Field Analytical Chemistry & Technology最新文献

A compact optical device and disposable strips for the simultaneous determination of the biochemical oxygen demand (BOD) of multiple samples have been developed. The compact optical device was constructed using three pairs of light emitting diodes (LEDs) and silicon photodiodes (Si-PDs), and the disposable strips were fabricated using inexpensive, transparent polycarbonate plates. Pseudomonas fluorescens bacteria were immobilizedin a layer at the bottom of each reaction cell on the sensor strip using a photocrosslinkable resin (ENT-2000). Using the redox electron acceptor 2,6-dichlorophenolindophenol sodium salt as the chromophore, a linear relationship was observed between the response of the Si-PDs and the BOD value of Organization of Economic Cooperation synthetic wastewater. Real samples from a wastewater treatment plant and a kitchen in our factory were examined, and good correlations were observed between the BOD values derived using this system and those determined by the conventional BOD₅ method. In addition, in spite of the sensor response decreasing to approximately half its initial value after 2 weeks, the correlation coefficients (r²) of calibration curves remained above 0.9 upon storage of the strips in 0.1 M NaCl solution at 4°C for up to 6 weeks. In conclusion, this system is transportable and compact as well as being simple to operate and suitable for rapid, on-site measurements. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 222–227, 2001

The U.S. Navy program Damage Control-Automation for Reduced Manning is focused on enhancing automation of ship functions and damage control systems. A key element of this objective is the improvement of current fire-detection systems. An early warning fire-detection system is being developed by properly processing the output from sensors that measure different physical and chemical parameters of a developing fire or from analyzing multiple aspects of a given sensor output (e.g., rate of change as well as absolute value). The classification and speed of the probabilistic neural network (PNN), deployed in real-time, have been evaluated during a recent field test aboard the ex-USS SHADWELL, the Advanced Damage Control Fire Research Platform of the Naval Research Laboratory. The real-time performance is documented and as a result of optimization efforts, improvements in performance have been recognized. Early fire detection, while maintaining nuisance source immunity, has been demonstrated. A detailed examination of the PNN during fire testing has been undertaken. Using real and simulated data, a variety of scenarios (taken from recent field experiences) have been used or recreated for the purpose of understanding potential failure modes of the PNN in this application. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 244–258, 2001

A simple field-flow preconcentration system has been developed for lead determination in seawater. Seawater samples are collected in situ by passing them with a pump through minicolumns packed with poly(aminophosphonic acid) chelating resin to retain and preconcentrate lead, and remove the saline matrix. Minicolumns loaded with lead are then returned to the laboratory where they are inserted into a flow-injection system and eluted with a small volume of hydrochloric acid into the nebulizer-burner system of a flame atomic absorption spectrometer. The detection limit for lead in seawater was 2.8 ng l⁻¹. This procedure was applied to the determination of lead in seawater samples from Galicia (Spain). © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 239–243, 2001

On-site determination of nitroaromatic and nitramine residues in soils was performed using a field-portable gas chromatograph (GC) equipped with a thermionic ionization detector selective for compounds with nitro functional groups. Soil samples were extracted with acetone. A 1-μl volume of the filtered extract was manually injected into the GC, allowing for the rapid determination of the suite of explosives that often coexist in explosives-contaminated soils at military training facilities and other defense-related sites. Good agreement was established for the concentrations of several explosives when results obtained using this method of analysis were compared with those from either high-performance liquid chromatography (Method 8330) or GC electron capture (Method 8095) analysis. Comparisons were performed for sample extracts and for soil subsample replicates distributed for on-site analysis during a field verification test performed under the auspices of the U.S. Environmental Protection Agency's Environmental Technology Verification Program. This on-site GC method for the determination of explosives residues in soils is well suited for dynamic site characterization activities. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 228–238, 2001

Vapor detection of plastic explosives is difficult because of the low vapor pressures of explosive components (i.e. RDX and PETN) present in the complex elastomeric matrix. To facilitate vapor detection of plastic explosives, detection agents (taggants) with higher vapor pressures can be added to bulk explosives during manufacture. This paper investigates the detection of two of these taggants, ethyleneglycol dinitrate (EGDN) and 2,3-dimethyl-2,3-dinitrobutane (DMNB), using a handheld ion mobility spectrometer. These two taggants were detected both from neat vapor sources as well as from bulk explosives (nitroglycerin (NG)-dynamite and C-4 tagged with DMNB). EGDN was detected from NG-dynamite as EGDN·NO₃⁻ at a reduced mobility value of 1.45 cm² V⁻¹ s⁻¹ with detection limits estimated to be about 10 ppb_v. DMNB was identified from tagged C-4 as both negative and positive ions with reduced mobility values of 1.33 cm² V⁻¹ s⁻¹ for DMNB·NO₂⁻ and 1.44 cm² V⁻¹s⁻¹ for DMNB·NH₄⁺. Positive ions for cyclohexanone were also apparent in the spectra from tagged C-4 producing three additional peaks. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 215–221, 2001

We have developed techniques to map the distribution and composition of clay-rich soils with portable field spectrometers on the ground. Spectral reflectance measurements in the 1800–2400-nm region with 10-nm resolution can distinguish smectites, which cause swelling, from illites and kaolinite that do not swell significantly. Illites and smectites are often mixed in the soil and result in varying swell potential. Standard engineering soil tests are too time consuming and costly to be used in areas where there is highly varying swell potential. Therefore, in many instances in regions of steeply dipping sedimentary layers, beds of swelling clay go undetected. We show that it is possible to determine smectite content with a standard cross-validation error of 10% based on partial least-squares analysis of second-derivative reflectance spectra. Loadings show that the 1800–2000- and 2150–2250-nm regions contain the most relevant information for the detection and quantification of smectite content and these correspond to the bound water in the clay lattice interlayer and the Al–OH combination band, respectively. Correlations as high as 87% were obtained with the Seed swell-potential index. The correlations are higher when the samples were dried rather than measured in their moist condition shortly after collection in the field, as in an earlier study. Correlation with other swell indices shows that reflectance spectroscopy would be a reliable indicator that could divide samples into low, medium, and high swell potential. The effect of sample moisture was studied and the results show that the surface of the field samples must first be dried before measurement, in order to obtain a reliable swell potential value from the model. © 2001 John Wiley & Sons, Inc., Field Analyt Chem Technol 5: 143–155, 2001

In recent years, it has been demonstrated that SPME in polymer-clad optical fibers can be efficiently combined with NIR evanescent-wave spectroscopy for on-site monitoring of apolar hydrocarbons (HCs) in aqueous samples. Typically, the time to reach analyte partition equilibrium between sample matrix and fiber cladding for well-agitated solutions and low-molecular-weight HC species is in the range of 2–20 min. Thus, spectral absorbance data measured in extraction equilibrium are used for calibration and evaluation. However, for samples with no or only low agitation (e.g., in situ measurement in a monitoring well) and even for well-stirred samples containing HCs with higher molecular weight (>C8–C10), it may take several hours to reach equilibrium, which is by far too long for applications in field analysis. In this context, a calibration and evaluation algorithm based on HC extraction kinetics has been developed, which allows performing quantitative measurements of such samples within 20 min. This method uses the initial gradient of the response curve of a given HC compound or mixture recorded by the SPME-NIR instrument, which is linearly dependent on analyte concentration. The algorithm has been implemented in the control and evaluation software of an SPME-NIR photometer system and tested with different aqueous HC samples. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 131–142, 2001

A new gas chromatography system, based on the use of a water electrolyzer as its only source of gases, was designed, built, and tested. An electrolyzer-powered flame ionization detector (EFID) served as the GC detector for the sensitive, carbon-selective detection of a broad range of volatile organic compounds. The concept of electrolyzer-operated GC-EFID is based on the use of the electrolyzer-produced oxygen and hydrogen gas mixture for sample desorption and sweeping in a purge-and-trap sampling system, as the analytical column carrier gas and as the only required EFID combustible gas mixture. It was found, as it has been found previously, that standard columns with dimethyl polysiloxane adsorption film could be operated with oxygen up to 200 °C. A styrene-divinylbenzene–based PoraBOND porous-layer open tubular column was used for the GC separation, and it was found that the system could be operated up to 140 °C with the electrolyzer-produced hydrogen and oxygen gas mixture. Thus, the use of a water electrolyzer enabled the creation of a gas-cylinder-free GC-FID system with enhanced transportability and ease of use and with lower cost of operation. The gas-cylinder-free system operation was demonstrated with fast chromatography separation (under 1-min total analysis time) of acetone, ethanol, benzene, toluene, and xylene with an estimated detection limit below 1 ppb. The capability of exhaled human breath analysis for industrial hygiene and medical diagnostic applications is demonstrated. An additional capability of total hydrocarbon content in air analysis is shown and the required minor modifications are discussed. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 107–115, 2001

Storage structures (silos, warehouses, and similar structures) are routinely fumigated for disinfestation of pests. This process includes sealing the structure, adding a fumigant (phosphine, methyl bromide, and other fumigants), maintaining a certain concentration of the fumigant, and aerating the structure after all fumigant has been removed or has dissipated. Phosphine concentrations in the air surrounding large fumigated structures at a tobacco storage facility were measured using an open-path Fourier transform infrared (FTIR) spectrometer system. These measurements provided more comprehensive data than could be obtained with multiple single-point detection devices. Specifically, this novel application of open-path FTIR was investigated to more completely characterize phosphine concentrations over long path lengths using a single FTIR. Phosphine levels were below the detection limit [<0.07 parts per million (ppm)] approximately 20 meters (m) east of a warehouse. Phosphine was detected at approximately 4 ppm inside a warehouse at the end of fumigation and just prior to aeration. Levels of phosphine directly in front of the doors of another fumigated warehouse, immediately after aeration, ranged from <0.07 to 8.3 ppm. Six different sampling paths were also used to investigate the levels of phosphine in various areas of the facility. Average phosphine levels in air around sealed warehouses under active fumigation were found to be the below detection limit. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 116–120, 2001