Methods Monitoring Polar Compounds Using Membrane Extraction and High-Speed Gas Chromatography Authors: Jonathan Maurer, Dr. Anthony J. Borgerding* Department of Chemistry, University of St. Thomas, St. Paul, MN Introduction  Overview  Volatile organic compounds (VOCs) are found throughout our environment and can be toxic to humans.  The dangers of VOCs make their monitoring important, and many methods have been devised to do so.  Much of this research has focused mostly on analyzing nonpolar compounds, largely ignoring polar analytes.  Solid phase microextraction (SPME) is one technique that has been explored in the analysis of polar compounds.  However, there is great room for improvement in this area of monitoring.  Goal  Devise a method that can be used to monitor polar analytes in living systems Main compounds to monitor: methanol, ethanol, acetaldehyde Acetaldehyde, a toxic metabolite of ethanol, has yet to be monitored  Present Study  Therefore, a process to develop previous and new techniques into a usable method was investigated.  Using high-speed gas chromatography (HSGC), various techniques were attempted to monitor polar compounds.  HSGC enables rapid separation of compounds, which means it is possible to monitor a system. Semi-permeable membranes Nafion tubing Custom-made SPME fibers coated with liquid Nafion Results & Discussion  Diaphragm Valve Installation  Diaphragm valve more physically efficient (See Figure 1) Shortest possible injection time = 6 ms  75 ms was shortest attained in previous testing with 2-position rotor valve Faster separation, more reproducible, more effective monitoring  Silicon Membrane Systems  System not used to monitor polar compounds, but as a model for later systems  Data gave representation of how analytes permeate through a membrane (Figure 3)  Future work will continue the development of techniques to monitor polar compounds, specifically methanol, ethanol, and acetaldehyde.  Nafion-coated SPME fibers are promising, but more work is needed to enable monitoring in solution Rougher, more porous fiber surface so that coating does not scrape off so easily More uniform coatings, perhaps glued onto fiber, again to keep coating intact in solution  Another custom SPME fiber, made of anodized aluminum, showed some capability for monitoring polar compounds Studies done by other scientists left room for exploration into the monitoring ability of the fiber Implications and Future Work  Gas Chromatography System  Hewlett Packard 5890A Chromatograph with an FID  Used a 6-port, 2-position diaphragm valve secured to the ceiling of the oven (Figure 1) Actuated by a 3-port solenoid valve Solenoid driven by a pulse generated by computer program  Positive flow system connected to sample port of valve so controllable flow could continuously flush sample into valve to be injected (Figure 2)  Sample Preparation  Gas samples made in 1-liter sample bags with septum  Aqueous samples prepared in 20 mL vials and 250 mL flasks Typical concentrations between 1 and 20 parts per million (1,000-20,000 ng/mL)  Silicon Membrane Systems  Systems constructed so that a flow could be obtained through membrane and into sample port of diaphragm valve (Figure 2)  Analytes permeated through membrane and were carried by helium flow into GC to be monitored  Nafion Tubing Systems  Systems constructed much like silicon membrane systems Nafion tubing integrated into flow system using compression fittings and epoxy  Nafion-coated SPME Fibers  Initially, fused-silica rods from commercial SPME fibers were used  These rods were extremely fragile, so custom fibers were made from syringe cleaning wire (~.25 mm diameter)  Fibers then dipped in liquid Nafion until coating was visible Figure 2: Diagrams of GC and silicon membrane systems Figure 1: Diagram of physical operation of diaphragm valve Images taken from Valco catalog Load PositionInject Position  Nafion Tubing Systems  Only high concentrations of methanol in water (> 1 part per thousand or 1,000,000 ng/mL) could be detected with system placed in headspace  System submerged in solution was more sensitive (Figure 4), but detection limits still too high for effective monitoring (> 10 part per million or 10,000 ng/mL)  Permeation times much greater than for silicon membranes Adsorption: ~ 3-5 minutes vs. 1-2 minutes for silicon membranes Desorption: > 1 hour vs. ~10 minutes for silicon membranes Figure 3: 10 ppm sample of toluene (dissolved in methanol) in water. First peak = methanol. Second peak = toluene  Nafion-coated SPME Fibers  Commercial SPME fibers are typically used for analysis of nonpolar compounds  Nafion, a polar substance, was coated on a SPME fiber and used to detect polar analytes  Nafion fibers performed ~10 times better than commercial fibers in the detection of methanol (Figure 5)  To be useful in natural systems the fiber must be able to monitor in a liquid environment Nafion coating swelled and was stripped off metal fiber when placed in solution, so no results could be obtained -- more work needed Figure 4: 1% methanol in water solutions used in both trials. Top = Nafion tubing placed in headspace of flask. Bottom = Nafion tubing submerged in solution. Figure 5: 20 ppm methanol in water solutions used in both trials. Left = Poly(dimethylsiloxane) SPME fiber. Right = Nafion SPME fiber