| METHOD |
Vibrational spectroscopy is also used by military scientists. Steven D. Christesen, a research chemist at Edgewood Chemical Biological Center, Aberdeen Proving Ground, in Maryland, discussed the use of Raman spectroscopy to detect nerve agents, mustard gas (a blister agent), and cyanide (a blood agent) in water samples. Christesen noted that the U.S. military is aiming to develop detection methods for these types of substances based on portable instruments that can be used to complete analyses in 10 minutes or less. To maximize detection sensitivity, Christesen deposits the analytes on roughened surfaces of gold and silver and probes them with surface-enhanced Raman spectroscopy (SERS), a highly sensitive variation of the Raman technique. He noted that the time required for analysis--including dipping a metal probe tip into an analyte solution, allowing it to dry, and recording spectra--is just a few minutes. Christesen reported that the lower limit of detection for CN– is roughly 2 ppb, which is lower than the military's detection goals, but added that the measurements exhibit poor reproducibility. He proposed that the inconsistencies may be due to subtle differences in the surface properties of the metal substrates. Mustard gas can be detected at concentrations as low as 50 ppm, Christesen said, but it hydrolyzes quickly to thioldiglycol, low levels of which are not easily detected by the SERS method. Although the technique is a sensitive probe for blister and blood agents, "we're having problems with nerve agents," Christesen acknowledged. He presented data from detection limit studies of VX and its hydrolysis products, ethyl methyl phosphonic acid and EA2192, a highly stable and toxic product. He also reported findings from investigations of GD hydrolysis products and other organophosphates. Christesen noted that the SERS method can be used to detect most of the analytes in the low parts-per-million range but added that the goal is to improve sensitivity by three orders of magnitude. |
| AUTHOR | Steven D. Christesen, a research chemist at Edgewood Chemical Biological Center, Aberdeen Proving Ground, in Maryland, |
| LITERATURE REF. | This data is not available for free |
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