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Time-resolved fluoroimmunoassay as an advantageous analytical method for assessing the total concentration and environmental risk of fluoroquinolones in surface waters.

Due to the widespread occurrence in the environment and potential risk toward organisms of fluoroquinolones (FQs), it is of importance to develop high efficient methods for assessing their occurrence and environmental risk. A monoclonal antibody (Mab) with broad cross-reactivity to FQs was produced by immunizing BALB/c mice with a synthesized immunogen prepared by conjugating ciprofloxacin with bovine serum albumin. This developed Mab (C2F3C2) showed broad and high cross-reactivity (40.3-116%) to 12 out of the 13 studied FQs. Using this Mab and norfloxacin conjugated with carrier protein ovalbumin as coating antigen, a time-resolved fluoroimmunoassay (TRFIA) method was developed for determining the total concentration of at least 12 FQs in environmental waters. The respective detection limit (LOD) and IC(50) calculated from the standard curve were 0.053 μg/L and 1.83 μg/L for enrofloxacin (ENR). The LODs of the other FQs, estimated based on the corresponding cross-reactivity and the LOD of ENR, were in the range of 0.051-0.10 μg/L. The developed TRFIA method showed good tolerance to various interfering substances present in environmental matrix at relevant levels, such as humic acids (0-10 mg/L DOC), water hardness (0-2% Ca(2+) and Mg(2+), w/v), and heavy metals (0-1 mg/L). The spiked recoveries estimated by spiking 0.5, 1, and 2 μg/L of five representative FQs into various water samples including paddy water, tap water, pond water, and river water were in the range of 63-120%. The measured total FQ concentration by TRFIA agreed well with that of liquid chromatography-tandem mass spectrometry and was applied to directly evaluate the occurrence and environmental risk of FQs in the surface water of a case area. TRFIA showed high efficiency and great potential in environmental risk assessment as it measures directly the total concentration of a class of pollutants.