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Highly accurate measurement technique for detection of trace amounts of water
Sartorius WDS400
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The WDS 400 Water Detection System, called WDS 400 for short, is an analyzer for selective detection of water in solids, and developed by Sartorius AG, Goettingen, for use in the chemical and pharmaceutical industries. Unlike thermogravimetric methods, which do not distinguish between water and other volatile components such as oils, fats and alcohols in the analysis of moisture content, the WDS 400 specializes in the analysis of pure water content. The unit achieves this through the combination of oven drying, coulometry (Karl-Fisher-titration) and phosphorus pentoxide (the reference method for determining moisture in gas) measuring methods, resulting in a powerful and remarkably accurate detection technique. The WDS 400 has a detection limit of 1 µg of water, and covers a measuring range from just a few parts per million (ppm) up to 40% absolute water content.
Sample Testing and Measurement Procedure
The sample to be tested is initially weighed on a microbalance or semi-microbalance using a nickel sample scoop, and then heated in the WDS 400's built-in stainless steel oven. The user-defined temperature curve permits gradual heating up to a maximum temperature of 400°C. Nitrogen is used as the inert carrier gas, which absorbs the evaporated water and transfers
it to an electrochemical sensor coated with phosphorous pentoxide. This sensor is the electrolytic cell where the actual measurement takes place. The reaction with the phosphorous pentoxide causes an electrolytic breakdown of the water molecules into their hydrogen and oxygen components. The two electrons from each electrolyzed water molecule generate a measurable electric current, and Faraday's Law is applied to convert the current measured directly into the number of water molecules present. This calculation yields the mass of water that evaporated from the sample.
A computer running the Windows® operating system is interfaced with the WDS 400 to record measurements and evaluate the fractions of surface water, capillary water and water of crystallization, using control and evaluation software that is supplied with the WDS 400 analyzer.
New!
In a modified version, the WDS400 now offers added benefits. An integrated air pump with a drying module connected downstream enables you to use room air as the carrier gas for non-flammable materials. This ideal solution considerably reduces the operating costs for many analyses as you no longer need to use nitrogen. Only for flammable samples that react with oxygen in the air will you need to continue using nitrogen.
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