Water in Various Gases – Fully Automated Determination by Coulometric Karl Fischer Titration

Water is an unwanted constituent of all kinds of gases. Precise determination is therefore a must, e. g., in medical gases, noble gases, process gases, and welding gases. The 875 KF Gas Analyser, from Metrohm (Switzerland), is a highly robust solution for this kind of analysis, combining precise sampling with the accuracy of coulometric Karl Fischer titration in a fully integrated, software controlled analyser.

Water can be determined with various analytical techniques at trace levels. However, water in gases is a particular challenge: Most of the feasible methods need to be calibrated and can only determine the water content indirectly. In contrast, Karl Fischer titration measures the absolute amount of water in the gaseous matrix. Moreover, results do not tend to drift, as the reagent is exchanged at regular intervals. As Karl Fischer titration is a primary method, the sensor does not need to be calibrated either. Detection limits of the method lie in the single digit ppm range (µg water/g gas).

The 875 KF Gas Analyser is controlled by tiamo, the leading control and database software for titration. The analyser module consists of a robust sampling system with a mass flow controller at its heart. Moreover, the system is equipped with an integral evaporator for liquefied gases, an inlet filter to separate out particles, and an oil filter. The titration vessel with indicator and generator electrode (with diaphragm), and an 851 Titrando coulometer are also included in the module. Safety is provided by the strict separation of the gas-carrying system and the electronic area.

Application Notes for the determination of the water content in the following gaseous matrices are available: AB-357 - Determination of water in gases and liquefied gases with the 875 KF Gas Analyser, AN-K-055 - Validation of the 875 KF Gas Analyser with certified reference gas, and AN-K-056 - Determination of the water content in hydrogen gas.