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FTIR SPECTROSCOPY REFERENCE GUIDE
INTRODUCTION
Infrared spectroscopy is the study of the interactions between infrared
electromagnetic energy and matter. The technique of infrared spectroscopy
measures the vibrations of molecules, allowing for qualitative and quantitative
measurements of samples. A Fourier transform infrared (FTIR) spectrometer is
an ideal tool for the identification of unknown organic and inorganic samples
whether they exist in the form of a gas, liquid or a solid.
SPECTRAL RANGE COVERAGE
CARY 600 SERIES
SPECTROMETER OPTICS
Spectral range coverage for common sources, beamsplitters, and detectors.
The combination of these components generate a spectrometer’s working scan range.
Sources
Detectors
Wavenumbers (cm-1)
Wavenumbers (cm-1)
50,000
Reference laser
40,000
20,000
10,000 5,000
0
65,000 60,000 50,000
Deuterium
53,000 – 12,000
40,000
30,000
20,000
Radiation in the infrared region is commonly referred to in terms of a unit
called a wavenumber (ν), rather than wavelength (λ). Wavenumbers are
expressed as reciprocal centimeters (cm-1) and are the preferred unit as they
are directly proportional to energy. A higher wavenumber corresponds to a
higher energy.
Beamsplitter storage
Wavenumbers (cm-1)
Ceramic
9,000 – 29
50,000
40,000
Mercury Arc
600 – 10
Wavenumbers (cm-1)
30,000
20,000
10,000 5,000
0
10,000
7,500
5,000
UV-Vis Quartz
53,000 – 4,000
2,500
DLaTGS
18,000 – 150
Far-IR DLaTGS
700 – 20
Potassium Bromide
11,000 – 375
Convert a wavenumber (ν) to Energy (E) by multiplying it by the speed of light
(c, in centimeters per second) and Planck's constant (h):
0
Far-IR
detectors
Calcium Fluoride
18,000 – 1,200
Detector
1,250
MCT*
12,000 – 450
Near-IR Quartz
20,000 – 2,800
1
λ (cm)
10,000 5,000 0
Mid-IR
detectors
Convert a wavenumber (ν) to a wavelength (λ) by using the following formula:
20,000
Lead Selenide
16,000 – 2,000
Wavenumbers (cm-1)
40,000
30,000
Silicon
18,000 – 8,600
Beamsplitters
50,000
0
Silicon
18,000 – 8,600
Tungsten-Halogen
25,000 – 2,100
Interferometer
Infrared source
10,000
R446 Photomultiplier Tube
54,000 – 11,500
Xenon
40,000 – 10,000
ELECTROMAGNETIC SPECTRUM
ν (cm-1) =
30,000
*Multiple MCT detectors (narrow, mid & wide band) are available.
Cesium Iodide
6,000 – 225
Mylar (6-125 µm)
700 – 10
E (J) = h (J.s) x c (cm.s-1) x ν (cm-1)
4000
Sample compartment
Radio
Microwave
Far-IR
Mid-IR
Low
Near-IR
Wavenumber (ν)
Visible
High
UV
Low
X-Rays
Energy
Gamma
High
THE COMPLETE SOLUTION
400
(cm-1)
Short
Wavelength (λ)
Long
A portion of the electromagnetic spectrum showing the relationship of the
infrared region to other types of radiation (not shown to scale). The relationship
between energy, wavenumber, and wavelength is also highlighted.
COLLECTING AN FTIR SPECTRUM
There are three quick, simple steps involved in obtaining a spectrum of a sample:
INTERPRETING SPECTRA
Bond
C–H
Type of Vibration
Alkane
(stretch)
–CH3
(bend)
–CH2–
(bend)
Alkene
(stretch)
(out-of-plane bend)
Aromatic
(stretch)
(out-of-plane bend)
Alkyne
(stretch)
Aldehyde
Wavenumber Range (cm-1)
3000 – 2850
1450 & 1375
1465
3100 – 3000
1000 – 650
3150 – 3050
900 – 600
~ 3300
2900 – 2700
Bond
C–O
Type of Vibration
Alcohols, esters, ethers,
carboxylic acid, anhydrides
O–H
Alcohols, phenols
Free
H-Bonded
Carboxylic acids
Alkene
Aromatic
1680 – 1600
1600 & 1475
C–N
Amines
1350 – 1000
C^C
Alkyne
2250 – 2100
C=N
Imines & oximes
1690 – 1640
C=O
Aldehyde
Ketone
Carboxylic acid
Ester
Amide
Anhydride
1740 – 1720
1725 – 1705
1725 – 1700
1750 – 1730
1680 – 1630
1810 & 1760
C^N
Nitriles
2260 – 2240
N=O
Nitro (R–NO2)
1550 & 1350
S–H
Mercaptans
2550
C–X
Halides
Fluoride
Chloride
Bromide, iodide
1400 – 1000
785 – 540
< 650
STEP 1 Record a spectrum with no sample present. (Known as a ‘background’.)
STEP 2 Insert the sample into the spectrometer.
STEP 3 Record a second spectrum and interpret the data.
The key collection parameters are:
• The number of scans (background and sample)
• The scan range
• The spectral resolution.
In general increasing the number of scans that are co-added improves the
signal-to-noise ratio of the spectrum and can assist in the analysis of weakly
absorbing samples. The spectral resolution is user-defined and helps to
distinguish closely spaced absorption peaks, and is expressed in wavenumbers.
The simplified correlation table on the right allows users to extract structural
information from IR spectra. Computer-based search programs are also available
for assisting in compound identification.
C=C
N–H
Wavenumber Range (cm-1)
1300 – 1000
3650 – 3600
3400 – 3200
3400 – 2400
Primary & secondary amines & amides
(stretch)
3500 – 3100
(bend)
1640 – 1550
Several different accessories facilitate sample preparation
and spectral acquisition, including:
• Fiber Optic Probes
• Attenuated Total Reflectance (ATR)
• PM-IRRAS
• Diffuse Reflectance
• Photoacoustic Spectroscopy
• Specular Reflectance
• TGA-FTIR
• Grazing Angle Reflectance
• GC-FTIR
• Microscopy and Chemical Imaging
• GPC-FTIR
• ATR Chemical Imaging
(Micro and Macro)
A HISTORY OF COMMERCIAL 'FIRSTS'
First commercial
FTIR spectrometer
First FTIR
microscope
First dynamicallyaligned step-scan
interferometer
First rapidscanning FPA
chemical imaging
Cary 600
series FTIR
spectrometers
and microscopes
1969
1982
1992
2001
2008
1971
1991
1997
2004
2010
First use of an
MCT detector in
an FTIR
First infinitycorrected FTIR
microscope
First Mid-IR FPA
detector system for
chemical imaging
Varian, Inc.
acquired Digilab
Varian, Inc.
acquired by
Agilent
This information is subject to change without notice.
© Agilent Technologies, Inc. 2013
Published in Australia, Feburary 1, 2013
K8000-90009
*K8000-90009*
*K8000-90009*