1. Monitoring the desorption of analytes from nonpolar SPME fibers using high speed gas chromatography Authors: Kimberly Jasch, Tony Borgerding* Department of Chemistry, University of St. Thomas, St. Paul, MN 55105 Introduction  Why study this?  Volatile Organic Compounds (VOCs) Can be found all over the world  Many are toxic i.e. over exposure to benzene can contribute to leukemia  Very reactive in the atmosphere i.e. methane contributes to global warming  How do we study this?  Gas chromatography is a widely accepted practice used to separate and identify compounds.  However, not an efficient method for continuous monitoring.  Other methods that could be used for monitoring are forms of spectroscopy (MS or IR).  However, these are not practical for identifying between similar molecules.  Typically, an analyte is injected into a long capillary column where a Flame Ionization Detector (FID) detects a signal which is sent to a recording device.  Longer columns means long separation times of 15 minutes or longer  Concentrations can change significantly in that time interval  Continuous monitoring the presence of VOCs is not possible  Solution?  High speed gas chromatography (HSGC) fast separation continuous monitoring possible  Goals  Make using the GC for monitoring a more efficient process  Use the developed HSGC process to monitor more complex systems Results  Separation of BTEX  Completed in as fast as 5.4 seconds Refer to Figure 4  Desorption Time and Injection Variation  Effect of Flow Refer to Figure 5 Peaks will come off faster Note: differences in integrated results within each graph are independent of the flow rates Retention times remain constant PDMS tends to hold analyte longer than carboxen  Effect of Temperature Amplitudes of peaks increase significantly Temperatures of 70˚C and lower will have good resolution. No changes in retention times of BTEX Note: each peak in Figure 6 is separated into four separate peaks like those in Figure 4  Carboxen vs. PDMS On average, PDMS will release the analyte slower as the flow rates increase Amplitudes from PDMS consistently greater than those given from Carboxen Refer to Figure 7 for integrated results of the signals recorded  Fast, reproducible gas chromatography will be good for monitoring: Extractions Environmental processes  Smaller oven unit Portable HSGC to be brought outdoors  More investigation on desorption from SPME Analytes beyond BTEX Nonpolar and polar analytes Future Exploration  Gas Chromatography Apparatus  Hewlett Packard 5890A Chromatograph with a Flame Ionization Detector (FID)  Uses a 6-port valve secured to the ceiling of the oven  Samples made in 1-liter Tedlar sampling bag with septa  Gaseous samples injected with syringe or SPME and pushed through the valve with a flow of helium gas.  When injected, sample travels through column, separates, and is detected by FID  Diaphragm Valve  6-port, 2-position diaphragm valve. Requires only a small amount of pressure to switch positions Figures 1 and 2 Quick injection pulses possible  Injection Pulse  Narrower injection pulse allows for less sample to be placed into the loop Better resolution More reproducibility  Pulses of 6ms were possible from the diaphragm valve  Pulses of 5ms or less, consistency is lost  Sampling  benzene, toluene, ethylbenzene, and o-xylene  8  L of each syringed into 1-L bag  Solid-Phase Microextractor (SPME)  What is it? Refer to Figure 3 A sampling device for liquids or gases Nonpolar fibers of PDMS or Carboxen were used HSGC can monitor the desorption of the analytes from the fibers  Limitations: not many studies of desorption time performed Methods a.) b.) Figure 1 - Plunger Position of Diaphragm Valve Figure 4 - BTEX Separation Figure 5 - Various flows with a.) PDMS and b.) carboxen fibers. Figure 2 - Direction of flow in diaphragm valve a.) load position, b.) inject position a.)b.) Figure 6 - Effect of peak amplitude and desorption time of a.) 70˚C and b.) 40˚C injector temperature a.) b.) Figure 7 - Comparing PDMS and carboxen fibers in amplitudesand desorption time. Runs performed at 5mL/min with an injector temperature of 30˚C. Picture taken from Valco catalogue Figure 3 - SPME Device Picture taken from works by Pawliszyn