Field Analytical Chemistry & Technology最新文献

A flow-through analyzer that can determine trace amounts of chemical components in ice cores was examined. To obtain the vertical profiles of ammonia and calcium in the ice core, which can be a measure of the climate change, sensitive fluorescence signals were examined. For the determination of ammonia, a reaction with o-phthalaldehyde and sulfite salt was performed. This system had the potential to measure down to 2 nM, with a 1-mm ice-core resolution, equivalent to the thickness of the monthly ammonia profiles during the last interglacial maximum. A trace calcium analyzer was simultaneously examined, with the use of the fluorescent enhancement of Fura2 with a detection limit of 15 nM. Ammonia and calcium in the Antarctic ice core showed similar variation patterns, different from that of the Greenland ice core. The ammonia analyzer was also applied to the analysis of lake water. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 29–36, 2001

An automated analyzer based on solid-phase microextraction (SPME) coupled to gas chromatography (GC) for monitoring organic compounds in water is presented. The instrumental setup, which was tested previously with direct SPME, is now tested in the headspace mode. Memory effects observed in the earlier design were reduced by using glass instead of plastic tubing. Parameters that potentially influence the extraction yield were studied in the laboratory with the use of spiked water samples. These parameters were temperature, salt content, methanol content, pH value, and excess components. The extraction efficiency as a function of the extraction time (absorption profiles) was determined for 24 standard compounds. The method was validated in the laboratory. Good precision (in general <5%) and linearity were observed. With the use of flame ionization, detection limits of quantitation were in the low-ppb range, sufficient for wastewater monitoring. The instrument was tested continuously for 6 days at the wastewater plant of a chemical company in northern Germany. Better stability and robustness were observed in the headspace SPME compared to the direct SPME. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 37–49, 2001

This article describes the collection and analysis of organic contaminants at depth without bringing soil to the surface. A thermal extraction cone penetrometer (TECP) probe was used to extract soil-bound semivolatile organics, transferring them to the surface for analysis by ultrafast gas chromatography/mass spectrometry (GC/MS). Findings showed that polychlorinated biphenyls, polycyclic aromatic hydrocarbons, chlorinated pesticides, and explosives could be collected and analyzed in 5 min when the soil-water content was <20% and in 15 min when it was between 20 and 35%. When the TECP was directly connected to the GC/MS, trinitrotoluene (TNT) and four of its synthetic precursors were speciated in 20 sec. Moreover, 51 VOCs were detected by membrane-inlet mass spectrometry in ∼10 sec. Organics were “sniffed” from a vial and identified using the Ion Fingerprint Detection™ software. The algorithms provide the means to untangle complex mass spectra making real-time, electronic nose detection and identification by MS possible. © 2001 John Wiley & Sons, Inc. Field Analyt Chem Technol 5: 60–68, 2001

The bubble stripping method was developed for use at field sites to measure the concentration of dissolved hydrogen (H₂) in ground water. This information is useful in assessing the viability of employing monitored natural attenuation (MNA) as a strategy to influence the restoration of sites contaminated with chlorinated solvents. In laboratory studies, a reservoir containing water was employed to simulate a well. The system was constructed so that the concentration of dissolved H₂ could be maintained at a constant level. The method was applied by pumping water from the reservoir into a sample cell, and then injecting 20 ml of nitrogen into the cell to produce a headspace (the “bubble”). Stripping was accomplished by pumping water through the cell, which produced agitation between the aqueous phase and the headspace. Pumping was continued for a length of time sufficient for dissolved H₂ to partition between the two phases. Analysis of H₂ in the headspace by gas chromatography enabled the concentration of dissolved H₂ in solution to be calculated with the use of Henry's law. Two sample cell designs were compared in this study, the Microseeps Cell and the Chapelle Cell. Kinetics of equilibration studies were conducted with each cell, employing solution flow rates of 200, 300, and 400 ml/min, at 4 and 21 °C. The Microseeps Cell compared favorably with the Chapelle Cell with regards to kinetics of equilibration, with the added benefit of costing significantly less. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 283–296, 2000

A radio-frequency-based ion-mobility analyzer with a micromachined drift tube was operated continuously to monitor volatile organic compounds (VOCs) in ambient air inside a building and in an open space near the union of I-10 and I-25 at Las Cruces, New Mexico. Air was drawn directly, without enrichment or preseparation, through the analyzer, which was regulated to 35 °C. The ion source was a photo-discharge lamp at 10.6 eV, providing a preliminary level of selectivity in response to chemicals with low ionization potentials. The compensation voltage was scanned continuously from −40 to +20 V at rates of 60 V/s, providing profiles of ions obtained from VOCs in air. Solvents were detected at 1-ppm levels as fugitive emissions from other experiments under way in the laboratory from 8:00 a.m. to 6:00 p.m. However, patterns in VOC levels from 1 to 5 ppb between 6:00 p.m. and 7:00 a.m. and on weekends was attributed to air exchange between ambient air and the ventilation system of the building. The mobility analyzer results were consistent with VOCs from traffic on major city thoroughfare adjacent to the building. In-field studies near two interstate highways demonstrated that analyzer response could be correlated to traffic patterns and exhibited diurnal trends. These findings demonstrate the concept and practice of micromachined mobility analyzers as continuous monitors for VOCs as airborne vapors in buildings and on site. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 297–308, 2000

A flow-through analytical method has been developed for the determination of trace amounts of aluminum in seawater with the use of Lumogallion fluorometric detection. Because iron was selectively removed by passing the sample through an 8-quinolinol immobilized chelating resin column (MAF-8HQ), this method could be applied to samples collected at the hydrothermal oceanic regime. Several known organic complexing agents were studied as a model group to examine the effect of naturally occurring organic ligands on the detection of aluminum in seawater. The detection limit was 0.17 nM for 10 ml of sample. The standard deviation was 2.7% at 2 nM of aluminum. This method permitted the sensitive, precise, and rapid determination of subnanomolar Al in seawater without contamination onboard ship. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 274–282, 2000

Colorimetric determination of analytes with comparators is characterized by stepwise measuring. Standard deviation as well as confidence interval are based on the distribution of measuring values. No continuous distribution of measuring values can be obtained with the use of colorimetric methods. The measuring range is cut in intervals and the measuring values show discrete distribution (measuring steps or bins). The measuring steps are nonuniformly distributed over the measuring range. This is an attempt to calculate statistical measurements for these determination methods. It is shown that adding two measuring steps to the measuring value is a quick way to check whether limit levels are exceeded. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 270–273, 2000

Ion mobility spectrometry (IMS) is a popular field analyzer. The reason for its popularity is its small size, its sensitivity, and the amount of information contained in the ion mobility spectrum. Several research groups are working on smaller IMS cells using microelectromechanical systems (MEMS) technology. New principles of operation will be needed to achieve this goal. The theory supporting the development of the radio frequency (RF) IMS is described. RF-IMS separates ions by applying an asymmetric RF field across two parallel plates and passing the ions through the separator. The performance of the device no longer depends on a simple linear relationship between the drift velocity and an electric field, but rather on a nonlinear relationship between these parameters. Consequently, a more detailed momentum-transfer theory is needed. The required theory is developed and applied to the interpretation of experimental data here. The importance of using momentum transfer theory in combination with the continuity equation is demonstrated. © 2000 John Wiley & Sons, Inc. Field Analyt Chem Technol 4: 255–267, 2000