Determination of C-0-C-3 alkylphenols in crude oils and waters

Three rapid methods for the isolation and determination of alkylphenols from crude oils are described. Two of the methods are based on a novel approach involving the preconcentration of crude oil phenols using non-end-capped C18 solid-phase extraction and a normal-phase solvent program, To our knowledge, this is the first report of a C18 sorbent being used in ''normal-phase mode'' to isolate relatively polar compounds from a more nonpolar matrix. Determination of alkylphenols is performed by reversed-phase high-performance liquid chromatography (RP-HPLC), combined with oxidative electrochemical detection (ED), or by gas chromatography/flame ionization detection (GC/FID) and gas chromatography/mass spectrometry (GC/MS) after chemical derivatization, A direct alkaline extraction RP-HPLC/ED approach is also described. The reversed-phase HPLC method affords rapid sample turnovers with accurate quantitation of phenol, cresols, and major dimethylphenols and is suitable for screening large numbers of samples. Alternatively, the GC/FID-GC/MS method allows the determination of phenol, cresols, dimethylphenols, ethylphenols, and trimethylphenols at levels suitable for routine use in petroleum geochemistry. We illustrate the methods with two petroleum geochemical examples: determination of the partition coefficients of alkylphenols in oil/brine systems under high pressure and temperature conditions, and study of alkylphenol distributions in a migration case history from the North Sea.