Extraction of alcohols from gasoline using HS-SPME method, Artykuły naukowe, SPME i HS-SPME
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//-->EXTRACTION OF ALCOHOLS FROM GASOLINEUSING SOLID PHASE MICROEXTRACTION (SPME)Iris StadelmannThesis submitted to the faculty of theVirginia Polytechnic Institute and State Universityin partial fulfillment of the requirements for the degree ofMASTER OF SCIENCEInChemistryDr. Harold M. McNair, ChairDr. Herve MarandDr. Larry T. TaylorMay 11, 2001Blacksburg, VirginiaKey words: GC, SPME, Sample preparation, GasolineCopyright 2001, Iris StadelmannEXTRACTION OF ALCOHOLS FROM GASOLINE USING SPMEByIris Stadelmann(Abstract)It is common practice to add oxygenates, such as ethers or alcohols, to gasoline inareas suffering from ozone or smog problems in order to reduce pollution. The mostcommonly used oxygenates are ethanol (EtOH) and methyl tert-butyl ether (MTBE).However, MTBE is now forbidden by the environmental protection agency (EPA)because of the possibility of ground water contamination. The current trend is to useEtOH, therefore this work focuses on the analysis and quantification of EtOH in gasolineby solid phase microextraction (SPME). The major problem in quantifying EtOH ingasoline is the coelution of hydrocarbons with EtOH. There have been severalapproaches to solve this problem; among the chromatographic ones, three major typeshave been proposed: (1) the first one uses a detector selective for oxygen containingcompounds; (2) the second one uses two or more columns; (3) and the third one uses anextraction step prior to GC analysis. In this work an extraction step with water is usedprior to a solid phase microextraction (SPME) sample preparation coupled to a gaschromatographic (GC) analysis.Solid phase microextraction is a recent technique, invented by Pawliszyn in 1989,and available commercially since 1994. A fiber is used to extract small amounts (ppm,ppb, ppt) of analytes from a solution, usually water. The fiber is beneficial inconcentrating analytes. Most work using SPME has been done with hydrophobic (nonpolar) analytes, extracted using a polydimethylsiloxane (PDMS; non polar) coating on afused silica fiber. Since very little work has been done with polar analytes, the novelapproach of this work is the extraction of EtOH.Since EtOH is the analyte of interest, a polar fiber, carboxen/polydimethylsiloxane (Car/PDMS) is used. Two methods are used for quantification of EtOH ingasoline: the method of a standard calibration curve, and the method of standard addition.They are both successful in quantifying the amount of EtOH in gasoline. The relativeerrors, with the method of standard addition, vary from 5.3% to 14%, while the ones withthe method of calibration curve vary from 1.6% to 7.2%. Moreover, some extraction timestudies for both direct and headspace sampling are performed. Direct sampling shows thepresence of an equilibrium condition for the carboxen/PDMS fiber, for which noextraction theory is available. Conversely, headspace sampling shows no equilibriumstate; after a sampling time of one hour, the amount of EtOH extracted decreases withsampling time. This is probably due to displacement of EtOH by other compounds in thefiber.iiiACKNOWLEDGEMENTSI would like to thank my advisor, Dr. Harold McNair, for his knowledge andguidance. I would also like to thank my committee members, Dr. Herve Marand and Dr.Larry Taylor, for reviewing my thesis and giving me some good comments andsuggestions.Thanks to the chemistry department for providing me a teaching assistantshipduring my graduate studies.Thanks to my group members for the pleasant lab environment, help, friendshipand technical knowledge. Special thanks to Dr. Yvonne Fraticelli, who gave me somehelpful suggestions in my research, to Jennifer Brown and Laura Nakovich, alwaysfriendly and ready to help, to the usual or occasional “evening lab buddies”, who broughtlife to the lab at night, to Kevin Schug, Arash Kamangepour, and Amy Kinkennon.Thanks also to the “older” lab members who graduated some months ago, especiallyGail, Mark, and Xiling.Thanks to my chemistry buddies, those who came in with me as well as the otherones, especially Paco, Brian, Emre, Lee, and Luis. Special thanks to Paolo Dadone,Aysen Tulpar, and Christos Kontogeorgakis, for their great friendship and personalities.Paolo’s argumentative nature made for interesting and helpful discussions.I would also like to thank my old and new friends, as well as my family, for theirlove and support, and especially my parents Victor and Elizabeth, who made all thispossible.ivTable of contentsABSTRACT.................................................................................................................. iiACKNOWLEDGEMENTS .........................................................................................ivTABLE OF CONTENTS ..............................................................................................vLIST OF FIGURES.....................................................................................................viiLIST OF TABLES..................................................................................................... viiiLIST OF MULTIMEDIA OBJECTS ..........................................................................ixCHAPTER 1- INTRODUCTION............................................................................ 11.1 Background..............................................................................................................11.1.1 History................................................................................................................11.1.2 Advantages and disadvantages ............................................................................21.1.3 Gasoline components ..........................................................................................51.2: State of the Art .......................................................................................................7CHAPTER 2 - SOLID PHASE MICROEXTRACTION........................................ 112.1 Introduction ...........................................................................................................112.2 Technique...............................................................................................................112.3 Theory ....................................................................................................................152.3.1 Determination of amount of analyte extracted at equilibrium (thermodynamics)162.3.2 Dynamic process (kinetics) of direct SPME ......................................................202.3.3 Dynamic process (kinetics) of headspace SPME ...............................................212.4 Fibers......................................................................................................................22CHAPTER 3 - EXPERIMENTAL SETUP AND METHODS................................ 253.1 Instrumentation .....................................................................................................253.2 Sample preparation ...............................................................................................273.2.1 Gasoline samples ..............................................................................................273.2.2 Mixing procedure..............................................................................................283.2.3 SPME conditions ..............................................................................................29v
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