| METHOD |
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. For example, the group uses films made from salts of a ferrocenium complex to detect perchlorate ions, nerve agents, and other weakly hydrated anion species. Strauss noted that the coating procedure is simple and that the films are easily recycled via redox chemistry. Presenting results of detection limit studies, Strauss reported that perchlorate ion (used in rocket propellants) can be detected in concentrations as low as 4 ppb. Data were measured in roughly 30 seconds following a 10-minute ion-exchange period during which the coated crystal was exposed to perchlorate solution. "If we wait longer, we can detect even lower concentrations," he asserted. But in keeping with analytical chemistry practices common to military applications, Strauss reported the results as a 10-minute limit of detection. He added that compared with uncoated ATR crystals, the organometallic compound, which was synthesized by the Colorado State group, improves the method's sensitivity by a factor of 6,000. Strauss Christesen Hill PHOTOS BY MITCH JACOBY 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. Strauss reported that the ATR-FTIR method has also been used to measure parts-per-billion levels of perfluorinated sulfonate ions and other analytes. |
| UPDATE | 03.03 |
| AUTHOR | Colorado State University, chemistry professor Steven H. Strauss |
| LITERATURE REF. | This data is not available for free |
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