The pHe value is a measure of the acidity of alcohol-based fuels. In ethanol, pHe is an important parameter for fuel quality specification with respect to the risk of motor damage. The Metrohm Titration Application Note T-173 describes pHe determination in a denatured ethanol mixture in accordance with ASTM D6423. Determination is implemented using a 913 pH Meter and the EtOH-Trode.
Acidity in alcohol based fuels can accelerate engine corrosion
Excessive acidity in alcohol based fuels accelerates engine corrosion. Total Acid Number (TAN) accounts for all titratable acids regardless of their strength and is therefore not suitable to accurately predict the corrosion potential.
pHe measures the strength of the acids present in the sample
pHe, on the other hand measures the strength of the acids present in the sample. Therefore, pHe is the better parameter for manufacturers to monitor the corrosion potential, maintain the quality of their product, and maximize profits.
Standardized by ASTM D6423 and EN 15490
Sensor design is crucial
The design of the sensor is crucial for accurate pHe measurements. The ASTM standard recommends a high leak-rate sleeve junction reference electrode and a large membrane glass measuring electrode, as these perform best for measurements of alcohol fuels. The Metrohm EtOH Trode is one of two sensor explicitly mentioned by ASTM D6423 as suitable for pHe measurements in ethanol and ethanol fuel blends.