Portable gas chromatographs (PGC) capable of direct detection of ambient concentrations of toxic organic vapors in air were operated in field studies, while simultaneous data were taken for comparison by the Canister/TO-14 Method. Samples were obtained downwind of Superfund hazardous waste sites, highways, chemical plants, and in locations where there was concern about odors or nasal/respiratory irritation. Reasonable agreement between methods was found, even though sampling techniques were not equivalent.
A high-speed gas chromatography from optimizing column operating conditions has been shown to minimize the injection band width, thus shortening the separation time to a few seconds. The system was evaluated using common organics including alkanes, aromatics, alcohols, ketones, and chlorinated hydrocarbons. Quantitative trapping and reinjection was achieved for all tested compounds. Limits of detection (LOD) for many compounds, based on a 1 cm3 gas sample, were less than 1 ppb. By using the cold trap inlet with a low dead volume detector and a high-speed electrometer, the efficiency available from commercial capillary columns can be better utilized and retention times for some routine separations may be reduced to a few seconds.
Two different types of direct sampling mass spectrometers were evaluated for use as rapid screening tools for volatile organics in a wide range of environmental matrices. They are a commercially available ion trap mass spectrometer (ITMS) and a specially designed tandem source glow discharge quadruple mass spectrometer. Both are equipped with versatile sampling interfaces, which enable direct monitoring of volatile organics at ppb levels in air, water, and soil samples. Direct sampling mass spectrometry does not utilize chromatographic or other separation steps prior to admission of samples into the analyzer. Instead, individual compounds are measured using one or more of the following methods: spectral subtraction, selective chemical ionization, and tandem mass spectrometry (MS/MS). For air monitoring applications, an active "sniffer" probe is used to achieve instantaneous response. Water and soil samples are analyzed by means of high-speed direct purge into the mass spectrometer. Both instruments provide a range of ionization options for added selectivity and the ITMS can also provide highefficiency collision-induced dissociation MS/MS for target compound analysis.
A fully portable GC/MS system was based on the combination of an automated vapor sample inlet, a "transfer line" gas chromatography module system. The unit weighs approximately 70-75 lb (1 lb=454 g) and uses 150-200 W of battery power. The MS and computer are carried in front of the operator by means of a shoulder harness whereas the battery pack, carrier gas supply, and roughing vacuum system are carried as a backpack. Air samples can be analyzed using a special automated air sampling inlet. The system is designed to be supported by a vehicle transportable docking station.
Newly designed instrumentation for multimedia environmental trace organic analysis was described for onsite application. The automated prototype units feature advanced sample processing with interfaces for online analyses with chromatographic and/or spectral detectors. Thermal sample processing is provided by an Environmental Pyroprobe Analyzer, including modules for purge and trap/thermal desorption, dynamic headspace, and pyrolysis. Nonthermal multisample processing is conducted with a Chemical Hazards Automated Multi Processor based on supercritical fluid extraction and specialty interface units. Analyses of low ppb levels of vapors, aerosols/particulates, gasoline, and soils illustrate the proven capabilities of the integrated modular systems.
Field GC/MS applications have utilized Bruker Instruments' mobile mass spectrometer. The MS, initially designed for NATO as a chemical warfare detector, was manufactured from the outset as a field instrument. The MS was transported from site to site in a midsized truck and was battery operated for about 8-10 hours at ambient conditions. Simple field methods have been developed based on analyte introduction by thermal desorption followed by fast GC separation and MS detection. The goal was to provide a practical GC/MS tool that can deliver the quality of data required for the study with minimal sample cleanup.
Thermal extraction was offered as a fast and safe alternative to classical, cumbersome solvent extractions for a wide range of semivolatile pollutants in GC/MS analysis. Samples are loaded into porous quartz crucibles with no preparation other than weighing required prior to analysis. Analytes are volatized into the helium carrier gas flow at controlled preprogrammable temperature profiles and subsequently cryo-condensed onto a conventional gas chromatographic column. The method was demonstrated by analyzing for a representative group of organic pollutants covering a wide range of polarity/volatility contained in natural soil matrices at concentrations as low as 0.5 ppm using a Pyran Thermal Chromatograph. Average correlation coefficients for calibration curves range from 0.938 to 0.997 for compounds less volatile than naphthalene. Naphthalene and more volatile compounds experienced variable losses during open-air sample loading. Diakylphthalates underwent partial decomposition during the thermal extraction process. Recoveries varied depending on soil types as well as on the physical and chemical nature of analytes, with generally the highest thermal extraction yields for river silt and the lowest yields for clay. Typical recoveries were 10-30% for polynuclear aromatic hydrocarbons, 60-70% for hexachlorobenzene, and nearly 100% for chloronaphthalenes. However, the pesticide aldrin showed recoveries of at most 19%. A majority of the analytical results are within an accepted range for quantitative analysis. With sample turnaround times of typically 30-60 minutes this instrument should greatly facilitate many onsite monitoring and analytical efforts.
Examples have been presented on the use of a mobile ITMS for onsite environmental screening and monitoring of vapors by GC/MS. The instrument is built around a miniaturized ITMS system, with a novel direct vapor sampling inlet and coupled to a high-speed transfer line GC column (short capillary column with fixed pressure drop). The column is temperature controlled inside the standard ion trap transfer line housing. This provides for high-speed analyses using an automated sampling system constructed with only inert materials in the sample path. The system demonstrated the following capabilities: detection limits of less than 10 ppb for a variety of volatile organic compounds; selective analysis of 21 compounds or more in a single one minute chromatogram with boiling point windows depending on column type and temperature; repetitive sampling as frequent as every 10 seconds for monitoring transient vapor concentrations; and direct variation of sample size with sample pulse time to readily optimize GC resolution vs. ultimate sensitivity. The instrument is rugged enough for most field screening and hazardous waste site investigations.
A second-generation transportable gas chromatograph/ion trap detector was developed for the in situ characterization of chemical waste sites. The instrument is extensively based on commercial instrumentation and can be used for field analysis of volatile organic compounds in soil and water. A purge and trap GC is used for sampling and separation of VOCs from the environmental matrix before their introduction to the ion trap detector for mass spectral analysis. A secondary microprocessor controls the sampling and GC hardware in parallel with the ion trap detector, which in turn is controlled by the host PC. It has been claimed that the ion trap detector provides many advantages as a mass analyzer, such as being simple to maintain and operate. The high sensitivity of the ion trap and the inherent universality of the modular mass spectrometer system are the most important features for a field analytical instrument. The instrument provides high specificity for compound identification due to the two-dimensional information provided by chromatographic retention time and mass spectral library identification. Mobile ion trap mass spectrometers operating in the MS/MS mode have been successfully applied for the direct, continuous, or near-continuous analysis of permanent gases and condensable vapors. Ion trap mass spectrometer systems have also been developed for rapid screening of volatile organics in environmental matrices by MS/MS techniques.
29.10 ANALYSIS OF POLYCHLORINATED BIPHENYL
The USEPA has compiled the following field methods for the analysis of polychlorinated biphenyl (PCB).
29.10.1 Hexane/Methanol/Water Extraction
As in other methods, hexane/methanol/water extraction requires a field laboratory with a GC and linearized electron capture detector for PCB analysis of soil samples. Identification is carried out by comparing peak retention time with external standards. Quantification is determined by comparing peak heights and volumes of the standard and sample. Sample preparation consists of mixing 0.8 g of soil with a 1:4:5 ratio of distilled water/methanol/hexane. An optional step is to dry and grind the sample before extraction. The sample is agitated and allowed to sit, allowing the hexane layer to separate. The hexane layer is transferred to a test tube containing sulfuric acid and mixed. This step is optional, as it is used to eliminate matrix interferences. The sample is then withdrawn from the hexane layer for GC analysis.
This method is most appropriate for Aroclors 1242, 1248, 1254, and 1260, and good for 1016, 1221, and 1232. If the concentrations are above 100,000 pg/kg, these contaminants will be underestimated by 60%. The results are approximations. The detection limit is 200 pkg. The recovery of Aroclor 1242 spike is 80-105%. Based on the results of 300 samples, the accuracy is equivalent to CLP when the concentration is below 100,000 pg/kg. Relative standard deviation of four samples is 10-12%.
The calibration is determined by peak heights and retention times of PCB standards. Standards and blanks should be run every ten samples. The analysis time is 5 to 10 samples per hour.
Sample preparation for water consists of adding 1.5 mL hexane to 15 mL of water, mixing and separating the hexane layer. Sample preparation for soil consists of mixing 2 g of soil with 2 g sodium sulfate. Then 10 mL of hexane is added to the sample, mixed with an ultrasonic probe, and the hexane layer separated, which is ready for GC analysis.
The detection limits are 25 pg/L in water and 2500 pg/kg in soil. The analysis time is 20 to 25 minutes per sample.
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