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ANALYTICAL CURRENTS Identifying explosive oxidizers with confidence post-explosion debris. They find that a series of cluster ions are predominant in positive- and negative-ion modes, which allows them to characterize the oxidizers. Although inorganic explosives are routinely analyzed using ion chromatography, the relevant positive and negative ions are analyzed separately on a cationic and an anionic column. This segregation may make identifiImage not available cation of the oxifor use on the Web. dizer doubtful in some cases, say the researchers.
Jehuda Yinon and Xiaoming Zhao at the University of Central Florida use electrospray ionization MS (ESI-MS) to identify the inorganic oxidizers used in explosives–a method that might be useful for analyzing
The researchers used ESI-MS on three samples. For Powermite, a commercially available explosive, the positive-ion spectrum obtained at a heated capillary temperature of 100 ºC showed the presence of ammonium nitrate and sodium nitrate. Analysis of the water extract of gunpowder at a heated capillary temperature of 220 ºC revealed that potassium nitrate was the major oxidizer. And analysis of “match heads”, which have been used in pipe bombs or in improvised explosives, at a heated capillary temperature of 100 ºC showed that potassium chlorate was the main oxidizer. The researchers confirmed their results using isotopically labeled compounds in MS/MS with collisioninduced dissociation. (Rapid Commun. Mass Spectrom. 2002, 16, 1137–1146)
Full-scan positive-ion (upper trace) and negative-ion (lower trace) ESI mass spectrum of black powder sample. (Adapted with permission. Copyright 2002 John Wiley & Sons, Ltd.)
NSOM scheme tracks single molecules m2/s, the researchers discovered that molthe researchers. In addition, the spatial As a step toward studying the diffusion of ecules can be tracked within ~40 nm over resolution of the NSOM is ~10-fold better. molecules in lipid bilayers, R. S. Decca and several seconds. Decca’s group predicts The key to the new method, the recolleagues at Indiana University–Purdue searchers explain, is to move the NSOM tip that, with minor modifications, it should be University Indianapolis use a new nearpossible to obtain a collection time of ~0.5 with a circular motion that covers an area field scanning optical microscope (NSOM) –2 2 that is small compared with the spatial res- ms or a D of up to 5 10 m /s, which is scheme to measure the diffusion of single relevant to many liquid crystalline systems, olution of the instrument, yet is large fluorescent molecules in quasi two-dimenespecially lipids in bilayer membranes. enough to observe variations in the colsional systems. However, the new method is only good lected light. The researchers simulated the Researchers, particularly biophysicists, have tried to come up with a fast, sensitive, diffusion of a fluorescent molecule by mov- if the molecule doesn’t go into a dark state for a time period that is long compared ing the sample in random diand local system for dewith the time interval , which is estimated rections, choosing the patecting single-molecule by the NSOM tip diameter divided by four rameters to correspond to diffusion. One big advanImage not times the molecule’s diffusion constant. If particular diffusion coeffitage of using NSOM is that happens, the molecule will be lost for cients (D). that its excitation volume available the detection process, the researchers say. Using a 100-nm tip and a is >3 orders of magnitude for use on (Rev. Sci. Instrum. 2002, 73, 2675–2679) simulated D of ~1 10–12 smaller than that for farthe Web. field observation, which reduces background noise A 1.28- 1.28-µm image indicating the positions of five rhodamine molecules. (Adapted with permission. Copyright 2002 American Institute of Physics.) and improves the S/N, say 456 A
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