Improved HME detection

The quick detection of explosives is highly desirable and a new portable device has been developed for the rapid separation of anions relevant to the identification of inorganic homemade explosive devices (HMEs). This simple sequential injection-capillary electrophoresis instrument with capacitively-coupled contactless conductivity detection can detect HMEs about 20 times faster than was previously possible.1

Four of the most common explosive tracer ions: nitrate, perchlorate, chlorate and azide, and the most common background ions: chloride, sulphate, thiocyanate, fluoride, phosphate and carbonate were investigated. Using a separation electrolyte comprising 50 mM tris(hydoxymethylamino methane), 50 mM cyclohexyl-2-aminoethanesulphonic acid, pH 8.9 and 0.05% poly(ethyleneimine) (PEI) in a hexadimethrine bromide (HDMB)-coated capillary it was found to be possible to partially separate all 10 ions within 90 s. The combination of PEI and HDMB was necessary to achieve adequate selectivity with a sufficiently stable electroosmotic flow. This was not possible with only one polymer. Careful optimization of variables affecting the speed of separation and injection timing allowed a further reduction of separation time to 55 s, all the while maintaining adequate efficiency and resolution. Software control means that 60 samples can be produced an hour, with very high repeatability of migration times. Sensitivity is not compromised, with limits of detection ranging from 23 to 50 µgL−1 for all the explosive residues tested. As the ions move past a conductivity detector, they can be identified based on their electrical charge and the time it took them to travel through the capillary. The combination of automation, high sample throughput, high confidence of peak identification and low limits of detection makes this methodology ideal for the rapid identification of inorganic HME residues.

1. Gustavo Blanco et al., Anal. Chem., 2011, DOI: 10.1021/ac2020195

This story originally appeared in The Column. Click here to view that issue.