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FTIR Spectroscopy: Picking up Steam in Nontraditional Markets Print E-mail
Fourier transform infrared (FTIR) spectroscopy, a subset of infrared (IR) spectroscopy, uses a mathematical algorithm, Fourier transform, to translate raw infrared data into a spectrum.

Conventional IR spectroscopy is an absorbance technique that produces spectra that are unique for every IRabsorbing compound. The spectrum from 4000-1000 cm-1, known as the “functional group” region, is diagnostic for alcohols, ketones, hydrocarbons, halogenated materials, and others. While functional groups may absorb at precisely the same wavelength, the spectrum below 1000 cm-1, the “fingerprint” region, is unique for every compound.

By replacing the monochromator with a single, discrete light pulse transmitting all IR wavelengths simultaneously, FT represents a revolutionary improvement. FTIR generates a representation known as an interferogram, from which a computer subsequently performs an operation, known as Fourier transformation, to generate the spectrum. FTIR acquires a spectrum in one pulse, or collect many pulses and adds them to improve signal-tonoise. Thirty-two one-second pulses are about average for FTIR analysis.


FTIR spectrum of polystyrene.

Like IR, FTIR is useful for the analysis of organic and inorganic compounds that exhibit changes in polarity as a result of the vibration, spinning, or perturbation of molecular bonds. FTIR methods are common in such industries as foods, materials, chemicals, pharmaceuticals, forensics, and others. Advantages of FTIR over conventional IR are higher resolution, better signal-to-noise, easier analysis of very small samples and poorly-absorbing species, and much more rapid analysis.

Instrumentation

“FTIR instrumentation may be categorized according to specific enduser and application types,” says Brian C. Smith, Ph.D., founder of FTIR training firm Spectros Associates (Boston, MA).

• Routine instruments that test raw materials or final products, about the size of a laptop computer, employing a single detector and costing about $20,000.

• Routine instruments that test raw materials or final products, about the size of a laptop computer, employing a single detector and costing about $20,000.

• Spectrometers that are used in pure research or high-end applications in academia or large corporations. These instruments perform sophisticated tasks such as IR imaging of cells, or biopsies and inspections of semiconductors. Depending on the bells and whistles, these instruments can cost more than $100,000.

“Changes in basic FTIR technology have slowed as the technique has matured, but subcomponents continue to improve,” says Jerry Sellors, Ph.D., manager for FTIR at PerkinElmer (Beaconsfield, U.K.). Among these are underlying electronics, digital sampling, more reliable lasers, and generally better performance for a given price.

“Instruments are rapidly becoming turnkey solutions while getting smaller and easier to use,” observes Haydar Kustu, global marketing communications manager at Bruker Optics (Billerica, MA).

“There’s a lot of pressure to bring FTIR out of the lab and into the field.” One of the most exciting scientific advances in this regard are MEMS (microelectromechanical systems), which enable rugged, low-cost handheld devices. “MEMS shrink the interferometer,” Kustu says. Another enabling technology has been quantum cascade lasers (QCLs), which are brighter and more sensitive than conventional lasers. “MEMS and QCLs will open up many more niche or field applications for FTIR.”

Unlike laboratory instruments, field analyzers are typically dedicated for single analytes. “These are built for specific purposes. You cannot swap out accessories, change from transmission to reflectance, or change the detector or the source. You cannot configure them on the go,” says Kustu.

Purchase factors

The proliferation of FTIR into materials, fuels, biology, environmental testing, and homeland security raises issues of usability and user-friendliness that did not exist a decade ago. “Users today are more likely to be nonspecialists or occasional users than IR spectroscopists,” Dr. Sellors says. In this environment instrument makers must emphasize user-friendliness for both hardware and software. “Users today are less interested in buying an FTIR spectrophotometer than they are in acquiring a biodiesel or contaminant analyzer. Purchase decisions are influenced more by how well an instrument performs a specific task than by its technical specifications.”

Cost and the performance/price ratio remain factors, perhaps more so due to the economic downturn, but remain unchanged in nature over the past two decades. Another factor that still matters very much is the perception of how well vendors support their products, both around the sale and afterward. In this regard, Sellors suggests that global communication within and among companies helps spread the word about which instrument manufacturers make the cut.

“In addition to budget issues, purchasers need to be clear, before they buy an FTIR spectrometer, on their applications,” advises Dr. Smith. “It’s too easy to get taken in by the ‘gee whiz’ factor. Most vendors offer quality instruments; the difference for the average user may be the software. It’s imperative to take the software for a test drive, and not just let the salesman show you how it works. Take a spectrum yourself before you buy, and get references [from people] who can vouch for the manufacturer’s service.”