Light Source: GlobarSilicon Carbide Rod (5mm diameter, 50 mm long)
Heated electrically to 1300 – 1500 K
Positive temperature coefficient of resistance
Electrical contact must be water cooled to prevent arcing
Ingle and Crouch, Spectrochemical Analysis
Suspension Media for Solid Samples
Pretsch/Buhlmann/Affolter/Badertscher, Structure Determination of Organic Compounds
Ingle and Crouch, Spectrochemical Analysis
Michelson Interferometer
Split source into two beamswhose path lengths can bevaried periodically to giveinterference patterns.
Michelson Interferometer
http://www.newport.com/Introduction-to-FT-IR-Spectroscopy/405840/1033/catalog.aspx
Interferograms
Douglas A. Skoog and James J. Leary, Principles of Instrumental Analysis, Saunders College Publishing, Fort Worth, 1992.
Fourier Transform of the Interferogram Gives the Spectrum
Ingle and Crouch, Spectrochemical Analysis
Resolution: mx
1
Jacquinot’s Advantage: Resolution is not limited by aperture width. Can increase light throughput by 10-200 fold.
Multiplex Advantage (aka Fellget’s Advantage): Signal from all l are continuously monitored, increasing S/N.
S/N for average of n measurements:
Advantages of FT-IR over Dispersive IR
xNn
N
S xS
How long would it take to capture a dispersive IR spectrumfrom 500 – 5000 cm-1 with 3 cm-1 resolution elements if youcould scan one resolution element every 0.5 seconds? If youwant to increase your S/N by a factor of 2, how long will youhave to scan? If you collect FT-IR for the same length of time,what is the theoretical S/N advantage?
Are you getting the concept?
Evanescent Waves for TIR Microscopy
http://www.olympusmicro.com/primer/java/tirf/penetration/index.html
2
12
322
0
sin2 cf
p
nnd
Increased l → Increased dp
ATR-FTIR Spectroscopy(Attenuated Total Reflection FTIR)
Ingle and Crouch, Spectrochemical Analysis
ZnSe or Ge
Schematic of a FTIR Imaging Spectrometer
Koenig, J.L.; Wang, S.-Q.; Bhargava, R., Anal. Chem. 2001, 73, 361A.
Focal Plane Array
Colarussa, P. et al. Appl. Spectroscopy. 1998, 52, 106A.
Square array of MCT pixels
Indium electrical contactbetween each MCT contactand readout electronics layer
Total area ~ 1 mm2
Total time < 10 sec
FTIR Imaging: Dissolution of a Polymer
(a) Two materials are brought into contact and allowed to diffuse across the interface. The diffusion region develops over time. (b) An image is obtained by monitoring radiation passing through the sample at a direction perpendicular to the diffusion direction. (c) Concentration profiles for three different functional groups obtained from the same sample as in (b) (diffusion of a liquid crystal monomer at 265 K for 3 h).
Koenig, J.L.; Wang, S.-Q.; Bhargava, R., Anal. Chem. 2001, 73, 361A.
FTIR Imaging: Dissolution of a Polymer
FTIR images of the dissolution of poly(alpha-methylstyrene) with a mole weight of 31,000 as a function of time with a mixture of the good solvent methyl isobutyl ketone and the nonsolvent (C6D12).
Koenig, J.L.; Wang, S.-Q.; Bhargava, R., Anal. Chem. 2001, 73, 361A.