Improved Infrared Chemical Analysis Possible With New NIST Invention

A new device and technique recently patented by a National Institute of Standards and Technology scientist may lead to dramatic improvements in infrared spectroscopy, a process used to identify and quantify the components making up a chemical sample.

The improved analysis technique is possible because of a NIST-designed sample-holding cell that provides a simple, efficient and cost-effective means of cooling samples (to temperatures as low as minus 40 degrees Celsius or minus 40 degrees Fahrenheit) during the measurement of their infrared radiation absorption spectra. The patent (no. 5,280,177) was issued to Thomas J. Bruno, a physical chemist and group leader in NIST's Thermophysics Division in the Chemical Science and Technology Laboratory in Boulder, Colo.

Cooling of a chemical sample during measurement of its IR spectrum is important for two reasons. During the procedure, the sample is unavoidably heated by the radiation. This can cause the evaporation of solvents and chemical samples in the cell, yielding inaccurate readings. Moreover, many samples are thermally sensitive and may be degraded by the heat.

Conventional chilled sample cells use a small cryogenic fluid container placed above the cell, the cooling of which is counterbalanced by heaters mounted on the sides of the cell. This design suffers from a number of drawbacks. Unfavorable temperature gradients are produced within the sample, and heating that occurs through the primary (or "entry") window (through which the IR radiation enters the sample cell) is always present. The cryogenic container requires frequent filling with fluid to maintain a constant cooling.

The new cell features a sample chamber that is chilled with the cold air stream produced from a vortex tube. This gives it the advantage of chilling the entire surface of the entry window with the cold air, thus minimizing the heating from the IR beam. It is much smaller than the conventional chilled IR sample cell, is easier to use and will fit any spectrophotometer.

Bruno estimates that the complete cell could be produced for about $300, significantly less than the approximately $6,000 price tag for a conventional chilled IR cell.

For technical information about the new invention, contact Bruno at Div. 838.01, NIST, Boulder, Colo. 80303-3328, (303) 497-5158, e-mail: bruno [at] bldrdoc.gov (bruno[at]bldrdoc[dot]gov) (via Internet). For licensing information, contact Nancy Hale, B256 Physics Building, NIST, Gaithersburg, Md. 20899-0001, (301) 975-4188.

As a non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.