« Perfluorooctanoic acid levels in human blood (Andrew Szeliga) | Main | Erik Sahlin - Analytical Problem- Brevetoxin levels in Ocean »

Megan Hartmann-Analytical Problem- PFOA and Teflon

Polytetrafluoroethene, commonly known as Teflon, is a polymer that is used in many pots and pans today to make them non-stick. To create Teflon coated pans many companies will use compounds called perfluorooctanoic acid, or PFOA, to act as a surfactant to the Teflon. It has recently been discovered that PFOA is a carcinogenic and persists in the environment for many years. Although most of the PFOA is burnt off when the pans are cured at high temperatures there are still small levels that are given off during the first few times the pans are used. As the pans used small defects can become another source of PFOA's entering the air and the food that is being cooked at the time. Due to the nature of Teflon, it is very easy to scratch pans and cause tiny defects that could later lead to PFOA entering the body or environment. Many companies have said they will no longer use PFOA's by 2015 but will continue to use Teflon. This also causes problems because when Teflon reaches certain temperatures (250oC) it begins to break down and releases a compound similar to PFOA.

UV-Vis absorption spectrometry

Teflon does not absorb in the UV-VIS range due to the fluorine in the compound. The fluorines cause Teflon to have a large band gap and would therefore require a high energy to excite the electrons. PFOA also has a low UV-VIS absorption for the same reason. To use UV-VIS absorption to detect a derivatization of PFOA must occur. One way to do this is by adding benzylamine in N2¬ and xylene using the catalyst Al2¬O3. The solution was then heated at 140°C for ten hours. The derivative was found to absorb at 248 nm or higher and had a molar absorption coefficient of 103.(2) There are not many papers found on UV-VIS absorption for PFOA and Teflon because other methods are more promising for determining if they are present such as LC/MS.(3)

Similar Analytical Problem

One analytical problem similar to mine is DEHP Leaching from PVC into Contents of Medical Devices from Rajvi Mehta. Our problems are similar because they are both polymers leaching out of other substances. Both PFOA and DEHP are detrimental to humans at high levels. Both problems have similar issues when it comes to setting up studies and tests for our analytes. Such as mine there are easily ways to get both positive and negative controls whereas hers, it may be hard to find a negative control.

Chemical Structures and Standards

Perfluorooctonoic Acid
View image

From Sigma-Aldrich, 171468, 5g for $34 or 25g for $130

Teflon
View image

From Sigma-Aldrich, 430935, 5g for $35.40 or 100g for $130

Mass Spectrum using ESI-triple Quad

View image

Kadar, H. "Comparative study of low- versus high-resolution liquid chromatography-mass spectrometric strategies for measuring perfluorinated contaminants in fish." Food additives & contaminants. Part A. Chemistry, analysis, control, exposure & risk assessment 28.9 (2011):1261.


1.King, Anthony. "Sticking point", Chemistry and Industry. 2007, 17, 24-25

2.Lindstrom, Andrew, and A B BLindstrom. "Polyfluorinated Compounds: Past, Present, and Future." Environmental science & technology 45.19 (2011):7954.

3.Huang, Ke, and KHuang. "Determination of trace PFOA in textiles with HPLC-UV spectrometry." 印染 37.9 (2011):37.

Comments

Blog 13? - 1 pt

Tracy, M., Liu, X., and Pohl, C. “Analysis of Perfluorooctane Sulfonate and Perfluorooctanoate in Water Samples Using Reversed-Phase Liquid Chromatography with Suppressed Coonductivity Detection.” Dionex Corporation. 2009.

I was not able to find any information on PFOA being electoractive. Therefore a suppressed conductivity detector could be used to quantify PFOA. This techniques removes ions of the opposite charge of the ones of interest. These are then replaced with either hydronium ion or hydroxide ion depending on what you are detecting. Then using a borate buffer and a anion suppressor the PFOA will be ionized and can be detected.

Blog 9? (-1 pt).
Blog 10. Good answer
Blog 11. What would be the separation conditions? (-0.25).

I was not able to find any articles using capillary electrophoresis analyzing PFOA. This is most likely due to only one of the techniques (CZE) possibly working. MEKC would not work because PFOA and other PFCs being surfactants and therefore cannot be surrounded by another surfactant. PFOA is not an amphiprotic species and therefore cIEF would not work. CGE would not be probable because PFCs all have very similar sizes and it would only separate teflon from the other PFCs which would all have bad separation. CZE may work to separate PFOA from the other PFCs due to the different charges present on the ends of the molecules. Teflon has no charge and can vary in size due to it being a polymer, PFOA has a carboxyl group on the end, and PFOS, for example, has a sulfonic acid group on the end. If I had to pick a detector it would be MS due to absorbance and fluorescence not being practical for Teflon and PFCs.

The best technique for my analytical problem would be, using Reverse Phase HPLC and a mass spec. There were several people who could also use this technique such as:Vinh Tran, John Raia, and Ian Ronningen.

If pressurized extraction is used, what liquid is brought into contact with the pan? (-0.5 pt).

Consider that the extraction procedures will need to be modified to test your hypothesis. For instance, I would be concerned that pressurized extraction does not represent the PFOA loss under normal conditions of cookware usage.

One article used pressurized liquid extraction to remove PFOA from solid samples (Conditions: temperature,
100˚C; extraction time, 16 min; pressure, 100 bar; cell volume 33 mL; static mode, 2 cycles; flush volume, 100% and purge
time, 120 s). They were then blown dry using nitrogen and used for GC/MS. If an air matrix is used by heating up the pans and collecting the released gasses, the collected gas would have to be cooled to a liquid/solid state and then analyzed. The gases collected would contain several different derivations of Teflon. No sample preps of this type were found, therefore the solid matrix may be more plausible.

Lv, Gang, GLV, andLv. "Determination of perfluorinated compounds in packaging materials and textiles using pressurized liquid extraction with gas chromatography-mass spectrometry." Analytical Sciences 25.3 (2009):425.

Good answers for both Blogs 6 and 7

Two types of mass spectrometries used to analyze PFOA are ESI-Q-TOF or ESI-triple quad, or ESE LTQ-Orbitrap. PFOA has a molecular weight of 414.07 g/mol. A picture of a sample MS spectrum can be found above in the post, with relevant details on the graph from an ESI-Triple Quad.

Blog 4. Where is your hypothesis? The studies that you are proposing to do must be designed to test the hypothesis (-0.5 pt).

The answer to Blog 5 is good.

PFOA and Teflon are not fluorescent due to the long carbon chain and the fluorines on the molecule. PFOA and Teflon both have large band gaps and therefore are hard to excite. Instead of using fluorescence and developing a compound that would work, it would be easier to use IR spectroscopy. The carbonyl group on the end of PFOA would have a large broad peak around 3000 cm-1 and another sharp peak at 1780 cm-1. The Teflon does not have the carbonyl group and would therefore not show these peaks; therefore the difference between the two molecules should be very apparent in an IR spectrum.
Skoog, Douglas A., F. James. Holler, and Stanley R. Crouch. Principles of Instrumental Analysis. 6th ed. Belmont, CA: Thomson Brooks/Cole, 2007.

The studies needed for my analytical problem would be to first collect samples of Teflon (PTFE) non-stick surfaces that used PFOA as a surfactant. The control would be a pan with Teflon that did not use PFOA as a surfactant. The problem with this control is that there is speculation that Teflon can be converted to PFOA at high temps, to avoid this yet another control could be used that has neither Teflon or PFOA surfactants. The controls and a variety of different brands of non-stick pans would then be heated up to various temperatures to see if there are any levels of PFOA coming out of the pans during cooking. It is predicted from a USEPA study that there is about 4.3 ppb PFOA in Teflon (PTFE) cookware.
Guo, Zhishi, and X. Liu, and K. Krebs, “Perfluorocarboxylic Acid Content in 116 Articles of Commerce.” National Risk Management Research Laboratory, Environmental Protection Agency, 2009.

My problem involves how chlorinated hydrocarbons accumulate in groundwater and soil, and how the vapors eventually find their way into homes. Our problems are similar because both our analytes are carcinogenic and can persist in the environment for numerous years. We also have a similar matrix (air in homes) where the analyte becomes a vapor and can be deleterious to human health.

In this problem, PFOA is a surfactant that persists after it leaches out of Teflon, which can be compared with the DEHP plasticizer that leaches out of PVC. PFOA is also a carcinogenic, and DEHP has adverse effects that can be equally harmful to the human body.

The problem may need to be refined further. You seem to be addressing several problems at once (-0.1 pt).
What is the hypothesis that you plan to test? (-0.2 pt)
What is the matrix? (-0.2 pt)