Infrared Spectroscopy (FTIR) Analytical Capabilities
- Identifies chemical bond functional groups by the absorption of infrared radiation which excites vibrational modes characteristic of various chemical bonds
- May be used in transmission mode
- In attenuated total reflectance (ATR) mode, the detection depth is generally 1-2μm deep, but can be much less or a bit more dependent upon the material. Black, absorbing materials tend to have lower sampling depths and sometimes provide too weak a signal as a result
- Especially capable of identifying the chemical bonds of organic materials
- Detects and identifies organic contaminants or additives
- Determines bonds undergoing degradation reactions or changing with processing
- Identifies water and carbonate, phosphate, sulfate, nitrate, nitrite, and ammonium ions, silica and other inorganic chemicals
- Detection limits vary greatly, but are sometimes <1013 bonds/cm3 or sometimes sub monolayer
- Useful with solids, liquids, or gases
FTIR Spectroscopy System Capabilities
- In transmission mode, area of analysis is about 1mm x 1mm. Liquid layer thickness may be from sub-micrometer to a few millimeters. Sample material may be dispersed on KBr pellets. The sample lateral dimensions may be at least 12in x 12in.
- Using the Specac Golden Gate ATR, the area analyzed is about 0.6 mm x 0.6mm. The thickness may be from sub-micrometer to a few millimeters. The width of a sample must be less than 108 mm or about 4¼ inches. The window is a rugged type IIa diamond. Pressure is applied on the sample at a uniform setting of 80lbs. by a sapphire anvil. This will deform many samples and may make the analysis destructive.
- Using the Pike Technologies Veemax II variable angle specular reflectance accessory, the sample may be many centimeters thick. The surface should be flat and relatively smooth. Sample widths must be less than 196mm or about 7¾ inches. This accessory is especially useful for thin coatings on metal surfaces, polymer films on semiconductor wafer surfaces, or thin films on glass slides where a high sensitivity to a thin layer is required. Variable angle specular reflectance allows the depth of analysis to be varied and can be useful for looking deeper into a surface than ATR FTIR does. This technique can be useful for measuring organic film thicknesses as well.
- The spectral range is from 7800 cm-1 to 400 cm-1
- Resolution up to ½ cm-1
- Signal-to-noise ratio greater than 42000:1
- Temperature controlled DLATGS detector
- 62° Michelson interferometer with retro-reflecting corner cube mirrors
- KRS-5 interferometer and DTGS detector windows
FTIR Spectra Databases
While chemical bond type identifications can be very useful for identifying strange and unusual material compositions or to understand materials degradation or processing problems, it is very useful to have large databases of FTIR spectra when one wants to match a particular substance to various specific manufactured products. Even when a particular material does not precisely match a manufactured material in a database, it is often helpful to know what products are similar to it. We presently have the following materials databases to assist us in these identifications:
- Fiveash Data Management FTIR Databases (24,470 Total Spectra)
Polymers and Polymer Additives (577 Spectra)
Surfactants (429 Spectra)
Organic Compounds Important to Industrial Processes (951 Spectra)
Minerals and Inorganic Compounds (311 Spectra)
Drugs and the Canadian Forensic Laboratory Spectra (3,750 Spectra)
Vapor Phase Spectra of Organic Compounds (5,227 Spectra)
Comprehensive Organic Compounds (10,321 Spectra)
Organics ATR FTIR (1005 Spectra)
Polymer, Plasticizer, and Monomer ATR FTIR Spectra (793 Spectra)
Essential Oil and Food Oil ATR FTIR Spectra (424 Spectra)
Inorganic Compound ATR FTIR Spectra (470 Spectra)
Dye, Stain, and Pigment ATR FTIR Spectra (163 Spectra)
Pharmaceuticals and Illicit Drug ATR FTIR Spectra (445 Spectra)
Adhesive and Sealant ATR FTIR Spectra (177 Spectra)
Cosmetic and Personal Care Product ATR FTIR Spectra (567 Spectra)
Forensic Vapor Phase FTIR (644 Spectra)
High Resolution Vapor Phase FTIR (434 Spectra)
- JASCO compound database of 900 compounds with emphasis on polymers
- Know It All JASCO Edition compound database with 10,000 compounds with a per use fee to obtain matching spectra
- AME, Inc. Compiled Compound and Materials Database
Sample Spectrum: Adhesive of Double Sided 3M Tape
Sample Spectrum: Low Density Polyethylene (LDPE) Trash Bag
Applying FTIR to the Identification of Products Formed from an Overheated Silicone Material
A composite aerospace structure was subjected to a flame resistance test with longer burning after the flame was removed than expected. The metal hardware in the structure was found afterward to have a melted red material at the base of the metal anchored in the composite material known to be a red siloxane based material. Further out on the metal hardware, the surface was covered with a black material, and still further out there was a thin layer of a slightly milky to clear material. FTIR was used to determine the chemical nature of these materials. XPS analysis was also used to characterize them.
The FTIR spectra taken with the ATR attachment of the three materials, the melted red (spectrum in black), charred black (spectrum in green), and the nearly clear material thin layer (spectrum in blue), are shown in the overlaid spectra below:
We searched the databases of FTIR spectra below and found a match with a high spectral correlation between the melted and bubbled red material on the metal hardware and a red RTV gasket forming material made by Permatex with product number 28BR with a good resistance to thermal degradation. Our unknown red material spectrum is shown in black and the red spectrum is the Permatex RTV 28BR material. The small differences in these spectra are explained by a small loss of methyl groups and increased oxidation. XPS analysis measured the decrease in carbon relative to a good dimethyl siloxane to be 2.5% and the increase in oxygen to be 21%, with much of the increase in the form of hydroxyl groups.
The milky white to clear material from the hardware is shown in blue in the overlaid spectrum above and the reference silica gel material is shown in blue. XPS showed this material to be a highly disordered silica, but not really a silica gel. Silica gel is often similar and has a high degree of disorder, but this material was quite devoid of hydroxyl groups.
It appeared that the melted red material, the black charred material, and the milky to clear materials were the degradation products simply of the overheated siloxane material from the composite material. We had a red gasket forming Permatex RTV 26BHTR material available in the laboratory. We overheated it and obtained similar bubbled and melted red material, black charred material, and a nearly clear material of silica, depending on the temperature of heating and the time of heating. No other material was found, so the highly combustible material was apparently completely vaporized. The unexpected burn in the flame test may have been caused by under-cured siloxane resin or by a flammable volatile contaminant. It was apparent that raw composite material unexposed to such heat needed to be examined in addition to the residues on the hardware. We had requested such material for the investigation from the beginning with this in mind, but did not receive it. Sample selection is usually critical in investigations.
Questions specifically about FTIR analyses should be directed to Kevin A. Wepasnick, Ph.D. by phone or by e-mail at email@example.com