Basics
The expression „free Chlorine“ represents Chlorine dissolved in water, and that covers three different Chlorine compounds that form depending on pH: Chlorine as Cl2 gas can only be found in acidic solutions. With increasing pH Chlorine reacts with water to form Hypochloric acid - HOCl. At pH 2 and higher almost all Cl2 has reacted to HOCl.
- chlorine in water
At approx. pH 6, neutralisation starts, and the Hypochloric acid is transformed into Hypochlorite ion - ClO-. At pH 9 and higher almost all Hypochloric acid has turned into Hypochlorite salt. Set aside from the free Chlorine is the organic bound Chlorine that results from reaction of Chlorine with nitrogen- or carbon-containing substances, often as unwanted disinfection-byproducts. Most prominent among these are monochloramine and trichlormethane.
Effect
The pH-effect described above has consequences for the disinfection strength: with increasing pH the disinfection strength decreases. Hypochloric acid is a hundred times more efficient than Hypochlorite salt. On the other hand, due to the chemical reaction with water and the formation of Hypochlorite salt, Chlorine can be stored in alkaline solutions for quite long periods and shows a long-term effect of several hours.
Applications
Chlorine is used as disinfectant, for example for swimming pool water, and is part of many household detergents. The chemical industries use Chlorine both for processes and and for products, such as PVC, bleaching agents, for the synthesis of polycarbonate… Chlorine is one of the few disinfectants allowed for drinking water disinfection in Germany.
Dr. A. Kuntze measurement
- diagram sensor
We measure free Chlorine potentiostatically with measuring and counter electrodes of pure gold and a Ag/AgCl reference. The measurement shows good selectivity towards Chlorine. A precise potential is applied to the measuring electrode, leading to an accumulation of negative charges on the metal surface. Chlorine dioxide molecules that hit the surface take a defined portion of the charge with them. The controller measures the potential between measuring and reference electrode and readjusts the charge on the electrode surface. The current necessary to maintain a constant charge is a direct measure for the concentration of free Chlorine.
You would like to monitor the Chlorine dioxide concentration in your process?
We recommend our Krypton K: a complete measuring system with all necessary components, including a sampling point!
For a more individual set-up select an instrument – either K 100 Cl2 for panel installation or K 100 W Cl2 with wall-mounting housing -, our membrane-free sensor AuAu-600-OO-2-1-PG, a flow assembly GD 3VG with defined incident flow, a sensor cable 5 SCR-M12-AE-X, and – if desired – our patented sensor cleaning ASR (cable included).
We will be delighted to help you! Give us a call: +49 (0) 2150-7066-0
… Does the pH value change frequently in your application?
We recommend our Krypton K: a complete measuring system with all necessary components, including a sampling point for measuring chlorine and the pH-value!
- measuring point Krypton K
- measuring point individual
- measuring point Krypton D
You would like to monitor the Chlorine concentration in ambient air?
We recommend our K 100 (W) Gas. You can connect one or two gas sensors type GE 710 CL2. The diagram shows a typical measuring set-up to monitor the ambient air in storage rooms.
- gas measuring point
For each sensor two limit values can be defined, which operate separate relays. The first is supposed to activate an acoustic signal: by overstepping the limit value the alarm is set off. Manual acknowledgement switches off the relay. The second is supposed to activate the sprinkling system. A dela ycan be adjusted so that the sprinkling system starts only if the limit value is exceeded for a certain time. This relay can be switched off by digital input: if you connect a door contact, the sprinkling system will be switched off as soon as the maintenance personnel opens the door.
