Laser Ablation-Aerosol Mass Spectrometry-Chemical Ionization Mass Spectrometry for Ambient Surface Imaging.

Mass spectrometry imaging is becoming an increasingly common analytical technique due to its ability to provide spatially resolved chemical information. Here, we report a novel imaging approach combining laser ablation with two mass spectrometric techniques, aerosol mass spectrometry and chemical ionization mass spectrometry, separately and in parallel. Both mass spectrometric methods provide the fast response, rapid data acquisition, low detection limits, and high-resolution peak separation desirable for imaging complex samples. Additionally, the two techniques provide complementary information with aerosol mass spectrometry providing near universal detection of all aerosol molecules and chemical ionization mass spectrometry with a heated inlet providing molecular-level detail of both gases and aerosols. The two techniques operate with atmospheric pressure interfaces and require no matrix addition for ionization, allowing for samples to be investigated in their native state under ambient pressure conditions. We demonstrate the ability of laser ablation-aerosol mass spectrometry-chemical ionization mass spectrometry (LA-AMS-CIMS) to create 2D images of both standard compounds and complex mixtures. The results suggest that LA-AMS-CIMS, particularly when combined with advanced data analysis methods, could have broad applications in mass spectrometry imaging applications.

Dynamic vapor microextraction of ignitable liquid from casework containers.

Dynamic vapor microextraction (DVME) is a headspace concentration method that can be used to collect ignitable liquid (IL) from fire debris onto chilled adsorbent capillaries. Unlike passive headspace concentration onto activated carbon strips (ACSs) that must be eluted with a toxic solvent (carbon disulfide), DVME employs a relatively benign solvent (acetone) to recover the adsorbed IL residue, and each headspace collection is monitored for breakthrough. Here, for the first time, we extend DVME to casework containers while exploring a realistic range of oven temperatures and collection volumes. We investigated metal cans sealed with friction lids (container 1), metal cans sealed within polymer bags (container 2), and glass jars sealed with two-piece lids (container 3). Without additional containment, container 1 was found to leak so excessively that flow through the capillary was unreliable. Therefore, for containers 2 and 3 only, we determined the total number of target compounds collected from 50% weathered gasoline for oven temperatures from 54 °C to 96 °C and collection volumes from 47 standard cubic centimeters (scc) to 90 scc. Only high-volatility species with retention times (tR)< n-decane on a non-polar column were recovered from polymer bags, whereas headspace concentration from glass jars led to the recovery of target compounds across the entire volatility range. DVME at 90 °C from 2-mL containers showed that the presence of polymer bag material leads to IL vapor losses, particularly for low-volatility species with tR> n-decane. DVME was strongly influenced by the casework container, whereas oven temperature and collection volume had a minor influence for the IL samples explored here.

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.

The Impact of Molecular Oxygen on Anion Composition in a Hazy Archean Earth Atmosphere.

Atmospheric organic hazes are common in planetary bodies in our solar system and likely exoplanet atmospheres as well. In addition, geochemical data support the existence of an organic haze in the early Earth's atmosphere. Much of what is known about organic haze formation derives from studies of Saturn's moon Titan. It is believed that on Titan ions play an important role in haze formation. It is possible, by using Titan as an analog for the Archean Earth, to consider that an Archean haze could have formed by similar processes. Here, we examine the anion chemistry that occurs during laboratory simulations of early Earth haze formation and measure the composition of gaseous anions as a function of O2 mixing ratio. Gaseous anion composition and relative abundances are measured by an atmospheric pressure interface time-of-flight mass spectrometer and are compared to previous photochemical haze mass loading measurements. Numerous anions are observed spanning from mass-to-charge ratio 26 to 246, with a majority of the identified anions containing carbon, hydrogen, nitrogen, and/or oxygen. A shift in the anion composition occurs with increasing the precursor O2 mixing ratio. With 0-20 ppmv O2 in CH4/CO2/N2 mixtures, ions contain mostly organic nitrogen, with CNO- being the most intense ion peak. As the precursor O2 is increased to 200 and 2000 ppmv, inorganic nitrogen ions become the dominant chemical group, with NO3- having the most intense ion signal. The clear shift in the ionic composition could be indicative of a modification to the gas-phase chemistry that occurs in the transition from an anoxic atmosphere to an oxygen-containing atmosphere, with potential astrobiological significance.

The effect of tinnitus retraining therapy on chronic tinnitus: A controlled trial.

OBJECTIVES: The goal of this study was to compare treatment outcomes for chronic bothersome tinnitus after Tinnitus Retraining Therapy (TRT) versus standard of care treatment (SC) and to determine the longevity of the effect over an 18-month period. STUDY DESIGN: A randomized controlled trial comparing TRT to SC for chronic tinnitus. METHODS: Adults with subjective, stable, bothersome chronic tinnitus associated with hearing loss amenable to aural rehabilitation with hearing aids were recruited. The Tinnitus Handicap Inventory (THI) was the primary outcome measure and the Tinnitus Functional Index (TFI) the secondary outcome measure of tinnitus severity and impact. Data were collected at screening, entry (0 months), and 6, 12, and 18 months after the beginning of treatment, using an integrated digitized suite of evaluation modules. TRT consisted of directive counseling and acoustic enrichment using combination hearing aids and sound generators; SC consisted of general aural rehabilitation counseling and hearing aids. RESULTS: Significant improvement in tinnitus impact occurred after both TRT and SC therapy, with a larger treatment effect obtained in the TRT group. Lasting therapeutic benefit was evident at 18 months in both groups. THI initial scores were unstable in 10% of enrolled participants, showing moderate bidirectional fluctuation between screening and baseline (0 month) assessment. CONCLUSION: Adults with moderate to severe tinnitus and hearing loss amenable to amplification, benefit from either TRT or SC treatment when combined with hearing aid use. TRT benefit may exceed that of SC. The global improvement in tinnitus severity that accrued over an 18-month period appeared to be robust and clinically significant. LEVEL OF EVIDENCE: I.