Sampling and recovery of ignitable liquid residues (ILRs) from fire debris using capillary microextraction of volatiles (CMV) for on-site analysis.

A new, fast, and ultra-sensitive headspace sampling method using the Capillary Microextraction of Volatiles (CMV) device is demonstrated for the analysis of ignitable liquid residues (ILRs) in fire debris. This headspace sampling method involves the use of a heated can (60°C) to aid in the recovery of volatile organic compounds (VOCs) from medium and heavy petroleum distillates. Our group has previously reported the utility of CMV to extract gasoline at ambient temperature in less than 5 min in the field. This work evaluates the recovery and analysis of low mass loadings (tens of ng) of VOCs from charcoal lighter fluid, kerosene, and diesel fuel. Nonane, decane, undecane, tridecane, tetradecane, and pentadecane were selected for evaluation of recovery to represent these ILR classes. The face-down heated can headspace sampling technique was compared to the previously reported, non-heated, paper cup headspace sampling technique. Mass recovery improvements of 50%-200% for five of the six target compounds in diesel fuel were achieved compared to the non-heated sampling method. The average relative standard deviation (reported as % RSD) between the replicate trials decreased from an average of 28% to 6% when using the heated can method. Ignitable liquids were spiked onto burned debris in a live burn exercise and sampled using the heated can and paper cup headspace sampling techniques. The heated sampling technique reported here, for the first time, demonstrates an effective extraction method that when coupled to a portable GC-MS instrument allows for a sampling and analysis protocol in the field in less than 30 min.

Multi-element comparisons of tapes evidence using dimensionality reduction for calculating likelihood ratios.

Computing the likelihood ratio (LR), as a measure of weight of evidence, has traditionally been difficult for multi-element evidence. A solution based on multivariate random effects models has been adopted by the forensic community but suffers from instability and has a tendency toward extreme values. This problem is magnified by increasing the number of variables. In this study, we consider reducing the dimensionality of the problem using principal component analysis (PCA) and a post-hoc calibration step suggested by van Es et al. [1] and evaluate the performance of this method using multi-element data collected from electrical tapes with up to 18 elements measured. A set of 90 tapes known to originate from different sources were analyzed by LA-ICP-MS. We used additive log-ratio transformation with respect to the signal of 208Pb to transform the 18-dimensional data. This transformation altered the scale of the signals and more importantly, the transformed signals exhibited characteristics similar to a normal distribution. We used scores of the first five principal components (PCs) as input to the LR formula given by Aitken and Lucy [2] where we assumed multivariate normal between-sources distribution (LR MVN) to compare the tapes. We observed that the calculated LRs were extremely positive and negative and did not conform with the definition of well-calibrated LRs. Thus, we used the post-hoc calibration method given by van Es et al. [1] to calibrate the likelihood ratios. The calibrated LRs were obtained within an appropriate range. Five scenarios, each related to the number of principal components used to compare the samples formed part of this study. The first scenario made the comparisons using only the first PC, the second scenario used the first two PCs together and so on. The last scenario, LR5, used 5 PCs for the comparisons. Comparing the results of these 5 scenarios provided an understanding around sensitivity of the method based on the percentage of information used for the comparisons. The lowest false exclusion (Type I) and false inclusion (Type II) error rates were obtained for LR5 scenario in comparison to all the other scenarios. False inclusion and false exclusion error rates of 3.7% and 2.2% were reported by using only 5 out of 17 PCs. False exclusion error rates of 2.2% indicated that only two same-source comparisons had LR<1. The proposed method overcomes the problem of using highly-dimensional data for the comparisons, while using a high percentage of information present in the original data.

Capillary microextraction of volatiles device for enhanced BTEX vapors sampling based on a phenyl modified PDMS sol-gel adsorption phase.

A novel phenyl modified PDMS (PhPDMS) sol-gel adsorption phase was developed for use with the capillary microextraction of volatiles (CMV) device, and determined to provide significant enhancement in BTEX recoveries when sampling trace (ng) amounts of these volatiles at ambient conditions. The previously reported reusable PDMS-CMV device has been demonstrated to rapidly and efficiently extract target compound's vapors in forensic and environmental applications. An improved recovery for VOCs was achieved with a cryofocusing system while extracting at -10 °C, but it was found to be impractical for field sampling. This report details a modification to the CMV's chemistry, by the successful introduction of phenyl groups to the PDMS sol-gel adsorption phase, allowing enhanced performance at ambient extraction conditions. Higher average recoveries, determined through a broad concentration range, were demonstrated for PhPDMS-CMV over its original PDMS-CMV, from cans simulating a closed space set-up. Within 7.8 (±10%) and 3.5 (±6%) folds higher for benzene and toluene, respectively and 2 (±2%) folds for ethylbenzene and xylenes. Significant higher retaining capabilities were demonstrated also at the more challenging set-up, simulating an open space environment. Whereas, benzene had completely breakthrough the PDMS-CMV, its reliable detection was still confirmed with PhPDMS-CMV pumping at 2 L or 6 L air, concentration dependent. At least 50 folds (±26%) more toluene was retained with PhPDMS-CMV at 6 L air than with PDMS-CMV. The enhanced overall performance lead to determination of trace LODs with the new CMV of 0.002, 0.00035 and 0.00015 ppm for benzene, toluene, ethyl benzene and xylenes, respectively. As proof of concept, for the first time solvent extraction is presented for the new CMV as an alternative to thermal desorption extraction. Extraction efficiencies of 60% for TEX, and lower concentration dependent for benzene, were demonstrated with the ease and rapid application of 100 µL acetone through the device. The improvements described in this study continues to build on the potential for the use of the reusable new CMV device by expanding its possible potential applications for fast and sensitive air sampling of VOCs. The solvent extraction step may offer compatibility with LC-based systems.

The Capability of Raman Microspectroscopy to Differentiate Printing Inks.

This study applies Raman microspectroscopy to differentiate the chemical components in printing inks of different brands, colors, and type using the 532 nm and 785 nm excitation wavelengths. Spectra were collected from 319 inks (78 inkjet, 76 toner, 79 offset, and 86 intaglio) representing various colors. Comparisons were performed to calculate discrimination capability percentages for each ink type. Overall, Raman microspectroscopy differentiates according to the following hierarchy: intaglio (96%), inkjet (92%), offset (90%), and toner (61%). The ability of Raman microspectroscopy to differentiate between same-colored inks from different brands was dependent on the color and ink analyzed. Based on ink color, the discrimination capability ranged from 75 to 94% (inkjet), 0 to 86% (toner), and 0 to 77% (offset). Copper phthalocyanine was detected in cyan inks and various intaglio inks, while carbon black was identified in black inkjet, offset, and intaglio inks.

Characterization of Printing Inks Using DART-Q-TOF-MS and Attenuated Total Reflectance (ATR) FTIR.

The rise in improved and widely accessible printing technology has resulted in an interest to develop rapid and minimally destructive chemical analytical techniques that can characterize printing inks for forensic document analysis. Chemical characterization of printing inks allows for both discrimination of inks originating from different sources and the association of inks originating from the same source. Direct analysis in real-time mass spectrometry (DART-MS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used in tandem to analyze four different classes of printing inks: inkjets, toners, offset, and intaglio. A total of 319 samples or ~ 80 samples from each class were analyzed directly on a paper substrate using the two methods. DART-MS was found to characterize the semi-volatile polymeric vehicle components, while ATR-FTIR provided chemical information associated with the bulk components of these inks. Complimentary data results in improved discrimination when both techniques are used in succession resulting in >96% discrimination for all toners, 95% for all inkjets, >92% for all offset, and >54% for all intaglio inks.

Evaluation of the Forensic Utility of Scanning Electron Microscopy-Energy Dispersive Spectroscopy and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry for Printing Ink Examinations.

Improvements in printing technology have exacerbated the problem of document counterfeiting, prompting the need for analytical techniques that better characterize inks for forensic analysis and comparisons. In this study, 319 printing inks (toner, inkjet, offset, and Intaglio) were analyzed directly on the paper substrate using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). As anticipated, the high sensitivity of LA-ICP-MS pairwise comparisons resulted in excellent discrimination (average of ~ 99.6%) between different ink samples from each of the four ink types and almost 100% correct associations between ink samples known to originate from the same source. SEM-EDS analysis also resulted in very good discrimination for different toner and intaglio inks (>97%) and 100% correct association for samples from the same source. SEM-EDS provided complementary information to LA-ICP-MS for certain ink types but showed limited utility for the discrimination of inkjet and offset inks.

Fast detection and characterization of organic and inorganic gunshot residues on the hands of suspects by CMV-GC-MS and LIBS.

A rapid method for the characterization of both organic and inorganic components of gunshot residues (GSR) is proposed as an alternative tool to facilitate the identification of a suspected shooter. In this study, two fast screening methods were developed and optimized for the detection of organic compounds and inorganic components indicative of GSR presence on the hands of shooters and non-shooters. The proposed methods consist of headspace extraction of volatile organic compounds using a capillary microextraction of volatiles (CMV) device previously reported as a high-efficiency sampler followed by detection by GC-MS. This novel sampling technique has the potential to yield fast results (<2min sampling) and high sensitivity capable of detecting 3ng of diphenylamine (DPA) and 8ng of nitroglycerine (NG). Direct analysis of the headspace of over 50 swabs collected from the hands of suspected shooters (and non-shooters) provides information regarding VOCs present on their hands. In addition, a fast laser induced breakdown spectroscopy (LIBS) screening method for the detection of the inorganic components indicative of the presence of GSR (Sb, Pb and Ba) is described. The sampling method for the inorganics consists of liquid extraction of the target elements from the same cotton swabs (previously analyzed for VOCs) and an additional 30 swab samples followed by spiking 1µL of the extract solution onto a Teflon disk and then analyzed by LIBS. Advantages of LIBS include fast analysis (~12s per sample) and high selectivity and sensitivity, with expected LODs 0.1-18ng for each of the target elements after sampling. The analytical performance of the LIBS method is also compared to previously reported methods (inductively coupled plasma-optical emission spectroscopy). The combination of fast CMV sampling, unambiguous organic compound identification with GC-MS and fast LIBS analysis provides the basis for a new comprehensive screening method for GSR.

Rapid screening of 35 new psychoactive substances by ion mobility spectrometry (IMS) and direct analysis in real time (DART) coupled to quadrupole time-of-flight mass spectrometry (QTOF-MS).

The recent propagation of new psychoactive substances (NPS) has led to the development of new techniques for the rapid characterization of controlled substances in this category. A commercial bench-top ion mobility spectrometer (IMS) with a (63) Ni ionization source and a direct analysis in real time (DART) coupled to quadrupole time-of-flight (QTOF) were used for the rapid characterization of 35 NPS. The advantages of these techniques are fast response, ease of operation, and minimal sample preparation. The characteristic reduced mobilities of each substance are reported as are the mass spectra of the 35 compounds. The acquired product ion scan mass spectra were also compared to a library database constructed by QTOF with a electrospray ionization (ESI) source and showed a consistent relative abundance for each peak over time. A total of four seized drug samples provided by the local forensic laboratory were analyzed in order to demonstrate the utility of this approach. The results of this study suggest that both IMS and DART-QTOF are promising alternatives for the rapid screening and characterization of these new psychoactive substances.

Qualitative analysis of seized synthetic cannabinoids and synthetic cathinones by gas chromatography triple quadrupole tandem mass spectrometry.

Designer drugs are analogues or derivatives of illicit drugs with a modification of their chemical structure in order to circumvent current legislation for controlled substances. Designer drugs of abuse have increased dramatically in popularity all over the world for the past couple of years. Currently, the qualitative seized-drug analysis is mainly performed by gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) in which most of these emerging designer drug derivatives are extensively fragmented not presenting a molecular ion in their mass spectra. The absence of molecular ion and/or similar fragmentation pattern among these derivatives may cause the equivocal identification of unknown seized-substances. In this study, the qualitative identification of 34 designer drugs, mainly synthetic cannabinoids and synthetic cathinones, were performed by gas chromatography-triple quadrupole-tandem mass spectrometry with two different ionization techniques, including electron ionization (EI) and chemical ionization (CI) only focusing on qualitative seized-drug analysis, not from the toxicological point of view. The implementation of CI source facilitates the determination of molecular mass and the identification of seized designer drugs. Developed multiple reaction monitoring (MRM) mode may increase sensitivity and selectivity in the analysis of seized designer drugs. In addition, CI mass spectra and MRM mass spectra of these designer drug derivatives can be used as a potential supplemental database along with EI mass spectral database.

Elemental analysis of soils using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and laser-induced breakdown spectroscopy (LIBS) with multivariate discrimination: tape mounting as an alternative to pellets for small forensic transfer specimens.

Elemental analysis of soil is a useful application of both laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and laser-induced breakdown spectroscopy (LIBS) in geological, agricultural, environmental, archeological, planetary, and forensic sciences. In forensic science, the question to be answered is often whether soil specimens found on objects (e.g., shoes, tires, or tools) originated from the crime scene or other location of interest. Elemental analysis of the soil from the object and the locations of interest results in a characteristic elemental profile of each specimen, consisting of the amount of each element present. Because multiple elements are measured, multivariate statistics can be used to compare the elemental profiles in order to determine whether the specimen from the object is similar to one of the locations of interest. Previous work involved milling and pressing 0.5 g of soil into pellets before analysis using LA-ICP-MS and LIBS. However, forensic examiners prefer techniques that require smaller samples, are less time consuming, and are less destructive, allowing for future analysis by other techniques. An alternative sample introduction method was developed to meet these needs while still providing quantitative results suitable for multivariate comparisons. The tape-mounting method involved deposition of a thin layer of soil onto double-sided adhesive tape. A comparison of tape-mounting and pellet method performance is reported for both LA-ICP-MS and LIBS. Calibration standards and reference materials, prepared using the tape method, were analyzed by LA-ICP-MS and LIBS. As with the pellet method, linear calibration curves were achieved with the tape method, as well as good precision and low bias. Soil specimens from Miami-Dade County were prepared by both the pellet and tape methods and analyzed by LA-ICP-MS and LIBS. Principal components analysis and linear discriminant analysis were applied to the multivariate data. Results from both the tape method and the pellet method were nearly identical, with clear groupings and correct classification rates of >94%.

Discrimination of unprocessed cotton on the basis of geographic origin using multi-element stable isotope signatures.

RATIONALE: Cotton is the most commonly used natural plant product for the manufacture of yarns and textiles. Consumer perception regarding differences in textile quality in relation to geographic provenance of cotton as well as stringent product labelling requirements demand for the supply chain to furnish proof of geographic provenance beyond merely paper-based audit trails. METHODS: We have applied isotope ratio mass spectrometry to generate multivariate data sets of raw cotton. A two-point equilibration process with water at ambient temperature was used to account for hydrogen exchange between free hydroxyl groups in the cellulose lattice at ambient humidity, prior to hydrogen isotope analysis. RESULTS: The molar fraction of exchangeable hydrogen in cotton at ambient temperature was found to be 0.046, which is in good agreement with the expected exchange fraction of 0.05. Hierarchical cluster analysis of multivariate stable isotope abundance data from 17 US cotton and 15 non-US cotton samples was able to cluster 15 of the 17 US cotton samples in one group. CONCLUSIONS: Hierarchical cluster analysis of multivariate stable isotope signatures of raw cotton showed great promise as an analytical tool to differentiate between US and non-US cotton and possibly even to be able to group unprocessed cotton according to geographic origin.

Separation mechanism of chiral impurities, ephedrine and pseudoephedrine, found in amphetamine-type substances using achiral modifiers in the gas phase.

A new mechanism is proposed that describes the gas-phase separation of chiral molecules found in amphetamine-type substances (ATS) by the use of high-resolution ion mobility spectrometry (IMS). Straight-chain achiral alcohols of increasing carbon chain length, from methanol to n-octanol, are used as drift gas modifiers in IMS to highlight the mechanism proposed for gas-phase separations of these chiral molecules. The results suggest the possibility of using these achiral modifiers to separate the chiral molecules (R,S) and (S,R)-ephedrine and (S,S) and (R,R)-pseudoephedrine which contain an internal hydroxyl group at the first chiral center and an amino group at the other chiral center. Ionization was achieved with an electrospray source, the ions were introduced into an IMS with a resolving power of 80, and the resulting ion clusters were characterized with a coupled quadrupole mass spectrometer detector. A complementary computational study conducted at the density functional B3LYP/6-31g level of theory for the electronic structure of the analyte-modifier clusters was also performed, and showed either "bridged" or "independent" binding. The combined experimental and simulation data support the proposed mechanism for gas-phase chiral separations using achiral modifiers in the gas phase, thus enhancing the potential to conduct fast chiral separations with relative ease and efficiency.

Fast detection of triacetone triperoxide (TATP) from headspace using planar solid-phase microextraction (PSPME) coupled to an IMS detector.

Triacetone triperoxide (TATP) is a high explosive synthesized from easily available reactants making it accessible for illicit uses. In this study, fast detection of TATP is achieved using a novel planar solid-phase microextraction (PSPME) as a preconcentration and sampling device for headspace analysis offering improved sensitivity and reduced sampling time over the conventional fiber-based solid-phase microextraction (SPME) when followed by ion mobility spectrometer (IMS) detection. Quantitation and comparison of the retention capabilities of PSPME as compared to the commercially available SPME were determined using TATP standards and analyzed using gas chromatography-mass spectrometry for SPME analysis and a commercial IMS with no instrumental modification for PSPME. Static and dynamic headspace extractions were used and compared for PSPME extractions, in which low milligram quantities of TATP were detected within 30 s of static mode sampling and less than 5 s in the dynamic mode sampling for PSPME-IMS.

Quantitative analysis of liquids from aerosols and microdrops using laser induced breakdown spectroscopy.

Laser induced breakdown spectroscopy (LIBS) is shown to be capable of low volume (90 pL) quantitative elemental analysis of picogram amounts of dissolved metals in solutions. Single-pulse and collinear double-pulse LIBS were investigated using a 532 nm dual head laser coupled to a spectrometer with an intensified charge coupled device (CCD) detector. Aerosols were produced using a micronebulizer, conditioned inside a concentric spray chamber, and released through an injector tube with a diameter of 1 mm such that a LIBS plasma could be formed ~2 mm from the exit of the tube. The emissions from both the aerosols and a single microdrop were then collected with a broadband high resolution spectrometer. Multielement calibration solutions were prepared, and continuing calibration verification (CCV) standards were analyzed for both aerosol and microdrop systems to calculate the precision, accuracy, and limits of detection for each system. The calibration curves produced correlation coefficients with R(2) values > 0.99 for both systems. The precision, accuracy, and limit of detection (LOD) determined for aerosol LIBS were averaged and determined for the emission lines of Sr II (421.55 nm), Mg II (279.80 nm), Ba II (493.41 nm), and Ca II (396.84 nm) to be ~3.8% RSD, 3.1% bias, 0.7 µg/mL, respectively. A microdrop dispenser was used to deliver single drops containing 90 pL into the space where a LIBS plasma was generated with a focused laser pulse. In the single drop microdrop LIBS experiment, the analysis of a single drop, containing a total mass of 45 pg, resulted in a precision of 13% RSD and a bias of 1% for the Al I (394.40 nm) emission line. The absolute limits of detection of single drop microdrop LIBS for the emission lines Al I (394.40 nm) and Sr II (421.5 nm) were approximately 1 pg, and Ba II (493.41 nm) produced an absolute detection limit of approximately 3 pg. Overall, the precision, accuracy, and absolute LOD determined for single microdrop LIBS resulted in a typical performance of ~14% RSD, 6% bias, and 1 pg for the elements Sr II (421.55 nm), Al I(394.40 nm), Mg II (279.80), and Ba II(493.41 nm).

Elemental analysis of glass by laser ablation inductively coupled plasma optical emission spectrometry (LA-ICP-OES).

The elemental analysis of glass evidence has been established as a powerful discrimination tool for forensic analysts. Laser ablation inductively coupled plasma optical emission spectrometry (LA-ICP-OES) has been compared to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and energy dispersive micro X-ray fluorescence spectroscopy (µXRF/EDS) as competing instrumentation for the elemental analysis of glass. The development of a method for the forensic analysis of glass coupling laser ablation to ICP-OES is presented for the first time. LA-ICP-OES has demonstrated comparable analytical performance to LA-ICP-MS based on the use of the element menu, Al (Al I 396.15 nm), Ba (Ba II 455.40 nm), Ca (Ca II 315.88 nm), Fe (Fe II 238.20 nm), Li (Li I 670.78 nm), Mg (Mg I 285.21 nm), Sr (Sr II 407.77 nm), Ti (Ti II 368.51 nm), and Zr (Zr II 343.82 nm). The relevant figures of merit, such as precision, accuracy and sensitivity, are presented and compared to LA-ICP-MS. A set of 41 glass samples was used to assess the discrimination power of the LA-ICP-OES method in comparison to other elemental analysis techniques. This sample set consisted of several vehicle glass samples that originated from the same source (inside and outside windshield panes) and several glass samples that originated from different vehicles. Different match criteria were used and compared to determine the potential for Type I and Type II errors. It was determined that broader match criteria is more applicable to the forensic comparison of glass analysis because it can reduce the affect that micro-heterogeneity inherent in the glass fragments and a less than ideal sampling strategy can have on the interpretation of the results. Based on the test set reported here, a plus or minus four standard deviation (± 4s) match criterion yielded the lowest possibility of Type I and Type II errors. The developed LA-ICP-OES method has been shown to perform similarly to LA-ICP-MS in the discrimination among different sources of glass while offering the advantages of a lower cost of acquisition and operation of analytical instrumentation making ICP-OES a possible alternative elemental analysis method for the forensic laboratory.

Characterization and forensic analysis of soil samples using laser-induced breakdown spectroscopy (LIBS).

A method for the quantitative elemental analysis of surface soil samples using laser-induced breakdown spectroscopy (LIBS) was developed and applied to the analysis of bulk soil samples for discrimination between specimens. The use of a 266 nm laser for LIBS analysis is reported for the first time in forensic soil analysis. Optimization of the LIBS method is discussed, and the results compared favorably to a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method previously developed. Precision for both methods was <10% for most elements. LIBS limits of detection were <33 ppm and bias <40% for most elements. In a proof of principle study, the LIBS method successfully discriminated samples from two different sites in Dade County, FL. Analysis of variance, Tukey's post hoc test and Student's t test resulted in 100% discrimination with no type I or type II errors. Principal components analysis (PCA) resulted in clear groupings of the two sites. A correct classification rate of 99.4% was obtained with linear discriminant analysis using leave-one-out validation. Similar results were obtained when the same samples were analyzed by LA-ICP-MS, showing that LIBS can provide similar information to LA-ICP-MS. In a forensic sampling/spatial heterogeneity study, the variation between sites, between sub-plots, between samples and within samples was examined on three similar Dade sites. The closer the sampling locations, the closer the grouping on a PCA plot and the higher the misclassification rate. These results underscore the importance of careful sampling for geographic site characterization.

Analysis of the headspace composition of smokeless powders using GC-MS, GC-µECD and ion mobility spectrometry.

Smokeless powder additives are usually detected from an extraction of post-blast residues or unburned powder particles followed by chromatographic analyses. This work presents the first comprehensive study of the detection of volatile and semi-volatile additives of smokeless powders using solid phase microextraction (SPME) as a sampling and pre-concentration technique. The goal of this study is to generate a list of compounds that can be used as target compounds for the vapor phase detection of smokeless powders. Sixty-five smokeless powders were studied using laboratory-based gas chromatography techniques and a field deployable ion mobility spectrometer (IMS). The detection of diphenylamine, ethyl and methyl centralite, 2,4-dinitrotoluene, diethyl and dibutyl phthalate by IMS is suggested as a method to indicate the presence of smokeless powders. A previously reported SPME-IMS analytical approach facilitates rapid sub-nanogram detection of the vapor phase components of smokeless powders. The analyte mass present in the vapor phase was sufficient for a SPME fiber to extract and concentrate most analytes at amounts above the detection limits of both the GC and the IMS methods. Analysis of 65 different smokeless powder samples revealed that diphenylamine was present in the headspace of 96% of the powders studied. Ethyl centralite was detected in 47% of the powders and 8% of the powders contained methyl centralite. Nitroglycerin was the dominant peak present in the headspace of the double-based powders. Another important headspace component, 2,4-dinitrotoluene, was detected in 44% of the powders comprising both double and single-based powders. Static headspace SPME of small amounts (∼100 mg) of smokeless powder samples for ∼5 min at room temperature resulted in the successful detection of the headspace components, demonstrating the applicability of the technique for field detection of smokeless powders using IMS as a detector.

Solid-phase microextraction (SPME) calibration using inkjet microdrop printing for direct loading of known analyte mass on to SPME fibers.

Solid-phase microextraction (SPME) is a widely used sampling technique that has been proved to enable efficient extraction of a broad range of analytes. Generally, SPME achieves non-exhaustive extraction, and therefore the analyte mass transfer distribution in the sampled multiphase system should be considered while developing a calibration method. Here, a new method, aimed at quantifying the extracted analytes without the need to consider their mass distribution, is proposed. This method relies on the generation of mass response curves by loading a known analyte mass onto the absorbent phase of a SPME fiber, and then conducting analysis by the preferred technique. Precise and accurate deposition of analyte over the restricted dimension of a fiber is demonstrated for the first time by utilizing a drop-on-demand microdrop printer. This system enables direct, non-contact deposition of micron-sized drops containing negligible solvent volumes (<1 nL), on the center of the extraction phase of the fiber which enables immediate analysis. Printed fiber response curves were determined herein, with three model compounds of different volatility-2,4-dinitrotoluene (2,4-DNT), diphenylamine (DPA), and 1,3 diethyl-1,3-diphenylurea (ethyl centralite, EC), using two analytical techniques, gas chromatography-mass spectrometry (GC-MS) and ion mobility spectrometry (IMS). Quantification of the absolute amounts extracted by headspace SPME yielded comparable results between the two methods of analysis with only less than 10% variation for 2,4-DNT and EC and less than 30% for DPA. In comparison, quantification by the traditional liquid injection/spike response curves determined by each technique led to mass estimates that were significantly greater by hundreds of percent.