Field Quantification of Hydroxyl Radicals by Flow-Injection Chemiluminescence Analysis with a Portable Device

Hydroxyl radical ((OH)-O-center dot) is a powerful oxidant abundantly found in nature and plays a central role in numerous environmental processes. On-site detection of (OH)-O-center dot is highly desirable for real-time assessments of (OH)-O-center dot-centered processes and yet is restrained by a lack of an analysis system suitable for field applications. Here, we report the development of a flow-injection chemiluminescence analysis (FIA-CL) system for the continuous field detection of (OH)-O-center dot. The system is based on the reaction of (OH)-O-center dot with phthalhydrazide to generate 5-hydroxy-2,3-dihydro-1,4-phthalazinedione, which emits chemiluminescence (CL) when oxidatively activated by H2O2 and Cu3+. The FIA-CL system was successfully validated using the Fenton reaction as a standard (OH)-O-center dot source. Unlike traditional absorbance- or fluorescence-based methods, CL detection could minimize interference from an environmental medium (e.g., organic matter), therefore attaining highly sensitive (OH)-O-center dot detection (limits of detection and quantification = 0.035 and 0.12 nM, respectively). The broad applications of FIA-CL were illustrated for on-site 24 h detection of (OH)-O-center dot produced from photochemical processes in lake water and air, where the temporal variations on (OH)-O-center dot productions (1.0-12.2 nM in water and 1.5-37.1 x 10(7) cm(-3) in air) agreed well with sunlight photon flux. Further, the FIA-CL system enabled field 24 h field analysis of (OH)-O-center dot productions from the oxidation of reduced substances triggered by tidal fluctuations in coastal soils. The superior analytical capability of the FIA-CL system opens new opportunities for monitoring (OH)-O-center dot dynamics under field conditions.