Field Analytical Chemistry & Technology最新文献

Eli Lilly and Company utilizes a mass balance procedure to track solvent usage at its manufacturing and pilot plant locations. Although the mass balance procedure provides accurate usage information, it is not useful as a tool for rapid identification and quantitation of fugitive volatile organic compounds (VOCs). As government regulations and permitting requirements demanded more specific information, it became obvious that a system was needed for rapid identification and quantitation of fugitive VOCs. In 1991, Eli Lilly and Company investigated both technology and methodology which would identify and quantitate specific VOCs. The objective was to reduce fugitive VOC emissions by understanding both the sources of emissions and the operating parameters that allowed their occurrence. After reviewing existing technologies such as FT-IR, mass spectrometry, and gas chromatography, the company purchased five portable microchip gas chromatographs. These instruments were incorporated into a routine monitoring program that profiled various production facilities and tank farms for specific VOC emissions. Once baseline emissions were established, the instruments were strategically located to monitor the effect of various improvement activities. The result of using portable gas chromatographs to establish an emission profile was an 86% reduction in fugitive VOC emissions over a 2-year period. This article presents a portable gas chromatograph and sample interface that quantitates methyl alcohol, ethyl alcohol, acetone, acetonitrile, ethyl acetate, methylene chloride, and toluene in 2 minutes. A typical linear range for these compounds is 5 ppm to 1%. The philosophy of incorporating this technology into routine manufacturing processes will also be discussed. © 1997 John Wiley & Sons, Inc. Field Analyt Chem Technol 1:367–374, 1997

A portable instrument with a high-speed multiple-wavelength LED array source, and simultaneous detectors for absorbance and 90° nephelometry, was tested from 420 to 950 nm. Absorbance values and simultaneous 90°-scatter intensities at six different wavelengths can be determined and stored every 0.02 s. An advantage of this LED instrument is that its sensitivity is equal to or better than many research-grade spectrophotometers. Also, unlike diode array spectrometers, which emit white light through samples, the LED instrument emits monochromatic light through samples, enabling us to obtain turbidity, turbidity ratio, and particle size information in addition to the absorption spectrum. Field applications can range from simple turbidity and multiple-wavelength absorbance measurements to kinetic experiments with temporal acquisition of multiple-wavelength absorbance and simultaneous turbidity data. Rugged, laptop compatible, portable, and inexpensive, the LED instrument is useful for discrete or on-line VIS–NIR absorption analysis and turbidity, or turbidity ratio, analysis. © 1998 John Wiley & Sons, Inc. Field Analyt Chem Technol 2: 21–28, 1998

A portable colorimeter equipped with light-emitting diodes (LEDs) and two photodiodes (PDs) as light sources and detectors, respectively, was developed. LEDs were electronically modulated with square waves. Light from an LED was divided by optical fibers and conducted to a sample and reference cell. The sample or reference light was detected by each PD. Then detected signals were fed to a notebook computer through a dual-channel analog-to-digital converter. Neither monochromator nor bandpass filter was necessary, because an LED's spectral bandwidth is relatively narrow. A signal from an LED in the time domain was converted into a frequency-domain signal by fast Fourier transformation on a computer. Absorbance was calculated from intensities of sample and reference signals. This colorimeter was successfully applied to the determination of cobalt in a synthetic water sample and to the on-site analysis of nitrite ions in river water. © 1998 John Wiley & Sons, Inc. Field Analyt Chem Technol 2: 173–178, 1998

Site characterization for subsurface contaminants is time-consuming and costly. The Tri-Service Site Characterization and Analysis Penetrometer System (SCAPS) has been developed to reduce the time and cost required for site characterization. Probes are designed to detect specific classes of contaminants such as petroleum products, explosive compounds, volatile organic compounds (VOC), and others. This article describes the Hydrosparge VOC sensor, an in situ VOC detection system that is capable of rapid subsurface site characterization of VOC contaminant distribution. The system consists of a direct push well for groundwater access, an in situ sparge module, and a direct-sampling ion-trap mass spectrometer. The results obtained with the SCAPS in situ technique indicate a strong linear relationship with EPA methods (r² = 0.84). SCAPS Hydrosparge VOC sensor has been demonstrated to reduce the time and cost required to characterize sites by directing the placement of a reduced number of conventional monitoring wells. © 1998 John Wiley & Sons, Inc. Field Analyt Chem Technol 2: 89–96, 1998

Use of GC/MS instrumentation outside of the traditional laboratory setting has grown significantly over the past several years. Considerable progress has also been achieved in developing GC/MS instrumentation and operating systems. Recent advances in this area will be illustrated with the use of results obtained with Viking SpectraTrak™ GC/MS systems. The multidisciplinary nature of GC/MS lends itself to a variety of sample introduction techniques while providing consistent, defensible, reliable results. Instrumentation and applications are inextricably linked, and the demands made on the sampling interface need to be met, particularly for field applications in which the advantages of having a GC/MS system at the point of sampling cannot be compromised. With its versatile sampling capabilities, the fieldable GC/MS instrument can be a very powerful and cost-effective tool for on-site, in-plant, and other out-of-laboratory analysis situations. This report focuses primarily on the deployment and application issues confronted in the field GC/MS instrumentation industry, and specifically on trends toward integrated miniaturization. The uses of field-portable GC/MS systems are expanding; however, because many of the uses are client- proprietary, some very interesting real-world applications could not be included here. This report attempts to present an overview of field-portable GC/MS system uses that hopefully will provide insights into the possibilities and growing applications of this relatively new analytical capability. © 1998 John Wiley & Sons, Inc. Field Analyt Chem Technol 2: 3–20, 1998

A commercially available SRI gas chromatograph (model 9300B) has been adapted to enable the use of solid phase microextraction (SPME) as the sample preparation and introduction technique for fast GC separations in the field. SPME utilizes a small-diameter fused silica fiber coated with a polymeric stationary phase for extraction of organic analytes from aqueous or gaseous matrices. The analytes extracted are thermally desorbed in the injector of a gas chromatograph. Modifications to the instrument included a new injector and modifications to the PID detector. The injector enables very fast fiber heating rates (∼4000 °C/s), which produce narrow injection bands suitable for fast GC. Separation of BTEX (100 ppb each compound) within 15 s has been demonstrated with FID and PID detection. The precision of the results was very good. Separation of purgeables (trichlorofluoromethane, 1,1-dichloroethene, dichloromethane, 1,1-dichloroethane, trichloromethane, tetrachloromethane, trichloroethene, 1,2-dichloropropane, 2-chloroethyl vinyl ether, 1,1,2-trichloroethane, tetrachloroethene, dibromochloromethane, chlorobenzene; 200 ppb each compound) was accomplished in 2 min with good precision with the use of a dry electrolytic conductivity detector (DELCD). The instrument was tested in the field in the analysis of trichloroethylene in soil extracts. PID was used for detection because its dynamic range is better as compared to DELCD. Almost 500 samples were analyzed in 10 days without major problems. © 1997 John Wiley & Sons, Inc. Field Analyt Chem Technol 1: 277–284, 1997

Direct sampling mass spectrometry (DSMS) is an increasingly popular technique for rapid and sensitive measurement of organic pollutants in air, water, soil, and wastes. Detection limits are typically in the range of 1 ppb for volatile organic compounds (VOCs in water) with little or no sample preparation required and sample analysis times of less than 3 min. Despite the fast sample analysis time and consequent large sample throughput capability, there are numerous situations that would benefit from the ability to continuously monitor the concentration of targeted VOCs in real time. These include incinerator stack emissions, industrial wastewater streams, chemical process streams, vent emissions, exhaust emissions, groundwater and soil remediation process systems, waste-site off gas during remediation, fugitive emissions, hazardous workplace atmospheres, and soil gas analysis with the use of a dynamic depth profiling probe such as a cone penetrometer. During the past year, several pilot studies have been conducted with a DSMS field instrument for various real-time continuous monitoring applications. These studies have included the monitoring of VOCs in an incinerator stack, monitoring of VOCs in pilot-scale photolytic groundwater remediation systems, measurement of automobile exhaust in a moving vehicle, soil gas measurements in conjunction with a cone penetrometer, and in situ measurement of VOCs in groundwater with the use of a special sampling probe. In each instance, the DSMS instrument was configured with special sampling probes that extracted the VOCs from the sample matrix and transported them through an appropriate transfer line into a direct capillary restrictor interface to the ion trap. Targeted compounds were monitored based on unique peaks in the electron impact and proton transfer chemical ionization mass spectra. The real-time detection limits for VOCs in aqueous systems are in the range of 1 ppb, and in gaseous streams detection limits are in the range of approximately 10 ppb by volume. Temporal resolution ranges up to a maximum of 10 full-scan mass spectra per second, which provides the ability to monitor transient events in a sample stream that might be missed by discrete sample collection and analysis. © 1997 John Wiley & Sons, Inc. Field Analyt Chem Technol 1: 251–276, 1997

Methyl isocyanate (MIC), CH₃NCO, is a relatively simple molecule, but ion mobility spectra derived from studies of this molecule are complex. MIC is known to polymerize, which would lead one to expect that proton-bound monomer, proton-bound dimer, and even larger proton-bound ions could be observed. Indeed, this is the case, and a number of other species can also be observed. In this case headspace above a relatively fresh (i.e., recently purchased) MIC sample was analyzed, and numerous peaks were observed in a single spectrum. Peak identities and intensities were, of course, concentration dependent. Over a range of concentrations, as many as 16 peaks were observed. IMS systems used for these studies included chemical agent monitors (both water and acetone chemistry), a miniaturized hand-held IMS device (Mini-IMS) and an IMS-MS/MS instrument. Although ion mobility spectra are complex, it has been shown that hand-held IMS devices can be useful for detecting or monitoring airborne concentrations of this toxic and hazardous compound. IMS/MS/MS experimentation yielded some mass identifications, and possible ion compositions are proposed. Reduced ion mobility of H⁺(CH₃NCO)(H₂O)_n was tentatively determined to be 1.91±0.02 cm₂ / V s. © 1997 John Wiley & Sons, Inc. Field Analyt Chem Technol 1: 285–294, 1997

Measurement of chlorophyll fluorescence induction kinetics was carried out during a phytoremediation technology field experiment in order to monitor heavy-metal uptake from contaminated soil. A new portable chlorophyll fluorometer was used to identify the most applicable parameter (RFd=fluorescence decay) to monitor the process. Good correlation was demonstrated between this parameter and accumulated heavy-metal concentration. Application of the monitoring technique for remedial technology optimization is proposed. © 1998 John Wiley & Sons, Inc. Field Analyt Chem Technol 2: 241–249, 1998