Shipboard determination of hydrogen peroxide in the western Mediterranean sea using flow injection with chemiluminescence detection

Abstract

Field studies at a variety of sampling locations in the western Mediterranean have endorsed the use of a novel flow injection-chemiluminescence method (FI-CL) for the determination of hydrogen peroxide in seawater. Analysis time for a depth profile of 12 samples including standard additions was 45 min, repeatability (relative standard deviation; RSD; n=5) was typically <5% and reproducibilities at two different sampling stations were 2.5% RSD (mean concentration=83.6 nM H 2O 2; n=3) and 1.8% RSD (mean concentration=42.5 nM H 2O 2; n=4). Depth profile data, characterised by H 2O 2 concentrated at the surface (16.0–154 nM H 2O 2) and decreasing rapidly below the thermocline, were in agreement with previous studies in similar oceanographic environments. Samples collected during Lagrangian drift mode indicated that diurnal maxima can occur in the mid-late afternoon. Batches of sampled and treated seawater were incubated under ambient light conditions whilst onboard ship to investigate the photogeneration of H 2O 2. Surface waters had a higher H 2O 2 photogenerative efficiency than deeper waters and samples collected close to the River Rhône plume were particularly effective at generating H 2O 2, suggesting that the chromophoric material responsible for the photogeneration of H 2O 2 had a terrestrial source. Additional incubation experiments in the laboratory showed that humic material was more efficient at photogenerating H 2O 2 than fulvic material or hydrophilic macromolecular acids.