José R. Almirall

Identification of dominant odor chemicals emanating from explosives for use in developing optimal training aid combinations and mimics for canine detection.

Despite the recent surge in the publication of novel instrumental sensors for explosives detection, canines are still widely regarded as one of the most effective real-time field method of explosives detection. In the work presented, headspace analysis is performed by solid phase microextraction (SPME)/gas chromatography-mass spectrometry (GC-MS), and gas chromatography-electron capture detection (GC-ECD), and used to identify dominant explosive odor chemicals seen at room temperature. The activity of the odor chemicals detected was determined through field trials using certified law enforcement explosives detection canines. A chemical is considered an active explosive odor when a trained and certified explosives detection canine alerts to a sample containing that target chemical (with the required controls in place). A sample to which the canine does not alert may be considered an inactive odor, but it should be noted that an inactive odor might still have the potential to enhance an active odors effect. The results presented indicate that TNT and cast explosives share a common odor signature, and the same may be said for plasticized explosives such as Composition 4 (C-4) and Detasheet. Conversely, smokeless powders may be demonstrated not to share common odors. The implications of these results on the optimal selection of canine training aids are discussed.

Laser-induced breakdown spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) is an emerging technique for materials analysis that is rapidly maturing and is becoming increasingly accepted as an important tool in analytical chemistry. LIBS is also advancing as a technology as new commercial instruments are becoming available. The core attributes of (1) real-time analysis; (2) no sample preparation; (3) high sensitivity; (4) high specificity for materials identification; (5) sensitivity to all chemical elements in each laser shot; as well as (6) uncommon versatility of point, standoff, as well as underwater-sensing provides a strong argument that LIBS will make a significant impact on science and society. A bibliometric study of the LIBS literature shows clearly that the importance and the number of application areas related to LIBS and laser-based techniques continues to grow. The driving force for this growth appears to be its rapid and remote analysis capabilities for a wide variety of sample types, including the analysis where the requirement for little or no sample preparation is important and the consumption of very small amounts of the sample is critical. Additionally, the relative ease with which LIBS can be combined with other techniques, particularly molecular techniques such as Raman spectroscopy is an advantage. For proof of the impact that LIBS is already making, one needs to go no further than to learn about the next Mission toMars scheduled for 2011/2012 where LIBS is the prime chemical analytical tool of choice. This special issue on LIBS presents the latest progress in this rapidly evolving spectroscopic technique. The 18 articles represent a good balance between fundamental research on the LIBS phenomenology and the applied use of this technique. The papers presented indicate to the reader the active areas in the LIBS field. For example, research is focused on improving the sensitivity of the technique shows that the approach of double-pulse is still of interest. The understanding of physical phenomenon at the early stage of the plasma or the comparison between singleand double-pulse is still attracting further research. While Nd:YAG lasers operating at the fundamental wavelength 1,064 nm or its harmonics are most used for the laser-induced plasma generation in LIBS applications; some papers are focused on the use of the CO2 laser at 10.6 μm. In some cases, the use of this infrared laser may present benefits which can be further exploited. The analysis of slurries is a field of application where LIBS can offer a powerful tool for real-time analysis as the current analytical approaches in this field by conventional This article was published in the special issue Laser-Induced Breakdown Spectroscopy with Guest Editors Jagdish P. Singh, Jose Almirall, Mohamad Sabsabi, and Andrzej Miziolek.

Application of solid-phase microextraction to the recovery of explosives and ignitable liquid residues from forensic specimens

A current review of the application of solid-phase microextraction (SPME) to the analysis of ignitable liquids and explosive residues is presented along with experimental results demonstrating the relative effects of controllable variables. Variables discussed include fiber chemistry, adsorption and desorption temperatures, extraction and desorption times, fiber sampling placement (direct, headspace, and partial headspace) and matrix effects, including water content. SPME is shown to be an inexpensive, rapid and sensitive method for the analysis of ignitable liquids and high explosives residues from solid debris samples and from aqueous samples. Explosives are readily detected at parts per trillion concentrations and ignitable liquids are reproducibly detected at levels below those using conventional methods.

Laser induced breakdown spectroscopy as a tool for discrimination of glass for forensic applications

Materials analysis and characterization can provide important information as evidence in legal proceedings. The potential of laser induced breakdown spectroscopy (LIBS) for the discrimination of glass fragments for forensic applications is presented here. The proposed method is based on the fact that glass materials can be characterized by their unique spectral fingerprint. Taking advantage of the multielement detection capability and minimal to no sample preparation of LIBS, we compared glass spectra from car windows using linear and rank correlation methods. Linear correlation combined with the use of a spectral mask, which eliminates some high-intensity emission lines from the major elements present in glass, provides effective identification and discrimination at a 95% confidence level.

Dynamic planar solid phase microextraction-ion mobility spectrometry for rapid field air sampling and analysis of illicit drugs and explosives.

A preconcentration device that targets the volatile chemical signatures associated with illicit drugs and explosives (high and low) has been designed to fit in the inlet of an ion mobility spectrometer (IMS). This is the first reporting of a fast and sensitive method for dynamic sampling of large volumes of air using planar solid phase microextraction (PSPME) incorporating a high surface area for absorption of analytes onto a sol-gel polydimethylsiloxane (PDMS) coating for direct thermal desorption into an IMS. This device affords high extraction efficiencies due to strong retention properties at ambient temperature, resulting in the detection of analyte concentrations in the parts per trillion range when as low as 3.5 L of air are sampled over the course of 10 s (absolute mass detection of less than a nanogram). Dynamic PSPME was used to sample the headspace over the following: 3,4-methylenedioxymethamphetamine (MDMA) tablets resulting in the detection of 12-40 ng of piperonal, high explosives (Pentolite) resulting in the detection of 0.6 ng of 2,4,6-trinitrotoluene (TNT), and low explosives (several smokeless powders) resulting in the detection of 26-35 ng of 2,4-dinitrotoluene (2,4-DNT) and 11-74 ng of diphenylamine (DPA).

Characterization of background and pyrolysis products that may interfere with the forensic analysis of fire debris

Abstract An important aspect of an investigation of a suspected arson case involves the chemical analysis of the debris remaining after the fire. Forensic chemists apply the tools of analytical chemistry for the extraction, isolation and analysis of the target compounds that characterize ignitable liquid residues (ILR). Complex organic mixtures such as automobile gasoline, diesel fuel and other volatile mixtures that could be used to accelerate an intentionally set fire are routinely identified in forensic laboratories. The presence of these target compounds suggests the presence of ILR originating from these mixtures and this information could aid a fire investigator in determining the cause of the fire, including whether or not arson is suspected. The current study aims to characterize the background and pyrolysis products resulting from controlled burns of materials commonly found in homes and businesses in order to determine their chemical composition. A list of compounds found from the pyrolysis (and combustion) of different substrate types is compared with the target compound list for the identification of ILR. The results show that the burning of some types of commonly found materials creates some of the target compounds commonly found in ILR mixtures. The sources of these compounds are: substrate background products (in the substrate matrix prior to burning), pyrolysis products and, possibly, combustion products.

Analysis of the volatile chemical markers of explosives using novel solid phase microextraction coupled to ion mobility spectrometry.

Ion mobility spectrometry (IMS) is routinely used in screening checkpoints for the detection of explosives and illicit drugs but it mainly relies on the capture of particles on a swab surface for the detection. Solid phase microextraction (SPME) has been coupled to IMS for the preconcentration of explosives and their volatile chemical markers and, although it has improved the LODs over a standalone IMS, it is limited to sampling in small vessels by the fiber geometry. Novel planar geometry SPME devices coated with PDMS and sol-gel PDMS that do not require an additional interface to IMS are now reported for the first time. The explosive, 2,4,6-trinitrotoluene (TNT), is sampled with the planar SPME reaching extraction equilibrium faster than with fiber SPME, concentrating detectable levels of TNT in a matter of minutes. The surface area, capacity, extraction efficiency, and LODs are also improved over fiber SPME allowing for sampling in larger volumes. The volatile chemical markers, 2,4-dinitrotoluene, cyclohexanone, and the taggant 4-nitrotoluene have also been successfully extracted by planar SPME and detected by IMS at mass loadings below 1 ng of extracted analyte on the planar device for TNT, for example.

Development and evaluation of a standard method for the quantitative determination of elements in float glass samples by LA-ICP-MS.

Forensic analysis of glass samples was performed in different laboratories within the NITE-CRIME (Natural Isotopes and Trace Elements in Criminalistics and Environmental Forensics) European Network, using a variety of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) systems. The main objective of the interlaboratory tests was to cross-validate the different combinations of laser ablation systems with different ICP-MS instruments. A first study using widely available samples, such as the NIST SRM 610 and NIST SRM 612 reference glasses, led to deviations in the determined concentrations for trace elements amongst the laboratories up to 60%. Extensive discussion among the laboratories and the production of new glass reference standards (FGS 1 and FGS 2) established an improved analytical protocol, which was tested on a well-characterized float glass sample (FG 10-1 from the BKA Wiesbaden collection). Subsequently, interlaboratory tests produced improved results for nearly all elements with a deviation of < 10%, demonstrating that LA-ICP-MS can deliver absolute quantitative measurements on major, minor and trace elements in float glass samples for forensic and other purposes.

Application of laser ablation (LA-ICP-SF-MS) for the elemental analysis of bone and teeth samples for discrimination purposes

Human bone and teeth fragments can be useful evidence when found in crime scenes and/or mass burials sites. The elemental and isotopic composition of these samples can provide information about environmental exposure events and could also be used to distinguish different individuals. The development and application of robust analytical methods for the quantification of trace elements in these biological matrices may lead to a better understanding of the potential utility of these measurements in forensic analyses. In this paper, we demonstrate the possibility of conducting quantitative analysis of trace metals found in bone remains and suggest a strategy to discriminate between individuals, based on this information. A LA-ICP-SF-MS method using non-matrix matched standard calibration was developed and optimized with bone standard reference materials (SRMs) and subsequently applied to the analysis of real samples. The developed method requires micrograms amount of sample (vs. milligrams required for solution-based analysis) while also reducing the analysis time and resulting in good accuracy (typically <10% bias) and precision (<15% RSD). Additionally, laser ablation allowed using spatial resolution analysis to assess the biogenic elemental composition in buried bone samples. Elemental analysis of bone samples from 12 different individuals provided better discrimination between the individuals when the femur and humerus bones were considered separately (42.7% correct classification with all bones vs. 75.2% and 63.1% for femur bones and humerus bones, respectively). Separation of individuals was achieved by elemental composition of whole teeth samples from 14 individuals, except one case where not all the teeth from the same individual were associated together. Separation of individuals was improved when using elemental composition of the enamel and dentine+cementum layers separately in a set of samples from 7 individuals. These are promising results for the use of elemental analysis by laser ablation ICP-MS for discrimination purposes.

Analysis of volatile components of drugs and explosives by solid phase microextraction‐ion mobility spectrometry

Current ion mobility spectrometry (IMS) devices are used to detect drugs and explosives in the form of particles and, in cases where the vapor pressure of the drugs or explosives is sufficiently high, the gas can be sampled and detected directly. The aim of this study is to demonstrate the use of solid phase microextraction (SPME) as a preconcentration technique coupled to an IMS for the detection of odor signature compounds of drugs and explosives. The reduced mobilities (K(o)) and IMS operating conditions for the odor signature compounds of cocaine, marijuana, and 3,4-methylenedioxy-N-methylamphetamine (MDMA) are reported for the first time. LODs, linear dynamic ranges (LDRs), and the precision of the analysis of these odor signature compounds, and the explosive taggant 2,3-dimethyl-2,3-dinitrobutane (DMNB) were obtained by SPME-IMS and normal IMS conditions. The systematic optimization of the IMS operating parameters for the detection of these odor compounds is also reported incorporating the use of genetic algorithms (GAs) for finding the optimal settings for the detection of these compounds of interest. These results support the case for targeting volatile components as a presumptive detection for the presence of the parent compounds of drugs and explosives. Furthermore, the IMS-specific GA developed can be used as an optimization tool for the detection of other compounds of interest in future work.