Thin-layer chromatography/flame ionization detection (TLC/FID) allows for the fractionation of bitumen into four fractions, namely, the saturates, the aromatics, the resins A and the resins B (SARAB). The technique is rapid and economical, but it lacks reproducibility. The effect of chromarod aging on reproducibility was investigated along with that of the time between bitumen dissolution and its analysis (time lapse effects). It is found that chromarod aging causes a 2-5% variation in SARAB content, and that time lapse causes a 50-75% variation in the aromatics and resins A content. The effect of time lapse stems from the aging of bitumen in solution. A mechanism for this aging is provided. It is demonstrated to be a physical rather than a chemical transformation of bitumen that reveals itself as a conversion of aromatics into resins. The physical nature of aging is shown by the absence of oxidation and aromatization in solution and by the successful modeling of aging after a reversible process. The conversion of aromatics into resins is explained by the grouping of alkyl-aromatics into micelles. Micelles mimic resins during chromatography and cause an apparent increase in resins concentration.