Steranes, detection

Cyclic Hydrocarbons. Some of the cyclic hydrocarbons found in the CHX coal extracts are shown in Table V. They were tentatively identified by capillary GC/MS except for the naphthalenes, for which authentic standards were available. Selected ion profiles were used to detect sesquiterpenes (m/e 206, 191), sesquiterpanes (m/e 208), o alkanes (m/e 141), alkyl benzenes (m/e 191, 163), steranes (m/e 217),... 

A number of hydrocarbon fractions from liquefaction products produced at GFETC from the coals studied here were investigated using selected ion profiles of the capillary GC/MS data. None of the hydrocarbon biological markers other than the acyclic alkanes already discussed were detected. There were no sesquiterpenes, sesquiter-panes, steranes, triterpanes or other cyclic terpenoids found. 

Figure 16. HV scan spectra of m/z 191 (a) and m/z 217 ions (b) produced by decomposition of terpanes and steranes. Precursors of m/z 191 (c) and m/z 217 (d) ions detected in the El mass spectra of Green River Shale mixture [116],...

Based on the apparent occurrence of 24-n-prop-24(28)-enylcholesterol (a C30 sterol) only in certain extant marine members of the chrysophytes (order Sarcinochrysidales Bdlard et al. 1990), the presence of the corresponding 24-n-propylcholestanes in oils and ancient sediments is considered to indicate a contribution from marine algae (Moldowan et al. 1990). Low levels of these C30 steranes have been detected in some coals, in which they can be interpreted as resulting from a marine transgression, and are often accompanied by other signs of marine contributions (e.g. lower relative abundance of C29 steranes and elevated chedanthane content Kdlops et al. 1994). 

C23 terpane is the most abundant, but nearly no homohopanes of C31 to C35 were detected. Different from most Bunker C type oils, the concentrations of terpanes and steranes are quite low in HFO 6303. As for refined products, only traces of C20 to C24 terpanes and C20 to C22 steranes were detected in Diesel No. 2. In contrast, most lube oils contain very high quantity of biomarkers. Obviously, refining processes have removed or concentrated high molecular mass biomarkers from the corresponding crude oil feed stocks. 

Figure 3 Gas chromatography-mass spectrometric reconstructed ion chromatogram (RIC) of a typical crude oil. A RIC is equivalent to a GC flame ionization detection trace. The presence of triterpanes and steranes eluting between /j-C and n-C i are not evident due to low abundance and interference of coeluting compounds. Conditions Finnigan (San Jose, CA), 9610 gas chromatograph, Supelco (Bellefonte, PA), 30 m X 0.25 mm ID (0.1- Xm film thickness) DB-1 fused silica capillary column, temperature programmed from 120 to 310°C at 8°C/min, 1-pl injection at 50 1 split. Mass spectrometer Finnigan TSQ-46B, 70-eV electron ionization, full-scan mode from 35 to 500 Da in 1 sec cycle time.

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