Fourier Transform Infrared Spectroscopy (FTIR)
Introduction:
FTIR analysis is one of the most widely used techniques in identifying compounds and bonds in organic and inorganic materials. It is part of spectroscopic analyses. FTIR analysis is based on studying the infrared radiation absorbed by the analyzed sample. By examining the infrared spectrum emitted from the device, it is possible to identify chemical bonds, molecular interactions, and especially the types of functional groups present in the materials.
Principle of the Test:
Fourier Transform Infrared Spectroscopy (FTIR) is an advanced technique used to explore chemical bonds and functional groups in materials. Through this method, it is possible to determine the presence or absence of certain bonds, as well as measure changes in their levels, making it an essential tool in various fields, including chemistry, polymers, pharmaceuticals, material engineering, nanotechnology, biotechnology, environmental protection, and the oil and gas industries.
When the sample is exposed to infrared radiation, its molecules start vibrating. To understand this phenomenon, it is important to know that molecular energy consists of four components: electronic energy, vibrational energy, rotational energy, and translational energy.
Infrared radiation only affects the vibrational modes of molecules. In their normal state, molecules vibrate at their equilibrium positions without changing their center of gravity. The number of vibrational modes varies according to the type of molecule; diatomic molecules have one vibrational mode, while more complex molecules have multiple modes.
Not every vibrational mode can be detected by FTIR; only the modes known as “infrared-active” can absorb radiation. When the infrared frequencies match the natural vibration frequencies of the molecules, energy is absorbed, leading to increased amplitude of the chemical bond movements. It is important to note that only bonds with a dipole moment can absorb infrared radiation.
FTIR is a unique technique as no two molecules with different atomic structures can absorb infrared radiation in the same way. Thus, the resulting spectrum serves as a unique fingerprint for each material, facilitating the identification of functional groups, bonds, and molecular structures.
The infrared region is characterized by the complexity of its spectrum, containing more absorption regions compared to ultraviolet and visible ranges. The results are presented as vibrational frequencies, and using Fourier transforms produces a spectrum showing the absorption or transmission percentage according to the wavelength.
To distinguish functional groups, specific tables indicating the vibrational positions of different bonds can be used. For example, absorption at a wavelength of 3400 nm corresponds to C-H stretching, while absorptions in the range of 5000 to 6800 nm correspond to triple bonds, highlighting the superior capability of FTIR in analyzing chemical substances.
Measurement Benefits:
FTIR is an advanced technique used in a variety of applications, including:
Sample Analysis: Solids, powders, and liquids.
Powders: Studying physical and chemical properties.
Gases: Analyzing gas components in the air.
Determining Solution Concentrations.
Drug Release Studies: Analyzing drug release from specific delivery systems, enhancing treatment efficacy.
Pollution and Organic Impurity Diagnosis: Identifying and evaluating pollutants such as particles and organic waste.
Organic Material Identification and Analysis: Studying solids, powders, films, and liquids to determine their chemical composition.
Quantifying Oxygen and Hydrogen Ratios: Measuring the amounts of O and H in silicon and SiN wafers (e.g., Si-H and N-H).
Functional Group Diagnosis: Identifying specific functional groups and their elements.
Comprehensive Sources for Composition Determination: Providing rich sources for identifying chemical compositions through the resulting spectrum.
Environmental Conditions: Operating in non-vacuum conditions, making it suitable for volatile elements.
Typically Non-Destructive: Does not affect the sample during analysis, preserving its integrity.
Studying Absorption and Transmittance Characteristics: Analyzing material absorption and transmission in a specific wavelength range.
Types of Samples That Can Be Measured:
Powder Samples:
Preparation Method: The target material powder is mixed with KBr salt powder using a special mortar (usually made of sapphire). The mixture is then placed in a special mold and pressed under relative vacuum to remove air, forming a disk with specific dimensions.
Advantage of Using KBr: KBr salt does not absorb infrared radiation, making it suitable for preparing powder samples.
Gaseous Samples
Liquid Samples:
Preparation Method: Usually, liquid samples are poured directly into special containers, similar to powder sample preparation.
Solid Samples Capable of Infrared Transmission:
Preparation Method: These samples often require more complex preparation depending on the sample type and device specifications. A common method involves converting samples into powder and using powder analysis techniques.
Solid Samples Not Capable of Infrared Transmission:
Preparation Methods: Due to their inability to transmit infrared radiation, two main methods are used:
1. Converting the bulk sample into powder and using powder analysis techniques.
2. Using an FTIR device equipped with ATR (Total Reflectance) technology, where chemical bonds are analyzed through the surface reflection of the sample.
Result Analysis:
FTIR is an advanced technique used in analyzing various materials, offering broad capabilities across different infrared ranges. These include:
Wavelength Range:
Analysis can be performed in the MidIR and NIR regions, allowing the study of a wide range of materials.
Chemical Bond Analysis:
FTIR provides the ability to analyze chemical bonds and identify unknown samples in various fields, including pharmaceuticals, polymers, dyes, ceramics, and metallic materials.
Total Reflectance Analysis (ATR):
Allows FTIR analysis using ATR technology, requiring flexible samples and enabling the study of materials in different states.
Specialized analysis using FTIR or ATR can study:
Vibrations of ceramic and metallic materials: Understanding the physical and chemical properties of these materials.
Vibrations of functional groups under different conditions: Studying the impact of environmental factors or chemical composition on material behavior.
Additive Studies: Understanding the impact of additives on material properties.
Analyzing Molecular Interactions in Composite Materials: Studying how different components interact and affect the overall performance of the materials.