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Corrosion of metallic components is an inherent problem for engines, because metals naturally tend to oxidize in the presence of water and/or acids. Increased acid content is indicated by a low pH value, and could lead to a variety of problems like a shorter storage life (stability) or a reduced buffer capacity of the used engine coolant or antirust. This in turn leads to a reduced lifetime of engines, for example. Without proper coolants and antirust agents, engines can overheat and seize up, resulting in costly damage and extra maintenance, or even necessitating a full replacement of the affected parts.

In this Application Note, engine coolants or antirust samples are dissolved in water, and the pH measurement using the Profitrode is carried out according to ASTM D1287.

The application is demonstrated for anhydrous ethylene glycol, anhydrous glycerol, engine coolant, and antirust oil.

No sample preparation is required.

OMNIS Basic Titrator. Example setup for the determination of the pH value.
Figure 1. OMNIS Basic Titrator. Example setup for the determination of the pH value.

This analysis is performed on an OMNIS Basic Titrator equipped with a Profitrode and a temperature sensor.

An aliquot of sample is pipetted into the sample beaker. While stirring, deionized water is added. After stirring for 1 minute, the pH value is measured until a stable drift is reached. Afterwards, the sensors are rinsed with deionized water for cleaning. The Profitrode is then conditioned for 2 minutes by immersing the glass membrane alone in deionized water.

The analysis demonstrates reproducible results with a SD(rel) smaller than 1%, which are summarized in Table 1. An exemplary measurement chart is displayed in Figure 2.

Table 1. Mean pH value for different samples determined by an OMNIS titration system (n = 6).
pH SD(rel) in %
Ethylene glycol 5.69 0.5
Glycerol 6.11 0.5
Engine Coolant 8.94 0.2
Antirust oil 3.13 0.8
Figure 2. Example measurement chart for the pH value of engine coolant.

Using an OMNIS Basic Titrator equipped with a Profitrode allows operators to measure the pH value of engine coolants and antirust according to ASTM D1287 efficiently and reliably. Due to the modularity of OMNIS, the system can easily be upgraded to perform other applications for the analysis of engine coolants or antirust such as the determination of the reserve alkalinity or the moisture content.


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