pH-Metric method for acid number determination in hydraulic oils without titration

A heptane-mediated extraction of acids from hydraulic oils is proposed for pH-metric acid number determination without titration. The acids are extracted in the reagent consisting of triethanolamine and potassium nitrate dissolved in water and isopropanol. The use of heptane allows us to overcome the influence of additives in the hydraulic oil on the glass electrode. Simultaneously the extraction of acids from the oil into the water–isopropanol phase is simplified. The method is validated and suitable metrological characteristics of the acid number determination are obtained.