title: Determination and characterization of oxy-naphthenic acids in oilfield wastewater.
abstract: Oxy-naphthenic acids (oxy-NAs) are one of the major components of NA mixtures in wastewaters from petroleum industries. The limited available data indicated that oxy-NAs were considered as a potential marker for the degradation of NAs, and some oxy-NAs exhibited endocrine disrupting activities. However, the lack of information on the structures and occurrences of oxy-NAs in oilfield wastewaters limited the interpretations of the biotransformation pathways of NAs and structure-specific toxicity. A sensitive method for simultaneous determination of oxy-NAs together with NAs was developed by combining MAX extraction column and UPLC-ESI(-)-QTOF-MS. The 2000-fold SPE preconcentration step was highly specific for acids and the prewash solvent greatly reduced matrix effects in the UPLC-ESI(-)-QTOF-MS analysis, resulting in an increase in sensitivity down to detection limits in the ng/L range. To provide structural information within each oxy-NA isomer class, a new method was developed by derivatizing oxy-NAs with dansyl chloride by UPLC-ESI(+)-QTOF-MS. The molecular ion dansyl derivatives from the corresponding oxy-NAs and characteristic fragmentation ions, not detected before derivatization, were observed in the extracts of oilfield wastewater, providing evidence that O3-NAs and O4-NAs were mainly composed of OH-NAs and (OH)2-NAs, respectively. Semiquantification of oxy-NAs and NAs in various oilfield wastewaters revealed NAs, O3-NAs, and O4-NAs present at concentrations of 187-397, 44-146, and 40-108 μg/L, respectively. Significantly different profiles of NA mixtures were observed in petroleum refinery wastewater and oil sands extraction water, but the profile of oxy-NAs was similar to NAs in different wastewaters suggesting the existence of biotransformation between NAs and oxy-NAs in the environment, and hydroxylation could be one of the major biotransformation pathways of NAs.
authors.affiliation: Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.
authors.forename: Beili
authors.initials: B
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Wan
authors.forename: Yingxin
authors.initials: Y
authors.lastname: Gao
authors.forename: Min
authors.initials: M
authors.lastname: Yang
authors.forename: Jianying
authors.initials: J
authors.lastname: Hu
mesh_terms: D002264:Carboxylic Acids / Q000032:analysis* / Q000737:chemistry; D003619:Dansyl Compounds; D010084:Oxidation-Reduction; D059392:Petroleum Pollution / Q000032:analysis*; D052616:Solid Phase Extraction; D062065:Wastewater / Q000032:analysis*
chemical_list: D002264:Carboxylic Acids; D003619:Dansyl Compounds; D062065:Wastewater; C029038:dansyl chloride; C046170:naphthenic acid