FTIR Analysis – Infrared Spectroscopy

Infrared Spectroscopy (FTIR)

 

FTIR Analysis or Infrared Spectroscopy Capabilities

  • Identifies chemical bond functional groups by their characteristic absorption of infrared radiation in vibrational modes 
  • 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, highly 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, silicones and other inorganic chemicals
  • Detection limits vary greatly, but are sometimes <1013 bonds/cm3 or sometimes sub monolayer
  • Useful in characterizing 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 MKII Diamond single-reflection ATR with KRS-5 lenses, 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 IIIa 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, though most spectra of solids or liquids are taken with 4 cm-1 resolution
  • 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
  • KRS-5 lenses are thallium bromoiodide lenses and have a nearly flat response in the entire IR range from 400 to 4500 cm-1 range, compared to ZnSe which is only flat above about 650 cm-1 and Ge which is only flat above 900 cm-1

The KRS-5 thallium bromoiodide lenses offer a flatter transmission to a lower energy in the infra-red spectrum than do ZnSe and Ge lenses


FTIR Analysis 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 or product types or even to a simple material. 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 (29,046 Total Spectra)

  • Polymers and Polymer Additives (580 spectra, 500-4000 cm-1 range, 4 cm-1 resolution)
  • Surfactants (430 spectra, 500-4000 cm-1 range, 4 cm-1 resolution)
  • Organic Compounds Important to Industrial Processes (950 spectra, 400-4000 cm-1 range, 4 cm-1)
  • Minerals and Inorganic Compounds (310 spectra, 450-4000 cm-1 range, 4 cm-1 resolution)
  • Drugs and the Canadian Forensic Laboratory Spectra (3,750 spectra, 500-4000 cm-1 range, 4 cm-1 resolution)
  • Vapor Phase Spectra of Organic Compounds (5,220 spectra, 500-3800 cm-1 range, 8 cm-1)
  • Comprehensive Organic Compounds (10,320 spectra,500-4000 cm-1 range, 8 cm-1)
  • Organics ATR FTIR (1515 spectra, 400-4000 cm-1 range, 2 cm-1 resolution, monolithic diamond crystal)
  • Organics ATR FTIR (422 spectra, 600-4000 cm-1 range, 2 cm-1 resolution, germanium crystal)
  • Polymer, Plasticizer, and Monomer ATR FTIR Spectra (1138 spectra, 400-4000 cm-1 range, 2 cm-1 resolution, monolithic diamond crystal except for 54 spectra Ge crystal)
  • Essential Oil and Food Oil ATR FTIR Spectra (460 spectra, 400-4000 cm-1 resolution, monolithic diamond crystal)
  • Inorganic Compound ATR FTIR Spectra (586 spectra, 400-4000 cm-1 range, 2 cm-1 resolution, monolithic diamond crystal)
  • Inorganic Compound ATR FTIR Spectra (498 spectra, 550-4000 cm-1 range, 2 cm-1 resolution, germanium crystal)
  • Dye, Stain, and Pigment ATR FTIR Spectra (150 spectra, 400-4000 cm-1 range, 2 cm-1, monolithic diamond crystal)
  • Dye, Stain, and Pigment ATR FTIR Spectra (150 spectra, 550-4000 cm-1 range, 2 cm-1, germanium crystal)
  • Pharmaceuticals and Illicit Drug ATR FTIR Spectra (439 spectra, 500-4000 cm-1 range, 2 cm-1 resolution, monolithic diamond crystal)
  • Adhesive and Sealant ATR FTIR Spectra (458 spectra, 400-4000 cm-1, 2 cm-1 resolution, monolithic diamond crystal)
  • Cosmetic and Personal Care Product ATR FTIR Spectra (570 spectra, 650-4000 cm-1 range, 2 cm-1 resolution, diamond Zn/Se or Ge crystal)
  • Forensic Vapor Phase FTIR (670 spectra, 500-4000 cm-1 range, 8 cm-1 resolution)
  • High Resolution Vapor Phase FTIR (430 spectra, 400-4000 cm-1 range, 2 cm-1 resolution)

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

FTIR Sample Spectrum
Sample Spectrum: Adhesive of Double Sided 3M Tape

FTIR Sample Spectrum
Sample Spectrum: Low Density Polyethylene (LDPE) Trash Bag

Applying FTIR Analysis 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.

We found that the unknown nearly clear thin layer on the hardware was a good match with a silicon gel material found in the FTIR spectral databases:

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 appears to have been completely vaporized.  We concluded that the unexpected burn in the flame test may have been caused by under-cured siloxane resin or by a flammable volatile contaminant.

In time, we were able to prevail upon our customer to supply the silicone materials in an unheated, but supposedly cured condition.  We were able to show that surfaces were covered with short-chain dimethyl siloxanes and that heating the materials, especially a silicone sealant used in the structure, caused an outpouring of very short-chain siloxanes which we measured using mass spectroscopy.  Such short-chain siloxanes are highly flammable.  The long-chain siloxanes are resistant to flame, while the short-chain siloxanes readily combust.

Further Applications of FTIR to Materials Analysis:

Distinguishing the Polytypes 4H and 6H of SiC Single Crystals, Known as Moissanite

Identifying Vile Liquid as Urine

Questions specifically about FTIR analyses should be directed to Kevin A. Wepasnick, Ph.D. by phone or by e-mail at ftir@andersonmaterials.com