The HI38018-200 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate free chlorine measurements with the chemical test kit. These reagents follow the DPD (N,N-diethyl-p-phenylenediamine) method to determine free chlorine concentration.

For determination of free chlorine, the DPD powder reagent is added to a sample containing chlorine. The reaction between chlorine and the reagent causes a pink colored complex to form; the greater the concentration, the deeper the color. A Checker Disc is included for an accurate, side-by-side, visual analysis to determine free chlorine concentration. These reagents are designed to be used with low range samples that have an expected free chlorine range of 0.00 to 0.70 mg/L (ppm) Cl₂ and high range samples that have an expected free chlorine range of 0.0 to 3.5 mg/L (ppm) Cl₂.