Avoiding hydrolysis of fuel ether oxygenates during static headspace analysis.

Area of Science:

• Environmental Chemistry
• Analytical Chemistry

Background:

• Fuel oxygenates, such as methyl tert-butyl ether (MTBE), are common groundwater contaminants.
• Acidic sample preservation at pH < 2 can lead to hydrolysis of fuel ether oxygenates during heated headspace analysis.
• This hydrolysis compromises the accurate determination of these contaminants.

Purpose of the Study:

• To investigate the detrimental effect of acidic preservation on fuel ether oxygenate determination using heated headspace sampling.
• To identify an effective sample preservation strategy to ensure accurate analysis of fuel oxygenates in groundwater.

Main Methods:

• Analysis of groundwater samples using heated headspace sampling at 80°C.
• Testing the impact of acidic preservation (pH < 2) on fuel ether oxygenates (MTBE, ETBE, TAME).
• Evaluating trisodium phosphate as a buffering agent to prevent acid-catalyzed hydrolysis.

Main Results:

• Acidic conditions (pH 2) caused hydrolysis of tert-amyl methyl ether, ethyl tert-butyl ether, and methyl tert-butyl ether during heating.
• No hydrolysis was observed in samples stored at 4°C for 28 days at pH 2.
• Trisodium phosphate effectively prevented hydrolysis, yielding excellent recovery of spiked ethers.
• The method accurately determined a wide range of fuel oxygenates and gasoline components with low detection limits.

Conclusions:

• Acidic preservation of groundwater samples is incompatible with heated headspace analysis of fuel ether oxygenates due to hydrolysis.
• Employing trisodium phosphate to buffer samples is a crucial step for accurate quantification of fuel oxygenates and related compounds.
• The optimized heated headspace method is reliable for analyzing diverse fuel-derived contaminants in groundwater.