Herbert Tobias

Metal oxide-filled reactors constructed with ceramic tubes or fused silica capillary are widely used for combustion in gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). However, they tend to be easily cracked or broken and prone to leaks at operating temperatures of ∼950 °C. Here we introduce a modified commercially available catalytic combustion/reduction methanizer to quantitatively convert organics to CO2 for δ13C analysis while retaining chromatographic resolution… Show more

Metal oxide-filled reactors constructed with ceramic tubes or fused silica capillary are widely used for combustion in gas chromatography combustion isotope ratio mass spectrometry (GCC-IRMS). However, they tend to be easily cracked or broken and prone to leaks at operating temperatures of ∼950 °C. Here we introduce a modified commercially available catalytic combustion/reduction methanizer to quantitatively convert organics to CO2 for δ13C analysis while retaining chromatographic resolution. These modified “ARC” reactors operate with a transition-metal catalyst that requires a flowing O2 gas to enable complete conversion to CO2 at lower temperature (620 °C) with acceptable reactor life, reduced complexity, and improved robustness. Performance of two versions of the ARC reactors with different combustion volumes was characterized by analysis of steroid and alkane isotopic standard materials. Show less

High‐precision carbon isotope ratio analysis of urinary steroids by gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS) is the official test to detect illicit doping of synthetic versions of endogenous steroids, such as testosterone. Our group created the first steroid isotopic standards (SIS) specifically for World Anti‐Doping Agency (WADA) accredited laboratories. The standards contain mixtures of steroids as acetates or free steroids at ~400 μg each per ampoule and have… Show more

High‐precision carbon isotope ratio analysis of urinary steroids by gas chromatography–combustion–isotope ratio mass spectrometry (GC–C–IRMS) is the official test to detect illicit doping of synthetic versions of endogenous steroids, such as testosterone. Our group created the first steroid isotopic standards (SIS) specifically for World Anti‐Doping Agency (WADA) accredited laboratories. The standards contain mixtures of steroids as acetates or free steroids at ~400 μg each per ampoule and have been widely distributed to anti‐doping laboratories to facilitate comparability of inter‐laboratory results. Here we report on the creation and characterization of 3 new high‐volume single component SIS suitable for use as working standards. They contain ~50 times more steroid mass per ampoule than previous SIS. Show less

The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology 1 to climate science 2, yet these properties are surprisingly difficult to measure in the particles’ native environment. Electron microscopy requires collection of particles on a substrate 3; visible light scattering provides insufficient resolution 4; and X-ray synchrotron studies have been limited to ensembles of particles 5. Here we demonstrate an in situ method for imaging… Show more

The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology 1 to climate science 2, yet these properties are surprisingly difficult to measure in the particles’ native environment. Electron microscopy requires collection of particles on a substrate 3; visible light scattering provides insufficient resolution 4; and X-ray synchrotron studies have been limited to ensembles of particles 5. Here we demonstrate an in situ method for imaging individual sub-micrometre particles to nanometre resolution in their native environment, using intense, coherent X-ray pulses from the Linac Coherent Light Source 6 free-electron laser. We introduced individual aerosol particles into the pulsed X-ray beam, which is sufficiently intense that diffraction from individual particles can be measured for morphological analysis. Show less

We report the first demonstration of comprehensive two-dimensional gas chromatography combustion–isotope ratio mass spectrometry (GC×GCC–IRMS) for the analysis of urinary steroids to detect illicit synthetic testosterone use, of interest in sport doping. GC coupled to IRMS (GCC–IRMS) is currently used to measure the carbon isotope ratios (CIRs, δ13C) of urinary steroids in antidoping efforts; however, extensive cleanup of urine extracts is required prior to analysis to enable baseline… Show more

We report the first demonstration of comprehensive two-dimensional gas chromatography combustion–isotope ratio mass spectrometry (GC×GCC–IRMS) for the analysis of urinary steroids to detect illicit synthetic testosterone use, of interest in sport doping. GC coupled to IRMS (GCC–IRMS) is currently used to measure the carbon isotope ratios (CIRs, δ13C) of urinary steroids in antidoping efforts; however, extensive cleanup of urine extracts is required prior to analysis to enable baseline separation of target steroids. With its greater separation capabilities, GC×GC has the potential to reduce sample preparation requirements and enable CIR analysis of minimally processed urine extracts. Challenges addressed include online reactors with minimized dimensions to retain narrow peak shapes, baseline separation of peaks in some cases, and reconstruction of isotopic information from sliced steroid chromatographic peaks. Show less

The rapid chemical analysis of individual cells is an analytical capability that will profoundly impact many fields including bioaerosol detection for biodefense and cellular diagnostics for clinical medicine. This article describes a mass spectrometry-based analytical technique for the real-time and reagentless characterization of individual airborne cells without sample preparation. We characterize the mass spectral signature of individual Bacillus spores and demonstrate the ability to… Show more

The rapid chemical analysis of individual cells is an analytical capability that will profoundly impact many fields including bioaerosol detection for biodefense and cellular diagnostics for clinical medicine. This article describes a mass spectrometry-based analytical technique for the real-time and reagentless characterization of individual airborne cells without sample preparation. We characterize the mass spectral signature of individual Bacillus spores and demonstrate the ability to distinguish two Bacillus spore species, B. thuringiensis and B. atrophaeus, from one another very accurately and from the other biological and nonbiological background materials tested with no false positives at a sensitivity of 92%. This example demonstrates that the chemical differences between these two Bacillus spore species are consistently and easily detected within single cells in seconds. Show less

Diesel engines are known to emit high number concentrations of nanoparticles (diameter < 50 nm), but the physical and chemical mechanisms by which they form are not understood. Information on chemical composition is lacking because the small size, low mass concentration, and potential for contamination of samples obtained by standard techniques make nanoparticles difficult to analyze. A nano-differential mobility analyzer was used to size-select nanoparticles (mass median diameter ∼25−60 nm)… Show more

Diesel engines are known to emit high number concentrations of nanoparticles (diameter < 50 nm), but the physical and chemical mechanisms by which they form are not understood. Information on chemical composition is lacking because the small size, low mass concentration, and potential for contamination of samples obtained by standard techniques make nanoparticles difficult to analyze. A nano-differential mobility analyzer was used to size-select nanoparticles (mass median diameter ∼25−60 nm) from diesel engine exhaust for subsequent chemical analysis by thermal desorption particle beam mass spectrometry. Mass spectra were used to identify and quantify nanoparticle components, and compound molecular weights and vapor pressures were estimated from calibrated desorption temperatures. Show less

The chemical composition of secondary organic aerosol formed in an environmental chamber from ozonolysis of 1-tetradecene in humid and dry air was determined using a thermal desorption particle beam mass spectrometer (TDPBMS). The major products are α-hydroxytridecyl hydroperoxide and bis(α-hydroxytridecyl) peroxide in humid air and symmetric C26 and asymmetric C14 secondary ozonides in dry air. The hydroperoxide is formed by reaction of stabilized Criegee biradicals with water vapor, and the… Show more

The chemical composition of secondary organic aerosol formed in an environmental chamber from ozonolysis of 1-tetradecene in humid and dry air was determined using a thermal desorption particle beam mass spectrometer (TDPBMS). The major products are α-hydroxytridecyl hydroperoxide and bis(α-hydroxytridecyl) peroxide in humid air and symmetric C26 and asymmetric C14 secondary ozonides in dry air. The hydroperoxide is formed by reaction of stabilized Criegee biradicals with water vapor, and the peroxide (a peroxyhemiacetal) is formed by subsequent reaction of the hydroperoxide with tridecanal. The secondary ozonides are formed by reactions of stabilized Criegee biradicals with tridecanal and formaldehyde. Tridecanoic acid was also observed in both experiments. Show less

Topics:
Mass Spectrometry
Anti-doping / Doping Control
Isotope Ratio Mass Spectrometry
Atmospheric Chemistry
Aerosol Chemistry