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At Colorado State University, chemistry professor Steven H. Strauss measures parts-per-billion quantities of hazardous materials in water with Fourier transform infrared (FTIR) spectroscopy methods. Specifically, Strauss uses a technique known as attenuated total-reflectance (ATR) in which an IR beam is reflected from the surfaces of an ATR crystal as the beam propagates along the length of the crystal. The IR spectrum of a thin sample--for example, a solid film or a thin layer of liquid--in contact with the crystal can be probed with this method because as the light bounces off the crystal surfaces, it penetrates the film slightly.
To maximize the method's detection sensitivity, Strauss, graduate student Gretchen N. Hebert, and their coworkers coat ATR crystals with metal-complex extractant films that serve as analyte concentrators. Strauss noted that the coating procedure is simple and that the films are easily recycled via redox chemistry. APPLYING THE ATR-FTIR spectroscopy method to nerve agents, Strauss's group determined that the 10-minute limit of detection for PMPA, a long-lived hydrolysis product of GD (also known as soman), is 125 ppb. At present, however, the calibration curve is linear only in the range of 1.8 to 180 ppm, he said. The group has developed a similar method for detecting cyanide ions. By exchanging Cl– for CN– in a film of a diphosphine-chelated NiCl2 compound, the researchers can detect as little as 2.3 ppb of CN– in 10 minutes
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