An Automated HPLC Method for SARA Fractionation of Asphalts: Operational Assessment and Comparison with ASTM D4124.

The composition of asphalts and other heavy petroleum-derived materials is usually subdivided into four fractions called saturates, aromatics, resins, and asphaltenes (SARA), which have different polarities and solubilities. The separation and quantification of these fractions using chromatographic methods provide essential information on the colloidal stability, chemical reactivity, and processing behavior. However, the measured distribution of SARA fractions is inherently dependent on the analytical procedure adopted. Based on a liquid chromatographic separation in open columns, ASTM D4124 is still the most widely applied standard, despite being time-consuming, solvent-intensive, and operator-dependent. Although numerous HPLC-based alternatives have been proposed, their broader implementation has been limited by the methodological variability and the lack of a clear framework for interpreting the results across different separation schemes, particularly for asphaltic systems rich in aromatics, resins and asphaltenes. This work presents an automated HPLC workflow for SARA fractionation which is applied to four different penetration-grade asphalts and systematically compared to ASTM D4124. The study highlights the practical aspects of HPLC implementation, including the critical methodological steps that affect the reproducibility and transferability between laboratories. Additional analyses of ASTM-isolated fractions and selected model compounds provide insights into the origins of systematic differences between HPLC- and ASTM-derived SARA compositions. These differences are shown to arise from distinct separation mechanisms and operational cut points rather than from analytical inaccuracies. This reflects the intrinsically method-dependent nature of SARA classification in materials characterized by a continuous distribution of molecular polarity. By clarifying the methodological and conceptual basis of these differences, this work provides practical guidance for the interpretation of HPLC-SARA data and supports more consistent and transferable approaches to asphalt characterization.