Abstract
Measuring the dynamic release of aroma compounds from ethanolic solutions by direct gas phase mass spectrometry (MS) techniques is an important technique for flavor chemists but presents technical difficulties as the changing ethanol concentration in the source makes quantitative measurements impossible. The effect of adding ethanol into the source via the sweep gas (0–565 μL ethanol/L N 2), to act as the proton transfer reagent ion and thereby control ionization was studied. With increasing concentrations of ethanol in the source, the water ions were replaced by ethanol ions above 3.2 μL/L. The effect of source ethanol on the ionization of eleven aroma compounds was then measured. Some compounds showed reduced signal (10–40%), others increased signal (150–400%) when ionized via ethanol reagent ions compared to water reagent ions. Noise also increased in most cases so there was no overall increase in sensitivity. Providing the ethanol concentration in the source was >6.5 μL/L N 2 and maintained at a fixed value, ionization was consistent and quantitative. The technique was successfully applied to measure the partition of the test volatile compounds from aqueous and 12% ethanol solutions at equilibrium. Ethanolic solutions decreased the partition coefficient of most of the aroma compounds, as a function of hydrophobicity.
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