Field Analytical Chemistry & Technology最新文献

Traditional mass-spectrometry (MS) instruments have been confined to laboratory usage because of their large size, power and high-vacuum requirements, which make them unsuitable for use in most field environments. Developments in mass spectrometers and small vacuum pump systems have now made possible the development of transportable mass-spectrometer instruments. A portable MS device based on a miniature double-focusing (ExB) sector-field mass spectrometer has been developed for in situ gas analysis and monitoring applications. The device (acronym Portable-CDFMS) uses a 1.1-Tesla NdFeB permanent magnet, a lithographically defined electric sector, a molecular-flow frit inlet, a spiral filament in a closed ion source, and a miniature channeltron detector. The high vacuum is provided with the use of a very compact hybrid turbomolecular and diaphragm pump combination. This MS system weighs 18 lb., is able to detect atmospheric species at the part-per-million (ppm) level, and has a mass range up to 200 amu, which makes this miniature mass spectrometer well suited for field applications. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 156–167, 2001

An automated field analysis strategy for aqueous environments is proposed with the use of a mobile robot equipped with an underwater mass spectrometer aided by linked remote numerical models or natural intelligence. Intelligent search strategies were made possible through the use of numerical models, and natural intelligence was in the form of a man in the loop. The field-analysis strategy is useful for local- and wide-area in situ chemical surveying for environmental and economical tasks. The operation of chemoreceptive field underwater robots is demonstrated during two field trials, one using numerical models to aid in characterization of chemical dispersion, and the other discriminating a chemical gradient in the field. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 121–130, 2001

Ion-mobility spectrometry (IMS) in conjunction with radioactive ionization sources has been employed for field-portable applications for the past two decades. Recently, electrospray ionization (ESI) sources have been shown as a viable ionization source with IMS instruments, enabling the analysis of many nonvolatile compounds. Introduction of a liquid-sheath-flow ESI source enabled the direct analysis of water samples. The ESI source was built with relatively simple lightweight components, making it feasible for use in field applications. A comparison between traditional ESI solvent conditions (water plus organic solvent) and the liquid-sheath-flow concept shows the new source to be able to spray water samples directly without prior sample preparation. The novel electrospray ionization source was evaluated with two nonfiltered water samples, one from a snow sample and the other obtained from a local stream. In both cases, 1 ppm of Terbutryn (a widely used herbicide) was easily detected. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 91–96, 2001

A device for the continuous monitoring of the volatile and semivolatile organic compounds in air by membrane extraction followed by sorbent concentration and gas chromatographic separation is discussed. The device samples headspace and makes automatic injections followed by rapid separation and quantification. The main components of the system include membrane module, microtrap, and transfer line. A membrane module, microtrap, and fan are mounted in a housing, together constituting a MESI (membrane-extraction sorbent interface) sampling unit. A heated silicosteel capillary column was used as the transfer line, avoiding adsorption and condensation of analytes and performing separation of the analytes prior to detection. The device demonstrated potential for field monitoring of aromatic hydrocarbons, chlorinated compounds, and terpenoids. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 69–74, 2001

Continuous environmental air monitoring is possible with open-path FTIR spectroscopy. Efficient chemometric tools are needed for the identification of unknown compounds that are observable in remote sensing of volatile emissions into the atmosphere. A qualitative analysis using spectra recorded at a resolution of 0.2 cm⁻¹is proposed, based on the cross-correlation function and calculated with data from component-specific intervals from library absorbance spectra. The characteristic wave-number intervals were selected on the grounds of the most intense component absorption bands for which negligible overlap was present with atmospheric absorption lines. The algorithm has been implemented for 36 different gaseous substances into an expert system for the evaluation of atmospheric FTIR spectra, recorded for routine work in active open-path monitoring. Detection limits for substance identification from mixture spectra are discussed. The influence from overlapping spectral features of co-existing atmospheric compounds can be reduced by preprocessing, including such techniques as scaled absorbance subtraction with appropriate spectra of the known gases. A discussion of identification strategies previously presented in the literature is included. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 50–59, 2001

Environmental contaminants are found in a wide variety of molecular shapes and sizes, with organic pollutants exhibiting vapor pressures in the 10³–10⁻⁶ torr range. This translates into a need for chemical analyzers that are capable of analyzing both volatile compounds (i.e., those compounds that have high vapor pressures at ambient temperatures) as well as semivolatile substances (i.e., those compounds that must be heated before they exhibit substantial vapor pressures). Volatile environmental analytes are found in gaseous, liquid, or solid sample matrices, whereas semivolatile analytes exist as either liquids or solids, including aerosol dispersions. Unfortunately, conventional field-portable GC analyzers are only capable of analyzing for volatile analytes. A small, fast, dual-high-resolution-column GC instrument that is capable of analyzing both volatile and semivolatile analytes has been developed and patented. As typically configured, it uses two narrow-bore, 100-micron ID separation columns, is temperature programmable at rates of 5–20 °C per second, and uses less than 150 W of dc power. Typical separation times for compounds with Kovatt's retention indices of <1000 are 10–15 s, and compounds with retention indices of up to 2500 are separated in <1min. Because the instrument has dual columns and detectors, analytes are simultaneously analyzed on columns with different liquid phases, thus providing added confidence in the quality of the analytical data. Because this fieldable GC device uses a solid-sorbent trapping system with a conventional heated injector inlet system, it can analyze a wide variety of sample matrices, including gases, dilute gases, thermal extracts from VOS tubes, purge-and-trap water/soil extracts, headspace samples, membrane extracts, SPME, thermal and SCF extracts, liquid organic solvent extracts, and direct aqueous samples. This report describes this new instrument and presents typical data from analysis of volatile and semivolatile analytes in a variety of sample matrices. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 97–105, 2001

A new automated instrument for the near–real-time measurement of atmospheric formaldehyde is described. The chemistry involves the cyclization reaction of formaldehyde with 1,3-cyclohexanedione (CHD) in the presence of ammonium ions to form a fluorescent dihydropyridine derivative. A GaN-based light-emitting diode (LED) emitting in the near UV was used as the excitation source in a miniature flowthrough fluorescence detector based on a transversely illuminated liquid-core waveguide. The instrument is configured to operate in a periodic autozero mode where the exhaust from the sampling pump is chemically treated to provide zero gas for automated periodic checks of the baseline. The liquid-phase portion of the system provides a S/N = 3 limit of detection (LOD) of 10-nM aqueous formaldehyde. A thermostated Nafion®-membrane–based diffusion scrubber is used to collect atmospheric formaldehyde into pure water with an absorption efficiency of ∼70%, which results in an LOD of 30 pptv HCHO. (In cases where the H₂O₂ to HCHO ratio is very high, as in background polar atmospheres, the LOD will deteriorate markedly.) Design, performance details, and illustrative results from a 1999 field campaign (Atlanta Supersite Study) are presented. Interference from H₂O₂ is discussed in detail. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 2–12, 2001

Passive remote sensing by Fourier-transform infrared (FTIR) spectrometry allows detection and identification of toxic clouds in the atmosphere. However, the probability of detection is dependent upon the background of the field of view of the spectrometer because the signal is a function of the difference between the temperature of the cloud and the brightness temperature of the background. For small temperature differences the signal is proportional to this difference. Thus, it is possible to enhance the probability of detection by aiming the spectrometer in a direction that yields a high temperature difference between the cloud and the background. If this alignment is performed manually, the probability of detection is strongly influenced by the operator. By scanning all fields of view within the area in which a cloud is expected the probability of detection is maximized. Moreover, it is possible to visualize the cloud. An imaging passive remote-sensing system comprised of an FTIR spectrometer, an azimuth-elevation–scanning mirror, a data-acquisition and control system with a digital signal processor (DSP), and a personal computer has been developed. The DSP system controls the scanning mirror, collects the interferograms of the FTIR spectrometer, and performs the Fourier transformation. The spectra are transferred to the personal computer and analyzed by a real-time identification algorithm that does not require background spectra for the analysis. The results of the identification algorithm are visualized in false color images. The system has a high selectivity and low noise-equivalent spectral radiance, and it allows localization of clouds and their sources. The automatic identification algorithm, the scanner system, the software for real-time identification and imaging, and the results of field measurements are presented. © 2001 Field Analyt Chem Technol 5: 75–90, 2001

FTIR spectroscopy has been established for the monitoring of diffuse emissions into the open atmosphere. The method of choice for the evaluation of the atmospheric spectra uses the fitting of reference spectra by classical least squares. Important refinements can be achieved by selecting the optimal wavelength ranges based on objective mathematical criteria, improved spectral background strategies, and high-quality reference spectra that allow for the adaptation of nonlinearity effects. Under these improved conditions, new detection limits for atmospheric trace components are presented. The chemometric tools developed were integrated into an expert system, affording the evaluation of the atmospheric spectra with a minimum of user interaction. Results from several field campaign measurements within a municipal waste-treatment plant are presented, illustrating the reliability of the methods applied. Furthermore, extensive trace-gas concentration data were collected simultaneously with two FTIR spectrometer systems under various meteorological conditions and spatial scenarios for dispersion modeling of diffuse emissions from different sites. Emission rates of ammonia area sources were determined from path-integrated spectroscopic remote measurements and inverse dispersion modeling based on Lagrangian model calculations. The results were obtained within a factor of 1.4 times the actual emission rate values. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 13–28, 2001