The direct complexometric determination of metals in unused lubricating oils and additives by automatic non-aqueous potentiometric titration

Abstract

Methods are described for the determination of calcium, barium, zinc and magnesium in any combination in additive concentrates and unused lubricating oils. The samples are dissolved in a mixed aqueous-organic solvent and titrated directly with 1,2-bis(2-aminoethoxy)ethane-NNN′N′-tetraacetic acid [ethylene glycol bis(2-aminoethyl)tetraacetic acid; EGTA] or 1,2-diaminocyclohexane-NNN′N′-tetraacetic acid (DCTA), the end-points being indicated by metal ion sensitive electrodes. By use of a masking agent and the appropriate buffer solutions the individual metals in any combination can be determined following a maximum of three titrations.

The results are compared with those obtained by established procedures. The accuracy of the complexometric methods is comparable with that of established wet-chemical methods, but the former are up to ten times faster and are therefore suitable for blending control.