During the last years, it has been demonstrated that δ18O isotope analysis of ethanol in juices and alcoholic beverages provides powerful information to assess their adulteration by addition of water, or to authenticate their geographical origin. However, it is difficult to accurately and conveniently quantify it due to the measurement principle and its water miscibility. To eliminate the impact of water on ethanol δ18O analysis, a porouspolymerbonded GC column was used to achieve a baseline separation of ethanol and water, then the water was vented by backflush function and the ethanol was converted and analyzed. This is the first manuscript presenting a systematic evaluation and characterization of a method for δ18O isotope analysis of ethanol in aqueous samples by direct injection of the sample (diluted with acetone) into a GCTCIRMS system, with the consequent benefits of eliminating sample pretreatment, minimum sample amounts required and minimum sample throughput. This method has the following advantages: only 70200 μL of the sample was required for up to 300 possible injections, and high throughput was observed, caused by short analysis time (18 min for each run), the influences of oxygencontaining compounds on ethanol δ18O analysis were eliminated by the use of a capillarycolumn bonded porous polymer to obtain a baseline separation prior to hightemperature conversion. Precision was determined to be less than 05‰ (1σ), and accuracy was validated by spiked samples and proficiency test samples. During the last years, it has been been characterized that δ18O isotope analysis of ethanol in juices and alcoholic beverages provides powerful information to assess their adulteration by addition of water, or to authenticate their geographical origin. However, it is difficult to accurately and conveniently quantify it due to the measurement principle and its water miscibility. To eliminate the impact of water on ethanol δ18O analysis, a porouspolymerbonded GC column was used to achieve a baseline separation of ethanol and water, then the water was vented by backflush function and the ethanol was converted and analyzed. This is the first manuscript presenting a systematic evaluation and characterization of a method for δ18O isotope analysis of ethanol in aqueous samples by direct injection of the sample (diluted with acetone) into a GC-TC-IRMS system with the consequent benefits of eliminating sample pre-treatment, minimum sa mple amounts required and minimum sample throughput. This method has the following advantage:  only 70  200 μL of the sample was required for up to 300 possible injections, and high throughput was observed, caused by short analysis time (18 min for each run), the influences of oxygencontaining compounds on ethanol δ18O analysis were eliminated by the use of a capillarycolumn bonded porous polymer to obtain a baseline separation prior to hightemperature conversion. Precision was determined to be less than 05 ‰ (1σ), and accuracy was validated by spiked samples and proficiency test samples.