William H. McClennen

Field‐portable, automated pyrolysis‐GC/IMS system for rapid biomarker detection in aerosols: A feasibility study

A prototype automated pyrolysis-gas chromatography/ion mobility spectrometry (Py-GC/IMS) instrument was developed for (bio)aerosol characterization. The system combines a commercially available, hand-held GC/IMS device with a specially built platinum wire grid heater, a 1-in.-diam. quartz microfiber filter and a 60-l/min air pump. The prototype Py-GC/IMS system can be operated in stand-alone mode or in series with a particle concentrator. Fully automated collection/desorption/pyrolysis of aerosols and other particulate matter can be performed at repetition rates of up to 60 h−1 by means of a special remote control and display software package. The feasibility of detecting submicrogram quantities of Bacillus endospores with the use of picolinic acid and pyridine as biochemical marker compounds for the characteristic dipicolinic acid moiety in spore cell walls was demonstrated by laboratory experiments as well as preliminary field tests. Other particulate matter that could be collected and analyzed includes allergens such as pollen or home dust, as well as a broad range of bioaerosols and reaerosolized organics like explosives or drugs. In addition to its potential use as a screening device for the presence of specific classes of aerosol components, the Py-GC/IMS system has been demonstrated to retain its capability to detect and identify a broad range of volatile and semivolatile organic compounds.

Mechanistic aspects of the pyrolytic methylation and transesterification of bacterial cell wall lipids

Abstract Coating a pyrolysis filament with whole bacterial cells, cell walls or lipid extracts followed by the addition of a suitable derivatizing agent (e.g. tetramethylammonium hydroxide or sodium metasilicate with alcohol) and subsequent pyrolysis, enables on-line derivatization and thermal extraction of volatile esters of the various fatty acid moieties present. It is shown that at least two competing reaction pathways appear to be involved, namely transesterification vs. hydrolysis (saponification) followed by methylation. In combination with a short capillary column gas-chromatographic separation and mass-spectrometric detection, the pyrolytic derivatization technique provides a rapid way for generating a chemotaxonomically characteristic profile of fatty acid methyl esters from a single bacterial colony.

Characterization of phenols and indanols in coal-derived liquids: Use of Curie-point vaporization gas chromato-graphy/mass spectrometry

A combination of liquid chromatography, gas chromatography and mass spectrometry techniques was used to characterize (alkyl)hydroxyaromatic compounds in several coal liquefaction process fractions, including Exxon Donor Solvent (EDS) atmospheric bottoms and hydrotreated atmospheric bottoms. Solvent extraction failed to provide representative subfractions independent of overall sample composition. Satisfactory subfractionation was achieved by liquid chromatography with increasingly polar solvents on a silica gel column. Subfractions as well as parent samples were analysed by g.c.-m.s. using a Curie-point flash vaporization technique for splitless injection onto glass SCOT columns. C0-C6 alkylphenols and C0-C3 alkylindanols were almost completely recovered in the benzene/ether subfractions and were found to be the dominant hydroxyaromatic series in both liquids. Whereas phenol distributions were virtually identical in both samples, indanol distributions differed markedly, indicating strong differences in reactivity towards hydrotreatment. The possible role and origin of indanols, the only major class of hydroxyhydroaromatic compounds in these coal-derived liquids, is discussed.

Field-portable hyphenated instrumentation: The birth of the tricorder?

Abstract Since hyphenated methods have all but replaced one-dimensional methods in the laboratory and demands for definitive field methods are increasing, hyphenated methods may well represent the next generation of field-portable analytical instruments. Gas chromatography—mass spectrometry (GC-MS) and GC-ion mobility spectrometry (GC-IMS) are discussed in terms of their current capability and potential for further development as powerful field-portable instruments.

Roving GC/MS: Mapping VOC gradients and trends in space and time

Obtaining representative VOC (volatile organic compound) measurements in ambient environments which exhibit complex concentration gradients and/or trends is difficult when relying upon limited numbers of analyses obtained by simple pooling or averaging techniques. A more effective approach is to perform large numbers of analyses over a period of time to permit detailed mapping or profiling of local gradients and trends. Until recently, use of GC/MS (gas chromatography/mass spectrometry) techniques for rapid profiling or mapping operations was not feasible because of sample speed limitations. This article describes a roving GC/MS system based on the combination of a Hewlett-Packard model 5972 MSD (mass selective detector), a FemtoScan Enviroprobe repetitive vapor sampling inlet with short capillary GC column, an Alcatel Micro HV olliess vacuum pump stack, and a Pentium notebook PC running under Windows 95. The roving system is further equipped with differential GPS (global positioning system) and radio transceiver capabilities thereby permitting remote tracking of vehicle location and local VOC concentrations. Laboratory tests demonstrate lower detection limits of approx 4 ppb for BTX (benzene, toluene, and xylene), corresponding to minimum detectable quantities of approximately 25 femtograms, and maximum analysis speeds of up to 5 GC peaks per second on a mixture of volatile ketones. Demonstrated outdoor performance, using a zero-emission electric vehicle, includes measurement of low ppb BTX levels along a 6 km urban route at 15 s (∼150 m) intervals while moving at an estimated average speed of 35 km h−1. Indoor measurements of toluene concentrations in the low to mid ppm range at 6 s (∼5 cm) intervals along a 6 m long path reveal a high degree of spatial and temporal variability in VOC concentrations. Mobility, specificity, sensitivity, and speed of the roving GC/MS method make this a promising candidate method for rapid outdoor and indoor screening, monitoring, and mapping of VOCs.

Fast, Repetitive GC/MS Analysis of Thermally Desorbed Polycyclic Aromatic Hydrocarbons (PAHs) from Contaminated Soils

Abstract A syslem for on-line analysis of organic vapors by short column gas chromatography/mass spectrometry (GC/MS) has been used to monitor products from a thermal soil desorption reactor. The system consists of a unique air sampling inlet with a 1 meter long capillary column coupled directly to a modified Ion Trap Mass Spectrometer (Finnigan MAT) with demonstrated detection limits for alkylbcn-zencs in the low ppb range. In this work the mobile instrument is used for repetitive GC/MS and GC/MSn (tandem MS) analysis at 30 to 60s intervals of PAH products from coal tar contaminated soils in a bed characterization reactor. Results for naphthalene through dibenzanthracenes arc compared to conventional. more detailed GC/MS analyses of extracts from soil before and after thermal treatment.

Rate limiting processes in the rotary-kiln incineration of contaminated solids

Abstract A study of transport processes during the desorption of organic and metallic contaminants from solids is being conducted using several fundamental experiments. This paper presents results from three experimental systems, a Particle-Characterization Reactor, Bed-Characterization Reactor, and Metals Reactor. The organic experiments attempt to identify the controlling transport process within a particle of soil and through a bed of particles, as well as quantify the necessary parameters to model these processes. Gas and solid-phase speciation data for field samples, soils contaminated with a variety of organics (boiling points from 220°C to 495°C), are discussed. The data suggest that local temperature and gas/solid contacting are important in the desorption process. As expected, lighter components desorb faster than the heavier hydrocarbons. Moisture content was also important in the desorption of contaminant. The metals reactor has been used to determine the fate of metals, specifically the partit...

Design considerations in field-portable GC-based hyphenated instrumentation

The use of hyphenated GC-based methods in the development of portable chemical-monitoring instruments can offer considerable advantages to the instrument maker. Foremost among these advantages are specificity, speed, and lower costs. In this article, the authors describe the basis for achieving these advantages using examples of three prototype and breadboard instruments developed in their laboratories and give an extended theoretical discussion of the basis for what has been called “transfer-line GC” or TLGC. This TLGC approach to fixed pressure drop chromatography can be used to illustrate overall theoretical limitations of various approaches to high-speed GC for real-time monitoring applications. The three example instruments are a “roving” automated vapor sampling (AVS) TLGC/MS instrument, a breadboard AVS-TLGC/IMS (ion mobility spectrometry) instrument, and a breadboard AVS-TLGC/GC instrument. Discussion will include the application of TLGC theory to instrument design and will use example analyses that focus on the eventual application of this technology to the near real-time detection of highly toxic chemical vapors.

Hydrocarbon and formaldehyde emissions from the combustion of pulverized wood waste

Abstract Hydrocarbon and formaldehyde emissions from the combustion of pulverized wood waste were measured in a 100 kW, cylindrical combustion chamber measuring 0.61 by 0.61 m. The wood was pneumatically conveyed to the burner and natural gas was used as an auxiliary fuel. The wood was screened prior to feeding so that its size distribution was representative of the suspension phase of a stoker boiler. Chamber wall and gas temperatures ranged from 920 to 1200 K and oxygen concentrations ranged from 2 to 9 percent, dry. Two types of waste were studied, plain wood and wood that was impregnated with a phenol-formaldehyde resin. The latter was a by-product of particle board production. In general, the emissions of products of incomplete combustion (PICs) from the resinated waste were higher than those produced by plain wood. This may have been due to three factors: (1) the resinated wood was slightly wetter than the plain wood (6-9% by weight vs. 3%), (2) there was a difference in particle size distribution b...