Fourier transform infrared spectroscopy
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| Fourier transform infrared spectroscopy | |
|---|---|
| Name | Fourier transform infrared spectroscopy |
| Caption | Typical FTIR spectrometer with Michelson interferometer |
| Inventor | Samuel F. H. Morse; Albert A. Michelson; Peter Fellgett; Norman J. Moorcroft |
| Introduced | 1960s |
| Manufacturers | PerkinElmer; Thermo Fisher Scientific; Bruker; Shimadzu |
| Applications | Chemical identification; materials characterization; environmental monitoring; pharmaceuticals; art conservation |
Fourier transform infrared spectroscopy
Fourier transform infrared spectroscopy (FTIR) is an analytical technique that records an infrared spectrum by measuring an interferogram and applying a Fourier transform to obtain frequency-domain data. Developed through contributions by Albert A. Michelson, Peter Fellgett, and instrumentation advances by companies such as PerkinElmer and Bruker, FTIR integrates optical interferometry, infrared detector technology, and digital signal processing to characterize molecular vibrations and chemical composition. It is widely used across laboratories at institutions like National Institute of Standards and Technology and industrial settings including BASF and Pfizer for qualitative and quantitative analysis.
Introduction
FTIR combines a broadband infrared source, an interferometric modulator, and a detector to convert time-domain interferograms into spectra through the Fourier transform algorithm pioneered in signal processing and optics. Early foundational work by Albert A. Michelson on interferometry and by Peter Fellgett on multiplex advantage set the stage for commercial FTIR instruments sold by firms such as Bruker and Thermo Fisher Scientific. FTIR's capacity to probe vibrational transitions makes it complementary to techniques used at facilities like CERN and Lawrence Berkeley National Laboratory for materials characterization.
Principles and Instrumentation
FTIR instrumentation centers on a Michelson interferometer architecture developed from Albert A. Michelson's designs, comprising a beamsplitter, fixed mirror, and moving mirror to produce an interferogram. The interferogram encodes spectral information that is recovered via the discrete Fourier transform algorithms associated historically with mathematicians and engineers at institutions like Bell Labs and Massachusetts Institute of Technology. Key hardware components include broadband IR sources (e.g., globar or Nernst elements), beamsplitters made by specialty optics manufacturers, detectors such as thermoelectrically cooled pyroelectric sensors or cryogenically cooled mercury cadmium telluride devices often produced by companies like Hamamatsu, and environmental purging assemblies used by construction and museum laboratories such as Smithsonian Institution conservation labs. Ancillary subsystems include attenuated total reflectance modules manufactured by PerkinElmer and microscope accessories developed in collaboration with suppliers to University of Oxford analytical facilities.
Data Acquisition and Processing
Acquisition begins with interferogram collection, where mirror displacement is translated into optical path difference; modern systems employ laser metrology (often using a helium–neon laser developed in part through Bell Labs research) for precise mirror position encoding. Signal processing applies apodization windows and zero-filling followed by fast Fourier transform implementations originating from computational work at Massachusetts Institute of Technology and software libraries used by vendors like Thermo Fisher Scientific. Baseline correction, atmospheric compensation routines referencing standards from National Institute of Standards and Technology, and multivariate calibration techniques informed by chemometrics groups at universities such as University of Cambridge enable quantitative analysis. Data formats and instrument control often interoperate with laboratory information management systems deployed at corporations like GlaxoSmithKline.
Applications
FTIR serves diverse sectors: in pharmaceuticals at Pfizer and GlaxoSmithKline for polymorph screening and API identification; in petrochemicals at ExxonMobil and Royal Dutch Shell for hydrocarbon fingerprinting; in environmental monitoring by agencies like United States Environmental Protection Agency for air and water pollutant analysis; in cultural heritage conservation at institutions such as the British Museum and Metropolitan Museum of Art for binder and pigment identification; and in academia at universities including Stanford University and University of California, Berkeley for polymer and nanomaterials research. FTIR microscopy is employed in semiconductor fabs run by Intel and TSMC for contaminant analysis, while remote sensing adaptations have been used in planetary science missions coordinated with NASA centers.
Advantages and Limitations
FTIR offers multiplex (Fellgett) and throughput (Jacquinot) advantages recognized in optical spectroscopy history, enabling rapid acquisition with high signal-to-noise compared to dispersive instruments produced historically by firms like PerkinElmer. It provides non-destructive, minimal-preparation analysis, compatible with microattenuated total reflectance accessories developed in collaboration with laboratory equipment manufacturers. Limitations include sensitivity to water and carbon dioxide atmospheric absorptions necessitating purging systems specified by standards bodies such as International Electrotechnical Commission; spectral congestion for complex mixtures requiring chemometric deconvolution developed at places like University of Manchester; and spatial resolution constrained by infrared diffraction limits unlike techniques refined at Lawrence Berkeley National Laboratory for near-field optics.
Recent Developments and Advanced Techniques
Recent advances integrate quantum cascade lasers commercialized by companies such as Daylight Solutions for tunable mid-IR sources, synchrotron-based FTIR beamlines operated at facilities like Diamond Light Source for enhanced brightness, and coupling with atomic force microscopy in techniques pioneered at research centers including IBM Research for nanoscale IR spectroscopy. Computational enhancements leverage machine learning approaches developed at institutions such as University of Toronto for spectral interpretation, while cryogenic detector innovations from laboratories at NASA and Max Planck Society improve sensitivity. Portable and handheld FTIR analyzers produced by companies like Thermo Fisher Scientific and Agilent Technologies expand field applications in environmental monitoring and customs enforcement at agencies like U.S. Customs and Border Protection.