The direct determination of additive metals in lubricating oils by complexometric titration. Part II. The use of small-scale methods

Abstract

The mixed solvents used in the methods described in Part I are cloudy because of the presence of suspended oil or water. Not only does this cloudiness obscure some end-points but the presence of two phases implies difficulties of pH control, and delays in the attainment of titration equilibria. By reducing the amount of oil, homogeneous solutions are obtained.

Methods are described for the determination of zinc by using diethylene-triaminepenta-acetic acid (DTPA), with dithiozine as indicator, and of total metals by using excess of DTPA and standard magnesium solution as backtitrant, in the presence of Eriochrome black T indicator.

The methods discussed are comparable with those described in Part I in simplicity and speed, but incorporate certain improvements, one of which is that the determination of total metals is extended to include barium present as a sulphonate.