Grantee Research Project Results
Final Report: Field Determination of Organics from Soil and Sludge using Sub-critical Water Extraction Coupled with Solid Phase Extraction
EPA Grant Number: R825368Title: Field Determination of Organics from Soil and Sludge using Sub-critical Water Extraction Coupled with Solid Phase Extraction
Investigators: Hawthorne, Steven B.
Institution: University of North Dakota
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1996 through September 30, 1999
Project Amount: $279,935
RFA: Analytical and Monitoring Methods (1996) RFA Text | Recipients Lists
Research Category: Environmental Statistics , Water , Land and Waste Management , Air , Ecological Indicators/Assessment/Restoration
Objective:
The primary purpose of these investigations was to couple well-known extraction methods for water?solid phase extraction (SPE) and solid phase microextraction (SPME)?with subcritical water extraction (SWE) of soils and sludges to allow field-portable water methods to be applied to contaminated solids.Summary/Accomplishments (Outputs/Outcomes):
New methods for the extraction and collection of nonpolar and polar organics from environmental solids were developed that require only very simple (and inexpensive) apparatus, are easy to implement in the field, and yield quantitative results similar to conventional methods. Each method requires only a simple stainless steel extraction cell (no pump is needed), a few ml of water, and an oven to perform the extraction. The extracted organics (which are now in the extractant water) are collected and analyzed using SPME or SPE discs, followed by conventional gas chromatography (GC) determinations. Little or no organic solvent is required for any of the procedures.Coupled Subcritical Water Extraction with SPME for Rapid Estimation of Polychlorinated Biphenyls (PCBs), Polycyclic Aromatic Hydrocarbons (PAHs), and Other Organic Concentrations on Soil. A new and very simple approach for determining the concentration of moderately polar and nonpolar organics on solid samples was developed that uses a stainless steel extraction cell loaded with the sample, a few ml of water, and a small gas headspace. Extraction of the organics was performed by simply placing the loaded cell in an oven and heating (e.g., to 250 C) for 15 to 60 minutes. The cell was then cooled and the extracted organics were determined by exposing the extractant water to a SPME needle for 15 minutes, followed by GC analysis. These methods and results are described in detail in Hageman, et al., 1996, and Hawthorne, et al., 1998.
The subcritical water extraction step effectively transfers the analytes to the water phase, but nonpolar organics (e.g., PAHs and PCBs) repartition to the solid sample after the extraction cell is cooled. Therefore, quantitative calibration must account for two unknown equilibria: (1) soil/water partitioning, which occurs as the extraction cell is cooled; and (2) SPME sorption of the analytes from the extractant water.
For PAHs, quantitative calibration was performed by spiking the sample with deuterated PAH internal standards to account for the sample/water and water/SPME partitioning; this approach successfully accounts for both soil/water and SPME/water partitioning of individual PAH species. For PCBs, the chlorine isotope mass spectrometry (MS) pattern makes the use of deuterated (or 13C labeled) congeners as internal standards impossible because their mass spectra overlap with nonlabeled congeners. Therefore, two congeners that do not occur in PCB-contaminated samples, 103 (2,2',4,5',6-pentachlorobiphenyl) and 169 (3,3',4,4',5,5'-hexachlorobiphenyl), were added to the sample prior to subcritical water extraction and SPME analysis to account for the soil/water and water/SPME partitioning. Calibrations based on congener 169 to determine total PCB concentrations gave good agreement with standard methods. For individual congeners, the use of PCB 103 as the internal standard for tri- to pentachlorobiphenyls, and PCB 169 for hexachloro- and more highly chlorinated biphenyls gave good quantitative agreement with standard methods.
It is important in developing the method for PCBs to have an understanding of the mechanism(s) that control the partitioning of individual PCB congeners from the extractant water to the SPME sorbent phase (polydimethylsiloxane). All previous SPME literature reported that the dominant mechanism for hydrophobic solutes was absorption into the phase, and could be predicted based on octanol/water coefficients. In short, the literature indicated that higher molecular weight PCBs would be VERY highly favored over lower molecular weight PCB congeners. This would make calibration of soil/water and water/SPME partitioning required for the quantitative method very difficult. However, initial work on the SPME partitioning of individual PCB congeners clearly demonstrated that the relative amounts of each PCB congener collected by the SPME fiber was reasonably similar, and not varying by the several orders of magnitude predicted by existing absorption theory. Instead, we clearly demonstrated that sorption of PCBs (and other higher molecular weight organics like PAHs) is controlled by adsorption to the fiber surface rather than absorption as predicted by the literature. This result was fortunate for the development of the subcritical water/SPME method for soil analysis (Hawthorne, et al., 1998), because it made the relative sensitivity for the method for different PCB congeners fairly similar, thus greatly simplifying quantitative determinations. In contrast, if absorption was the correct SPME mechanism, the relative sensitivity for different PCB congeners would vary by several orders of magnitude and quantitation of PCBs would be unreasonably difficult (see Yang, et al., 1998, for more details). Understanding the effect of water pH on the SPME sorption of organic acids and bases also was important to the development of the subcritical water extraction/SPME methods. A simple study on the pH effects on SPME sorption coefficients was performed, and the results are described in van Doorn, et al., 1998.
It should be noted that the apparatus used for the subcritical water/SPME determinations was very simple, small, and field portable. All determinations were performed with no organic solvents and with extraction times of 15 to 60 minutes. In addition, storing the water extracts for 24 hours after the subcritical water extraction, but before SPME and GC analysis, did not change the quantitative results for PCB-contaminated soils, demonstrating that soils could be extracted in the field with subcritical water, and 2 ml aliquots could be shipped to a conventional laboratory for SPME and GC analysis.
Coupled Subcritical Water Extraction with SPE Discs. The second approach for very simple extraction methods was developed by coupling subcritical water extraction with standard SPE discs ("Empore" discs). Coupled subcritical water extraction/SPME (discussed above) depends on being able to calibrate for the soil/water and water/SPME equilibria that occur. In contrast, the coupled subcritical water/SPE disc approach quantitatively collects analytes from the water during the subcritical water extraction step. As with the water/SPME method, a major goal was to keep any methods very simple and field-portable. We demonstrated that "Empore" SPE discs (C-18, styrene/divinyl benzene, and polymer-based anion exchange resins) are stable under 250oC subcritical water extraction. Therefore, these SPE discs can be placed in the cell during the heating step to collect extracted organics from the extractant water. The approach developed uses the same simple static extraction vessels described above. The sample soil (1?2 grams), a small portion of a sorbent disc (e.g., 1?2 cm2), and water (3 ml) are placed in the extraction cell and the cell is heated in an oven as described above. In contrast to the coupled water extraction/SPME approach, the water extraction/SPE approach allows contact of the extracted analytes with the collection sorbent during the extraction heated time and as the extraction cell is cooled. As the solubility of the extracted organics (e.g., PAHs) drops as the water is cooled, the organics have a choice of partitioning back to the soil, or to the sorbent resin. Experiments with coal tar-contaminated soil have demonstrated that subcritical water effectively extracts all of the molecular weight range of PAHs (from 128 to 278 amu), and that 80 to 95 percent of the extracted PAHs are collected on the styrene/divinyl benzene disc as the extraction cell is cooled. Increasing the disc size increases the PAH recoveries; however, 2 cm2 of the "Empore" disc is sufficient for 80 percent recovery of the PAHs. Because the recoveries are reproducible (and can easily be accounted for by an internal standard), quantitative results from soil can be achieved using the smaller sorbent discs. However, it is necessary to mix the contents of the cell during the cooling step (using a simple mechanical rotator) to ensure good contact between the extracted PAHs and the sorbent disc. Quantitative determinations of PAHs from a manufactured gas plant soil have been performed with this method and give good agreement with conventional Soxhlet extraction. The discs (with the sorbed PAHs) are stable after extraction (i.e., discs stored for 24 hours to simulate shipping from a field site yield the same results as those analyzed immediately), showing that the extractions can be performed in the field (using only 3 ml of water for each sample), and the discs can be shipped to the laboratory in 2 ml autosampler vials for analysis. Good quantitative agreement for the PAH concentrations on National Institute of Standards and Technology (NIST) certified sediment (SRM 1944) and urban air particulate matter (SRM 1649) also were achieved (these results will be published in the Journal of Chromatography).
Analogous studies using "Empore" discs with the anion-exchange resin were conducted for determining acid herbicides from soil as discussed below.
Incorporating Derivatization Reactions. Subcritical water extraction can be used to aid in hydrolysis or other useful analytical reactions. (Of course, analytes sensitive to hydrolysis may also be destroyed during subcritical water extraction.) Subcritical water extraction/reaction approaches were studied for two systems: (1) the hydrolysis of ester forms of natural pyrethrins (used as insecticide/repellants in many household products) to form chrysanthemic acid, followed by SPME/GC analysis of the resultant parent acid; and (2) the hydrolysis and extraction of acid herbicides from soil, followed by collection on an "Empore" anion-exchange disc. Both approaches yielded simple quantitative methods for subcritical water extraction/derivatization/GC analysis.
Natural pyrethrins typically are determined as chrysanthemic acid (the parent acid of pyrethrins) in flowers and household products. The goal of the investigations was to develop subcritical water conditions (using the simple static cell described above) for the simultaneous extraction and hydrolysis (to chrysanthemic acid) of the natural pyrethrins. Although the hydrolysis of pyrethrins in pure subcritical water (from 100 to 200oC) was slow, the addition of basic alumina yielded very rapid hydrolysis of the pyrethrins to the desired chrysanthemic acid. Following the extraction/hydrolysis step, the extractant water is simply analyzed using SPME and GC/flame ionization detection (FID) or GC/MS to determine the content of chrysanthemic acid. The new method has been applied to determine pyrethrin content in insecticidal shampoo, spray, and dried flowers (the source of the pyrethrins), and was found to give excellent quantitative agreement with standard methods. These methods and results are described in Krapp, et al., 1999.
The use of subcritical water extraction/reaction for the determination of acid herbicides was developed using the "Empore" anion-exchange discs and the simple static extraction cell as described above for PAH determinations. This development was complicated by the expected presence (in environmental samples) of both the ester and acid forms of the herbicides. Because the goal was to determine the total quantity of each herbicide (regardless of whether it was present in the acid or ester form), subcritical water extraction conditions were developed that hydrolyzed the esters to the acid forms, followed by quantitative collection on an "Empore" anion-exchange disc, which was placed in the extraction cell during the subcritical water extraction. Collected herbicide esters then were derivatized by placing the disc in 1 ml of N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) reagent and heating, followed by GC/electron capture detection (ECD) or GC/MS analysis. The method gives good quantitative comparison with EPA Method 8151, and detection limits were < 0.5 ppm for all herbicides tested using ECD or MS detection (refer to Lou, et al., 2000, for details).
Journal Articles on this Report : 6 Displayed | Download in RIS Format
Other project views: | All 15 publications | 6 publications in selected types | All 6 journal articles |
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Hageman KJ, Mazeas L, Grabanski CB, Miller DJ, Hawthorne SB. Coupled subcritical water extraction with solid-phase microextraction for determining semivolatile organics in environmental solids. Analytical Chemistry 1996;68(22):3892-3898. |
R825368 (1997) R825368 (Final) |
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Hawthorne SB, Grabanski CB, Hageman KJ, Miller DJ. Simple method for estimating polychlorinated biphenyl concentrations on soils and sediments using subcritical water extraction coupled with solid-phase microextraction. Journal of Chromatography A 1998;814(1-2):151-160. |
R825368 (1997) R825368 (Final) |
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Krappe M, Hawthorne SB, Wenclawiak BW. Heterogenic catalytic hydrolysis and analysis of natural pyrethrins in subcritical water coupled with solid phase microextraction (SPME) and GC-MS. Fresenius’ Journal of Analytical Chemistry 1999;364(7):625-630. |
R825368 (Final) |
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Lou X, Miller DJ, Hawthorne SB. Static subcritical water extraction combined with anion exchange disk sorption for determining chlorinated acid herbicides in soil. Analytical Chemistry 2000;72(3):481-488. |
R825368 (Final) |
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van Doorn H, Grabanski CB, Miller DJ, Hawthorne SB. Solid-phase microextraction with pH adjustment for the determination of aromatic acids and bases in water. Journal of Chromatography A 1998;829(1-2):223-233. |
R825368 (Final) |
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Yang Y, Hawthorne SB, Miller DJ, Liu Y, Lee ML. Adsorption versus absorption of polychlorinated biphenyls onto solid-phase microextraction coatings. Analytical Chemistry 1998;70(9):1866-1869. |
R825368 (Final) |
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Supplemental Keywords:
soil, sediment, polycyclic aromatic hydrocarbons, PAHs, polychlorinated biphenyls, PCBs, pesticides, green chemistry, organic analysis, field methods., Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Contaminated Sediments, Physics, Environmental Chemistry, Chemistry, Monitoring/Modeling, water extraction, field portable monitoring, contaminated sediment, gas chromatography, PAH, organics, soil, hydrocarbons, sludge, solid phase microextraction, sucritical waterProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.