BONDED STATIONARY PHASES FOR REVERSED-PHASE LIQUID-CHROMATOGRAPHY WITH A WATER MOBILE-PHASE - APPLICATION TO SUBCRITICAL WATER EXTRACTION

Reversed phase high-performance liquid chromatography (RP-HPLC) is dem onstrated for hydrophobic analytes such as aromatic hydrocarbons on a chemically bonded stationary phase and a mobile phase consisting of on ly water. Reversed phase liquid chromatography separations using a wat er-only mobile phase has been termed WRP-LC for water-only reversed ph ase LC. Reasonable capacity factors are achieved through the use of a non-porous silica substrate resulting in a chromatographic phase volum e ratio much lower than usually found in RP-HPLC. Two types of bonded WRP-LC columns have been developed and applied. A brush phase was synt hesized from an organochlorosilane. The other phase, synthesized from an organodichlorosilane: is termed a branch phase and results in a pol ymeric structure of greater thickness than the brush phase. A baseline separation of a mixture containing benzaldehyde, benzene, toluene, an d ethyl benzene in less than 5 min is demonstrated using a water mobil e phase with 12000 plates generated for the unretained benzaldehyde pe ak. The theoretically predicted minimum reduced plate height is also s hown to be approached for the unretained analyte using the brush phase . As an application, subcritical water extraction (SWE) at 200 degrees C is combined with WRP-LC. This combination allows for the extraction of organic compounds from solid matrices immediately followed by liqu id chromatographic separation of those extracted compounds all using a solvent of 100% water. We demonstrate SWE/WRP-LC by spiking benzene, ethyl benzene, and naphthalene onto sand then extracting the analytes with SWE followed by chromatographic separation on a WRP column. A san d sample contaminated with gasoline was also analyzed using SWE/WRP-LC . This extraction process also provides kinetic information about the rate of analyte extraction from the sand matrix. Under the conditions employed, analytes were extracted at different rates, providing additi onal selectivity in addition to the WRP-LC separation. (C) 1998 Elsevi er Science S.A.