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March 2003 LLISTLine Bulletin 43 Oxygenate Measurements in Groundwater Do We Need to Worry About MTBE Acid Hydrolysis? ® a by Bruce Bauman } { 4 Q 5 s there one clearly superior proto- techniques for extracting col for analyzing oxygenates in all oxygenates(especially a water samples? Of course not. alcohols such as TBA) Like many aspects of UST release from water samples, and prevention, detection, or corrective (b) the potential for action, there is no single "best" way transforming MTBE to to get the analytical job done.Rather, TBA by acid hydrolysis. decision makers must have a good As these issues can have profound provided in the LL#42 protocol is understanding of the general princi- implications on data quality and excellent,I would like to address two ples and site-specific variables that interpretations for corrective action of the recommendations that deserve can influence the performance of the decisions at any site,they deserve the a little more discussion, and, per- various approaches commonly used considerable discussion surrounding haps,debate: to generate data characterizing them. • To ensure good-quality TBA data, groundwater quality. P&T extraction procedures used In this article,I'd like to throw in "A tremendous amount of for oxygenates should preferably my two cents on the subject of oxy- oxygenate data from leaking UST be heated to 80°C genate analysis—especially with sites have been generated Over., To prevent hydrolysis of oxy- regard to questions surrounding the past several years, yet there` methyl tertiary-butyl ether (MTBE) is understandable concern as to genates, field preservation of transformations to tertiary-butyl alco- groundwater samples should use whether these data are valid. l _ a base (trisodium phosphate hol(TBA)via acid hydrolysis.Several general, these concerns are dodecahydrate [TSP]) instead of articles and conference presentations related to two issues:analytical_ hydrochloric acid. in the past year, including one in LUSTLine #42 (LL#42), "Analytical obstacles, and ether hydrolysis; Let me begin by summarizing a Methods for Fuel Oxygenates," dis- (particularly of MTBE to TBA).",I- few key "take-home messages' that cuss approaches to sample handling LusnPae s42- readers would have extracted from and analysis and how such ap- Analytical Methods for Fuel Oxygenates" the LL#42 article and that will serve proaches may influence the accuracy as the basis for my discussion. of results for MTBE, TBA (for more • It is important to analyze for all about TBA, see LUSTLine #36), and Points of Debate oxygenates known to be present in other oxygenates in groundwater. This discussion will focus on the gasoline using methods that pro- You also may have seen a draft copy LL#42 article, as many LUSTLine vide accurate results. of the U.S. EPA Office of Under- readers are familiar with it.That arti- ground Storage Tank's widely dis- cle did a very good job of addressing • Standard P&T at ambient temper- tributed "Environmental Fact Sheet: a broad variety of complex issues ature does not adequately extract Analytical Methods for Fuel Oxy- associated with chemical analysis of TBA from water samples,so sam- genates." oxygenates, not just purging effi- ples should be heated to 80°C. These discussions have focused ciency and MTBE hydrolysis. The a Existing conventional approaches on the most popular protocols for authors provided a good deal of key to groundwater sample preserva- oxygenate analysis, EPA SW-846 information about sampling and ana- tion,extraction,and analysis may methods 5030B(purge and trap)and lyzing gasoline oxygenates in be prone to the acid hydrolysis of 8260B (gas chromatograph/mass groundwater.They highlighted some MTBE,which could lead to under- spectrometer [GC-MSI). To some- obvious problems with certain ana- estimates of concentrations of what oversimplify those discussions, lytical methods and addressed the MTBE and overestimates of the questions have been raised regarding important steps associated with sam- TBA concentrations. the ability of these protocols to pro- ple preservation before analysis. vide accurate measurements of The authors also provided a"rec- MTBE,TBA,and other oxygenates in ommended protocol" that "will Do You Need to Analyze for groundwater. greatly improve the quality of the All Oxygenates? In particular, critics of the proto- data" by avoiding the some of the Yes, indeed. Only a few states cur- cols question the following: (a) the perceived problems with existing rently include TBA as a routine target effectiveness of purge and trap(P&T) methods.While the overall guidance ■continued on page 18 17