Sequential Elution Chromatography
One gram of organic precipitate was transferred to a flask. The material was adsorbed onto 30 g of silica gel (activated at 120 °C in a nitrogen-flushed oven) using methylene chloride. It was stirred for 24 h, before solvent removal by rotary evaporation.
The
adsorbed sample was next dried in a nitrogen-flushed oven at 60 °C for 48 h. It
was charged to a standard chromatography column. These Pyrex columns were
constructed with a 250 mL reservoir attached to a
14/20 joint, a 22 mm o.d. column approximately 1 m
long, a fritted disk (ASTM 145 - 175 Ìm), and
a detachable Teflon stopcock with removable Pyrex tip. A diagram of a packed
sequential elution chromatography column is supplied in Figure 1. The material
that eluted in heptane prior to the heptane’s color
change was considered to be the wax. The aromatics were eluted in 400 mL of heptane and toluene (17/8
v/v). Then the resins were eluted in 350 mL of a mix
of toluene, acetone, and methylene chloride (
Finally
a fraction called asphaltenes were eluted in 350 mL of THF and acetone (4/1 v/v). The silica was then placed
in pyridine for several days and the desorbed material added to the asphaltenes. The solvent was removed from all the fractions
except the asphaltenes via rotary evaporation, and
they were dried in a nitrogen-flushed vacuum oven at 70
Reference - B. A. Musser and P. K. Kilpatrick, Molecular Characterization of Paraffinic and Microcrystalline Wax in Crude Petroleum, Energy and Fuels, 12, 715-725 (1998).
