Talanta 85 (2011) 2226–2232 Contents lists available at ScienceDirect Talanta jo u r n al hom epage: www.elsevier.com/locate/talanta Rapid detection of nitroaromatic and nitramine explosives on chromatographic paper and their reflectometric sensing on PVC tablets Erol Erc ¸ a˘ g, Ays ¸ em Üzer, S ¸ ule Eren, S ¸ ener Sa˘ glam, Hayati Filik, Res ¸ at Apak ∗ Istanbul University, Faculty of Engineering, Department of Chemistry, Avcilar 34320 Istanbul, Turkey a r t i c l e i n f o Article history: Received 4 February 2011 Received in revised form 15 July 2011 Accepted 23 July 2011 Available online 29 July 2011 Keywords: Explosive sensing Nitro aromatics Nitramines Explosive detection Reflectance spectroscopy a b s t r a c t Rapid and inexpensive sensing of explosive traces in soil and post-blast debris for environmental and criminological purposes with optical sensors has recently gained importance. The developed sensing method for nitro-aromatic and nitramine-based explosives is based on dropping an acetone solution of the analyte to an adsorbent surface, letting the solvent to dry, spraying an analyt- ical reagent to produce a persistent spot, and indirectly measuring its reflectance by means of a miniature spectrometer. This method proved to be useful for on-site determination of nitro- aromatics (trinitrotoluene (TNT), 2,4,6-trinitrophenylmethylnitramine (tetryl) and dinitrotoluene (DNT)) and nitramines (1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine (HMX)) pre-adsorbed on a poly vinyl chloride (PVC) surface, with the use of different spray reagents for each group of explosives producing different colors. The calibration equations of the tested compounds as reflectance vs. concentration showed excellent linearity (correlation coefficient: 0.998–0.999). The linear quantification interval in terms of absolute quantity of analyte was 0.1–0.5 g. The developed method was successfully tested for the analysis of military explosives Comp B and Octol, and was validated against high performance liquid chromatography (HPLC). The reflectometric sensing method could also be used for qualitative identification of the nitrated explosives on a chromatographic paper. The reagent-impregnated paper could also serve as sensor, enabling semi-quantitative determi- nations of TNT and tetryl. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Fast and practical on-site analysis of nitroaromatic and nitramine type military explosives, preferably with the use of sensors, is important for preventing terrorist acts, for reclama- tion/remediation of contaminated land previously used for military purposes (e.g., explosive manufacture or ammunition dump- ing), and for forensic investigations. While trace explosive vapor detection methods requiring more sophisticated instrumentation continue to be plagued by the low volatility of many target ana- lytes [1], the more reliable HPLC methods suffer from long analysis times at the order of tens of minutes. Mass spectroscopic methods coupled to LC/GC [2] show a great promise in explosive detec- tion, but are still held back from routine portable application by their high cost and size [1]. Differential reflection spectroscopy in the ultraviolet–visible (UV–Vis) region may be used to dis- tinguish between the reflectivities of two adjacent parts of a specimen with and without adsorbed trinitrotoluene (TNT) [3]. Other sophisticated instrumental techniques used in this regard are ∗ Corresponding author. Fax: +90 212 4737180. E-mail address: rapak@istanbul.edu.tr (R. Apak). surface enhanced Raman spectroscopy (SERS), nuclear quadrupole resonance, energy-dispersive X-ray diffraction (XRD), neutron acti- vation analysis (NAA), cyclic voltammmetry (CV), and ion mobility spectrometry (IMS) [4]. Color reactions were also developed for soil contamination screening methods. Our research group has carried out extensive work on spectrophotometric determination of TNT by improving the water tolerance and color stability of the TNT-hydroxide or TNT- acetonate charge-transfer complexes formed as Meisenheimer and Janowsky anions, respectively [5,6]. A commercial colorimetric sys- tem using proprietary reagents is available as the ‘EXPRAY Field Test Kit’, with components appropriate for ‘Group A’ explosives (nitro-aromatics), ‘Group B’ explosives (RDX, HMX, pentaerythritol tetranitrate (PETN), etc.), and for inorganic nitrates [7], however such a commercial system neither has freely available reagents nor is capable of quantitative measurement. Electrochemical sen- sors not properly responding to mixtures may suffer from limited sensitivity and electrode fouling, while immunosensors are good for detecting explosive residues in soil but not for airport security screening applications [8]. Chemical sensors, portable detectors and analysis kits provide an on-site possibility of real-time analysis, exemplified by silicagel- coated [9] and amine-loaded PVC membrane [10] TNT sensors. Our 0039-9140/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2011.07.080