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Analytical Chemistry, Medical Device, Microbiology, Toxicology

FTIR – A Helpful Tool to Determine Chemical Composition

by Shalini Chandrasekaran

Fourier-transformed infrared spectroscopy, also known as FTIR, is a method of analyzing both organic and inorganic materials, and can provide a breakdown of their molecular makeup.

Using FTIR, one can analyze the chemical makeup of a material, by examining the chemical bonds and composition. FTIR is useful for both organic and inorganic material. It also measures covalent bonding pairs and functional groups within a material.

FTIR takes advantage of a material’s absorbance of light, using the way different molecular compounds react to the infrared beam in order to determine the makeup of the material under analysis. This method is known as absorbance spectroscopy, and can be performed in a variety of ways, including shining a beam of light with a limited group of frequencies through a material, or using monochrome light. FTIR in particular works by using multiple different frequencies in its beam, with each frequency reacting to the material in a different manner. In this way, one can isolate the FTIR signatures, and analyze what wavelengths are absorbed. Different compounds peak at different locations on the horizontal axis, such as the 2349^-1 cm peak of Carbon Dioxide, or the 1450^-1-1380^-1 cm peak of Sulfate. The vertical height of these peaks, meanwhile, reflects the amount of the material present. With these two known values, one can calculate the total molecular makeup of a material, and compare it to similar materials on record. Therefore one can accurately determine the composition of an unknown material.

Case Study – A Comparison of Polyethylenes

At Pacific Bio Labs, we utilize an Agilent Technologies Cary 630 FTIR to perform our spectroscopy. To demonstrate the FTIR’s ability to determine material compositions, we analyzed three polymers commonly used in medical device materials or packaging: High Density Polyethylene (HDPE), Medium Density Polyethylene (MDPE), and Linear Low Density Polyethylene (LLDPE). After storing the spectroscopy results, we exposed the polymers to constant UV light for 12 days, re-analyzed the materials, and then exposed the polymers to acid and oxidation, taking a reading after each stressor.

In Chart 1, you can see differences between the HDPE, MDPE, and LLDPE polymers based on differences in the presence of certain chemical bonds. Our Agilent software helped us confirm the compositions of the polyethylene, and also compared it to a list of other similar molecular candidates. After stressing the polymer with UV light, acid, and oxidation we analyzed for chemical changes. These changes were most notable for LLDPE (see Chart 2).


Chart 1: HDPE, MDPE and LLDPE polymers before exposure to stressors
Chart 2: Changes in LLDPE after exposure to stressors

FTIR can also detect material degradation, so one can test products under real-time or accelerated conditions.  At Pacific BioLabs, we use FTIR to test for the identity of raw materials, drugs, and medical device materials, as well as for impurities within a material or compound. It is also utilized in the search for unknown chemicals. FTIR analysis is often a part of medical device chemical characterization studies for leachable and extractable compounds.

-Written by Owen Dombrowski and Ben Foehr

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