Determination of environmental H2O2 for extended periods by chemiluminescence with real-time inhibition of iron interferences

Abstract

Soluble iron hinders the accurate analysis of hydrogen peroxide (H2O2) in environmental systems. We present a chemiluminescence sequential injection (SIA) system capable of the continuous analysis of H2O2 over extended periods (48 h) by the real-time addition of an iron complexing reagent (ICR; masking compounds) which inhibits >98% of the interference caused by iron species. The measurement error based on repeat analysis of a sample within 10 min was ±2.2%, and over 48 h was ±6%. The preparation and analysis of standards, the ability for discrete and continuous sampling, and the real-time addition of the ICR to minimize chemical interference were integrated within the SIA system. Evaluation of the analytical probe showed that the optimum concentration and pH of the luminol reagent for the analysis of H2O2 were 100 μM luminol and pH = 10.7, respectively; this enabled the analysis over a concentration range of 0.25–900 nM H2O2 at a detection limit of 0.14 nM. The proposed SIA system requires only small amounts of reagents (33 μL luminol and 24 μL ICR) and sample (240 μL). We used the system to measure the H2O2 concentration in a coastal seawater sample that was subject to natural photochemical reactions and the direct input of rainwater, both of which introduce soluble iron. Rainwater H2O2 increased the H2O2 concentration in the coastal seawater sample by a factor of up to 40 relative to the amounts produced by natural photochemical reactions. The H2O2 concentration in the coastal seawater sample showed high short-term variability.