The HI3810-100 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate dissolved oxygen measurements with the chemical test kit. These reagents follow a modified Winkler titration method to determine dissolved oxygen concentration. 

For determination of dissolved oxygen, manganous ions react with oxygen in the presence of potassium hydroxide to form a manganese oxide precipitate. An azide is present to prevent any nitrite ions from interfering with the test. With addition of acid, manganese oxide hydroxide oxidizes the iodide to iodine. Since the amount of iodine generated is equivalent to the oxygen in the sample, the concentration of iodine is calculated by titration of thiosulfate ions that reduce the iodine back to iodide ions. The color change from blue to colorless indicates the endpoint of the titration. The number of milliliters of titrant used to reach the appropriate endpoint will determine the dissolved oxygen concentration as mg/L O2. These reagents are designed to be used with samples that have an expected dissolved oxygen range of 0.0 to 10.0 mg/L O2.