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- Reference Material on InstrumentationArticle - A High Temperature Direct Probe for a Mass Spectrometer Design of a Direct Exposure Probe and Controller for use ona Hewlett-Packard 5989 Mass Spectrometer SIS AP1000 AutoProbe™ SIS AP2000 AutoProbe™ - Description of System HPP7: Direct Probe Electronics Console HPP7: Direct Probe for the Agilent (HP) 5973/5975 MSD HPP7: HP Direct Probe Application Notes HPP7: Installation Directions for the Direct Probe HPP7: Side Cover for the HP 5973 MSD HPP7: Support HPP7: Probe Inlet System for the Agilent (HP) 5973 and 5975 MSD with Automatic Indexed Stops HPP7: Theory of Operation of the Direct Probe and Probe Inlet System Direct Thermal Extraction Thermal Desorption Application Notes Environmental Thermal Desorption Application Notes Food Science Thermal Desorption Application Notes Forensic Thermal Desorption Application Notes GC Cryo-Trap Application Notes Headspace Application Notes Purge & Trap Thermal Desorption Application Notes Theory of Operation of the AutoDesorb® System AutoDesorb Notes for SIS Dealers Adsorbent Resin Application Notes Installation of the Short Path Thermal Desorption System on Agilent (HP) and Other GCs Installation of the Short Path Thermal Desorption System on a Varian 3400 GC AutoDesorb® System Development Team Thermal Desorption Applications and Reference Materials Installation of the Short Path Thermal Desorption System - TD5 Part I - Design & Operation of the Short Path ThermalDesorption System Installation Instructions for the Model 951 GC Cryo-Trap on the HP 5890 Series GC Installation Instructions for the Model 961 GC Cryo-Trap on the HP 5890 Series GC Operation of the Model 951/961 GC Cryo-Trap SIS GC Cryo Traps - Theory of Operation NIST/EPA/NIH Mass Spectral Enhancements - 1998 version (NIST98) SIMION 3D Ion Optics Class Mass Spectrometer Source Cleaning Methods MS Tip: Mass Spectrometer Source Cleaning Procedures Mass Spec Source Cleaning Procedures Micro-Mesh® Abrasive Sheets Research Papers Using New Era Syringe Pump Systems EI Positive Ion Spectra for Perfluorokerosene (PFK) Cap Liner Information How do I convert between fluid oz and milliliters? Which bottle material should I choose? Which bottle mouth should I choose? The Bottle Selection Guide CGA Connections for Gas Tanks Chemical Reaction Interface Mass Spectrometry (CRIMS)
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- AccessoriesTD Supply Kit Desorption Tubes Adsorbent Resins Desorption Tube Needles Desorption Tube Seals Desorption System Fittings GC Cryo-Trap Extraction Cell TD Sample Loader Prepacked, Conditioned Desorption Tubes Desorption Tube Packing Accessories Stainless Steel Purge Heads Injection Port Liners Tenax TA Poster TD Application Notes Customer Service
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- Thermal Desorption Applications and Reference MaterialsDirect Thermal Extraction Headspace Environmental Food Science Applications Pharmaceuticals Forensic Note 103: EPA Method 325B, Novel Thermal Desorption Instrument Modification to Improve Sensitivity Note 102: Identification of Contaminants in Powdered Beverages by Direct Extraction Thermal Desorption GC/MS Note 101: Identification of Contaminants in Powdered Foods by Direct Extraction Thermal Desorption GC/MS Note 100: Volatile and Semi-Volatile Profile Comparison of Whole Versus Cracked Versus Dry Homogenized Barley Grains by Direct Thermal Extraction Note 99: Volatile and Semi-Volatile Profile Comparison of Whole vs. Dry Homogenized Wheat, Rye and Barley Grains by Direct Thermal Extraction GC/MS Note 98: Flavor and Aroma Profiles of Truffle Oils by Thermal Desorption GC/MS Note 97: Flavor Profiles of Imported and Domestic Beers by Purge & Trap Thermal Desorption GC/MS Note 95: Detection of Explosives on Clothing Material by Direct and AirSampling Thermal Desorption GC/MS Note 94: Detection of Nepetalactone in the Nepeta Cataria Plant by Thermal Desorption GC/MS Note 93: Detection of Benzene in Carbonated Beverages with Purge & Trap Thermal Desorption GC/MS Note 88: Analysis of Silicone Contaminants on Electronic Components by Thermal Desorption GC-MS Note 84: Vacuum Pump Exhaust Filters - Charcoal Exhaust Traps Note 83: Vacuum Pump Exhaust Filters - Oil Mist Eliminators Note 82: Vacuum Pump Exhaust Filters Note 80: Design, Development and Testing of a Microprocessor ControlledAutomated Short Path Thermal Desorption Apparatus Note 79: Volatile Organic Compounds From Electron Beam Cured and Partially Electron Beam Cured Packaging Using Automated Short Path Thermal Desorption Note 77: The Determination of Volatile Organic Compounds in VacuumSystem Components Note 75: An Apparatus for Sampling Volatile Organics From LivePlant Material Using Short Path Thermal Desorption Note 73: The Analysis of Perfumes and their Effect on Indoor Air Pollution Note 71: Flavor Profile Determination of Rice Samples Using Shor tPath Thermal Desorption GC Methods Note 65: Determination of Ethylene by Adsorbent Trapping and Thermal Desorption - Gas Chromatography Note 64: Comparison of Various GC/MS Techniques For the Analysis of Black Pepper (Piper Nigrum) Note 63: Determination of Volatile and Semi-Volatile Organics in Printer Toners Using Thermal Desorption GC Techniques Note 60: Programmable Temperature Ramping of Samples Analyzed ViaDirect Thermal Extraction GC/MS Note 57: Aroma Profiles of Lavandula species Note 55: Seasonal Variation in Flower Volatiles Note 54: Identification of Volatile Organic Compounds in Office Products Note 43: Volatile Organic Composition In Blueberries Note 42: The Influence of Pump Oil Purity on Roughing Pumps Note 41: Hydrocarbon Production in Pine by Direct Thermal Extraction Note 40: Comparison of Septa by Direct Thermal Extraction Note 39: Comparison of Sensitivity Of Headspace GC, Purge and Trap Thermal Desorption and Direct Thermal Extraction Techniques For Volatile Organics Note 38: A New Micro Cryo-Trap For Trapping Of Volatiles At the Front Of a GC Capillary Column Note 37: Volatile Organic Emissions from Automobile Tires Note 36: Identification Of Volatile Organic Compounds In a New Automobile Note 35: Volatile Organics Composition of Cranberries Note 34: Selection Of Thermal Desorption and Cryo-Trap Parameters In the Analysis Of Teas Note 33: Changes in Volatile Organic Composition in Milk Over Time Note 32: Selection and Use of Adsorbent Resins for Purge and Trap Thermal Desorption Applications Note 31: Volatile Organic Composition in Several Cultivars of Peaches Note 30: Comparison Of Cooking Oils By Direct Thermal Extraction and Purge and Trap GC/MS Note 29: Analysis Of Volatile Organics In Oil Base Paints By Automated Headspace Sampling and GC Cryo-Focusing Note 28: Analysis Of Volatile Organics In Latex Paints By Automated Headspace Sampling and GC Cryo-Focusing Note 27: Analysis of Volatile Organics In Soils By Automated Headspace GC Note 26: Volatile Organics Present in Recycled Air Aboard a Commercial Airliner Note 25: Flavor and Aroma in Natural Bee Honey Note 24: Selection of GC Guard Columns For Use With the GC Cryo-Trap Note 23: Frangrance Qualities in Colognes Note 22: Comparison Of Volatile Compounds In Latex Paints Note 21: Detection and Identification Of Volatile and Semi-Volatile Organics In Synthetic Polymers Used In Food and Pharmaceutical Packaging Note 20: Using Direct Thermal Desorption to Assess the Potential Pool of Styrene and 4-Phenylcyclohexene In Latex-Backed Carpets Note 19: A New Programmable Cryo-Cooling/Heating Trap for the Cryo-Focusing of Volatiles and Semi-Volatiles at the Head of GC Capillary Columns Note 18: Determination of Volatile Organic Compounds In Mushrooms Note 17: Identification of Volatile Organics in Wines Over Time Note 16: Analysis of Indoor Air and Sources of Indoor Air Contamination by Thermal Desorption Note 14: Identification of Volatiles and Semi-Volatiles In Carbonated Colas Note 13: Identification and Quantification of Semi-Volatiles In Soil Using Direct Thermal Desorption Note 12: Identification of the Volatile and Semi-Volatile Organics In Chewing Gums By Direct Thermal Desorption Note 11: Flavor/Fragrance Profiles of Instant and Ground Coffees By Short Path Thermal Desorption Note 10: Quantification of Naphthalene In a Contaminated Pharmaceutical Product By Short Path Thermal Desorption Note 9: Methodologies For the Quantification Of Purge and Trap Thermal Desorption and Direct Thermal Desorption Analyses Note 8: Detection of Volatile Organic Compounds In Liquids Utilizing the Short Path Thermal Desorption System Note 7: Chemical Residue Analysis of Pharmaceuticals Using The Short Path Thermal Desorption System Note 6: Direct Thermal Analysis of Plastic Food Wraps Using the Short Path Thermal Desorption System Note 5: Direct Thermal Analysis Using the Short Path Thermal Desorption System Note 4: Direct Analysis of Spices and Coffee Note 3: Indoor Air Pollution Note 2: Detection of Arson Accelerants Using Dynamic Headspace with Tenax® Cartridges Thermal Desorption and Cryofocusing Note 1: Determination of Off-Odors and Other Volatile Organics In Food Packaging Films By Direct Thermal Analysis-GC-MS
- Application NotesNote 103: EPA Method 325B, Novel Thermal Desorption Instrument Modification to Improve Sensitivity Note 102: Identification of Contaminants in Powdered Beverages by Direct Extraction Thermal Desorption GC/MS Note 101: Identification of Contaminants in Powdered Foods by Direct Extraction Thermal Desorption GC/MS Note 100: Volatile and Semi-Volatile Profile Comparison of Whole Versus Cracked Versus Dry Homogenized Barley Grains by Direct Thermal Extraction Note 99: Volatile and Semi-Volatile Profile Comparison of Whole vs. Dry Homogenized Wheat, Rye and Barley Grains by Direct Thermal Extraction GC/MS Note 98: Flavor and Aroma Profiles of Truffle Oils by Thermal Desorption GC/MS Note 97: Flavor Profiles of Imported and Domestic Beers by Purge & Trap Thermal Desorption GC/MS Note 96: Reducing Warping in Mass Spectrometer Filaments, with SISAlloy® Yttria/Rhenium Filaments Note 95: Detection of Explosives on Clothing Material by Direct and AirSampling Thermal Desorption GC/MS Note 94: Detection of Nepetalactone in the Nepeta Cataria Plant by Thermal Desorption GC/MS Note 93: Detection of Benzene in Carbonated Beverages with Purge & Trap Thermal Desorption GC/MS Note 92: Yttria Coated Mass Spectrometer Filaments Note 91: AutoProbe DEP Probe Tip Temperatures Note 90: An Automated MS Direct Probe for use in an Open Access Environment Note 89: Quantitation of Organics via a Mass Spectrometer Automated Direct Probe Note 88: Analysis of Silicone Contaminants on Electronic Components by Thermal Desorption GC-MS Note 87: Design and Development of an Automated Direct Probe for a Mass Spectrometer Note 86: Simulation of a Unique Cylindrical Quadrupole Mass Analyzer Using SIMION 7.0. Note 85: Replacing an Electron Multiplier in the Agilent (HP) 5973 MSD Note 84: Vacuum Pump Exhaust Filters - Charcoal Exhaust Traps Note 83: Vacuum Pump Exhaust Filters - Oil Mist Eliminators Note 82: Vacuum Pump Exhaust Filters Note 81: Rapid Bacterial Chemotaxonomy By DirectProbe/MSD Note 80: Design, Development and Testing of a Microprocessor ControlledAutomated Short Path Thermal Desorption Apparatus Note 79: Volatile Organic Compounds From Electron Beam Cured and Partially Electron Beam Cured Packaging Using Automated Short Path Thermal Desorption Note 78: A New Solution to Eliminate MS Down-Time With No-Tool-Changing of Analytical GC Columns Note 77: The Determination of Volatile Organic Compounds in VacuumSystem Components Note 76: Determination of the Sensitivity of a CRIMS System Note 75: An Apparatus for Sampling Volatile Organics From LivePlant Material Using Short Path Thermal Desorption Note 74: Examination of Source Design in Electrospray-TOF Using SIMION 3D Note 73: The Analysis of Perfumes and their Effect on Indoor Air Pollution Note 72: 1998 Version of the NIST/EPA/NIH Mass Spectral Library, NIST98 Note 71: Flavor Profile Determination of Rice Samples Using Shor tPath Thermal Desorption GC Methods Note 70: Application of SIMION 6.0 To a Study of the Finkelstein Ion Source: Part II Note 69: Application of SIMION 6.0 To a Study of the Finkelstein Ion Source: Part 1 Note 68: Use of a PC Plug-In UV-Vis Spectrometer To Monitor the Plasma Conditions In GC-CRIMS Note 67: Using Chemical Reaction Interface Mass Spectrometry (CRIMS) To Monitor Bacterial Transport In In Situ Bioremediation Note 66: Probe Tip Design For the Optimization of Direct Insertion Probe Performance Note 65: Determination of Ethylene by Adsorbent Trapping and Thermal Desorption - Gas Chromatography Note 64: Comparison of Various GC/MS Techniques For the Analysis of Black Pepper (Piper Nigrum) Note 63: Determination of Volatile and Semi-Volatile Organics in Printer Toners Using Thermal Desorption GC Techniques Note 62: Analysis of Polymer Samples Using a Direct Insertion Probe and EI Ionization Note 61: Analysis of Sugars Via a New DEP Probe Tip For Use With theDirect Probe On the HP5973 MSD Note 60: Programmable Temperature Ramping of Samples Analyzed ViaDirect Thermal Extraction GC/MS Note 59: Computer Modeling of a TOF Reflectron With Gridless Reflector Using SIMION 3D Note 58: Direct Probe Analysis and Identification of Multicomponent Pharmaceutical Samples via Electron Impact MS Note 57: Aroma Profiles of Lavandula species Note 56: Mass Spec Maintenance & Cleaning Utilizing Micro-Mesh® Abrasive Sheets Note 55: Seasonal Variation in Flower Volatiles Note 54: Identification of Volatile Organic Compounds in Office Products Note 53: SIMION 3D v6.0 Ion Optics Simulation Software Note 52: Computer Modeling of Ion Optics in Time-of-Flight mass Spectrometry Using SIMION 3D Note 51: Development and Characterization of a New Chemical Reaction Interface for the Detection of Nonradioisotopically Labeled Analytes Using Mass Spectrometry (CRIMS) Note 50: The Analysis of Multiple Component Drug Samples Using a Direct Probe Interfaced to the HP 5973 MSD Note 49: Analysis of Cocaine Utilizing a New Direct Insertion Probe on a Hewlett Packard 5973 MSD Note 48: Demonstration of Sensitivity Levels For the Detection of Caffeine Using a New Direct Probe and Inlet for the HP 5973 MSD Note 47: The Application Of SIMION 6.0 To Problems In Time-of-Flight Mass Spectrometry Note 46: Delayed Extraction and Laser Desorption: Time-lag Focusing and Beyond Note 45: Application of SIMION 6.0 to Filament Design for Mass Spectrometer Ionization Sources Note 44: The Design Of a New Direct Probe Inlet For a Mass Spectrometer Note 43: Volatile Organic Composition In Blueberries Note 42: The Influence of Pump Oil Purity on Roughing Pumps Note 41: Hydrocarbon Production in Pine by Direct Thermal Extraction Note 40: Comparison of Septa by Direct Thermal Extraction Note 39: Comparison of Sensitivity Of Headspace GC, Purge and Trap Thermal Desorption and Direct Thermal Extraction Techniques For Volatile Organics Note 38: A New Micro Cryo-Trap For Trapping Of Volatiles At the Front Of a GC Capillary Column Note 37: Volatile Organic Emissions from Automobile Tires Note 36: Identification Of Volatile Organic Compounds In a New Automobile Note 35: Volatile Organics Composition of Cranberries Note 34: Selection Of Thermal Desorption and Cryo-Trap Parameters In the Analysis Of Teas Note 33: Changes in Volatile Organic Composition in Milk Over Time Note 32: Selection and Use of Adsorbent Resins for Purge and Trap Thermal Desorption Applications Note 31: Volatile Organic Composition in Several Cultivars of Peaches Note 30: Comparison Of Cooking Oils By Direct Thermal Extraction and Purge and Trap GC/MS Note 29: Analysis Of Volatile Organics In Oil Base Paints By Automated Headspace Sampling and GC Cryo-Focusing Note 28: Analysis Of Volatile Organics In Latex Paints By Automated Headspace Sampling and GC Cryo-Focusing Note 27: Analysis of Volatile Organics In Soils By Automated Headspace GC Note 26: Volatile Organics Present in Recycled Air Aboard a Commercial Airliner Note 25: Flavor and Aroma in Natural Bee Honey Note 24: Selection of GC Guard Columns For Use With the GC Cryo-Trap Note 23: Frangrance Qualities in Colognes Note 22: Comparison Of Volatile Compounds In Latex Paints Note 21: Detection and Identification Of Volatile and Semi-Volatile Organics In Synthetic Polymers Used In Food and Pharmaceutical Packaging Note 20: Using Direct Thermal Desorption to Assess the Potential Pool of Styrene and 4-Phenylcyclohexene In Latex-Backed Carpets Note 19: A New Programmable Cryo-Cooling/Heating Trap for the Cryo-Focusing of Volatiles and Semi-Volatiles at the Head of GC Capillary Columns Note 18: Determination of Volatile Organic Compounds In Mushrooms Note 17: Identification of Volatile Organics in Wines Over Time Note 16: Analysis of Indoor Air and Sources of Indoor Air Contamination by Thermal Desorption Note 14: Identification of Volatiles and Semi-Volatiles In Carbonated Colas Note 13: Identification and Quantification of Semi-Volatiles In Soil Using Direct Thermal Desorption Note 12: Identification of the Volatile and Semi-Volatile Organics In Chewing Gums By Direct Thermal Desorption Note 11: Flavor/Fragrance Profiles of Instant and Ground Coffees By Short Path Thermal Desorption Note 10: Quantification of Naphthalene In a Contaminated Pharmaceutical Product By Short Path Thermal Desorption Note 9: Methodologies For the Quantification Of Purge and Trap Thermal Desorption and Direct Thermal Desorption Analyses Note 8: Detection of Volatile Organic Compounds In Liquids Utilizing the Short Path Thermal Desorption System Note 7: Chemical Residue Analysis of Pharmaceuticals Using The Short Path Thermal Desorption System Note 6: Direct Thermal Analysis of Plastic Food Wraps Using the Short Path Thermal Desorption System Note 5: Direct Thermal Analysis Using the Short Path Thermal Desorption System Note 4: Direct Analysis of Spices and Coffee Note 3: Indoor Air Pollution Note 2: Detection of Arson Accelerants Using Dynamic Headspace with Tenax® Cartridges Thermal Desorption and Cryofocusing Note 1: Determination of Off-Odors and Other Volatile Organics In Food Packaging Films By Direct Thermal Analysis-GC-MS Tech No. "A" Note 14: Elimination of "Memory" Peaks in Thermal Desorption Improving Sensitivity in the H.P. 5971 MSD and Other Mass Spectrometers - Part I of II Improving Sensitivity in the H.P. 5971 MSD and Other Mass Spectrometers- Part II of II Adsorbent Resins Guide Development and Field Tests of an Automated Pyrolysis Insert for Gas Chromatography. Hydrocarbon Production in Pine by Direct Thermal Extraction A New Micro Cryo-Trap for the Trapping of Volatiles at the Front of a GC Capillary (019P) - Comparison of Septa by Direct Thermal Extraction Volatile Organic Composition in Blueberry Identification of Volatile Organic Compounds in Office Products Detection and Indentification of Volatiles in Oil Base Paintsby Headspace GC with On Column Cryo-Trapping Evaluation of Septa Using a Direct Thermal Extraction Technique INFLUENCE OF STORAGE ON BLUEBERRY VOLATILES Selection of Thermal Desorption and Cryo-Trap Parameters in the Analysis of Teas Redesign and Performance of a Diffusion Based Solvent Removal Interface for LC/MS The Design of a New Direct Probe Inlet for a Mass Spectrometer Analytes Using Mass Spectrometry (CRIMS) Application of SIMION 6.0 to Filament Design for Mass Spectrometer Ionization Sources A Student Guide for SIMION Modeling Software Application of SIMION 6.0 to Problems in Time-of-flight Mass Spectrometry Comparison of Sensitivity of Headspace GC, Purge and TrapThermal Desorption and Direct Thermal Extraction Techniques forVolatile Organics The Influence of Pump Oil Purity on Roughing Pumps Analysis of Motor Oils Using Thermal Desorption-Gas Chromatography-Mass Spectrometry IDENTIFICATION OF VOLATILE ORGANIC COMPOUNDS IN PAPER PRODUCTS Computer Modeling of Ion Optics in Time-of-Flight mass Spectrometry using SIMION 3D Seasonal Variation in Flower Volatiles Development of and Automated Microprocessor Controlled Gas chromatograph Fraction Collector / Olfactometer Delayed Extraction and Laser Desorption: Time-lag Focusing and Beyond A New Micro Cryo-Trap for the Trapping of Volatiles at the Front of a GC Column Design of a Microprocessor Controlled Short Path Thermal Desorption Autosampler Computer Modeling of Ion Optics in Time-of-Flight Mass Spectrometry Using SIMION 3D Thermal Desorption Instrumentation for Characterization of Odors and Flavors
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- Note 65: Determination of Ethylene by Adsorbent Trapping and Thermal Desorption - Gas Chromatography (This Page)
By Eric D. Butrym* and Thomas G. Hartman
* Scientific Instrument Services, Ringoes, NJ
Department of Food Science, Cook College, Rutgers
University, New Brunswick, NJ 08903
Center for Advanced Food Technology, Cook College, Rutgers University, New Brunswick, NJ 08903
Presented at PittCon 98, New Orleans, LA, March, 1998.
Abstract
Ethylene is of great economic and practical importance due to its use in polymers and its pronounced biological activity in plants. Low levels of ethylene (<1ppm) can produce changes in plant growth and senescence through hormonal activity. In the past, methods for detecting low levels of ethylene relied on trapping the gas with Mercuric salts or the application of specialized photoacoustic detectors. Direct Headspace methods have also been used for higher concentrations. Major limitations of these methods include the generation of toxic by-products, low sensitivity, low trapping efficiency, and high cost.
Thermal Desorption is a reagent-free analytical method that is applied here to ethylene detection. Carbosieve SIII is used to adsorb ethylene from prepared standards and humid air. Air samples are drawn through glass-lined steel tubes filled with the trapping material. Ethylene and other light hydrocarbons trapped from the air are then desorbed in a single step directly into a GC inlet for analysis. A 2 meter micropacked column (Carboxen 1004 Supelco, Inc.) is used for analysis with flame ionization detection.
Large concentration factors in the samples make routine detection of less than 1 ppb ethylene possible without major modification of the chromatograph. Sample size is limited only by the breakthrough volume of the adsorbent. This method represents a major improvement in the availability of precise, low-level ethylene measurement without expensive extra equipment or unwanted toxic by-products. Additionally, the method is useful for other light hydrocarbons such as propylene and isoprene that must be accurately measured in very low concentration.
INTRODUCTION
Detection of ethylene at trace (< 10 ppm) levels is necessary to study the effects of this hormone on plant development as well as monitor concentrations of the gas in commercial processes. In the past, Gas Chromatography (GC) with Flame Ionization Detection (FID) combined with static headspace analysis has been the most popular method for ethylene measurement.(1,2) However, this method is limited by the amount of gas that can be reliably introduced into the GC inlet. Even recent advances in column technology have kept detection limits for ethylene in the low ppm range without the use of expensive specialized detectors. One serious deficiency is the tendency for linearity to fall off dramatically at the lower limits of detection.
An alternative to static headspace measurement is the dynamic enrichment, or trapping technique. This has the advantage of concentrating analytes to detectable levels, thereby increasing detection limits. Solutions of Mercuric Acetate or Mercuric Perchlorate have been used as a non-specific trap for olefins due to the complexation reactions they undergo. Addition of chloride salts to these solutions degrades the complex and releases ethylene for headspace analysis.(3) These methods suffer from low trapping efficiency, considerable sample preparation time and the necessity of using toxic reagents.
The use of adsorbent materials for trapping ethylene has been largely overlooked, presumably due to the difficulty of finding materials which are aggressive enough to trap the highly volatile gas while not allowing water to interfere with the subsequent analysis. Due to the large sample volume needed for trace level analysis and because of the nature of the systems being studied (plant material, biofilter effluent, etc.), significant amounts of water are expected to be trapped along with ethylene. Thermal desorption technology combined with adsorbent trapping for light hydrocarbon analysis have in the past only been available in the form of specialized analyzers costing many thousands of dollars.
Materials and Methods
Carbosieve SIII was selected as the adsorbent material for the traps due to its relatively high affinity for light hydrocarbons. Porous polymer adsorbent materials have little affinity for gaseous hydrocarbons, and polymer type molecular sieves are unstable at the elevated temperatures needed to desorb ethylene as a discrete peak into the chromatograph. Carbosieve SIII displayes the highest affinity for ethylene as measured by breakthrough volume (L/g of adsorbent) of all the materials commonly used for thermal desorption (Figure 1). The breakthrough volume for ethylene on Carbosieve SIII was determined experimentally to be approximately 4 L/g at 20°C. (4)
Figure 1
Water is problematic with respect to normal thermal desorption analysis, because cryofocussing is generally used to immobilize analytes during the desorption step, thereby improving chromatography dramatically. Excess water in the sample freezes under cryotrapping conditions and results in decreased sensitivity and in some cases may extinguish the detector flame. Here the problem has been circumvented by the use of a chromatography column with a high loading capacity and a packing which enables resolution of ethylene from other light hydrocarbons and gasses as well as water in the sample. For this work, a 2 meter micropacked (1/16 inch O.D. stainless steel) Carboxen 1004 (Supelco Inc. Bellefonte, PA) was chosen. This choice of column combined with careful temperature programming allows samples to be injected without cryotrapping and provides excellent resolution of ethylene from water and other compounds present.
Standard mixtures of ethylene and helium (10 ppm and 100 ppm w/w, Scott Specialty Gasses Inc.) were used to prepare 1L dilutions of ethylene in dry nitrogen (JWS Inc. Piscataway, NJ) at various concentrations. The samples were prepared in Tedlar® sample bags (SKC Inc. Eighty-Four, PA) immediately before use.
Carbosieve SIII adsorbent (0.8 grams) (Supelco Inc. Bellefonte, PA) was packed into 4 mm I.D. glass-lined Thermal Desorption Tubes (SIS Inc. Ringoes, NJ) and secured with glass wool. The tubes were conditioned for three hours at 310 °C under a nitrogen purge. Standard dilutions of ethylene were drawn through the tubes at a rate of 100 mL/minute. Each sample was then analyzed using a Short Path Thermal Desorption System model TD-2 (SIS Inc. Ringoes, NJ) operated in manual mode and a Varian model 3400 Gas Chromatograph with FID detection (Varian Assoc. Walnut Creek, CA). Varian Star Chromatography software (version 4.0) was used for data collection and calculation of standard curves. Identities of ethylene and other compounds in the standards were confirmed by Mass Spectrometry in separate analyses. (Data not shown)
The samples were purged with carrier for 30 seconds before injection, and were desorbed for two minutes at 300°C into the injector which was held at 220°C . Desorption and the GC run were started simultaneously. The GC was programmed to remain at 100 °C for two minutes, then ramped to 225 °C at 30 °C/ minute. The FID detector was held at 300 °C and was supplied with 30 mL/ minute makeup gas. The column head pressure was kept at 46 psi , equivalent to approximately 12 mL/minute column flow.
Four sample replicates were analyzed at five different concentration levels spanning a three-log dynamic range. As a test of ruggedness, the method was used to analyze an actual sample from the effluent of an ethylene-degrading biofilter (Fig.5.).
Results
Figure 2
Figure 2 contains representative chromatograms for the five concentration levels used. In each chromatogram, Ethylene can be seen as a well-resolved peak at retention time ~ 5.6 minutes.
Figure 3
The standard curve shown in Figure 3 was generated using all five concentrations and displays excellent linearity over a wide dynamic range (R2 = 0.997). A separate curve (Figure 4) was generated using only the four lowest concentrations, and this also demonstrated good linear characteristics (R2 = 0.972) with only a minor change in the slope. Relative standard deviations for concentrations of 50, 10, 5, 1 and 0.5 ppb were 9.1%, 14.4%, 11.3%, 22.4% and 57.9% respectively. These results demonstrate an improvement over standard methods in linearity at the lower concentrations; however, the decreased precision at the lowest level indicates that the measurements are at or near the reliable limit of detection.
Figure 4
The sample taken from the ethylene-degrading biofilter was analyzed in order to evaluate the method under more stringent conditions. A chromatogram is shown in Figure 5. Biofilter efflutent was passed through a tube containing Mg2SO4 dessicant into a Tedlar® sample bag ( SKC Inc. Eighty-Four, PA). A 1L sample from the bag was drawn through an adsorbent trap in the same manner as described above for the standards. Analytical methodology was identical to that used for the standards, except that a Varian model 4200 integrator was used for data collection.
Figure 5
Conclusions
- A simple, reliable and accurate method has been developed for the analysis of trace levels of ethylene in air.
- The method avoids the use of expensive specialized equipment, permanent GC modification, and generation of toxic by-products.
- Improvements to the limit of detection are possible by merely increasing sample size.
Biofilter sample courtesy of Jyoti Tambwekar, Department of Environmental Sciences, Cook College, Rutgers University.
This work was funded by the New Jersey - NASA Specialized Center of Research and Training (NJ-NSCORT) for Bioregenerative Life Support Systems.
References
1. Ethylene in Plant Biology. 1973. Abeles, F.B. Academic Press, New
York.
2. Ethylene. 1987. Saltveit, M.E. Jr., and Yang, S.F. in
Principals and Practice of Plant Hormone Analysis. Vol. 2. L. Rivier
and A. Crozier eds. Academic Press, New York, NY. 367-401.
3. Manometric Determination of Low Concentrations of Ethylene. 1952.
Young, R.E., Pratt,H.K., and Biale, J.B. Anal. Chem. 24(3):551-555.
4. Selection and Use of Adsorbent Resins for Purge and Trap Thermal
Desorption Applications. 1995. Application Note No. 32 Scientific
Instrument Services, Inc. Ringoes NJ.