Selective detection of trace nitroaromatic, nitramine, and nitrate ester explosive residues using a three-step fluorimetric sensing process: a tandem turn-off, turn-on sensor

Detection of trace quantities of explosive residues plays a key role in military, civilian, and counter-terrorism applications. To advance explosives sensor technology, current methods will need to become cheaper and portable while maintaining sensitivity and selectivity. The detection of common explosives including trinitrotoluene (TNT), cyclotrimethylenetrinitramine, cyclotetramethylene-tetranitramine, pentaerythritol tetranitrate, 2,4,6-trinitrophenyl-N-methylnitramine, and trinitroglycerin may be carried out using a three-step process combining "turn-off" and "turn-on" fluorimetric sensing. This process first detects nitroaromatic explosives by their quenching of green luminescence of polymetalloles (lambda em approximately 400-510 nm). The second step places down a thin film of 2,3-diaminonaphthalene (DAN) while "erasing" the polymetallole luminescence. The final step completes the reaction of the nitramines and/or nitrate esters with DAN resulting in the formation of a blue luminescent traizole complex (lambda(em) = 450 nm) providing a "turn-on" response for nitramine and nitrate ester-based explosives. Detection limits as low as 2 ng are observed. Solid-state detection of production line explosives demonstrates the applicability of this method to real world situations. This method offers a sensitive and selective detection process for a diverse group of the most common high explosives used in military and terrorist applications today.     

Accumulation of explosives in hair--part II: factors affecting sorption

This study examines the sorption of eight explosives (2,4,6-trinitrotoluene [TNT]; pentaerythritol tetranitrate [PETN]; hexahydro-1,3,5-trinitro-s-triazine [RDX]; diacetone diperoxide [DADP]; triacetone triperoxide [TATP]; ethylene glycol [EGDN], nitroglycerin [NG]; and 2,4-dinitrotoluene [DNT]) to human hair. The study uses only cut hair, which is exposed to explosive vapor. The vapor transfer studies reported herein indicated that hair did not reach saturation even after 2.5 years of exposure to TNT. While previous studies showed black hair sorbed more explosive than blond or brown, this study reports that red hair sorption is similar to black, while grey hairs, exposed along with black hair from the same individual, sorbed significantly less explosive than the same individual's black hairs. In a study using only black hair, a slight racial bias was observed with sorption greater for Mongoloid hair as compared to Caucasian or Negroid. Only for Mongoloid hairs were enough samples studied to examine for a gender bias, but one was not observed. There was much variability in results in all categories (hair color, race, and gender) that trends were established only in general terms. Hair at different ages was tested for a few individuals. Detailed studies focused on the sorption of TATP and TNT as these appear to be sorbed most differently-TATP mainly on the hair surface and TNT both on the surface and in the cortex. The uptake of high vapor pressure explosives (e.g., TATP) and moderate vapor pressure explosives (e.g., TNT) by hair was rapid and could be detected within about 1 h of exposure. Both explosives were readily sorbed by pure melanin.     

Analysis of Explosives by GC‐UV

A mixture of explosives was analyzed by gas chromatography (GC) linked to ultraviolet (UV) spectrophotometry that enabled detection in the range of 178–330 nm. The gas‐phase UV spectra of 2,4,6‐trinitrotoluene (TNT), 2,4‐dinitrotoluene (DNT), ethylene glycol dinitrate (EGDN), glycerine trinitrate (NG, nitroglycerine), triacetone triperoxide (TATP), and pentaerythritol tetranitrate (PETN) were successfully recorded. The most interesting aspect of the current application is that it enabled simultaneous detection of both the target analyte and its decomposition products. At suitable elevated temperatures of the transfer line between the GC instrument and the UV detector, a partial decomposition was accomplished. Detection was made in real time and resulted in overlaid spectra of the mother compound and its decomposition product. Hence, the presented approach added another level to the qualitative identification of the explosives in comparison with traditional methods that relies only on the detection of the target analyte. As expected, the decomposition product of EGDN, NG, and PETN was NO, while TATP degraded to acetone. DNT and TNT did not exhibit any decomposition at the temperatures used.     

Highly sensitive screening method for nitroaromatic, nitramine and nitrate ester explosives by high performance liquid chromatography-atmospheric pressure ionization-mass spectrometry (HPLC-API-MS) in forensic applications

A highly sensitive screening method based on high performance liquid chromatography atmospheric pressure ionization mass spectrometry (HPLC-API-MS) has been developed for the analysis of 21 nitroaromatic, nitramine and nitrate ester explosives, which include the explosives most commonly encountered in forensic science. Two atmospheric pressure ionization (API) methods, atmospheric pressure chemical ionization (APCI) and electrospray ionization (ESI), and various experimental conditions have been applied to allow for the detection of all 21 explosive compounds. The limit of detection (LOD) in the full-scan mode has been found to be 0.012-1.2 ng on column for the screening of most explosives investigated. For nitrobenzene, an LOD of 10 ng was found with the APCI method in the negative mode. Although the detection of nitrobenzene, 2-, 3-, and 4-nitrotoluene is hindered by the difficult ionization of these compounds, we have found that by forming an adduct with glycine, LOD values in the range of 3-16 ng on column can be achieved. Compared with previous screening methods with thermospray ionization, the API method has distinct advantages, including simplicity and stability of the method applied, an extended screening range and a low detection limit for the explosives studied.     

The natural sampling of airborne trace signals from explosives concealed upon the human body.

An experimental study of the natural sampling of trace signals from explosives concealed upon the human body was performed by taking proper account of the thermal behavior of the air surrounding the human body and the particles therein. Experiments were conducted in a dispersal chamber to identify variables affecting the detectibility of concealed RDX and TNT patches. Movement by human volunteers was found to enhance the available explosive trace signal above a baseline level. Clothing blocked some of this movement-generated trace signal. The detected signal levels were also found to vary significantly from volunteer to volunteer, indicating that human variability is an issue in explosive trace detection. Further, under the conditions studied here, the detectibility of RDX and TNT was dependent upon the efficient sampling of contaminated particulate matter, not the vapor phase. The present results are now being applied to the design of a practical, nonintrusive trace detection portal for aviation security screening and related applications.     

Method for characterization of adhesion properties of trace explosives in fingerprints and fingerprint simulations

The near inevitable transfer of explosive particulate matter through fingerprints makes it possible to detect concealed explosives through surface sampling. Repeatable and well-characterized fingerprint simulation facilitates quantitative comparison between particulate sampling methods for subsequent detection of trace explosive residues. This study employs a simple, but reproducible sampling system to determine the accuracy of a fingerprint simulation. The sampling system uses a gas jet to entrain particles from a substrate and the resulting airborne particles are then aspirated onto a Teflon filter. A calibrated Barringer IonScan 400 ion mobility spectrometer was used to determine the mass of explosive material collected on the filter. The IonScan 400 was calibrated with known masses of 2,4,6-trinitrotoluene (TNT). The resulting calibration curve is in good agreement with that obtained by Garofolo et al. (1994) for an earlier model of the instrument. The collection efficiency of the sampling system was measured for three particle sizes (8.0. 10.0, and 13.0 microm) using spherical polystyrene particles laced with known quantities of TNT. Collection efficiency ranged from less than 1% for the larger particles to 5% for the smaller particles. Particle entrainment from the surface was monitored with dark field imaging of the remaining particles. The sampling system was then applied to two C4 test samples--a fingerprint transfer and a dry Teflon transfer. Over 100 ng of RDX was collected from the dry transfer sample, while less than 1 ng was collected from the fingerprint transfer. Possible explanations for this large difference are presented based on the system calibration.     

Quantification and aging of the post-blast residue of TNT landmines

Post-blast residues are potential interferents to chemical detection of landmines. To assess the potential problem related to 2,4,6-trinitrotoluene (TNT), its post-blast residue was identified and quantified. In the first part of this study laboratory-scale samples of TNT (2 g) were detonated in a small-scale explosivity device (SSED) to evaluate the explosive power and collect post-blast residue for chemical analysis. Initiator size was large relative to the TNT charge; thus, issues arose regarding choice of initiator, residue from the initiator, and afterburning of TNT. The second part of this study detonated 75 to 150 g of military-grade TNT (typical of antipersonnel mines) in 55-gal barrels containing various witness materials (metal plates, sand, barrel walls, the atmosphere). The witness materials were analyzed for explosive residue. In a third set of tests, 75-g samples of TNT were detonated over soil (from Fort Leonard Wood or Sandia National Laboratory) in an indoor firing chamber (100 by 4.6 by 2.7 m high). Targeted in these studies were TNT and four explosive-related compounds (ERC): 2,4-dinitrotoluene (DNT), 1,3-dinitrobenzene (DNB), 2- and 4-aminodinitrotoluene (2-ADNT and 4-ADNT). The latter two are microbial degradation products of TNT. Post-blast residue was allowed to age in the soils as a function of moisture contents (5 and 10%) in order to quantify the rate of degradation of the principal residues (TNT, DNT, and DNB) and formation of the TNT microbial degradation products (2-ADNT and 4-ADNT). The major distinction between landmine leakage and post-blast residue was not the identity of the species but relative ratios of amounts. In landmine leakage the DNT/TNT ratio was usually greater than 1. In post-blast residue it was on the order of 1 to 1/100th of a percent, and the total amount of pre-blast residue (landmine leakage) was a factor of 1/100 to 1/1000 less than post-blast. In addition, landmine leakage resulted in low DNT/ADNT ratios, usually less than 1, whereas pre-blast residues started with ratios above 20. Because with time DNT decreased and ADNT increased, over a month the ratio decreased by a factor of 2. The rate of TNT degradation in soil observed in this study was much slower than that reported when initial concentrations of TNT were lower. Degradation rates yielded half-lives of 40 and 100 days for 2,4-DNT and TNT, respectively.     

An enzyme-linked immunosorbent assay (ELISA) for trinitrotoluene (TNT) residue on hands

An enzyme-linked immunosorbent assay (ELISA) developed for the detection of trinitrotoluene (TNT) in munitions wastewater has been adapted to the detection of TNT residue on hands following contact. Using the procedure developed, as little as 50 pg of TNT could be detected. Accounting for sample size and dilution, the 50 pg equates to 15 ng of TNT recovered from the hands. Following contact with TNT, amounts ranging from 53 ng to more than 1500 ng were recovered from hands. The monoclonal anti-TNT antibodies showed no cross-reactivity with several other explosives or common contaminants. These preliminary results indicate promise for the development of a simple-to-use, immunoassay-based field test kit for TNT and, ultimately, other explosives.     

Application of LC−QTOF/MS for the validation and determination of organic explosive residues on Ionscan® swabs

The identification and confirmation of trace explosive residues along with potential precursors and degradation products require a comprehensive laboratory analysis procedure. This study presents the determination of organic explosives consisting of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT), 2,4,6,N-tetranitro-N-methylaniline (Tetryl), 1,3,5-trinitrobenzene (1,3,5-TNB) and pentaerythritol tetranitrate (PETN) by a high-resolution liquid chromatography quadrupole time-of-flight mass spectrometry (LC−QTOF/MS). The qualitative information including retention time, collision energy, precursor ions, and characteristic fragmentation pattern of each explosive were collected using an atmospheric pressure chemical ionization (APCI) in negative ion mode. The separation efficiency among five compounds was greatly achieved in this study. Four real explosive samples consisting of TNT, RDX, PETN and Tetryl and 12 Ionscan® quality control swabs from the Royal Thai Army were also tested to validate and verify the viability of the GC–MS method used to validate results from an Ionscan® system. The results showed that LC−QTOF/MS is a powerful technique for the identification and confirmation of thermally unstable organic explosives on Ionscan® swabs compared to a conventional GC−MS technique.     

有机爆炸物的现场非介入性检测——顶空固相微萃取一真空气相色谱质谱法

本文考察了顶空固相微萃取在有机爆炸物现场非介入性检测中的适用性。由固相萃取（SPME）纤维头吸附的有机爆炸物用真空气相色谱一质谱联用仪进行检测。该方法所需的洗脱温度低,色谱分离时间短。SPME适用于提取蒸汽压不低于2．4,6-三硝基甲苯（TNT）的挥发性和半挥发性有机爆炸物,如较易挥发且不稳定的化合物三过氧化三丙酮（TATP）的非介入性检测就可以应用该方法。本研究使用静态顶空,尽可能地减少顶空体积,实现了较高的灵敏度。在现场,SPME方法的灵敏度受环境温度的影响较大：由于样品的蒸汽压未达到平衡,在固定顶空体积和萃取时间的条件下,SPME纤维头萃取的样品总量随温度的提高而增加。在有合适容器的情况下SPME纤维头上萃取的样品在取样3天后仍然能顺利检测。     

Rapid screening of selected organic explosives by high performance liquid chromatography using reversed-phase monolithic columns

This study presents the rapid screening of various high grade explosives by high performance liquid chromatography (HPLC) with monolithic stationary phases. Two gradient methods were developed, the first for quantitative analysis of eleven explosives: HMX; RDX; Tetryl; TNT; 2,3-DNT; 2,6-DNT; 3,4-DNT; 2-NT; 3-NT; 4-NT; and PETN in under 14 min. The second method separated seven explosives in under two min and is suitable for rapid screening to determine the presence of specific and/or class of explosive. The rapid screening methods were successfully applied to soils spiked with known amounts of target explosives. This technology showed excellent potential for forensic explosives detection and analysis.     

X射线衍射法检验有机炸药初探

目的 建立X射线衍射法（XRD）检验有机炸药的方法.方法 使用X射线衍射仪对有机炸药苦味酸（PA）,太安（PTEN）,黑索金（RDX）,梯恩梯（TNT）进行测试分析.结果 准确测定出有机炸药的物质组成及结构.结论 该方法能够直接给出有机炸药的分子式及结构组成,定性准确,操作简便,可用于有机炸药的定性检测.     

The identification of the emulsifier component of emulsion explosives by liquid chromatography-mass spectrometry

ABSTRACT: The widespread availability of emulsion explosives for commercial blasting has inevitably lead to their diversion for criminal misuse. Present techniques for the characterization of emulsion explosives and their residues is generally based on the detection and identification of the oxidizer and the hydrocarbon components. Use of these components is problematic for residue identification because ammonium nitrate, waxes, and oils are relatively common in the urban environment and even their co-detection does not exclude them being sourced from materials other than explosives. The detection of the emulsifier component offers increased evidential value as certain emulsifiers used in explosive formulations are manufactured for that specific use, or have limited environmental distribution. In the current study liquid chromatography-mass spectrometry (LC-MS) was utilized for the characterization of two emulsifiers in common use; ethanolamine adducts of polyisobutylene succinic anhydride and sorbitol mono-oleate (SMO). The LC-MS technique enabled the detection of both emulsifiers in preblast samples; however, only SMO was detected in postblast residues. The analysis of the hydrocarbon component by gas chromatography-mass spectrometry was achieved in the same procedure.     

Preliminary investigation into the recovery of explosives from hair.

Sampling of hair has proved to be a useful non-invasive method for detecting illicit drugs. This study examined the viability of hair as a surface from which explosive traces can be recovered and showed that as little as one-hour vapour exposure can result in measurable traces of explosives. Contamination of the hair may result from direct contact with explosive particles or from secondary contact by hand. Also the paper demonstrates that hair can concentrate explosive from the ambient vapour of a variety of military explosives. It was found that the amount of TNT picked up by the hair increased with time of vapour exposure. The data also suggested that unwashed hair may pick up more TNT than washed hair.     

Determination of elemental sulfur in explosives and explosive residues by gas chromatography-mass spectrometry

A new method for the positive identification of elemental sulfur in explosives and explosive residues is developed. Following a carbon disulfide wash of explosives or explosive residues, a sample of the extracted material is injected onto a gas chromatography (GC) column, then analyzed via mass-selective (MS) detection. A positive identification of elemental sulfur is based on both retention time and fragmentation pattern. The GC-MS method is demonstrated to be useful in detecting and positively identifying elemental sulfur from both burned and unburned explosive mixtures. With a detection limit of 2.5 ng (2.5 x 10(-9) grams) of elemental sulfur on the column, it is shown to be 400 times more sensitive than the presumptive chemical color test that is currently the method employed for detection of small amounts of sulfur.     

Linking ammonium nitrate-aluminum (AN-AL) post-blast residues to pre-blast explosive materials using isotope ratio and trace elemental analysis for source attribution

Forensic science practitioners are often called upon to attribute crimes using trace evidence, such as explosive remnants, with the ultimate goal of associating a crime with a suspect or suspects in order to prevent further attacks. The explosive charge is an attractive component for attribution in crimes involving explosives as there are limited pathways for acquisition. However, there is currently no capability to link an explosive charge to its source via post-blast trace residues using isotope ratios or trace elements. Here, we sought to determine if pre-blast attribution signatures are preserved after detonation and can be subsequently recovered and detected. A field study was conducted to recover samples of post-blast explosives from controlled detonations of ammonium nitrate-aluminum (AN-Al), which were then analyzed via isotope ratio mass spectrometry (IRMS) and inductively coupled plasma-mass spectrometry (ICP-MS) for quantitation and profiling of isotopes ratio and trace element signatures, respectively. Oxygen and nitrogen isotope ratios from AN-Al yielded some of the most promising results with considerable overlap within one standard deviation of the reference between the spreads of pre- and post-blast data. Trace element results from AN-Al support the findings in the isotope ratio data, with 26 elements detected in both pre- and post-blast samples, and several elements including B, Cd, Cr, Ni, Sn, V, and Zn showing considerable overlap. These preliminary results provide a proof-of-concept for the development of forensic examinations that can attribute signatures from post-blast debris to signatures in pre-blast explosive materials for use in future investigations.     

Detection and Identification of Explosive Particles in Fingerprints Using Attenuated Total Reflection-Fourier Transform Infrared Spectromicroscopy

Abstract:  The application of attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectromicroscopy for detection of explosive particles in fingerprints is described. The combined functions of ATR-FTIR spectromicroscopy are visual searching of particles in fingerprints and measuring the FTIR spectra of the particles. These functions make it possible to directly identify whether a suspect has handled explosives from the fingerprints alone. Particles in explosive contaminated fingerprints are either ingredients of the explosives, finger residues, or other foreign materials. These cannot normally be discriminated by their morphology alone. ATR-FTIR spectra can provide both particle morphology and composition. Fingerprints analyzed by ATR-FTIR can be used for further analysis and identification because of its non-destructive character. Fingerprints contaminated with three different types of explosives, or potential explosives, have been analyzed herein. An infrared spectral library was searched in order to identify the explosive residues. The acquired spectra are compared to those of finger residue alone, in order to differentiate such residue from explosive residue.     

二维气相色谱检测爆炸残留物中TNT

目的建立二维气相色谱结合ECD检测爆炸残留物中TNT的方法。方法利用Dean-Switch系统进行二维无死体积切换，通过切换时间的准确选择，使粉尘样品提取液无需净化进样，即可达到分离彻底、高灵敏度。结果在案件检测应用中，效果良好。     

Accumulation of explosives in hair

The sorption of explosives (TNT, RDX, PETN, TATP, EGDN) to hair during exposure to their vapors is examined. Three colors of hair were simultaneously exposed to explosive vapor. Following exposure of hair, the sorbed explosive was removed by extraction with acetonitrile and quantified. Results show that sorption of explosives, via vapor diffusion, to black hair is significantly greater than to blond, brown or bleached hair. Furthermore, the rate of sorption is directly related to the vapor density of the explosive: EGDN > TATP >TNT > PETN > RDX. In some cases, the explosive-containing hair was subject to repeated washings with sodium dodecylsulfate or simply left out in an open area to determine the persistence of the explosive contamination. While explosive is removed from hair with time or washing, some persists. These results indicate that hair can be a useful indicator of explosive exposure/handling.     

Quantified Explosives Transfer on Surfaces for the Evaluation of Trace Detection Equipment

Trace explosive test surfaces are often required for the evaluation of trace detection equipment to determine the equipment performance. Test surfaces of C‐4, Detasheet, Semtex‐H, TNT, and HMTD were prepared by transferring trace amount of explosive deposited on polytetrafluoroethylene (PTFE) transfer strips onto different surfaces (Kraft paper, hard plastic, woven fabric, and soft vinyl). The amount of explosive transferred was deduced from the amount of explosive remaining on the PTFE strips after transfer, as quantified by direct analysis using tandem mass spectrometry with thermal desorption. From the data set of over 2000 transfers, we experienced lower transfer efficiency for Semtex‐H and Detasheet, and for soft vinyl and hard plastic. However, the rapid quantification mass spectrometric method allowed the transfer efficiency to be determined for all test surfaces used in an evaluation of trace explosive detectors, thereby permitting only the test surfaces with desired transfer to be accepted for the assessment.