ASTM D6423 Determination of pHe of Ethanol, Denatured Fuel Ethanol, and Fuel Ethanol (Ed75-Ed85)
4. Summary of Test Method
4.1 The sample is analyzed at room temperature using a specified electrode system and a pH meter with a sufficiently high impedance and recommended for use with ion specific electrodes.
4.2 Readings are taken at exactly 30 s because the meter reading will drift throughout the analysis due to solvent effects on the electrode.
4.3 The electrode is soaked in water-based pH 7 buffer between readings to prepare it for the next sample. This rehydrates the glass electrode, a necessary step to preserve the electrode's response characteristics.
5. Significance and Use
5.1 The acid strength, as measured by pHe, is a good predictor of the corrosion potential of ethanol fuels. It is preferable to total acidity because total acidity does not measure acid strength; overestimates the contribution of weak acids, such as carbonic acid; and may underestimate the corrosion potential of low concentrations of strong acids, such as sulfuric acid.
