What is Infrared Spectroscopy Used for Determination of?

This test method is applicable to the positive identification of material by determination of the material Infra red Spectrum. Using 2 different apparatus.

A. Perkin Elmer Spectrometer

B. Spectrum 100 FTIR

Principle of Infrared spectrum

The sample has its Infrared Spectrum recorded and its identity is confirmed by comparing it to that of a known reference standard.


Observe proper laboratory safety rules, personal protection and chemical handling procedures at all times.

Read MSDS before handling chemicals and products.


A. Perkin Elmer Spectrometer

Perkin Elmer Spectrophotometer, Model No. 1600

Roland Plotter, Model: SketchMate

1mm NaCl (or KBr) liquid cell

NaCl plates ( or KBr)

NaCl disks ( or KBr)

2mL glass Luer syringe

B. Spectrum 100 FTIR

Procedure for FTIR Testing 

i) General Operation

Irrespective of the machine used, a good spectrum will not be obtained unless the SOP for FTIR is in good working order, has been properly calibrated, and the background baseline scanned before each test on either a cell or KBr plate. Detailed below are the most important points, but for more detail, reference should be made to:

a) Perkin Elmer Reference Manuals.

b) The Standard Specification for that particular material.

ii) Sample Preparation and Start-up Procedures


Determining the IR Spectra of Liquids

There are two methods for obtaining IR spectra for liquid samples :

1) The Cell Method of IR

This is most commonly carried out using a 1mm NaCl liquid cell. The cell is filled with the sample by using the 2mL glass luer. The syringe should be first flushed twice with the sample concentrate - this also applies to the cell.

When the cell has been flushed and filled, seal off the two filling ports. Make sure the cell is completely filled with liquid and contains no air bubbles. Wipe the cell with a tissue so as to absorb any excess sample from the outside of the cell. Do not wipe the windows as they will scratch.

2) NaCl Plate/KBR disc method

A small drop of sample is placed between two KBr plates/discs and a spectrum is recorded. The plates should be rinsed off with n-Heptane and dried if necessary with a tissue. The plates should then be placed back in the heated cabinet.

Determining the IR Spectra of Solids

There are two methods for doing an IR scan on solid samples:

Identification of material by determination of the material Infrared Spectrum

1) Nujol Mull Method

A very small amount of sample is ground using the agate mortar and pestle, then a few drops of nujol (ratio sample: nujol is 1 : 100) is used to moisten the sample. This mull is placed between NaCl discs, mounted on the two-pin holder, and scanned.

2) KBr Disc Method

This method utilizes Potassium Bromide discs. The discs are made by using a KBr press. Spectroscopy grade KBr is

added, at approximately 100 times the sample weight, to a small amount of sample and the mixture ground to form a

uniform dispersion. The powder mixture, sufficient to form a disc 0.5 - 1.0mm thick, is added to the die and compressed.

The resulting disc is mounted on the appropriate holder and scanned.

Points to note:

a) Cleanliness - no spillage of liquids.

b) Care of cells and plates (the handle by the edges).

c) Solid samples must be ground extremely fine before Nujol or BKr is added.

d) All reagents especially KBr, must be dry.


First Sample of the Day - Startup

1. Start the computer connected to the FTIR machine. The login screen will appear with User Name: QC Lab, leave the password blank and hit enter, Window will start.

2. Double click on the Spectrum icon to start the scanning program.

3. Log into the program:

User Name = administrator

Password = administrator

4. A pop up will appear asking to select an instrument, the computer automatically selects the spectrum 100, click OK

5. Click on the Setup tab at the top of the screen, select Learn from the drop-down menu, check that a new toolbar has opened at the bottom of the screen.

Background Scan

A background scan is required every time the spectrum program is started.

1. Click on the Instrument tab at the top of the screen and select scan from the drop-down menu.

2. Double click on the Open folder icon in the pop-up screen and select the appropriate file (UATR if using the UATR and default if using the KBr cell), this will set the correct parameters for scans and comparison.

3. Click on the Sample tab and rename the file 'background'. Click on the scan tab and under the Scan type drop-down menu select Background. Click on the apply button and again on the Start button ( there is a warning about a duplicate name, click OK) a black plot will appear, click on Scan.

4. After the scan is complete, an overwrite message will pop up, overwrite the old file

iii) Procedures for the use of the F.T.I.R.


The FTIR spectrophotometer is left switched on permanently.

Restoring the Factory Set-up

To avoid any problems, because a previous user has altered operating parameters, it is advisable to restore the factory


Press: Shift Restore and the soft keys Setup Factory

Note: Soft keys are located at the bottom of the screen.

Monitoring Energy Throughput.

Make sure that there is no cell in the sample compartment.

Press: Shift Monitor and the soft key Energy

The reading should be between 95 - 105 %

The FTIR has a hard disk which enables the storage of spectra and test methods. See chapter 10 and 11 of the Tutorials

for New Users for more details.


Samples Scan

1. Click on the Instrument tab at the top of the screen and select Scan.

2. Enter the details of the sample to be scanned:

Name: RB code+ Year Code+sample number ( e.g. 12026p6)

Description: RB description + lot number + Date of analysis [DDMMYY] ( e.g. N-Paraffin MSKU77777 061207)

3. Click Start. Follow the instructions in blue at the top of the screen( apply force only for powder or solid)

To compare

1. Select the sample to be compared by clicking on the name in the plot screen.

2. Click Play at the bottom of the screen.

A. comparison against all scan will appear with a comparison graph.

iv) Notes


Spectrum Appearance

The appearance should be run under conditions to give a good, clear strong spectrum. These will usually be standard operating conditions as specified in the Perkin Elmer Reference Manuals. Conditions should be the same as those for the standard.

A good spectrum has a baseline of no less than 85% transmittance indicating good I.R light transmission and clarity of sample. The strongest important peak should be 10-20% transmittance. Organic compounds usually absorb at 2800-3000 cm, 1450cm, and 1380cm. These peaks need not be kept above 0% transmittance as this will make other peaks too weak.


Saving samples

Close the comparison screen and graph. Click on the File tab at the top of the screen and select Save As. Save the scan in the C drive under the RB Library FTIR100 folder

FTIR Cleaning Procedure 

Clean the sampling plate/KBr cell after use with alcohol

Results :

For the identification of a material, the sample spectrum should be exactly the same as the standard. The only allowable difference is the baseline intensity and sample strength. All peaks (including minor shoulders) should correspond.

The quickest way to check a spectrum is to compare it with the standard spectrum, stored on the hard disk

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