ARTICLE pubs.acs.org/ac
Identification of Inorganic Improvised Explosive Devices Using Sequential Injection Capillary Electrophoresis and Contactless Conductivity Detection Gustavo A. Blanco, Yi H. Nai, Emily F. Hilder, Robert A. Shellie, Greg W. Dicinoski, Paul R. Haddad, and Michael C. Breadmore* Australian Centre for Research on Separation Science, School of Chemistry, Faculty of Science, Engineering and Technology, University of Tasmania, Private Bag 75, Hobart, Tasmania, 7001, Australia ABSTRACT:
A simple sequential injection capillary electrophoresis (SI-CE) instrument with capacitively coupled contactless conductivity detection (C4D) has been developed for the rapid separation of anions relevant to the identification of inorganic improvised explosive devices (IEDs). Four of the most common explosive tracer ions, nitrate, perchlorate, chlorate, and azide, and the most common background ions, chloride, sulfate, thiocyanate, fluoride, phosphate, and carbonate, were chosen for investigation. Using a separation electrolyte comprising 50 mM tris(hydroxymethyl)aminomethane, 50 mM cyclohexyl-2-aminoethanesulfonic acid, pH 8.9 and 0.05% poly(ethyleneimine) (PEI) in a hexadimethrine bromide (HDMB)-coated capillary it was possible to partially separate all 10 ions within 90 s. The combination of two cationic polymer additives (PEI and HDMB) was necessary to achieve adequate selectivity with a sufficiently stable electroosmotic flow (EOF), which 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 while maintaining adequate efficiency and resolution. Software control makes high sample throughput possible (60 samples/h), with very high repeatability of migration times [0.63 2.07% relative standard deviation (RSD) for 240 injections]. The separation speed does not compromise sensitivity, with limits of detection ranging from 23 to 50 μg 3 L 1 for all the explosive residues considered, which is 10 lower than those achieved by indirect absorbance detection and 2 lower than those achieved by C4D using portable benchtop instrumentation. 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 IED residues.
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norganic improvised explosive devices (IEDs) are based on combinations of strong inorganic oxidizers and fuels. In contrast to the strictly controlled organic high explosives, inorganic IED components can be easily and legally obtained at low cost. The ease of acquisition and fabrication explains why inorganic IEDs have been employed in many of the largest terrorist attacks occurring during the last 2 decades, such as those in Oklahoma, U.S.A. (1995), Bali, Indonesia (2002), Prune, India (2010), and Oslo, Norway (2011). Their frequent use contrasts with the fact that there are relatively few publications related to the determination of inorganic explosives in comparison with the literature published concerning the analysis of organic explosives. Explosive analysis can be oriented to the identification of the explosive r 2011 American Chemical Society
after or prior to the detonation, known as post- and pre-blast analysis, respectively. Independent of the situation the identification of residues demands analytical methods with high requirements in terms of speed, selectivity, sensitivity, and instrument and separation robustness. Capillary electrophoresis (CE) offers a unique combination of characteristics which makes it a powerful technique to perform these analyses.1,2 CE provides very high efficiencies making it possible to perform rapid separations of complex mixtures. Existing Received: August 3, 2011 Accepted: October 17, 2011 Published: October 17, 2011 9068
dx.doi.org/10.1021/ac2020195 | Anal. Chem. 2011, 83, 9068–9075
Analytical Chemistry CE methods based on the use of commercial benchtop3 6 and portable7,8 instruments provide separations of the target analytes with adequate sensitivity for postblast analysis. The main limitations of all of these methods are the relatively long sample-tosample analysis times (typically >8 min), limited portability, and batch-type injection which makes the automation of sample pretreatment difficult. Rapid and potentially portable separations can be obtained in microchips; however, all reports to date showed the separation of only a small number of analytes9 11 due to the use of relatively low voltages (
