For determination of bromine, the sample is first adjusted to a pH near 6.3. When the DPD reagent is added to a sample containing bromine, the reagent is immediately oxidized. The reaction between bromine and the reagent causes a red colored complex to form; the greater the concentration, the deeper the color. A color comparator cube is included for an accurate, side-by-side, visual analysis to determine bromine concentration. These reagents are designed to be used with samples that have an expected bromine range of 0.0 to 3.0 mg/L (ppm) Br₂.