Eric E. Gard

Gas-phase hydrogen/deuterium exchange as a molecular probe for the interaction of methanol and protonated peptides.

The gas-phase hydrogen/deuterium (HID) exchange kinetics of several protonated amino acids and dipeptides under a background pressure of CH3OD were determined in an external source Fourier transform mass spectrometer. H/D exchange reactions occur even when the gas-phase basicity of the compound is significantly larger (> 20 kcal/mol) than methanol. In addition; greater deuterium incorporation is observed for compounds that have multiple sites of similar basicities. A mechanism is proposed that involves a structurally specific intermediate with extensive interaction between the protonated compound and methanol.

Bioaerosol Mass Spectrometry for Rapid Detection of Individual Airborne Mycobacterium tuberculosis H37Ra Particles

ABSTRACT Single-particle laser desorption/ionization time-of-flight mass spectrometry, in the form of bioaerosol mass spectrometry (BAMS), was evaluated as a rapid detector for individual airborne, micron-sized, Mycobacterium tuberculosis H37Ra particles, comprised of a single cell or a small number of clumped cells. The BAMS mass spectral signatures for aerosolized M. tuberculosis H37Ra particles were found to be distinct from M. smegmatis, Bacillus atrophaeus, and B. cereus particles, using a distinct biomarker. This is the first time a potentially unique biomarker was measured in M. tuberculosis H37Ra on a single-cell level. In addition, M. tuberculosis H37Ra and M. smegmatis were aerosolized into a bioaerosol chamber and were sampled and analyzed using BAMS, an aerodynamic particle sizer, a viable Anderson six-stage sampler, and filter cassette samplers that permitted direct counts of cells. In a background-free environment, BAMS was able to sample and detect M. tuberculosis H37Ra at airborne concentrations of >1 M. tuberculosis H37Ra-containing particles/liter of air in 20 min as determined by direct counts of filter cassette-sampled particles, and concentrations of >40 M. tuberculosis H37Ra CFU/liter of air in 1 min as determined by using viable Andersen six-stage samplers. This is a first step toward the development of a rapid, stand-alone airborne M. tuberculosis particle detector for the direct detection of M. tuberculosis bioaerosols generated by an infectious patient. Additional instrumental development is currently under way to make BAMS useful in realistic environmental and respiratory particle backgrounds expected in tuberculosis diagnostic scenarios.

A 3T external source quadrupole Fourier transform mass spectrometer for ion/molecule reactions and analysis

Abstract A versatile quadrupole Fourier transform mass spectrometry instrument for both ion/molecule chemistry and analysis is described. Preliminary results show that despite the relatively low field (3T), a large mass range (up to m/z 16 000) and high resolution (41 000 FWHH at m/z 1692) are obtained. Metal ions (e.g. Fe + ) for ion/molecule chemistry and organic ions (e.g. maltose) for analysis are routinely produced via secondary ion mass spectrometry (and liquid secondary ion mass spectrometry) in the external source.

Autonomous, broad-spectrum detection of hazardous aerosols in seconds.

Actual or surrogate chemical, biological, radiological, nuclear, and explosive materials and illicit drug precursors can be rapidly detected and identified when in aerosol form by a Single-Particle Aerosol Mass Spectrometry (SPAMS) system. This entails not only the sampling of such particles but also the physical analysis and subsequent data analysis leading to a highly reliable alarm state. SPAMS hardware is briefly reviewed. SPAMS software algorithms are discussed in greater detail. A laboratory experiment involving actual threat and surrogate releases mixed with ambient background aerosols demonstrates broad-spectrum detection within seconds. Data from a field test at the San Francisco International Airport demonstrate extended field operation with an ultralow false alarm rate. Together these data sets demonstrate a significant and important advance in rapid aerosol threat detection.

A dual vacuum chamber Fourier transform mass spectrometer with rapidly interchangeable FAB, MALDI and ESI sources: electrospray results

Abstract A versatile, inexpensive electrospray interface has been constructed and installed on an external source Fourier transform mass spectrometer with a quadrupole ion guide. This interface is readily interchangeable with FAB and MALDI sources, with the main time requirement for changing being the pump-down time. A heated capillary, two skimmers and a set of Einzel lenses are used to deliver ions to the quadrupole ion guide. SIMION (Idaho National Engineering Laboratory, Idaho Falls, Idaho) was used to model ion trajectories and determine optimal dimensions. Five stages of pumping are employed, using mechanical, turbomolecular and cryopumps. A solenoid-driven shutter on the final lens blocks neutrals after injection of the ion packet. Kinetic energy distributions of both small and large biomolecular ions were investigated. For large (104–105 Da), highly charged species, the kinetic energy distributions were quite favorable to trapping, with sharp peaks at less than 10 eV. Thus a 50 ms ion accumulation time is sufficient to obtain spectra of lysozyme with high S/N ratio. Distributions for smaller ions tended to be somewhat wider and peaked at higher energies. The spectra obtained to date illustrate the ability of the instrument to handle biomolecules ranging from bradykinin to bovine serum albumen.

Detection of biological particles in ambient air using Bio-Aerosol Mass Spectrometry

The Bio-Aerosol Mass Spectrometry (BAMS) system is an instrument used for the real time detection and identification of biological aerosols. Particles are drawn from the atmosphere directly into vacuum and tracked as they scatter light from several continuous wave lasers. After tracking, the fluorescence of individual particles is excited by a pulsed 266nm or 355nm laser. Molecules from those particles with appropriate fluorescence properties are subsequently desorbed and ionized using a pulsed 266nm laser. Resulting ions are analyzed in a dual polarity mass spectrometer. During two field deployments at the San Francisco International Airport, millions of ambient particles were analyzed and a small but significant fraction were found to have fluorescent properties similar to Bacillus spores and vegetative cells. Further separation of non-biological background particles from potential biological particles was accomplished using laser desorption/ionization mass spectrometry. This has been shown to enable some level of species differentiation in specific cases, but the creation and observation of higher mass ions is needed to enable a higher level of specificity across more species. A soft ionization technique, matrix-assisted laser desorption/ionization (MALDI) is being investigated for this purpose. MALDI is particularly well suited for mass analysis of biomolecules since it allows for the generation of molecular ions from large mass compounds that would fragment under normal irradiation. Some of the initial results from a modified BAMS system utilizing this technique are described.

Non-DNA Methods for Biological Signatures

Publisher Summary This chapter focuses on the methods that can determine chemical or structural features of biological agent particles that are signatures of particular methods of growth and post-growth processing (often referred to as “weaponization”). The detection of these signatures in a sample of a bio-weapon (BW) agent can aid the attribution by indicating: (1) the level of sophistication of the producer, (2) the access to particular types of agent weaponization information, (3) the likelihood that the material could be or has been produced at a significant scale, (4) and by providing essential sample matching data for ascertaining a putative relationship with other samples obtained in other venues. An example of the use of biologicals in forensic science is DNA, amplied by the Polymerase Chain Reaction (PCR) technique, legally admissible in courtas evidence. DNA evidence is successfully used in the court to convict or clear people of crimes because each persons DNA is unique. High-resolution techniques are being applied to investigations; such as Environmental scanning electron microscopy (ESEM) is used for taking high-resolution images under hydrated conditions; this avoids any artifacts associated with the critical point drying process that is required under normal Scanning Electron Microscopy (SEM) operations. ESEM is also equipped with Energy Dispersive X-ray (EDX) microanalysis and Backscatter capabilities. SEM is a standard “workhorse” technique for characterizing particulate samples, found in many laboratories worldwide. It provides excellent imaging of the surfaces of agent particles and other material in a sample, and is used for identifying likely agent particles for analysis by other instruments. When combined with EDX, the elemental composition of the material in the imaged region can be determined. These techniques continue to signature libraries of correlations between analyses and growth and processing conditions of growth, it will be necessary to develop an information system which combines types of data to determine unique signatures.

Characterization of ambient aerosols at the San Francisco International Airport using bioaerosol mass spectrometry

The BioAerosol Mass Spectrometry (BAMS) system is a rapidly fieldable, fully autonomous instrument that can perform correlated measurements of multiple orthogonal properties of individual aerosol particles. The BAMS front end uses optical techniques to nondestructively measure a particles aerodynamic diameter and fluorescence properties. Fluorescence can be excited at 266nm or 355nm and is detected in two broad wavelength bands. Individual particles with appropriate size and fluorescence properties can then be analyzed more thoroughly in a dual-polarity time-of-flight mass spectrometer. Over the course of two deployments to the San Francisco International Airport, more than 6.5 million individual aerosol particles were fully analyzed by the system. Analysis of the resulting data has provided a number of important insights relevant to rapid bioaerosol detection, which are described here.

DSP-Based Dual-Polarity Mass Spectrum Pattern Recognition for Bio-Detection

The bio-aerosol mass spectrometry (BAMS) instrument analyzes single aerosol particles using a dual-polarity time-of-flight mass spectrometer recording simultaneously spectra of thirty to a hundred thousand points on each polarity. We describe here a real-time pattern recognition algorithm developed at Lawrence Livermore National Laboratory that has been implemented on a nine digital signal processor (DSP) system from Signatec Incorporated. The algorithm first pre-processes independently the raw time-of-flight data through an adaptive baseline removal routine. The next step consists of a polarity dependent calibration to a mass-to-charge representation, reducing the data to about five hundred to a thousand channels per polarity. The last step is the identification step using a pattern recognition algorithm based on a library of known particle signatures including threat agents and background particles. The identification step includes integrating the two polarities for a final identification determination using a score-based rule tree. This algorithm, operating on multiple channels per-polarity and multiple polarities, is well suited for parallel real-time processing. It has been implemented on the PMP8A from Signatec Incorporated, which is a computer based board that can interface directly to the two one-Giga-sample digitizers (PDA1000 from Signatec Incorporated) used to record the two polarities of time-of-flight data. By using optimized data separation, pipelining, and parallel processing across the nine DSPs it is possible to achieve a processing speed of up to a thousand particles per seconds, while maintaining the recognition rate observed on a non-real time implementation. This embedded system has allowed the BAMS technology to improve its throughput and therefore its sensitivity while maintaining a large dynamic range (number of channels and two polarities) thus maintaining the systems specificity for bio-detection

Determination of the particle counting efficiency and chemical sensitivities of an aerosol time of flight mass spectrometer under ambient sampling conditions

Abstract Recently developed aerosol time-of-flight mass spectrometer (ATOFMS) instruments are capable of determining the size and chemical composition of single particles (Noble and Prather, 1996, Gard et al., 1997). These instruments provide convenient determination of atmospheric aerosol composition on a single particle basis in real time. To date, data from these instruments have been used qualitatively to study both the sources of ambient aerosols (Liu et al., 1997) and the atmospheric transformation of particles (Gard et al., 1998). However, quantitative reconstruction of a continuous time series of the actual size distribution and chemical composition of atmospheric aerosols requires that the absolute counting efficiency and chemical sensitivities of these instruments be known.