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Lauren Sauer- Analytical Problem- Vapor intrusion in buildings

Trichloroethylene and Tetrachloroethylene are resistant to breakdown by biological processes, which causes them to accumulate in soil and groundwater. These chlorinated hydrocarbons are released into the air as vapors and find their way into the indoor air of overlying homes and buildings. Relatively low concentrations of these volatile compounds can cause major indoor problems and are a health risk. They need to be able to be detected in the vapor form to decide whether land can be developed or added to the Superfund National Priority List for bioremediation.

The hypothesis is that these compounds are being released into the environment by industrial plants because of improper disposal. Trichloroethylene was used for many years in dry cleaning until the mid 1960's when its toxicity was called into question and it was replaced by halothane. Tetrachloroethylene was also used widely in dry cleaning and textile processing until recently when its safety was also questioned.

Sources:

1. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Tetrachloroethylene (Update). U.S. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. 1997.

2. Hanson, D. J. (2011). EPA moves on vapor intrusion. Chemical and Engineering News, 89(16), 32-34.

UV-Vis absorption spectrometry

Reagent grade TCE (trichloroethylene) in distilled, deionized water has a molar absorptivity of less than 10 L/mol cm for wavelengths longer than 260 nm, absorbances less than 4x10^-3, a concentration of 50 ppm, and a path length of 1.3 cm (1).

PCE (tetrachloroethylene) has a molar absorption coefficient of 225 L/mol cm at 254 nm in an aqueous solution of water (3).

PCE has a maximum wavelength, where the absorbance for a 10 mm pathlength of solvent exceeds 0.05 absorbance unit, of 320 nm. TCE has a maximum wavelength that slightly exceeds 400 nm under the same conditions (2).

Sources

1. Ahmed, Sohailuddin; Ollis, David F. Solar Photoassisted Catalytic Decomposition of the Chlorinated Hydrocarbons Trichloroethylene and Trichloromethan. Solar Energy 1984, 32, pp 597-601

2. Kaye and Laby Tables of Physical and Chemical Constants, http://www.kayelaby.npl.co.uk/chemistry/3_8/3_8_7.html (accessed 9/29/11).

3. Mertens, Ralf; Sonntag, Clemens von. Photolysis of Tetrachloroethene in Aqueous Solution. Journal of Photochemistry and Photobiology 1995, 85, pp 1-9.


Similar Analytical Problems

My analytical problem is similar to Shengsi Liu's CO Detections in Post Combustion Fuel. His matrix is fuel exhaust fumes and his hypothesis is that the exhaust of internal combustion engines contains a slight amount of CO which can be collected and analyzed in order to find the concentration of CO per volume. This is important because of the toxicity of carbon monoxide and its contamination of air quality. My problem is also similar to Nur Marzuki's Liquified Petroleum Gas in insecticide aerosol. Her analyte is LPG and her matrix is the insecticide aerosol. This is important to find also because of health reasons. Insecticide is sprayed directly on to the skin and absorbed into the bloodstream. If hazardous chemicals are being absorbed it is imperative to know so that a safer compound can be employed in the spray.

Our studies should be similar because we are all testing the concentration of a vapor in the air. Shengsi also has a similar analyte. They are both carbon based with relatively small molecular weights.

Nur, Shengsi and my studies will differ because they are both studying a matrix where the analyte is always present and can fairly easily be tested for. My analyte may not always be present in the vapor form even if it is present in the soil or groundwater. It is important to measure it in the vapor form because land contaminated with my analytes, TCE and PCE, can not be put on the National Superfund list for remediation unless these chemicals are present in the vapor form. Our studies will also differ because we have different matrices. Nur is dealing with the other components contained in aerosol sprays and Shengsi has to account for the other compounds in exhaust fumes, whereas my matrix is the air.

Studies needed to investigate my analytical problem

Hypothesis: TCE and PCE are being released into the environment because of their improper disposal by industrial plants utilizing them for dry cleaning products, metal degreasing, pharmaceutical production, weapons production, and pesticide formation.


(A) Identify soils and water that test positive for TCE and PCE. (There is already a list of known contaminated sites created by the EPA)
(B) Measure TCE and PCE vapor levels in regions of known contaminated soil and groundwater as well as known uncontaminated soil and groundwater (areas in forests not near buildings or weapons testing sites).
(C) Based on levels found, create a study in the laboratory to figure out how much TCE and PCE are released as vapors when soil or groundwater are contaminated.
(D) Create a calibration curve that represents ppm of analyte in groundwater or soil versus ppm of analyte in the air above groundwater or soil. This is important because land contaminated with PCE and TCE can only be put on the national superfund list for remediation if the air is contaminated, not the soil.

Alternative studies:
(E) Study how TCE and PCE are released into the air from soil or groundwater and in what concentrations.
(F) Figure out which factors increase the rate of TCE and PCE being released into the air.


Slight lightheadedness was reported by six male volunteers exposed to PCE at a concentration of 210-240 ppm for over 30 minutes. Increased host (mice) susceptibility to pulmonary bacterial infection occured after a 3-hour inhalation exposure to 50 ppm PCE. 63% of male mice developed hepatocellular carcinoma compared to the control at 35% when exposed to 100 ppm PCE for 103 weeks. Because of this I would put the detection level in air at 50 ppm.

1. Agency for Toxic Substances and Disease Registry. Toxicological Profile for Tetrachloroethylene (Update). U.S. Public Health Service, U.S. Department of Health and Human Services, Atlanta, GA. 1997.

Fluorescence Techniques

While the chlorine atoms in Trichloroethylene and tetrachloroethylene can be used as quenching agents in other molecules, TCE and PCE by themselves do not fluoresce. Neither TCE nor PCE have conjugated double bonds that are necessary for fluorescence. One article suggested adding a fluorescent dye such as Red Nile, which is TCE soluble but water insoluble. While this does make the molecule fluoresce, it is ineffective for distinguishing TCE and PCE from impurities when the analytes are found in a soil matrix. As a control, Freon 113 and pure TCE samples were added to previously centrifuged TCE contaminated soil samples. Most of the samples contained large numbers of shell fragments that fluoresced. Because of this, the minimal amount of TCE in the sample could not be distinguished from the impurities.

TCE is an alkene that will have a =C-H bend somewhere between 995-685 cm-1. Unfortunately this is in the fingerprint region and could be difficult to identify. Both TCE and PCE have a medium C=C stretch between 1680-1620 cm-1. Alkenes are very common compounds and an IR soil sample containing TCE or PCE could also contain numerous other alkenes. TCE and PCE found in the air will most likely not have other alkenes present because air contains approximately 20.95% oxygen, 0.03% carbon dioxide, 0.93% argon, and 78.09% nitrogen. None of these air components are an alkene. Because of this gas chromatography/ Fourier transform infrared spectroscopy could be used.

Because it is so difficult to distinguish the difference between dyed TCE and dyed PCE and other contaminants in soil I would not recommend any instrument that measures fluorescence. I'm not sure how you would dye TCE and PCE vapor that is released from soil, so there wouldn't be any way to make it fluoresce. Because of this I would recommend gas chromatography/ Fourier transform infrared spectroscopy to detect TCE and PCE in the air.


1. Griffin, Terry W.; Watson, Kenneth W. A Comparison of Field Techniques for Confirimg Dense Nonaueous Phase Liquids. GWMR. 2002, 22, 48-59.

2. Mohrig, Jerry R.; Hammond, Christina N.; Schatz, Paul F. Techniques in Organic Chemistry, 3rd ed.; W.H. Freeman and Company: New York; pp 464.

3. Smith, James S. Does Peer Review Mean That the Paper Is Scientifically Defensible? Trillium. 2002, 5, 1-5.


Chemical structure and standards

TCE
View image
(Sigma-Aldrich)

PCE
View image
(Sigma-Aldrich)

Sigma-Aldrich sells 5 mL analytical standard TCE, for environmental analysis (Fluka) for $38.60
catalogue number: T1115 (WWW Chemicals)

Sigma-Aldrich also sells 5 mL analytical standard PCE for $37.20
catalogue number T1023 (WWW Chemicals)

Sigma-Aldrich. http://www.sigmaaldrich.com/catalog/ProductDetail.do?lang=en&N4=02666|FLUKA&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC (accessed Oct 24, 2011)

WWW Chemicals
http://www.chem.com/catalogs/ (accessed Oct 24, 2011)


Mass Spectrums

TCE
View image

PCE
View image


Chromatographic techniques

For my analytical problem, gas chromatography would be the best choice for analysis. Both TCE and PCE need to be detected in the vapor form. Because the matrix is air, size-exclusion chromatography doesn't make much sense. Neither does chiral chromatography since the analytes are not chiral. It would be difficult to use any other form of chromatography since the analytes must be in the vapor form and are in ppb concentrations in the air.

A Supelco Equity-5 capillary column (30 m long, 0.25 mm inner diameter, 0.25 µm film thickness, Sigma-Aldrich) could be used. They can be purchased from Sigma-Aldrich for $450.00 (catalogue number 28089-U). An AS 2000 autosampler (Fisons) can be used with Helium as the carrier gas with a constant column head pressure of 60 kPa. The temperature is programmed to 40 °C for 7 minutes and then ramped to 130 at 30 °C/min and held for one minute. A quadripole MS system can be used to detect TCE and PCE levels using flame ionization. Flame ionization is ideal because of its sensitivity to hydrocarbons. It is not an issue that the sample is destroyed because it is not needed for further analysis.

Some indoor and above soil air samples were found to have interfering VOCs that could not be chromatographically removed. Because of this they require 2-D GC separation using DB-Wax as a polar phase and DB-MTBE as the nonpolar phase. This required the use of an aluminum oxide/ sodium sulfate PLOT column that is 50 m in length and 0.32 mm inner diameter. Ambient air samples can be acquired at a flow rate of 15 mL/min for 40 min. Quantification was also be performed using flame ionization and a q-MS system.

References
1.Aeppli, Christoph; Holmstrand, Henry; Andersson, Per; Gustafsson, Orjan. Direct Compound-Specific Stable Chlorine Isotope Analysis of Organic Compounds with Quadrupole GC/MS Using Standard Isotope Bracketing. Anal. Chem. 2010, 82, 420-426.

2.Air and Waste Management Associtation. Field Method Comparison between Passive Air Samplers and Continuous Monitors for VOCs and NO2 in El Paso, Texas. J. Air and Waste Manage. Assoc. 2004, 54, 307- 319.

3.http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=28089U|SUPELCO&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC

4.Kim, Sun Kyu; Chang, Hungwei; Zellers, Edward T.; Microfabricated Gas Chromatograph for the Selective Determination of Trichloroethylene Vapor at Sub-Parts-Per-Billion Concentrations in Complex Mixture. Anal. Chem. 2011, 83, 7198-7206.


BLOG 10. Problems using similar techniques

My preferred technique is GC-FTMS. Other analytical problems that are using the same technique are Nur Marzuki and Melissa Eubanks. Nur is using GC-MS to detect liquefied petroleum gas in insecticide aerosol, while Melissa is also using GC-MS to detect silicones (decamethylcyclopentasiloxane) in drain water and marine organisms.

Blog 11. Capillary electrophoresis technique

I could not find any instances where TCE or PCE were measured in the environment by way of capillary electrophoretic separations. Measuring it as a gas would be extremely difficult using this method if at all possible. If you were to measure their concentrations in a soil sample, the sample would have to be ground up extremely small to be able to fit into the tube. It is possible that the soil sample could be soaked in water and then the soil is filtered out, but I'm not sure how much of the soluble TCE and PCE would be in the filtrate and how much would still be present in the soil sample.

If a method was found to prepare a sample for my analytical problem I would not use cIEF because TCE does not have a proton to give up or the ability to receive one. MEKC would make distinguishing my analytes from each other difficult since they are so close in size. I would not use CGE because I don't believe it is possible to get the gas into the gel. Because of all these limitations I would use CZE with an MS detector, but I do not believe this is a reliable source for measurement. I would use an MS detector because of the low level of analytes that will be present in the sample.

BLOG 13. Analytical electrochemistry

TCE and PCE are not electroactive. Because of this I would use a conductivity detector in a chromatography column. This sensor consists of two electrodes that are housed in a glass flow cell. One electrode is grounded. The detector can sense an electrical impedance when ions move through the sensor cell, allowing for the collection of data.

An AC voltage is used when running a current across the electrodes in order to avoid electrode polarization. This occurs with DC voltage because of the generation of gases at the electrode surface.

For an electrical conductivity detector a sensitivity of 5x10^-9 g/mL is expected. The linear dynamic range is around 5x10^-9 to 1x10^-6 g/mL and the response index is 0.97 to 1.03.

References:

Scott, Raymond P. W.; Ion Chromatography: The Electrical Conductivity Detector. http://www.chromatography-online.org/ion-chromatography/Detectors-for-Ion-Exchange-Chromatography/The-Electrical-Conductivity-Detector.html.

Comments

Blog 13. Good answers.

BLOG 13. Analytical electrochemistry

TCE and PCE are not electroactive. Because of this I would use a conductivity detector in a chromatography column. This sensor consists of two electrodes that are housed in a glass flow cell. One electrode is grounded. The detector can sense an electrical impedance when ions move through the sensor cell, allowing for the collection of data.

An AC voltage is used when running a current across the electrodes in order to avoid electrode polarization. This occurs with DC voltage because of the generation of gases at the electrode surface.

For an electrical conductivity detector a sensitivity of 5x10^-9 g/mL is expected. The linear dynamic range is around 5x10^-9 to 1x10^-6 g/mL and the response index is 0.97 to 1.03.

References:

Scott, Raymond P. W.; Ion Chromatography: The Electrical Conductivity Detector. http://www.chromatography-online.org/ion-chromatography/Detectors-for-Ion-Exchange-Chromatography/The-Electrical-Conductivity-Detector.html.

Good answers for blogs 9, 10, and 11. If you ultimately consider using FTMS as a detector for a GC separation, you need to factor into your selection the cost of an FTMS (i.e, > $500,000). Do you need to have such a high-end instrument? Can you use an MS with lower resolution?

I could not find any instances where TCE or PCE were measured in the environment by way of capillary electrophoretic separations. Measuring it as a gas would be extremely difficult using this method if at all possible. If you were to measure their concentrations in a soil sample, the sample would have to be ground up extremely small to be able to fit into the tube. It is possible that the soil sample could be soaked in water and then the soil is filtered out, but I’m not sure how much of the soluble TCE and PCE would be in the filtrate and how much would still be present in the soil sample.

If a method was found to prepare a sample for my analytical problem I would not use cIEF because TCE does not have a proton to give up or the ability to receive one. MEKC would make distinguishing my analytes from each other difficult since they are so close in size. I would not use CGE because I don’t believe it is possible to get the gas into the gel. Because of all these limitations I would use CZE with an MS detector, but I do not believe this is a reliable source for measurement. I would use an MS detector because of the low level of analytes that will be present in the sample.

BLOG 10. Problems using similar techniques

My preferred technique is GC-FTMS. Other analytical problems that are using similar techniques are Nur Marzuki and Melissa Eubanks. Nur is using GC-MS to detect liquefied petroleum gas in insecticide aerosol, while Melissa is also using GC-MS to detect silicones (decamethylcyclopentasiloxane) in drain water and marine organisms.

Chromatographic techniques

For my analytical problem, gas chromatography would be the best choice for analysis. Both TCE and PCE need to be detected in the vapor form. Because the matrix is air, size-exclusion chromatography doesn’t make much sense. Neither does chiral chromatography since the analytes are not chiral. It would be difficult to use any other form of chromatography since the analytes must be in the vapor form and are in ppb concentrations in the air.

A Supelco Equity-5 capillary column (30 m long, 0.25 mm inner diameter, 0.25 µm film thickness, Sigma-Aldrich) could be used. They can be purchased from Sigma-Aldrich for $450.00 (catalogue number 28089-U). An AS 2000 autosampler (Fisons) can be used with Helium as the carrier gas with a constant column head pressure of 60 kPa. The temperature is programmed to 40 °C for 7 minutes and then ramped to 130 at 30 °C/min and held for one minute. A quadripole MS system can be used to detect TCE and PCE levels using flame ionization. Flame ionization is ideal because of its sensitivity to hydrocarbons. It is not an issue that the sample is destroyed because it is not needed for further analysis.

Some indoor and above soil air samples were found to have interfering VOCs that could not be chromatographically removed. Because of this they require 2-D GC separation using DB-Wax as a polar phase and DB-MTBE as the nonpolar phase. This required the use of an aluminum oxide/ sodium sulfate PLOT column that is 50 m in length and 0.32 mm inner diameter. Ambient air samples can be acquired at a flow rate of 15 mL/min for 40 min. Quantification was also be performed using flame ionization and a q-MS system.


Aeppli, Christoph; Holmstrand, Henry; Andersson, Per; Gustafsson, Orjan. Direct Compound-Specific Stable Chlorine Isotope Analysis of Organic Compounds with Quadrupole GC/MS Using Standard Isotope Bracketing. Anal. Chem. 2010, 82, 420-426.

http://www.sigmaaldrich.com/catalog/ProductDetail.do?N4=28089U|SUPELCO&N5=SEARCH_CONCAT_PNO|BRAND_KEY&F=SPEC

Kim, Sun Kyu; Chang, Hungwei; Zellers, Edward T.; Microfabricated Gas Chromatograph for the Selective Determination of Trichloroethylene Vapor at Sub-Parts-Per-Billion Concentrations in Complex Mixture. Anal. Chem. 2011, 83, 7198-7206.

Blog 8? (-1 pt)

Blog 6. Good answers.
Blog 7. I am not convinced that ICP is a good ionization source.

Mass Spectrometry

GC/CF-IRMS where the ms is a magnetic sector

Gas Chromatography coupled with continuous flow isotope-ratio mass spectrometry can be used. Intact noncombusted chlorinated ethylene molecules can be directly transferred in a helium carrier stream to the IRMS ion source. Electron ionization is a good choice for an ionization source for a gas because its beam has an energy of 50~100 eV, which provides excellent stability, linearity, and high ionization yield. If EI is unavailable inductively coupled plasma (ICP) and thermal ionization (TIMS) can also be used. The precision with TIMS is better than that possible with ICP-MS. Once the molecules are ionized and fragmented, selected isotopologue ions or isotopologue ion fragments are recorded. TCE and PCE standards can be calibrated to Standard Mean Ocean Chloride (SMOC).

GC/Q-TOF
Gas Chromatography/Quadripole Time of Flight can also be used. Samples can be preconcentrated by a purge and trap system (PTA 3000). Electron Ionization can be used.

GC/CF-IRMS provides a high precision for a narrow range of compounds, while the GC/Q-TOF is known to be less precise, but universal with respect to target analytes.

TCE
Molecular weight: 131.39 g/mol
Mass of molecular ion: 130

PCE
Molecular weight: 165.83 g/mol
Mass of molecular ion: 164

(spectrums can be seen in the blog posting)

Bernstein, Anat; Shouakar-Stash, Orfan; Ebert, Karin; Laskov, Christine; Hunkeler, Daniel. Compound-Specific Chloring Isotope Analysis: A Comparison of Gas Chromatography/ Isotope Ratio Mass Spectrometry and Gas Chromatography/Quadripole Mass Spectrometry Methods in an Interlaboratory Study. Anal Chem. 2011, 83, 7624-7634.

Good answers for BLOG 4 and 5.

BLOG 3? Parts (b) and (c)? (-0.5 pt)

What type of industrial plants may release the compounds of interest? From your blog it sounds as if their use has been discontinued.

What is the matrix in which your analyte is found? Although I appreciate that you know the answer, it is not explicitly state (-0.1 pt).