Grantee Research Project Results
Final Report: Rapid Field Determination of Organic Contaminants in Water by Solid Phase Microextraction and Infrared Spectroscopy
EPA Grant Number: R825343Title: Rapid Field Determination of Organic Contaminants in Water by Solid Phase Microextraction and Infrared Spectroscopy
Investigators: Tilotta, David C.
Institution: Columbia University in the City of New York
EPA Project Officer: Chung, Serena
Project Period: January 1, 1997 through December 31, 1998 (Extended to December 31, 1999)
Project Amount: $205,350
RFA: Analytical and Monitoring Methods (1996) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Ecological Indicators/Assessment/Restoration , Environmental Statistics
Objective:
The determination of organic compounds in water (such as petroleum hydrocarbons, crop protection chemicals, etc.) is an important means of monitoring for contamination arising from spills or leaking storage tanks. Currently available standard techniques for these analyses include solvent extraction procedures followed by either gravimetric, infrared (IR) spectrometric, or gas chromatographic (GC) determination of the extracted compounds or purge-and-trap techniques followed by GC determination. Although simple and sensitive, these standard methods have three serious disadvantages in that they generally use large quantities of solvents (e.g., hexane or trichlorotrifluorethane), they are generally not adaptable to field implementation, and different methods are required for different analytes (or analyte classes). In this work, we explored a new method of determining these organic compounds using solid-phase microextraction coupled with infrared transmission spectroscopy (SPME/IR). The SPME/IR technique eliminates (or greatly minimizes) the aforementioned disadvantages of the standard methods. Solid-phase microextraction is an equilibrium process that involves selectively concentrating analytes from the aqueous phase into a reusable polymeric solid phase. The sensitivity of SPME (i.e., its effectiveness at preconcentrating) is directly related to the partitioning distribution constant (Kd) of the organic in the solid phase/aqueous phase system. Quantitative SPME analysis is based upon the classical extraction equation: Cs = KdCa (1) where Cs is the concentration of analyte partitioned into the solid phase, Ca is the concentration of analyte in the aqueous phase prior to partitioning, and Kd is the distribution constant of the analyte. Simply, the larger the distribution constant, the greater the preconcentration into the solid phase. Infrared spectroscopy is a technique that is unparalleled with respect to its ability to determine molecular structure. Unlike mass spectroscopy or other analytical methods, IR spectroscopy provides direct information on molecular connectivity (i.e., on how the atoms in a molecule are arranged relative to one another). Typically, absorption "bands" occur in the 2.5 - 40 m (4000 - 400 cm-1) region of the electromagnetic spectrum, and different vibrational changes in a molecule absorb different energies (i.e., wavelengths or wavenumbers). Of course, the pattern of these absorptions (i.e., absorbence versus wavelength or wavenumber [cm-1]) constitutes its infrared spectrum, which functions as a "fingerprint" for the molecule. In the application of IR spectroscopy to SPME, the partitioned analytes are determined directly in a polymeric solid phase film (approximately 4-5 cm2) by measuring their IR absorptions. As opposed to the application of SPME in GC which uses a cylinder of solid or liquid coated on a fiber, this application utilizes a small square of polymer film because it is more compatible with IR spectroscopic sample handling. The specific objectives of this research project were to: (1) identify suitable solid phase films for determining organic contaminants in water by SPME/IR, (2) determine which organic contaminants are amenable to the SPME/IR method, and (3) adapt the basic methodology to field use.Summary/Accomplishments (Outputs/Outcomes):
Solid Phases. We examined approximately 20 films (and explored their analytical properties such as partition times, sensitivities, etc.), and found only four polymers to be "generally" useful. These films were: Parafilm MTM (a wax-impregnated polymer/rubber composite), poly(dimethylsiloxane) (PDMS, an important solid phase material of the SPME syringe technology), Teflon PFATM (a perfluoroalkoxy teflon polymer), and a poly(dimethylsiloxane)/polycarbonate copolymer (MEM-213). Other films (e.g., cyanoacrylate, poly(4-methyl-1-pentene), latex (polybutylene), polystyrene, and poly(methylmethacrylate)) were judged to be not analytically useful because they had excessively long equilibration times (e.g., hours) or exhibited poor sensitivities (e.g., high ppm/percent concentration ranges). Analyte Classes. Four classes of compounds were examined for their suitability as analytes for SPME/IR: crop protection chemicals (using either the Parafilm or the PDMS), petroleum hydrocarbons (using the Teflon PFA), chlorinated hydrocarbons (using either the Parafilm or the PDMS), and nitroaromatic explosives (using the MEM-213 polymer). Formal equilibration times, linear dynamic ranges, detection limits, and precision data for these classes for the appropriate solid phase film were acquired. For the volatile organic compounds (VOCs), equilibration times ranged from 30-300 minutes with limits of quantitation in the mid-ppb range. For the petroleum hydrocarbons, equilibration times were excessively long so the extractions were performed at non-equilibrium (30 minutes). The limits of quantitation for this class were found to be in the 0.5-2 ppm range. The nitroaromatic compounds could be determined after approximately 45 minutes, and provided detection limits in the 50-400 ppb range. Finally, the crop protection chemicals exhibited sensitivities by SPME/IR of 1-5 ppm and equilibration times of 80-120 minutes. For all classes, relative standard deviations (RSDs) were in the range of 3-11 percent for triplicate/quadruplicate determinations. Field and Laboratory Studies of "Real World" Samples. A comparison of the SPME/IR results with the existing U.S. Environmental Protection Agency (EPA) standard methods (e.g., purge-and-trap results or solvent extraction) generally revealed two features. First, the determination of sample concentrations by SPME/IR is somewhat dependent upon the calibration standard used. For example, the determination of total gasoline range organics in water required some knowledge of how "fresh" the sample was to better approximate its composition with the standard. Of course, for true unknowns, inspection of the infrared spectral profile will provide information about the component mixture, so this is not necessarily a serious problem. A second feature of the SPME/IR method is that, similar to the purge-and-trap/GC method, sample dilution will be required for samples that possess an extremely large amount of dissolved or suspended particles (as evidenced by their turbidity). We believe sample dilution provides a means of releasing compounds into the water that had adsorbed/absorbed onto the solids in the wastewater samples. Once diluted, SPME/IR will provide results similar to those of the standard purge-and-trap/GC method for these highly turbid samples. The RSDs obtained for the SPME/IR analyses of natural water samples are typically in the range of 5-20 percent. This degree of precision is acceptable for these types of samples. It should be noted that these RSDs are higher than those obtained by the purge-and-trap analyses. However, the purge-and-trap technique uses an internal standard that significantly improves the precision. To demonstrate that the SPME/IR approach was adaptable to field use, we transported an infrared spectrometer, six stir plates, bottled water (for the calibration standards), assorted glassware, and a 1500W generator to a site in Grand Forks, ND, that had water contaminated with petroleum hydrocarbon waste (e.g., benzene, toluene, ethylbenzene, xylene (BTEX); straight-chain aliphatic hydrocarbons; ethanol, etc.). All equipment was easily transported in a standard 1/4-ton pick-up truck. At the site, we performed total petroleum hydrocarbon (TPH) determinations on three water samples using the SPME/IR procedure developed by Stahl and Tilotta (see first publication below). This procedure employed a Teflon PFA extraction film with infrared detection. To obtain a standard reference, we collected and transported these same samples back to the laboratory for purge-and-trap/GC analysis. Overall, this study showed that SPME/IR could be applied in the field. The results we obtained using SPME/IR in the field compared reasonably well to those obtained in the laboratory. The FT-IR spectrometer and stir plates performed quite well on generator power, and the SPME/IR method demonstrated the degree of ruggedness required for a field method. However, we also noted that it was necessary to calibrate in the field with standard samples. Laboratory calibration, prior to the site work, did not provide an adequate (i.e., a correct) calibration because of differences in temperature, wind, and humidity. Thus, it was determined that site calibration prior to actual analysis is mandatory. General Conclusions. In this study, we developed the technique of SPME/IR for the determination of four classes of organic contaminants in water samples. Specifically, we examined approximately 20 polymer films for their suitability at preconcentrating and quantifying (through IR absorption spectroscopy) crop protection chemicals, petroleum hydrocarbons, chlorinated hydrocarbons, and nitroaromatic explosives. In general, we found SPME/IR to be a sensitive (ppb/ppm range), selective, and fast (approximately 30 minutes) analytical method. The method is generally comparable to the corresponding standard EPA protocols. Additionally, it is environmentally friendly because the films are reusable and the SPME/IR procedure does not require the use of any organic extraction solvents. As advantages, the instrumentation for SPME/IR is inexpensive and readily portable, and optical measurements are inherently simple to perform. However, the application of the SPME/IR technique currently is limited to aggregate determinations (e.g., total petroleum hydrocarbons or total nitroaromatics in water) or simple mixtures (e.g., the BTEX compounds in water) because of the difficulty in quantitating individual components in complex mixtures.Conclusions:
In conclusion, this study suggests that serum Asp13p21 protein is a useful biomarker of the effect of VC exposure. It appears to accurately reflect genetic changes that occur in the target tissue following VC exposure, and it appears to correlate in a highly statistically significant way with estimated cumulative VC exposure and other biomarkers of VC effect. Its detection in individuals exposed below the present permissible workplace exposure levels at a statistically significant rate suggests that the current risk assessment for VC may need to be re-evaluated to consider the use of such biomarkers.Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 6 publications | 4 publications in selected types | All 3 journal articles |
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Type | Citation | ||
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Merschman SA, Lubbad SH, Tilotta DC. Poly(dimethylsiloxane) films as sorbents for solid-phase microextraction coupled with infrared spectroscopy. Journal of Chromatography 1998;829(1-2):377-384. |
R825343 (1998) R825343 (Final) |
Exit |
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Stahl DC, Tilotta DC. Partition infrared method for total gasoline range organics in water based on solid phase microextraction. Environmental Science & Technology 1999;33(5):814-819. |
R825343 (1998) R825343 (Final) |
not available |
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Stahl DC, Tilotta DC. Screening method for nitroaromatic compounds in water based on solid-phase microextraction and infrared spectroscopy. Environmental Science & Technology 2001;35(17):3507-3512. |
R825343 (Final) |
not available |
Supplemental Keywords:
chemicals, toxic substances, volatile organic compounds, VOCs, nonaqueous phase liquid, NAPL, clean technologies, waste minimization, analytical, measurement methods, agriculture, petroleum, environmental chemistry., Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Physics, Chemistry, Monitoring/Modeling, Engineering, environmental monitoring, water extraction, gas chromatography, PAH, FTIR, rapid field determination, hydrocarbons, spectroscopic, chromatograph, solid phase microextraction, Fourier transform infrared, organic contaminantsProgress 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.