hand corner of the “Scan Instrument Setup” menu. (Blue & white dial with the red arrow)   A screen will appear with a green bar at the bottom of the menu labeled “Force Gauge”.  Place a small amount of your sample on the plate over the crystal.  Gently move the force gauge over your sample. Turn the knurled top of the force gauge slowly clockwise while monitoring the green bar on the display screen.   Do not exceed 100% force.  When the force is sufficient, click on stop.  This returns you to the “Scan Instrument Setup” display. Click on “start” then click on “scan” in the next display.

Analyze and print your data:

A. You can click on the Peaks icon to automatically label your peaks. Clicking a second time removes the labels. To label peaks in another way , click on the vertical cursor icon, Vcursr, then drag the green line over the peak and double click. (If you need to adjust the threshold, choose Peak Table from the Process menu drop down list and set a new threshold. Close Peak Table, then click on peaks twice, (once to remove the old labels and again to show the new) then click on the box to enlarge the image.)

B. You may zoom a region of the spectrum by dragging a box around the region of interest and then double clicking inside the box. The AutoX and AutoY icons will resize the spectrum to full scale.

C. Click on the Text icon to add text to your spectrum. You have control of the font, and you can drag the text to a new position after it is written.

D. Click on the Print icon to print a copy of your spectrum.

E. Click the Delete icon to clear the screen for the next user, or File...Exit if that is appropriate.

CLEAN UP! Follow the directions from your instructor to clean off the sample area.

The following is an example data table which you should use to display the data given in your infrared spectra.

(Literature IR frequency absorptions were taken from Table 1 below) 
 

Table 1: Principal IR Absorptions for Certain Functional Groups above 1400 cm^-1.

Printable IR Table