Ethylene glycol is an industrial compound that is used in antifreeze, coolant for engines, airplane de-icing, heat transfer agents, conditioning agent in adhesives, cork, fibers, films, synthetic rubber, cellulose sponges, printing inks, and paper products. Ethylene glycol is also used in the dehydration of natural gas as well as in the production of alkyd-type resins and unsaturated polyester resins. Ethylene glycol (monoethylene glycol (MEG), IUPAC name: ethane-1,2-diol) is a colorless, odorless, moderately viscous, hygroscopic liquid with a sweet taste (toxic!). Ethylene glycol is produced from ethylene, via liquid phase hydration of the intermediate ethylene oxide with a dilute sulphuric acid solution. An excess of water and different glycols are separated by vacuum distillation. Ethylene glycol, like most other alcohols, can also be manufactured by reacting chlorine and water with ethylene to form the chlorohydrin, which is then hydrolyzed to yield glycol. The desired concentrations are obtained by mixing a concentrated solution with water to achieve the desired percent concentration. The growing number of large-scale air-conditioning systems that contain a large amount of heat transfer liquid (mainly ethyleneglycol) require constant surveillance. This surveillance can be done automatically and in real-time with the Schmidt + Haensch iCS. With this inline sensor, maintenance of cooling systems can be reduced and hazardous leakages in the heat exchanger system can be detected early to prevent environmental pollution. The Process Refractometer IPR is used to measure the concentration of ethylene glycol as a quality control of e.g. the de-icing in airport facilities/de-icing trucks or antifreeze/coolant of the cooling system in compressor stations, etc. Typical measurement ranges are 0-40% or 0-70%, and the normal process temperatures range between -25 °C (13 °F) and 40 °C (104 °F) or 100 °C (212 °F), depending on the customer’s need.