Vapor pressure measurements on linalool using a rapid and inexpensive method suitable for cannabis-associated terpenes†.

Vapor pressure (psat) data are needed to assess the potential use of terpenes as breath markers of recent cannabis use. Herein, a recently introduced gas-saturation method for psat measurements, known as dynamic vapor microextraction (DVME), was used to measure psat for the terpene (±)-3,7-dimethylocta-1,6-dien-3-ol, commonly known as linalool. The DVME apparatus utilizes inexpensive and commercially available components, a low internal volume, and helium carrier gas to minimize nonideal mixture behavior. In the temperature range from 314 K to 354 K, DVME-based measurements of the psat of linalool ranged from 81 Pa to 1250 Pa. With a measurement period of 30 min, the combined standard uncertainty of these measurements ranged from 0.0358·psat to 0.0584·psat, depending on temperature. The DVME-based measurements agree with a Wagner correlation of available literature data. We demonstrate that DVME produces accurate results for values of psat that are 200 times higher than in the DVME validation study with n-eicosane (C20H42). The oxidative stability of linalool was improved by the addition of 0.2 mass % of the antioxidant tert-butylhydroquinone.

Rapid Vapor-Collection Method for Vapor Pressure Measurements of Low-Volatility Compounds.

Dynamic vapor microextraction (DVME) is a new method that enables rapid vapor pressure measurements on large molecules with state-of-the-art measurement uncertainty for vapor pressures near 1 Pa. Four key features of DVME that allow for the rapid collection of vapor samples under thermodynamic conditions are (1) the use of a miniature vapor-equilibration vessel (the "saturator") to minimize the temperature gradients and internal volume, (2) the use of a capillary vapor trap to minimize the internal volume, (3) the use of helium carrier gas to minimize nonideal mixture behavior, and (4) the direct measurement of pressure inside the saturator to accurately account for overpressure caused by viscous flow. The performance of DVME was validated with vapor pressure measurements of n-eicosane (C20H42) at temperatures from 344 to 374 K. A thorough uncertainty analysis indicated a relative standard uncertainty of 2.03-2.82% for measurements in this temperature range. The measurements were compared to a reference correlation for the vapor pressures of n-alkanes; the deviation of the measurements from the correlation was ≤2.85%. The enthalpy of vaporization of n-eicosane at 359.0 K was calculated to be ΔvapH = 91.27 ± 0.28 kJ/mol compared to ΔvapH(corr) = 91.44 kJ/mol for the reference correlation. Total measurement periods as short as 15 min (3 min of thermal equilibration plus 12 min of carrier gas flow) were shown to be sufficient for high-quality vapor pressure measurements at 364 K.

THC in breath aerosols collected with an impaction filter device before and after legal-market product inhalation-a pilot study.

An accurate cannabis breathalyzer based on quantitation of the psychoactive cannabinoid Δ9-tetrahydrocannabinol (THC) could be an important tool for deterring impaired driving. Such a device does not exist. Simply translating what is known about alcohol breathalyzers is insufficient because ethanol is detected as a vapor. THC has extremely low volatility and is hypothesized to be carried in breath by aerosol particles formed from lung surfactant. Exhaled breath aerosols can be recovered from electrostatic filter devices, but consistent quantitative results across multiple studies have not been demonstrated. We used a simple-to-use impaction filter device to collect breath aerosols from participants before and after they smoked a legal market cannabis flower containing ∼25% Δ9-tetrahydrocannabinolic acid. Breath collection occurred at an intake session (baseline-intake) and four weeks later in a federally-compliant mobile laboratory 15 min before (baseline-experimental) and 1 h after cannabis use (post-use). Cannabis use was in the participant's residence. Participants were asked to follow a breathing maneuver designed to increase aerosol production. Breath extracts were analyzed by liquid chromatography with tandem mass spectrometry with multiple reaction monitoring of two transitions for analytes and their deuterated internal standards. Over more than 1 yr, 42 breath samples from 18 participants were collected and analyzed in six batches. THC was quantified in 31% of baseline-intake, 36% of baseline-experimental, and 80% of 1 h post-use breath extracts. The quantities observed 1 h post-use are compared to those reported in six other pilot studies that sampled breath at known intervals following cannabis use and are discussed with respect to participant characteristics and breath sampling protocols. Larger studies with verified abstinence and more post-use timepoints are necessary to generate statistically significant data to develop meaningful cannabis breathalyzer technology.

The need for multicomponent gas standards for breath biomarker analysis.

Exhaled breath is a non-invasive, information-rich matrix with the potential to diagnose or monitor disease, including infectious disease. Despite significant effort dedicated to biomarker identification in case control studies, very few breath tests are established in practice. In this topical review, we identify how gas standards support breath analysis today and what is needed to support further expansion and translation to practice. We examine forensic and clinical breath tests and discuss how confidence has been built through unambiguous biomarker identification and quantitation supported by gas calibration standards. Based on this discussion, we identify a need for multicomponent gas standards with part-per-trillion to part-per-million concentrations. We highlight National Institute of Standards and Technology gas standards developed for atmospheric measurements that are also relevant to breath analysis and describe investigations of long-term stability, chemical reactions, and interactions with gas cylinder wall treatments. An overview of emerging online instruments and their need for gas standards is also presented. This review concludes with a discussion of our ongoing research to examine the feasibility of producing multicomponent gas standards at breath-relevant concentrations. Such standards could be used to investigate interference from ubiquitous endogenous compounds and as a starting point for standards tailored to specific breath tests.

Trace headspace sampling for quantitative analysis of explosives with cryoadsorption on short alumina porous layer open tubular columns.

Quantitative headspace (HS) measurements have been performed on the practical industrial and military plastic bonded explosives (PBX) tagged-C-4, Semtex-1A, Semtex-H, detonating cord (detcord), and sheet explosive (Detaflex). The measurements were made by a modified purge and trap technique developed in our laboratory on the basis of cryoadsorption on short alumina-coated porous layer open tubular (PLOT) columns. Trace compounds (of both high and low volatility) were identified and quantitated as a function of HS collection temperature. The data are presented in the form of van't Hoff equations. The linear relationship of the recovered mass as a function of inverse collection temperature reveals the predictive capabilities of the methodology employed here. Knowledge of the compounds that can be detected, along with the expected concentrations to be collected, can aid in detection of explosive materials. Additionally, these data can aid in the standardization, calibration, and certification of energetic material detection devices and can aid in the training of canines for explosive detection.

Complex fluid analysis with the advanced distillation curve approach.

An improved method for measuring distillation curves reveals the physicochemical properties of complex fluids such as fuels.

Determination of Cannabinoid Vapor Pressures to Aid in Vapor Phase Detection of Intoxication.

The quest for a reliable means to detect cannabis intoxication with a breathalyzer is ongoing. To design such a device, it is important to understand the fundamental thermodynamics of the compounds of interest. The vapor pressures of two important cannabinoids, cannabidiol (CBD) and Δ9-tetrahydrocannabinol (Δ9-THC), are presented, as well as the predicted normal boiling temperature (NBT) and the predicted critical constants (these predictions are dependent on the vapor pressure data). The critical constants are typically necessary to develop an equation of state (EOS). EOS-based models can provide estimations of thermophysical properties for compounds to aid in designing processes and devices. An ultra-sensitive, quantitative, trace dynamic headspace analysis sampling called porous layered open tubular-cryoadsorption (PLOT-cryo) was used to measure vapor pressures of these compounds. PLOT-cryo affords short experiment durations compared to more traditional techniques for vapor pressure determination (minutes versus days). Additionally, PLOT-cryo has the inherent ability to stabilize labile solutes because collection is done at reduced temperature. The measured vapor pressures are approximately 2 orders of magnitude lower than those measured for n-eicosane, which has a similar molecular mass. Thus, the difference in polarity of these molecules must be impacting the vapor pressure dramatically. The vapor pressure measurements are presented in the form of Clausius-Clapeyron (or van't Hoff) equation plots. The predicted vapor pressures that would be expected at near ambient conditions (25 °C) are also presented.

Application of the Advanced Distillation Curve Method to the Comparison of Diesel Fuel Oxygenates: 2,5,7,10-Tetraoxaundecane (TOU), 2,4,7,9-Tetraoxadecane (TOD), and Ethanol/Fatty Acid Methyl Ester (FAME) Mixtures.

Although they are amongst the most efficient engine types, compression-ignition engines have difficulties achieving acceptable particulate emission and NOx formation. Indeed, catalytic after-treatment of diesel exhaust has become common and current efforts to reformulate diesel fuels have concentrated on the incorporation of oxygenates into the fuel. One of the best ways to characterize changes to a fuel upon the addition of oxygenates is to examine the volatility of the fuel mixture. In this paper, we present the volatility, as measured by the advanced distillation curve method, of a prototype diesel fuel with novel diesel fuel oxygenates: 2,5,7,10-tetraoxaundecane (TOU), 2,4,7,9-tetraoxadecane (TOD), and ethanol/fatty acid methyl ester (FAME) mixtures. We present the results for the initial boiling behavior, the distillation curve temperatures, and track the oxygenates throughout the distillations. These diesel fuel blends have several interesting thermodynamic properties that have not been seen in our previous oxygenate studies. Ethanol reduces the temperatures observed early in the distillation (near ethanol's boiling temperature). After these early distillation points (once the ethanol has distilled out), B100 has the greatest impact on the remaining distillation curve and shifts the curve to higher temperatures than what is seen for diesel fuel/ethanol blends. In fact, for the 15% B100 mixture most of the distillation curve reaches temperatures higher than those seen diesel fuel alone. In addition, blends with TOU and TOD also exhibited uncommon characteristics. These additives are unusual because they distill over most the distillation curve (up to 70%). The effects of this can be seen both in histograms of oxygenate concentration in the distillate cuts and in the distillation curves. Our purpose for studying these oxygenate blends is consistent with our vision for replacing fit-for-purpose properties with fundamental properties to enable the development of equations of state that can describe the thermodynamic properties of complex mixtures, with specific attention paid to additives.

Composition of the C6+ Fraction of Natural Gas by Multiple Porous Layer Open Tubular Capillaries Maintained at Low Temperatures.

As the sources of natural gas become more diverse, the trace constituents of the C6+ fraction are of increasing interest. Analysis of fuel gas (including natural gas) for compounds with more than 6 carbon atoms (the C6+ fraction) has historically been complex and expensive. Hence, this is a procedure that is used most often in troubleshooting rather than for day-to-day operations. The C6+ fraction affects gas quality issues and safety considerations such as anomalies associated with odorization. Recent advances in dynamic headspace vapor collection can be applied to this analysis and provide a faster, less complex alternative for compositional determination of the C6+ fraction of natural gas. Porous layer open tubular capillaries maintained at low temperatures (PLOT-cryo) form the basis of a dynamic headspace sampling method that was developed at NIST initially for explosives in 2009. This method has been recently advanced by the combining of multiple PLOT capillary traps into one "bundle," or wafer, resulting in a device that allows the rapid trapping of relatively large amounts of analyte. In this study, natural gas analytes were collected by flowing natural gas from the laboratory (gas out of the wall) or a prepared surrogate gas flowing through a chilled wafer. The analytes were then removed from the PLOT-cryo wafer by thermal desorption and subsequent flushing of the wafer with helium. Gas chromatography (GC) with mass spectrometry (MS) was then used to identify the analytes.

Comprehensive Assessment of Composition and Thermochemical Variability by High Resolution GC/QToF-MS and the Advanced Distillation-Curve Method as a Basis of Comparison for Reference Fuel Development.

Commercial and military aviation is faced with challenges that include high fuel costs, undesirable emissions, and supply chain insecurity that result from the reliance on petroleum-based feedstocks. The development of alternative gas turbine fuels from renewable resources will likely be part of addressing these issues. The United States has established a target for one billion gallons of renewable fuels to enter the supply chain by 2018. These alternative fuels will have to be very similar in properties, chemistry, and composition to existing fuels. To further this goal, the National Jet Fuel Combustion Program (a collaboration of multiple U.S. agencies under the auspices of the Federal Aviation Administration, FAA) is coordinating measurements on three reference gas turbine fuels to be used as a basis of comparison. These fuels are reference fuels with certain properties that are at the limits of experience. These fuels include a low viscosity, low flash point, high hydrogen content "best case" JP-8 (POSF 10264) fuel, a relatively high viscosity, high flash point, low hydrogen content "worst case" JP-5 (POSF 10259) fuel, and a Jet-A (POSF 10325) fuel with relatively average properties. A comprehensive speciation of these fuels is provided in this paper by use of high resolution gas chromatography/quadrupole time-of-flight - mass spectrometry (GC/QToF-MS), which affords unprecedented resolution and exact molecular formula capabilities. The volatility information as derived from the measurement of the advanced distillation curve temperatures, Tk and Th, provides an approximation of the vapor liquid equilibrium and examination of the composition channels provides detailed insight into thermochemical data. A comprehensive understanding of the compositional and thermophysical data of gas turbine fuels is required not only for comparison but also for modeling of such complex mixtures, which will, in turn, aid in the development of new fuels with the goals of diversified feedstocks, decreased pollution, and increased efficiency.

Analysis of arson fire debris by low temperature dynamic headspace adsorption porous layer open tubular columns.

In this paper we present results of the application of PLOT-cryoadsorption (PLOT-cryo) to the analysis of ignitable liquids in fire debris. We tested ignitable liquids, broadly divided into fuels and solvents (although the majority of the results presented here were obtained with gasoline and diesel fuel) on three substrates: Douglas fir, oak plywood and Nylon carpet. We determined that PLOT-cryo allows the analyst to distinguish all of the ignitable liquids tested by use of a very rapid sampling protocol, and performs better (more recovered components, higher efficiency, lower elution solvent volumes) than a conventional purge and trap method. We also tested the effect of latency (the time period between applying the ignitable liquid and ignition), and we tested a variety of sampling times and a variety of PLOT capillary lengths. Reliable results can be obtained with sampling time periods as short as 3min, and on PLOT capillaries as short as 20cm. The variability of separate samples was also assessed, a study made possible by the high throughput nature of the PLOT-cryo method. We also determined that the method performs better than the conventional carbon strip method that is commonly used in fire debris analysis.

Detecting gravesoil with headspace analysis with adsorption on short porous layer open tubular (PLOT) columns.

Victims of crimes are often buried in clandestine graves. There are several techniques for finding buried bodies or the scattered remains of a victim; however, none of these methods are very reliable or work in all scenarios. One way to detect gravesoil is to detect the biochemical changes of the surrounding soil due to cadaver decomposition, for example, the release of nitrogenous compounds. A simple and low-cost way to detect these compounds is based on the reaction of alpha amino groups with ninhydrin to form Ruhemann's purple. This test for ninhydrin-reactive nitrogen (NRN) has, to date, only been performed by direct solvent extraction of soil samples. Here, we present a method that detects trace quantities of NRN in the headspace air above gravesoil. Our method is based on an improved purge and trap method developed in our lab for sampling low volatility compounds, as well as volatile compounds at trace quantities, by applying low temperature collection on short alumina-coated porous layer open tubular (PLOT) columns. We modified this method to sample the headspace air above gravesoil with a motorized pipetter and a PLOT column at ambient temperatures. We generated gravesoil using rat cadavers and local soil. Trace quantities of NRN were successfully detected in the headspace air above gravesoil. We report the quantities of NRN recovered for buried rats, rats laid on top of soil, and blank graves (no rats) as a function of time (weeks to months). This work is the first (and thus far, only) example of a method for detecting NRN in the vapor phase, providing another tool for forensic investigators to aid in locating elusive clandestine graves.

Prediction and preliminary standardization of fire debris constituents with the advanced distillation curve method.

The recent National Academy of Sciences report on forensic sciences states that the study of fire patterns and debris in arson fires is in need of additional work and eventual standardization. We discuss a recently introduced method that can provide predicted evaporation patterns for ignitable liquids as a function of temperature. The method is a complex fluid analysis protocol, the advanced distillation curve approach, featuring a composition explicit data channel for each distillate fraction (for qualitative, quantitative, and trace analysis), low uncertainty temperature measurements that are thermodynamic state points that can be modeled with an equation of state, consistency with a century of historical data, and an assessment of the energy content of each distillate fraction. We discuss the application of the method to kerosenes and gasolines and outline how expansion of the scope of fluids to other ignitable liquids can benefit the criminalist in the analysis of fire debris for arson.

The composition-explicit distillation curve technique: Relating chemical analysis and physical properties of complex fluids.

The analysis of complex fluids such as crude oils, fuels, vegetable oils and mixed waste streams poses significant challenges arising primarily from the multiplicity of components, the different properties of the components (polarity, polarizability, etc.) and matrix properties. We have recently introduced an analytical strategy that simplifies many of these analyses, and provides the added potential of linking compositional information with physical property information. This aspect can be used to facilitate equation of state development for the complex fluids. In addition to chemical characterization, the approach provides the ability to calculate thermodynamic properties for such complex heterogeneous streams. The technique is based on the advanced distillation curve (ADC) metrology, which separates a complex fluid by distillation into fractions that are sampled, and for which thermodynamically consistent temperatures are measured at atmospheric pressure. The collected sample fractions can be analyzed by any method that is appropriate. The analytical methods we have applied include gas chromatography (with flame ionization, mass spectrometric and sulfur chemiluminescence detection), thin layer chromatography, FTIR, corrosivity analysis, neutron activation analysis and cold neutron prompt gamma activation analysis. By far, the most widely used analytical technique we have used with the ADC is gas chromatography. This has enabled us to study finished fuels (gasoline, diesel fuels, aviation fuels, rocket propellants), crude oils (including a crude oil made from swine manure) and waste oils streams (used automotive and transformer oils). In this special issue of the Journal of Chromatography, specifically dedicated to extraction technologies, we describe the essential features of the advanced distillation curve metrology as an analytical strategy for complex fluids.

Mapping formation pathways and end group patterns of stimuli-responsive polymer systems via high-resolution electrospray ionization mass spectrometry.

"Smart" polymers and polymer-protein conjugates find a vast array of biomedical applications. Ambient temperature reversible addition fragmentation chain transfer (RAFT) polymerizations conducted in an aqueous environment are a favorable method of choice for the synthesis of these materials; however, information regarding the initiation mechanisms behind these polymerizations-and thus the critical polymer end groups-is lacking. In the current study, high-resolution soft ionization mass spectrometry techniques were used to map the product species generated during ambient temperature gamma-radiation induced RAFT polymerizations of N-isopropylacrylamide (NIPAAm) and acrylic acid (AA) in aqueous media, allowing the generated end groups to be unambiguously established. It was found that trithiocarbonate and *R radicals produced from the radiolysis of the RAFT agent, *OH and *OOH radicals produced from the radiolysis of water, and *H radicals produced from the radiolysis of water, RAFT agent, or monomer were capable of initiating polymerizations and thus contribute toward the generated chain ends. Additionally, thiol terminated chains were formed via degradation of trithiocarbonate end groups. The current study is the first to provide comprehensive mapping of the formation pathways and end group patterns of stimuli-responsive polymers, thus allowing the design and implementation of these materials to proceed in a more tailored fashion.

Kinetic chain lengths in highly cross-linked networks formed by the photoinitiated polymerization of divinyl monomers: a gel permeation chromatography investigation.

Highly cross-linked networks formed by the photoinitiated polymerization of multifunctional monomers are finding application in the field of biomaterials because of their chemical versatility, reaction control, and ability to polymerize under physiological conditions. Typically, degradation is introduced into these networks via the cross-links and leads to the release of nondegradable but water-soluble kinetic chains formed during the chain polymerization process. In this study, gel permeation chromatography (GPC) was used to characterize kinetic chain length distributions in highly cross-linked systems that are being developed for orthopedic applications. By polymerizing divinyl monomers to various conversions and subsequently degrading them, we investigated the aspects of network structural evolution related to kinetic chain formation. In general, the average kinetic chain length increased with conversion until the onset of autodeceleration, when the kinetic chains decreased in length as the propagation reaction became diffusion-controlled. The distribution of kinetic chains also changed when different initiation conditions (i.e., initiator concentration and incident light intensity) were used, and a decrease in the kinetic chain lengths was observed at higher initiation rates. Finally, kinetic chain lengths were examined as a function of depth in thick samples polymerized with different light intensities and with a photobleaching initiator. Light attenuation through the sample led to different initiation rates as a function of depth and, consequently, spatial heterogeneity in the network structure as measured by the distributions of kinetic chains.