Capillary electrophoretic separation of polycyclic aromatic sulfur heterocycles

Abstract

Capillary electrophoresis (CE) was used to separate polycyclic aromatic sulfur heterocycles (PASHs), a class of compounds that occurs in fossil fuels and refined products of petroleum. An electric charge was introduced into the compounds through methylation or phenylation of the sulfur atom. Separations of standard PASHs that are expected to be present in industrially desulfurized fuels showed that CE possessed a higher resolution than reversed phase liquid chromatography. The CE method can separate all the monomethylbenzothiophenes; this is not achieved in capillary gas chromatography. A linear relationship was found between migration time and the calculated volume of the compounds. The PASHs in deeply desulfurized diesel were separated after preconcentration, and the electropherogram was compared with the chromatograms from GC and HPLC. Finally, derivatized PASHs are often enantiomeric and the enantiomers can be separated if a suitable cyclodextrin is added to the running buffer.

Petroleum Analysis

“…Unstable crude oils, known to cause deposition, shared similar charge distributions, which differed from the stable crude oil and further studies to determine the applicability of the technique to downhole analysis to predict deposition. Capillary electrophoresis (CE) was used to separate polycyclic aromatic sulfur heterocycles in diesel after catalytic hydrodesulfurization (HDS) to determine the amount and functionality of recalcitrant sulfur-containing compounds after derivatization but required a preconcentration step for UV detection . Characterization of sulfur species which remain after deep HDS is critical for optimization of refinery processes to remove sulfur compounds to meet stringent government standards for sulfur quantities in gasoline and diesel fuel.…”

Desulfurized Fuels from Athabasca Bitumen and Their Polycyclic Aromatic Sulfur Heterocycles. Analysis Based on Capillary Electrophoresis Coupled with TOF MS

“…For instance, the separation of a standard mixture of dibenzothiophene (DBT), 4-methyl-DBT, 4,6-dimethyl-DBT, and 4,6-diethyl-DBT as their S-methyldibenzothiophenium ions is presented in Figure . The elution order of alkyldibenzothiophenes is linearly related to their size in an aqueous buffer. A baseline separation of all four compounds could easily be achieved in 16 min (Figure a); the number of theoretical plates ranged from 110 000 (4,6-diethyl-DBT) to 150 000 (DBT; t m = 13.28 min, w 1/2 = 0.08 min; N = (t m /w 1/2 ) 2 * 5.54, see the Experimental Section).…”

“…An alternative possibility for PASHs is the derivatization of the sulfur atom to thiophenium ions. In previous studies the derivatization was performed by methylation or phenylation , of the sulfur atom, and the subsequent separation was carried out in an aqueous phosphate buffer. Standard compounds as well as real world samples could be successfully separated, but the drawback of comigration remained when more complex samples were analyzed.…”