Development of a hydrophilic interaction chromatographic-mass spectrometry method for the analysis of the acid fraction of oil sands processing water

摘要

The acid fraction of the oil sands processing water (OSPW) consists of a large number of closely related, but structurally distinct entities, primarily naphthenic acids, which have the general formula of CnH2n+zO2, which represents several hundred possible molecular formulas, many of which may have multiple structural isomers. In addition, the acid fraction also contains di- and tri-acids as well as molecules containing heteroatoms such as N or S. As a result of the large number of compounds contained in the acid fraction of the oil sands, separation and identification of individual components remains elusive. This poster reports use of HILIC/LC/MS as an alternative to RP/LC/MS for the separation of the components of the acid fraction of Athabasca OSPW. HILIC/LC/MS has the advantage that acidic analytes are maintained in ionized form during the separation process as opposed to in neutral form in RP which greatly facilitates ionization using an ESI source. HILIC chromatographic separation of the acid fraction was carried out using a mobile phase consisting of water and a mixture of acetonitrile and ethyl acetate with 0.1percent ammonium hydroxide on Waters 2695 HPLC using an Allsphere HILIC column. Mass spectra were determined using a Waters Quattro Ultima triple quadrupole system operated in negative mode. Analysis of Athabasca oil sands OSPW acid fraction extracts by HILIC/LC/MS resulted in at least five distinct peaks. Analysis of the nominal masses to determine the z numbers represented by these peaks showed that the multi-ring structures were separated from straight chain acids or those containing a single ring. Several of the peaks had z numbers indicating little or no ring formation, yet were well resolved chromatographically. This separation may be due to branching, the presence of additional acid groups or the presence of hetero atoms. Determination of the structural characteristics leading to the chromatographic separation using high-resolution/ion mobility/MS is on-going. To our knowledge, this data represents the first use of HILIC/LC/MS for separation and identification of the acid fraction of oil sands processing water.