Which instrument is commonly used for colorimetric testing to determine chlorine levels?

• A. Bacon bombs
• B. The DPD kit
• C. Alpha samplers
• D. The DR 900

Answer: (B)

Colorimetric testing detects chlorine by a chemical reaction that produces a color, and the shade of that color indicates how much chlorine is present. For chlorine, the classic reagent is DPD (N,N-diethyl-p-phenylenediamine). When DPD reacts with chlorine, a pink/magenta dye forms, and the deeper the color, the higher the chlorine concentration. A DPD kit combines the reagent with the water sample and then you read the color either by eye against a comparator or with a simple photometer to get a numeric value. This method is widely used because it is straightforward, portable, cost-effective, and works well for measuring both free and total chlorine with the appropriate reagent steps. While a dedicated photometer (like a portable colorimeter) can read the color more precisely, the DPD kit itself is the most common, practical tool for everyday chlorine testing in many settings.