Application of Fenton reaction for nanomolar determination of hydrogen peroxide in seawater

A simple and sensitive method for the determination of nanomolar levels of hydrogen peroxide (H₂O₂) in seawater has been developed and validated. This method is based on the reduction of H₂O₂ by ferrous iron in acid solution to yield hydroxyl radical (OH) which reacts with benzene to produce phenol. Phenol is separated from the reaction mixture by reversed phase high performance liquid chromatography and its fluorescence intensity signals were measured at excitation and emission of 270 and 298 nm, respectively. Under optimum conditions, the calibration curve exhibited linearity in the range of (0-50) × 10³ nmol L⁻¹ H₂O₂. The relative standard deviations for five replicate measurements of 500 and 50 nmol L⁻¹ H₂O₂ are 1.9 and 2.4%, respectively. The detection limit for H₂O₂, defined as three times the standard deviation of the lowest standard solution (5 nmol L⁻¹ H₂O₂) in seawater is 4 nmol L⁻¹. Interference of nitrite ion (NO₂⁻) on the fluorescence intensity of phenol was also investigated. The result indicated that the addition of 10 μmol L⁻¹ NO₂⁻ to seawater samples showed no significant interference, although, the addition of 50 μmol L⁻¹ NO₂⁻ to the seawater samples decreases the fluorescence intensity signals of phenol by almost 40%. Intercomparison of this method with well-accepted (p-hydroxyphenyl) acetic acid (POHPAA)-FIA method shows excellent agreement. The proposed method has been applied on-board analysis of H₂O₂ in Seto Inland seawater samples.