The HI3818-100 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate carbon dioxide measurements with the chemical test kit. These reagents follow the phenolphthalein method to determine carbon dioxide concentration.

For carbon dioxide determination, dilute sodium hydroxide is used as the titrant. With addition of phenolphthalein indicator, the solution turns pink to visually indicate it is near the pH endpoint of pH 8.3. The number of milliliters of titrant used to reach the endpoint will determine the carbon dioxide concentration as mg/L CO₂. These reagents are designed to be used with samples that have an expected carbon dioxide range of 0.0 to 10.0 mg/L, 0.0 to 50.0 mg/L, and 0 to 100 mg/L CO₂.