Easy Analysis of Residual MTBE in Environmental Water and Soil

Introduction

MTBE (t-butyl methyl ether) is a compound that was added mainly to high-octane gasoline to boost the octane of the gasoline. In the US, MTBE caused pollution of soil and groundwater and, two or three years later, the decision was made to discontinue the addition of MTBE to gasoline. In Japan, an Environmental Agency investigation detected trace amounts of MTBE in well water. Because of the concern that leaking of gasoline containing MTBE, which has a stimulating odor and is suspected to be carcinogenic, would pollute the groundwater and the soil, major oil distribution companies decided to halt sales of high-octane gasoline containing MTBE in the summer of 2001. Not much has been done to measure and gain knowledge of the MTBE residue concentrations in environmental water and soil. Comprehensive studies about the affect of residual MTBE will be started in the near future. Headspace GC/MS and purge-and-trap GC/MS methods are commonly used for the analysis of volatile hydrocarbon compounds. GC-FID can be used instead of GC/MS for screening purposes, or when the sample concentration is relatively high. This Application News introduces the use of headspace GC-FID for easy analysis of residual MTBE in environmental water and soil. In headspace methods, when solid samples are directly enclosed in to the head space vial and analyzed, quantification may become poor in some cases. Therefore, in this analysis example, the soil was diluted to ten times in volume with blank water, sealed, and stirred with a magnetic stirrer for four hours. Then, 10mL of supernatant was taken and added to a headspace vial containing 3g sodium sulfate, enclosed, and analyzed. This test liquid adjustment method is in accordance with the low molecular halogenated hydrocarbon analysis methods stipulated in the Environmental Agency Bulletin No. 46 of August 23, 1991 (revisions: 1993 Environmental Agency Bulletin No. 19, 1994 Environmental Agency Bulletin No. 25; and 1995 Environmental Agency Bulletin No. 19. The solution with added gasoline was diluted with isopropanol, added to a headspace vial containing 3g sodium sulfate and 10mL blank water, enclosed, and analyzed. Figs. 2 and 3 show the chromatograms of solutions corresponding to 0.01 and 0.07ppm (V/V) MTBE. Fig. 4 shows the linearity of gasoline-added water for 0.01 to 0.07ppm (V/V) MTBE. The figure shows good linearity. The minimum detection limit is about 10ppb concentration in water solutions (about 100ppb in soil). Besides MTBE, toluenes and xylenes could be simultaneously analyzed with the same analytical conditions.

March 24, 2003 GMT