Industry: Environmental
Instrument: Velocity XPT
Analysis of Fuel Oxygenates in Water by Purge and Trap
Oxygenates such as methyl tert-butyl ether (MTBE) have been added to gasoline since the late 1970’s. In 1990 congress passed the Clean Air Act, and in 1995, implemented the requirements which led to an increased use of Reformulated Gasoline (RFG) containing oxygenates. These programs set minimum levels of oxygen content for gasoline sold in specific metropolitan areas to allow the fuel to burn cleaner and thus reduce air pollution. Several years ago MTBE was detected in water supplies throughout the country, but predominantly in areas using RFG. MTBE made its way from leaking underground storage tanks, gasoline spills, and two-stroke gasoline engines into surface and ground water. Because of this contamination, 16 States and Reno, Nevada enacted legislation to restrict or prohibit the use of MTBE in gasoline.1 In these areas MTBE will be replaced primarily with ethanol and to a lesser extent with other polar oxygenates.
With this increase in concern surrounding RFG comes increased requirements for analysis of oxygenates in water. Conventional methods used to detect BTEX compounds from gasoline work well for MTBE, but these methods have poor sensitivity for the very polar alcohols. Other oxygen containing compounds that can be added to gasoline include; tert-amyl methyl ether (TAME), ethyl tert-butyl ether (ETBE), di-isopropyl ether (DIPE), tert-butyl alcohol (TBA) and Ethanol. Analysis by purge and trap can be used to detect MTBE quickly and easily, but by optimizing each step of the analysis, very polar oxygenates can be successfully analyzed and with lower detection limits. For this study we examine stirring, salting and heating the samples using a SOLATek 72™ autosampler; varying dry purge volume and DryFlow™ temperatures using a Velocity XPT™; and utilizing different split flows, columns and detectors using an Agilent 6890 gas chromatograph (GC) and 5973 mass spectrometer (MS). After determining the optimal conditions, a 5-point calibration curve and an MDL were evaluated. The oxygenate compounds were then spiked into a 1ppm gasoline standard at the 50ppb level and analyzed.
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