DeanStark

Dean-Stark refers to the Dean–Stark apparatus, a laboratory device used to determine the water content of organic solvents and other material by azeotropic distillation. The method and apparatus were developed in the 1930s by F. Dean and D. Stark and are widely used in chemical, petrochemical, and polymer laboratories.

Principle and design. The apparatus consists of a boiling flask connected to a reflux condenser, with a sidearm water trap that directs the distillate into a calibrated receiver. When a sample containing water is heated with a solvent that forms an azeotrope with water (often immiscible with water, such as toluene or xylene), the water is carried over with the solvent. The condensate returns to the flask, while the water separates and accumulates in the trap. As distillation continues, the water level in the trap rises and can be read from the graduated receiver. The amount of water measured corresponds to the moisture content of the sample or solvent being analyzed.

Applications. The Dean–Stark method is used to determine water content in organic solvents, oils, fats, polymers, and solid samples that release water during heating. It is also used to monitor drying processes and assess moisture in reaction solvents prior to polymerizations or extractions.

Limitations and considerations. The method works best for systems where the solvent forms an azeotrope with water and is immiscible with water. If the solvent is fully miscible with water, the method may not provide accurate results. It can be time-consuming and involves heating flammable solvents, so appropriate safety measures and ventilation are required. In modern practice, Karl Fischer titration is sometimes used as an alternative for precise moisture determination.