Home | Business News | Browse by Publication | T | The Texas Journal of Science

An evaluation of modified IMS swabs for the screening of oxidizers and home-made explosives.

Article Excerpt
Abstract.--Two cotton wipe treatments were developed, and a commercial colorimetric wipe was evaluated with the goal of improving airline security screening of suspect articles for chemical oxygen generators (COG) and homemade peroxide-containing explosives (HME). Five redox indicators (2,3'-diphenylamine dicar-boxylic acid, diphenylaminesulfonic acid, diphenylamine, iodine:starch, and luminol) were evaluated against hydrogen peroxide and potassium chlorate. Diphenylamine and iodine:starch worked in the dry state but with very slow color-development times--negating their effectiveness as a primary security screening technique. The use of a color-developing spray reduced the detection times of the formulations prepared in this study. A commercial product (Drop-Ex Plus, Mistral Security Inc.) contained color developing solvents and produced similar results. The need for color-developing solvents relegates the colorimetric wipe systems to secondary screening where separate wipes can be used for the nitro-based explosives, COG, and HME.

**********

With the constant threat of terror attacks present in the minds of world travelers it is important to have a fast, cost-effective, and safe way to individually screen luggage and carry-on items for explosive residues and hazardous substances. The current primary security screening method employs ion mobility spectrometry (IMS) to detect nitro-containing explosives such as trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN) (Ewing et al. 2001) in approximately six seconds per screened article (DHS S&T 2006). Liquids in containers with a capacity greater than 59 mL (two fluid ounces) are currently confiscated because the TSA has not developed or deployed a primary screening procedure for chemical oxygen generators (COG) and peroxide-containing explosives (FAA 2007).

The typical single-tube IMS is set to detect negative ions because the volatile nitro-containing explosives readily form negatively-charged adducts with the reactant gas in the IMS ionization chamber, as illustrated: H-R-[NO.sub.2] (g) + [CI.sup.-] (g) [right arrow] [[C1 (H-R-[NO.sub.2])].sup.-] (g). The chloride-laden reactant gas is produced by beta-particle-induced dissociation of methylene chloride inside the IMS. (Eiceman & Stone 2004)

Triacetonetriperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) are homemade explosives (HME) that are becoming more widely used in attacks (Buttigieg et al. 2003). These peroxide-based explosives are dangerous to synthesize, but large amounts can be made from inexpensive items such as acetone, sulfuric acid, 3% hydrogen peroxide, citric acid, and hexamethy-lenetetramine (Shakashiri 1983).

The triperoxides form positive-ion adducts in the IMS and are not detected by single-tube IMS instruments in negative-ion mode (Buttigieg et al. 2003). Dual-mode instruments are now available that can detect HMEs and traditional explosives simultaneously....