EDITORIAL
Flying the Friendly Skies One of the more dramatic challenges to chemical analysts is the detection of ex plosives hidden by terrorists in airport luggage (1). Almost all explosives consist of nitrogen-containing compounds, and most detection systems are based on this characteristic. The main requirements of an explosives detector are sensitivity; specificity; reliability; speed; and, of course, safety. There are two classes of explosives de tectors: vapors and bulk. In the first class vapors are detected, either from the ex plosive itself or from decomposition products or volatile impurities and addi tives emanating from the explosive. The U.S. Federal Aviation Administration (FAA) and comparable government agencies in several other countries have been supporting a variety of programs to develop a routine airport screening sys tem that incorporates the important specifications mentioned earlier. Among the vapor-based detection systems, gas chromatography with electron capture detection and portable mass spectro meters with a variety of ion sources are used. Preconcentration techniques and chemiluminescence methods are also be ing investigated. Considerable progress has been made using bulk detection, particularly for the increasingly used and difficult to detect "plastic" explosives. X-ray analysis using an irradiating source together with a linear array of detectors constitutes one of the most common bulk analysis schemes. The system automatically de termines the presence of certain defined threats by means of a pattern recogni
tion algorithm. One of the more promis ing bulk analysis methods for detecting hidden explosives involves thermal neu tron activation. Prototype instruments using this approach are being placed at several high-risk airports around the world to detect the high concentrations of nitrogen that are indicative of hidden explosives. The method appears to be promising but currently lacks adequate sensitivity and specificity. A recently proposed simple and inex pensive method is based on the tagging of explosives during production with a distinctive marker (2). Using a marker element with a high neutron capture cross section to produce a short half-life species emitting a characteristic gamma ray upon prompt gamma activation, this simple method appears to possess all of the specifications required. There is an urgent need to provide ad equate protection to the more than 1 bil lion people who annually pass through security stations in U.S. airports alone. Although progress in explosives detec tion has been made, innovative ap proaches are desperately needed and more chemical analysts should rise to this vital challenge. References (1) Waldrop, M. M. Science 1989,243,165-66. (2) Williams, E. R.; Zare, R. N. Science 1990,248, 1471.
Ρ-
/ V -
>W^x-4-crw
ANALYTICAL CHEMISTRY, VOL. 62, NO. 13, JULY 1, 1990 • 999 A
