Originally Posted By: MolaKule
Suppose we observe ester peaks in an analysis plot? Many additives are themselves esters, such as the ashless dispersants, ZDDP, Boron, etc.
Unless you go further with more extensive analysis and more costly instrumentation, how would you know how much the additive contributes to the total ester content and how much the POE is contributing?
True for some analysis techniques, such as FTIR, but the beauty of gas chromatography is that the polymers and metal containing compounds do not elute and interfere. It basically shows just volatile components such as the base oils and some anti-oxidants and allows a pretty clear picture of petroleum distillates, PAOs, and esters. It cannot distinguish among Groups I, II, and III mixtures but easily identifies PAOs up to at least the pentamers, and commonly used POEs, Diesters, and ANs.