Field Analytical Chemistry & Technology最新文献

Contamination of soils with the explosives TNT and RDX is a worldwide problem that has resulted from inadequate disposal methods. Many of these contamination sites are currently being characterized or are undergoing remediation. The ability to obtain real-time, on-site results would save remediation time, reduce cost, and provide for efficient use of labor during cleanup. The NRL fiber-optic biosensor, which has been demonstrated for the on-site detection of explosives in ground water, has expanded its horizons to include detection in soil extracts. Soil samples from several sites in the United States were analyzed for TNT and RDX. The explosives were removed from the soil with a 3-min acetone extraction. The extract was mixed with buffer containing a fluorescent explosive analog and exposed to the antibody-coated optical probes. In the presence of either TNT or RDX, a decrease in the fluorescence signal, proportional to the explosive concentration, was observed. In less than 20 min, analysis on four optical probes was completed. Extract results from the fiber-optic biosensor were compared to those from U.S. EPA SW 846 Method 8330 (reverse-phase high-performance chromatography). Detection limits of 0.5 mg/kg (0.1 mg/l) of TNT and RDX in soil acetone extracts were obtained. © 2000 John Wiley & Sons, Inc.* Field Analyt Chem Technol 4: 239–245, 2000

The Triservice Site Characterization and Analysis Penetrometer System (SCAPS) was developed to reduce the time and cost required for site characterization. Direct-push sensors were developed to detect specific classes of contaminants, such as petroleum hydrocarbons, explosive compounds, radionuclides, metals, and volatile organic compounds (VOCs). This article describes the demonstration of a direct-push sensor that can quantify VOC contamination in the subsurface in real time. This system consists of a membrane interface probe (MIP) manufactured by Geoprobe Systems coupled to a direct sampling ion-trap mass spectrometer (ITMS). The ITMS-MIP system was shown to rapidly collect and analyze samples from the subsurface, regardless of matrix. Two of the five demonstrations discussed resulted in a strong linear correlation (r² = 0.9) with validation samples analyzed using EPA Method 8260. The other three demonstrations revealed that the calibration method used in this work introduced a bias compared to EPA methods.* © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 246–254, 2000

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. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 219–238, 2000

Solid-phase microextraction (SPME) was used as a rapid, simple, convenient, and cost-effective technique to sample volatile organic compounds (VOCs) in indoor air. Concentrations of five target VOCs, including benzene, toluene, ethylbenzene, m,p-xylenes, and hexane, were determined on site in several buildings around the city of Waterloo, Canada. Samples were collected with a polydimethylsiloxane/divinylbenzene (PDMS/DVB) porous polymer-coated fiber and 1-min sampling time, followed by 15-min analysis. Fast separation and speciation of common indoor air pollutants was possible with the use of a modified, SRI portable gas-chromatography (GC) instrument, equipped with a photoionization (PID), a flame ionization (FID), and a dry electrolytic conductivity detector (DELCD) in series. The mass calibration for target VOCs was based on the diffusion-controlled extraction onto the adsorptive SPME coating. The method detection limits for the target VOCs in air were between one and nine parts per billion (ppb). Target VOC concentrations measured with SPME/fast GC were comparable to those obtained with the National Institute of Occupational Safety and Health (NIOSH) 1501 method. The use of SPME coupled to a portable GC instrument allowed for at least a tenfold reduction of the total sampling and analysis time. The short SPME sampling time combined with fast, portable GC provided a near-real-time measurement of target VOCs. The results suggest that fast air sampling with adsorptive SPME fibers can be used for analyte speciation based on diffusion coefficients. The combination of SPME and a portable fast GC proved to be a very promising technique for conducting cost-effective indoor air quality surveys and making on-site decisions to control VOC emissions. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 73–84, 2000

Humic substances are of current interest because of their roles in environmental processes involving pollutants. It is also becoming recognized that humic substances may interfere in the analysis of environmental samples, though the possible adverse effects do not appear to be fully appreciated. The present effort focuses on determining whether humic materials interfere in the analysis of nitrite in water with the use of the Griess reaction. This is a well-known reaction that uses nitrosation to give a diazonium salt, then couples with an appropriate reagent to form a colored product. This colorimetric method continues to be applied in the laboratory and the field for nitrite. It was found that nitrite values at low ppm levels in water may be reduced by 50–60% in the presence of approximately 50-ppm quantities of specific humic acids. The greater the humic acid concentration, the greater the interference effect. However, it is projected, based on experiments with Fluka humic acid, that humic-substance concentrations of 10 ppm or less will have a measurable but small effect. It was shown that the interference is due to molecular association of the Griess dye with the humic acid. The interference results in less color, and, with some humic acids, a shift in the wavelength of maximum absorption. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 134–146, 2000

A thermal extraction cone penetrometer (TECP) has been developed to detect subsurface contaminants in situ without bringing soil to the surface or into a collection chamber. Coupled with thermal desorption gas chromatography/mass spectrometry (TD-GC/MS) sample collection and analysis can be accomplished in ∼20 min for the full range of U.S. Environmental Protection Agency Target Compounds (EPA). TECP extraction efficiencies of 50 to 100% can be obtained for most EPA Method 8270 compounds. Results of 99 volatile and semivolatile organics analyzed from the same TECP extracted soil in 16 and 40 min are presented. Measurement precision and accuracy were well within the Method 8270 benchmarks required for solvent-extracted soils analyzed by GC/MS. The total ion and reconstructed ion current chromatograms are shown for chlorinated solvents and gasoline constituents extracted from a hazardous waste site located at Hanscom Air Force Base (Bedford, MA). Data compared favorably against traditional purge and trap GC/MS. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 85–92, 2000

A rapid field method for routine checks on dissolved sulfate in surface, running, and potable waters is presented. The method uses reagent indicator paper strips and a thermometric unit. The RIS-Sulfate-Test was developed by immobilization of an Arsenazo III-barium complex together with buffer and masking reagents on cellulose paper. It was adapted to sulfate-ion determination with the use of visual, densitometric, and photometric techniques, the lower detection limit being 0.05– 0.1 g L⁻¹. The sensing principle is based on the reaction, which gives a colorless barium sulfate precipitate with a heat of formation of ΔH = 4.6 kcal M⁻¹. After the strip is immersed into a sample solution for 1 s, the color changes from black–blue to pink–violet because of sulfate-induced complex decomposition. Color changes are monitored with the use of a standard color scale and a miniaturized reflectometer with 660-nm light diode. A miniaturized calorimeter was used for determining high concentrations of sulfate. A 0.3-ml aliquot of sample solution is placed on the bottom of a 5-ml polyethylene vessel, and 0.1–0.2 ml of 0.3-M barium chloride is introduced into the vessel with a 1-ml syringe. The lower part of the syringe with the reagent is immersed into the sample solution for a quicker thermal equilibration. After 10 min, the reagent is injected into the solution and readings are taken with a small voltmeter. A linear dependence of the instrument readings on sulfate concentration was observed in the 0.2 to 5-g L⁻¹ range (P = 0.95, n = 3, RSD = 20%). Both methods were checked by standard addition and dilution procedures, and their reliability was confirmed by flow-injection analysis of seawater with the use of spectrophotometric detection of a turbidimetric indicator reaction. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 147–153, 2000

A detector based on an ion trap mass spectrometer is being developed for the U.S. Army for battlefield detection of both chemical and biological weapons (CW/BW). The primary operating modes for this instrument are selected via a multiport valve that directs the sample flow into the detector from one of several inlets designed to admit volatilized chemical agents, liquid chemical agents on the ground, or aerosolized particles that may contain a biological agent. The instrument is designed to be highly sensitive in order to minimize false negatives; it therefore makes use of an ion trap mass spectrometer as the detector. Significant effort is also being placed on efficient sample transmission using deactivated sample transport lines and in situ derivatization of the less volatile BW biomarkers. In addition to being sensitive, the instrument must be highly selective in order to minimize false positives. Particle-size discrimination, chemical ionization, and MS/MS experiments combine to provide a high degree of chemical selectivity. Fatty-acid standards, gamma-killed bacteria, dimethylmethylphosphonate, and methyl salicylate have been analyzed with the use of a preproduction instrument to demonstrate the primary operating modes of this instrument. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 93–110, 2000

Two characteristics of ambient background sources must be addressed: their low intensity and their instability. Reference spectra—normally subtracted from sample spectra to remove the source characteristics, instrument response, and other spectral characteristics common to both the reference and sample spectra—are impossible to obtain when an ambient background source that may change rapidly is used. Data collection must be rapid because the source temperature may change, producing changes in the overall shape and intensity of the spectra. The low intensity of ambient sources makes noise a problem that is compounded by subtracting the reference spectrum from the analyte spectrum. We have developed a quantitative method for measuring volatile organic compounds (VOCs), the slope-ratio method (SRM), which is less susceptible to these problems.

The absorbance and the concentration for each standard taken at the time the analyte is measured and the absorbance for the analyte are substituted into the equation created from the linear equations of the standard and analyte. For ambient backgrounds, artificial reference lines are created by using points on either side of the peak of interest to create a straight line that can be subtracted from the peak. The log of the artificial reference spectrum subtracted from the raw sample spectrum produces absorbance intensities that still follow Beer's Law. Representative absorbance equations are generated for a range of intensities in the laboratory for both the standard and the analyte. The raw spectrum of the analyte measured under experimental conditions must be included with the series because the spectra for standards and the spectrum of the unknown must match within ±10.0%. This procedure has been successfully used for VOCs such as methanol, acetone, and t-butyl ethyl ether, and shows promise in measuring methane under laboratory conditions. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 127–133, 2000