A fluorometric method for the selective determination of lipid hydroperoxides in river water

Abstract

Lipids are a component of the dissolved organic matter found in natural waters. The susceptibility of lipids to oxidation suggests that lipid hydroperoxides (LHPs) may be among the hydroperoxides present in natural waters. However, the selective determination of potential LHPs among other hydroperoxides in natural waters has not been investigated. In this study, a method was developed to selectively determine LHPs in river water using the fluorescent probe Liperfluo (2-(4-diphenylphosphanyl-phenyl)-9-(3,6,9,12-tetraoxatridecyl)-anthra[2,1,9-def:6,5,10-dʹeʹfʹ]diisoquinoline-1,3,8,10-tetraone). The probe reacted selectively with LHPs to form Liperfluo-Ox, which was quantified using a flow injection analysis system (FIA) equipped with a fluorescence detector (Excitation/Emission: 495 nm/546 nm). The linear range under the optimized conditions for the reaction of Liperfluo with LHPs in MilliQ and river water was 0–500 nM LHPs. The method detection limit for LHPs, defined as three times the standard deviation of five measurements of 100 nM LHPs, was 10.1 nM in river water and 7.3 nM in MilliQ. The coefficient of variation was ≤3.8% for five replicate measurements each for 100 nM and 500 nM LHPs. The conditions and the probe used in this study showed high selectivity for LHPs over other natural water hydroperoxides, including hydrogen peroxide, methyl hydroperoxide and ethyl hydroperoxide. The method was applied to the quantification and fate determination of LHPs in water from the Kurose River (Japan). The concentrations ranged from below the detection limit to 98 nM (ave. 37.2 nM; n =12). The LHPs in river water samples were found to quickly photo-decomposed within an hour. The irradiation of LHP-spiked river water using a solar simulator resulted in an increased H₂O₂ concentration, suggesting that H₂O₂ formation may be a possible sink for LHPs in river water.