5.1 Hydrogen peroxide (formed photochemically in the atmosphere) is a primary oxidizer of dissolved sulfur dioxide in atmospheric water. Detection of H₂O₂ in atmospheric water is useful for inferring gas-phase H₂O₂ concentrations and for assessing the relative importance of various acidifying mechanisms under specific atmospheric conditions.

5.2 Hydroperoxides in samples to be analyzed are unstable in water and can decay rapidly due to bacterial action or chemical reaction with other constituents. The test method includes procedures for sample derivatization and methods for estimating and correcting for hydroperoxide decay.

1.1 This test method covers the determination of hydroperoxides, which include hydrogen peroxide (H₂O₂) and combined organic peroxides, in samples of atmospheric water by the method of horseradish peroxidase derivatization and fluorescence analysis of the derived dimer.^2,3

1.2 The range of applicable hydrogen peroxide concentrations was determined to be 0.6 - 176.0 × 10⁻⁶ M from independent laboratory tests of the test method.

1.3 The primary use of the test method is for hydrogen peroxide, but it may also be used to quantitate organic hydroperoxides. Determinations of organic hydroperoxide concentration levels up to 30 × 10⁻⁶ M may be adequately obtained by calibration with hydrogen peroxide.^2,3 While organic hydroperoxides have not been detected at significant concentration levels in rain or cloud water, their presence may be tested by operation of the test method with the addition of catalase for destruction of H₂O₂³.

1.4 Because of the instability of hydroperoxides in atmospheric water samples, proper sample collection, at-collection derivatization, and stringent quality control are essential aspects of the analytical process.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.