Last week, as I was reflecting on a recent moisture content problem, I recalled our series “Loss-on Drying and Other Moisture Mysteries.” In that series I examined moisture chemistry in products. However, I did little to define moisture content.
In the world of material testing, moisture content is different things to different people. However, there is a common concern. Manufacturers, distributors and retailers each are concerned with how moisture content affects what they are making, shipping, storing or selling. This will be today's focus.
My experience with checking for moisture in numerous materials and in different environments makes me conclude that moisture levels, measurement precision and absolute moisture amounts are moving targets. Moisture content standards for individual products, services or environments vary greatly.
What is important involving moisture content? Sometimes it is process yield. Sometimes it is the economics of water vs. other components of products. It could also be health and safety or a unique measure of final quality. Sometimes it is what takes place over time.
Considering all that, we wonder how best to determine total water. When the complexity of that task becomes apparent, we are tempted to question whether we care.
Let us indulge in a short digression to the main techniques we use to get closer to some answers. We dry materials until they stop losing weight and tentatively assert that the difference between the starting and ending weights is that of the water. Stop! Are we certain that other volatiles did not leave with the water or decompose with the heat?
We have of necessity devised other ways of accounting for these possibilities. Chemical techniques like Karl Fischer Titration, desiccation, freeze-drying, distillation and chromatography are suitable alternatives.
Some users are oriented toward water activity, a technique that integrates temperature, vapor pressure, dew point and relative humidity to obtain accurate data
Frequently the results from each of these techniques differ from one another. It would seem, then, that determining “how much water” is technically challenging. An easy, catch-all method to get at water content levels remains elusive.
In the end, we must compromise rather than seek absolutes, focusing on what actually works for each product, process and end result desired.
Hope this stimulates some new solutions to your individual moisture content problems.
I continue to prove to myself, how little I know about the enigmas of determining moisture content.
I remain a mystified,
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