The HI3838-100 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate formaldehyde measurements with the chemical test kit. These reagents follow the Alizarin Yellow R method to determine formaldehyde concentration.

For formaldehyde determination, dilute hydrochloric acid is used as the titrant. Alizarin Yellow R reagent is used to form a red-orange color complex for visual indication. Sodium sulfite reagent is used to form an alkaline formaldehyde product. Dropwise addition of the acidic titrant causes the solution to turn from red-orange to yellow as it reaches the Alizarin Yellow R endpoint. The number of milliliters of titrant used to reach the endpoint will determine the formaldehyde concentration as mg/L CH₂O. These reagents are designed to be used with samples that have an expected formaldehyde range of 0.0 to 1.0 % and 0 to 10% Formaldehyde (CH₂O).