Corrosion of metallic components is an inherent problem for engines, because metals naturally tend to oxidize in the presence of water and/or low pH value. The reserve alkalinity of engine coolants and antirusts is a measure of the buffering ability to absorb acidity. Such acids might by introduced by exhaust gas leakage, by residual acid cleaner, or by the oxidation of ethylene glycol or propylene glycol. The reserve alkalinity is frequently used for quality control during production and often listed in the specifications of the coolants. A fast and accurate determination is therefore important.

This Application Note describes the straightforward determination of reserve alkalinity according to ASTM D1121. Engine coolants or antirusts are dissolved in water. After a pH measurement, the determination is carried out by potentiometric titration.

Using a fully automated system allows an accurate and reliable determination due to the reduction of human errors. Furthermore, the operator is free to carry out other tasks increasing the efficiency of the laboratory.

The method is demonstrated on engine coolant. No sample preparation is necessary.

The obtained results lay within the limits given by ASTM D1121 and are therefore acceptable. An example titration curve can be seen in Figure 2 and the results are summarized in Table 1.