Rapid and accurate SARA analysis of medium gravity crude oils

Crude oils can be described compositionally by a number of methods. SARA analysis is widely used to divide crude oil components according to their polarizability and polarity using a family of related analytical techniques. Problems arise because the analytical techniques do not necessarily produce identical results. Users of the data, however, rarely distinguish between the different techniques, assuming that SARA fraction values generated by any of the commonly used methods are essentially interchangeable. We examine this assumption for medium gravity crude oils and three SARA analysis methods:  gravity-driven chromatographic separation, thin-layer chromatography (TLC), and high-pressure liquid chromatography (HPLC). Results for a suite of six crude oil samples show that a significant volume of volatile material that contains both saturates and aromatics is lost in the TLC analysis. An improved HPLC method is introduced that gives analyses comparable to the ASTM-recommended chromatographic method in les...