Determination of Moisture Content

Water is a pervasive liquid. It has an ability to attach itself to most materials. This moisture can stick to the outside of the substance. This is known as free or surface moisture. Moisture can also get locked up in the molecular structure. This is known as bound moisture.

These differences in moisture content often require different moisture analysis methods. In addition, the composition of the material to be tested will influence the measurement technique needed.

Further complicating the selection of a method or technique is the length of time available to complete a moisture content test.

In order to provide solutions to most of these measuring problems, we offer instruments based on the following methods:

1. Loss on Drying (LOD)
2. Karl Fischer Titration

The following are the basics of each of these methods:

Loss on Drying (LOD)

The LOD method is the most widely used way of doing moisture analysis. This technique is based on the following steps: 1) weigh a sample of the substance, then heat the sample until the moisture is all driven off; 2) at this point, the sample is weighed again; 3) the difference in weight represents the amount of moisture that was in the original sample.

Limitations of this method involve two conditions. The first is when a material includes volatiles that are released at the same time as the moisture. Examples of such volatiles are the presence of sugars and fats. The second problem is with water that is tightly bound so that the heat energy needed to release the moisture will burn the sample first.

Karl Fischer Titration

The Karl Fischer test is water-specific, overcoming the problems of volatiles. The technique is based on using a solvent to separate water from the substance. This is done in a container closed off from the environment. The presence of the water is detected by an electrode. A reagent is introduced that converts the water to a non-conducting chemical. The electrode detects when the water is fully converted. The amount of reagent necessary to accomplish this is measured and convert to units of water.

For some materials, it is necessary to expose the sample to high temperatures and measure the amount of water in the resulting vapor. This process is accomplished in a Karl Fischer Oven.