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,4Z tCGC NO"AMERICA VOLUME ZI NUMBER IANUARY 2003 www.Chro.atog.phyoW nex.o A GC—MS Purge-and-Trap Method Comparison Study for MTBE Analysis in Groundwater The U.S. Environmental Protection Agency has proposed the term demonstration of method applicability for the process of analytical method evaluation and selection under a performance-based measurement system approach, wherein methods are selected based on their demonstrated ability to meet project-specified performance criteria in the specific matrices of interest. Such a demonstration recently has been undertaken at the Ventura County Naval Base (Port Hueneme, California). This study supported a treatment technology demonstration for methyl-tert-butyl ether(MTBE) in groundwater by assessing the ability of commercially available purge-and-trap gas chromatography—mass spectrometry methods to meet project sensitivity, precision, and accuracy criteria for MTBE and related oxygenate compounds in four groundwater matrices. The analytical methods used in site groundwater matrices. It demonstrates the and waste characterization histori- importance of laboratory selection for com- cally have been defined by pro- pound analysis based upon technical expert- ,._ .. ---.... ._ mulgated or other published ence and instrument capabilities. This method protocols such as those included method study was performed in support of a in the U.S. Environmental Protection treatment technology demonstration for Agencyfs (EPM) Test Methods for Evaluating MTBE conducted under the EPA Super- Solid Waste,more commonly called SW-846 fund Innovative Technology Evaluation pro- (1). Recently, however, performance-based gram. methodology has become a requirement for MTBE is an oxygenate added to gasoline several EPA programs. As opposed to the for improved combustion performance. default use of published methods as written, Regulatory concern about MTBE is increas- the performance-based approach requires ing,and the demand is growing for analyti- that methods be selected and approved cal methods for detecting this compound in based upon their ability to meet the data the environment. Oxygenates such as quality goals of a given project in the actual MTBE have significant water solubility, matrix to be sampled.To better define a per- which can present a particular problem; for Joseph D. Evans and formance-based approach to method selec- example, when MTBE is in groundwater Mark R. Colsman* tion, the general term demonstration of and the sample preparation technique is a Science Applications International method applicability has been cited by Lesnik purge-and-trap procedure such as SW-846 Corp.,950 Energy Drive, Idaho (2) and developed in the Resource Conner- Method 5030B. The primary concern with Falls, Idaho 83401,e-mail vation and Recovery Act (RCRA) program this approach is the purging efficiency of evansjo@saic.com as a process of validating a method for use in MTBE. Because MTBE is highly water sol- *Tetra Tech EM, Inc., 1099 18th the specific matrices of interest for a given uble, purging this compound to separate it Street, Suite 1900, Denver, sampling program. chemically from an aqueous matrix tan be Colorado 80202, e-mail This article describes a study that demon- less effective than desired,and it could limit mark.colsman®ttemi.com strated the applicability of purge-and-trap method sensitivity and cause low-biased gas chromatography—mass spectrometry results. Direct correspondence to (GC—MS) methods for methyl-cert-butyl Many researchers, however, have sug- JD. Evans. ether (MTBE) determination in specific gested that purge-and-trap methods tan pro-