What Is Fourier Transform Infrared Spectroscopy (FTIR)?
Fourier transform infrared spectroscopy (FTIR) is a non-destructive technique that reveals a material’s molecular structure from how it interacts with infrared light. Every chemical bond vibrates at characteristic frequencies. When infrared light hits a sample, the bonds absorb the wavelengths that match those vibrations, and the resulting spectrum works like a fingerprint of the material’s composition and structure.
Covalent uses FTIR in two ways. For chemical analysis, it identifies molecular bonds, contaminants, polymer composition, oxidation, degradation and formulation changes. For optical work, it measures how much infrared light passes through or reflects from a material across the IR range, so customers can evaluate the transmission, reflection and absorbance of optical films, windows, filters and coatings.
Non‑Destructive Analysis
Rapid Insights
Broad Material Coverage
Accurate IR optical spectra measurements
Why Use FTIR?
Covalent’s FTIR analysis supports both chemical identification and optical transmission characterization. Our FTIR workflows are used for molecular fingerprinting, contamination analysis, polymer and coating evaluation, and high-accuracy infrared optical transmission measurements.
- Bulk chemical identification.
- Failure analysis in polymers and coatings.
- Surface contamination analysis.
- Oxidation, cross-linking, or degradation studies.
- Incoming material inspection.
- IR transmission/reflection measurement for films, windows, filters, coatings, and optical components.
- Comparing optical performance across lots, process conditions, or environmental exposures.
Analytical Depth
Material Compatibility
How FTIR Works
Light from an infrared source (1) enters an interferometer (2), where a beam splitter divides it between a fixed mirror and a moving mirror. When the two beams recombine, they interfere in a way that changes as the mirror moves. The combined beam then passes through or reflects from the sample (3), which absorbs the wavelengths that match its chemical bonds. The detector (4) records an interferogram, which shows signal intensity against mirror position. A Fourier transform converts this into an IR spectrum (5) of absorbance or transmittance against wavenumber, typically from 4000 to 400 cm⁻¹. Each peak corresponds to a chemical bond, so the spectrum can be matched to reference libraries to identify the material.
Depending on the sample, we choose one of three sampling modes:
- Transmission mode: infrared light passes through the sample to the detector. Best for thin films and particles.
- Reflectance mode: light reflects off the sample or a reflective surface beneath it. Best for coatings and residues on metal or glass.
- ATR-FTIR spectroscopy: the sample is pressed against a diamond or germanium crystal, and the infrared light probes only the top few microns. Best for surfaces, opaque solids and liquids.
What FTIR-Optical Measurements Can Tell You
FTIR-optical measurements show whether a material performs as intended in an infrared optical system. Instead of only identifying peaks, Covalent measures how much the sample changes the transmitted infrared intensity across the spectral range.
Typical outputs include:
- Transmission spectrum: how much infrared light passes through the sample at each wavelength or wavenumber.
- Absorbance spectrum: where the material absorbs infrared light, and how strongly.
- Bandpass and blocking behavior: whether a filter or coating transmits and blocks in the intended regions.
- Material comparison: whether different lots, vendors, cure recipes, coating thicknesses or process conditions change infrared optical performance.
- Optical constants: transmission data combined with infrared spectroscopic ellipsometry in an optical model gives accurate refractive index and absorption coefficient across the infrared range.
Equipment Used for FTIR
ThermoFisher Scientific Nicolet iS50 FT-IR Spectrometer
- Spectral range: 7800 to 350 cm⁻¹
- Resolution: better than 0.09 cm⁻¹
- Wavenumber accuracy: better than 0.005 cm⁻¹
- Multi-detector configuration, including a temperature-controlled DLaTGS detector for stable intensity measurements
- Diamond ATR (standard and high-pressure) for hard samples, and Ge ATR for carbon-filled or opaque materials
- Variable-angle ATR and transmission for thin film analysis
- Reflectance mode for coatings and contaminants on metal and other reflective surfaces
- Beam-defining apertures that reduce stray IR radiation for accurate transmission (FTIR-optical) measurements
ThermoFisher Scientific Nicolet Continuum IR Microscope
- [15× and 32×] objectives
- Sampling modes: transmission, reflection, Ge ATR and diamond-cell transmission
- Dedicated ATR objective with interchangeable diamond, Ge, ZnSe and Si crystals and an integrated pressure sensor
- Grazing-angle objective (NA 0.99) for thin films and surface layers
- Dual detector bay for MCT-A, MCT-B and InGaAs detectors
Key Differentiators
Our FTIR systems combine analytical depth, broad material compatibility and versatile sampling modes. Whether the sample is a polymer, a coating or a trace contaminant, we deliver fast, high-resolution results for real-world materials problems.
- Analytical depth: transmission and reflection probe the full sample thickness. Diamond ATR probes about 2 µm, and germanium ATR about 0.66 µm, for surface-sensitive analysis.
- Material compatibility: organic compounds, polymers, films, coatings and surface residues, as solids or liquids.
- Sampling modes: ATR, specular reflectance, reflection-absorption and transmission, at macro and micro scale.
- Spectral range: 7800 to 350 cm⁻¹, covering mid-IR and near-IR.
- Resolution and accuracy: better than 0.09 cm⁻¹ resolution and 0.005 cm⁻¹ wavenumber accuracy.
- Micro-FTIR: spot identification and chemical mapping of features down to about [10 µm].
- FTIR-optical configuration: beam-defining apertures and a temperature-controlled DLaTGS detector give repeatable, accurate IR transmission intensity.
- Optical constants: combined with spectroscopic ellipsometry and optical modeling, FTIR-optical data gives accurate IR refractive index and absorption.
Strengths
FTIR is designed for efficient and reliable compound identification, ideal for complex organic materials, polymers, and coatings. It offers:
- Access to rich spectral libraries for confident compound classification.
- Chemical mapping capabilities for analyzing small sample regions.
- Modified FTIR-optical configuration enables accurate optical transmission measurements with precision often comparable to spectrophotometer-based measurements.
Limitations
FTIR is versatile and can be applied to any identification, but it is limited to certain diagnostic powers, which depend on contextual interpretation and, mainly, sample selection.
- A reference or standard sample is often required for spectral comparison.
- Many inorganic compounds like carbonates reveal overlapping peaks, resulting in blurry spectral specificity.
- Reflection and transmission modes demand thin samples for the IR light to penetrate or reach a reflective surface.
- Opaque or strongly IR-absorbing materials typically fall outside the usable range for these modes.
- The microscopes at Covalent are limited to a stage height of approximately 20 mm, restricting analysis of some larger samples.
- For rough or hazy samples, integrating sphere measurements are needed because specular FTIR transmission alone cannot fully capture scattered light or total transmitted intensity.
Why Standard FTIR Is Not Always Enough for Optical Intensity Measurements?
Standard FTIR is built to identify chemical peaks, but optical work needs confidence in the actual transmitted intensity. Thermal background, stray radiation, aperture effects, detector drift and beam-path mismatch can all distort that intensity.
Covalent has modified its FTIR configuration for intensity-based measurements. Beam-defining apertures cut unwanted IR radiation, and a temperature-controlled DLaTGS detector keeps readings stable, giving repeatable, high-confidence IR transmission data.
Example Outputs
An FTIR spectrum plots transmittance or absorbance against wavenumber. The peak positions and intensities identify molecular bonds and chemical structures.
- Covalent’s spectral library enables fast classification and spectral matching.
- Peak positions and intensities give a qualitative view of compound concentration.
- ATR mode analyzes surface layers such as coatings, residues and laminated materials.
Our FTIR reports answer chemical-level questions, from solving a failure to validating a formulation to tracking material degradation.
Calcium stearate spectrum: Reflection-mode FTIR identified contamination on a glass slide as calcium stearate.
Fiber spectra: Transmission FTIR in a diamond cell identified two small unknown fibers as cotton (top) and polyester urethane (bottom).
CO₂ filter transmission: FTIR transmission of CO₂ sensor filters under varying gas concentrations. Changes near the CO₂ absorption band show how FTIR evaluates optical filter performance and gas-path absorption for infrared CO₂ sensing.
FTIR vs UV-VIS-NIR comparison: Aperture-controlled FTIR-optical reduces stray and misaligned IR light, matching UV-VIS-NIR spectrophotometry more closely while keeping the same absorption peak positions.
Sample Requirements
Each sampling mode has its own requirements for a clean, accurate spectrum:
- Transmission: films ideally under 10 µm thick.
- Transmission and reflection: flat surfaces give the best data quality.
- Micro-FTIR: features from about [10 µm to 150 µm], on samples up to about 20 mm tall.
- All forms: solids and liquids are accepted, as long as they are stable under infrared light.
- FTIR-optical: samples must fully cover the roughly 1 cm measurement aperture, with uniform thickness across that area.
FTIR Applications by Industry
Electronics & Semiconductor
FTIR detects unknown residues on PCBs and electronic components, verifies polymer coatings and encapsulants, and compares raw materials across production lots. FTIR-optical measures how coatings, deposited films, surface treatments or contamination layers change IR transmission, using coated and uncoated references to isolate the effect of each layer.
Energy & Batteries
FTIR identifies chemical degradation in electrodes caused by electrolyte exposure, detects cross-linking or oxidation in battery polymers, and validates material formulations for energy storage components.
Industrial Manufacturing & Materials Science
FTIR reveals thin contamination films on metal tooling, pins and plates, confirms polymer compositions, evaluates coatings and films, and analyzes surface residues in failure investigations.
Consumer Goods & Polymers
FTIR verifies raw material identity by molecular fingerprinting, investigates degradation and aging in polymers and coatings, and detects contaminants in packaging, films and fibers to keep products safe and consistent.
Research & Development
FTIR gives rapid, non-destructive molecular fingerprinting of solids and liquids and characterizes functional groups in new materials. Combined with spectroscopic ellipsometry, FTIR-optical also determines the infrared optical properties of new materials.
Optics and Photonics
FTIR-optical evaluates transmission, absorption bands, passband and blocking performance, and cutoff regions in optical windows, lenses, filters and protective covers. It also characterizes IR transmission through wafers, substrates, dielectric layers and device materials.
Techniques That Complement FTIR
FTIR is often the first screening step. It is then paired with techniques that extend the analysis to inorganic, elemental and trace-level questions.
Identifies molecular structures and crystal forms that are weak or inactive in FTIR.
Identifies volatile organics and trace additives that FTIR spectra may not capture.
Resolves molecular structures and quantifies components in complex mixtures.
High-resolution imaging and elemental analysis for metals and inorganic materials.
Measures surface chemical composition and the oxidation states of elements.
IR ellipsometry measures thin film thickness and optical constants. Combined with FTIR-optical transmission data in an optical model, it gives accurate refractive index and absorption across the infrared.
Surface-sensitive FTIR that analyzes the top few microns of solids, liquids and coatings with almost no sample preparation.
FTIR Testing Services at Covalent
Covalent’s FTIR lab identifies polymers, organics, contaminants and residues for failure analysis, quality control and R&D. It also measures accurate IR transmission of optical films, filters, windows and coatings. Our scientists choose the right sampling mode for each sample, interpret every spectrum against our reference libraries, and pair FTIR with Raman, GC-MS, SEM-EDS or XPS when a question needs more than one technique.
Frequently Asked Questions
What can FTIR analysis be used for?
FTIR is most often used to identify polymers, organic materials and contaminants quickly. It’s also used to track oxidation and degradation, verify incoming materials, investigate failures in plastics and coatings, and measure IR transmission of optical components.
What information can be obtained from an FTIR spectrum?
The peaks show which functional groups and chemical bonds are present, such as C=O, N–H and O–H. Matching the full spectrum to reference libraries identifies the material, and changes in peak intensity reveal oxidation, curing or contamination.
What is the difference between IR and FTIR?
IR spectroscopy is the general technique. FTIR uses an interferometer and a Fourier transform to collect all wavelengths at once, giving faster, higher-resolution spectra. Almost all modern IR spectrometers are FTIR instruments.
What is the difference between FTIR and Raman spectroscopy?
Both identify materials from their molecular vibrations. FTIR is stronger for polar bonds such as O–H, C=O and N–H. Raman is better for non-polar bonds such as C–C and C=C, and for carbon materials and crystal phases. Many projects use both.
When is it appropriate to use transmittance vs. absorbance?
It depends on what you want to see. Absorbance is usually preferred because peaks and peak heights are clearer, and it follows Beer’s Law, so peak height correlates directly with concentration. Transmittance is the historical format, so older libraries often match better with it, and its log scale can make small peaks and valleys easier to spot.
What is the importance of the wavenumber in FTIR analysis?
Each functional group absorbs in a narrow wavenumber range. Recognizing a peak at a given position tells you which structural groups are present in the sample.
Are there different types of FTIR techniques?
Yes. Covalent offers diamond and germanium ATR, transmission and reflection on the bench system, plus micro-ATR, micro-transmission and micro-reflection on the IR microscope. The mode is chosen to suit the sample, but every spectrum shows absorbance or transmittance against wavenumber.
What are the differences among FTIR, Micro-FTIR and Nano-FTIR?
FTIR measures bulk samples by transmission, reflection or ATR. Micro-FTIR uses a microscope to analyze areas smaller than about 150 µm. Nano-FTIR couples atomic force microscopy (AFM) with infrared spectroscopy to map chemistry at the nanoscale.
Can FTIR be used for quantitative analysis?
Yes, under defined conditions. A calibration curve is built from samples of known concentration, and the unknown is measured against it.
How is FTIR-optical measurement different from standard FTIR chemical analysis?
Standard FTIR identifies molecular bonds and matches spectra to known materials. FTIR-optical focuses on the accuracy of transmitted IR intensity: how much infrared light passes through a material, coating, film, filter or optical component at each wavelength or wavenumber.
How long does FTIR analysis take?
Each measurement takes minutes. Project turnaround is typically 5–7 business days, with rush options available.