EXPERIMENTAL

Preparation of oil samples

About 30-45 ml of oil were poured into a tared flask, boiling chips were added and the oil was heated up to 210oC.  The fraction boiling below 210oC was distilled into a separate flask and weighed.  The remaining fraction was cooled and weighed. About 4-5 grams of the fraction boiling above 210oC was deasphalted by adding an excess of pentane (40 volumes).  About 100 milligrams of each deasphalted oil were then fractionated using open column liquid chromatography.

Open column chromatography

A mixture of 28-200 mesh silica gel and 80-200 mesh alumina (1:3, w/w) was used as a support for the column.  The support is activated at 120o-150oC for 12 hours.  A glass wool plug is placed at the bottom of column and covered with a 1 cm thick layer of sand.  The support, weighed as 1 g of support/10 mg of deasphalted sample, is slowly settled in pentane and any air trapped is released by gentle tapping on the column.  A deasphalted sample, dissolved in a minimal amount of previously measured pentane, is then added to the column.  Saturates are recovered by eluting with pentane (3.5 ml/g support), aromatics with a 50:50 mixture of pentane and dichloromethane (4 ml/g support), resins with methanol (4 ml/g support) and any remaining asphaltenes with chloroform.  The solvents are rotary-evaporated, separate fractions transferred to vials and dried in a slow stream of nitrogen and weighed to a constant weight.

Gas chromatography-mass spectrometry (GC-MS)

GC-MS analysis of saturate fractions was conducted using a VG 70SQ hybrid MS-MS system equipped with a HP 5890 GC.  The column used for these analyses was J&W DB-5  25m x 0.25mm capillary column.  Initial and final GC oven/column temperatures were 60oC and 320oC; however, different temperature programmings have been employed.  Despite this, the mass chromatograms acquired at different time periods are generally comparable.  Idetification of individual compounds is displayed as follows:
 m/z 217 ; m/z 191