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.
CSC Scientific Blog
“How Many Ways are there to Measure Moisture?”
That is a recurrent question in early discussions about moisture measurement problems. Is frequently asked in connection with specific products and applications. This is a basic primer on the main techniques.
Most Used Methods to Measure Moisture Content
There are four core methods. They include the use of heat, chemicals, electrical properties and electrro magnetic phenomena.
Regularly I’m asked the question; “How accurate is this moisture balance?”
The questioner asks for the answer in terms of percent (%) moisture. When I answer “it depends”, I always get the unspoken response, “Why did I ask this stupid idiot?”
When you ask about the accuracy of something like weight or temperature the answers are straight forward and relate to the instruments' precision. For example 25 grams or 50 degrees plus or minus (+/-) 0.1 gram or 1/2 degree.
Percent is Relative
When you ask the question of how accurate is my percentage reading, the answer becomes complicated. It’s complicated because percentage (%) is a relative term. For example, the answer for the result of a Loss on Drying (LOD) moisture test, is based on the size of the sample you use.
Using the example of a LOD moisture test we can understand the concept. The result of this type of test is calculated by subtracting the weight of the sample at the end of the test from the weight of the sample at the beginning of the test. This difference is divided by the initial weight of the sample. This procedure produces a % moisture result.
In the following analysis, the implication s of sample size and instrument precision will be illustrated. This will be based on a sample that has 23.5% moisture and an electronic LOD moisture balance that has a sensitivity of 0.001 grams and repeatability of ± .005 grams.
The answer to the question, “How Long Does a Water Activity Test Take?” is, as with most testing questions, “it depends.” Some water activity meters promise a test completed in a very short time; some in as little as five minutes. This time is an arbitrary selection that may or may not produce a satisfactory result.Read More
As people who measure moisture, we at CSC Scientific work to find the best technique.Read More
When we first started measuring moisture with Karl Fischer, I was instructed in the complex chemical reactions involved. I was also was told that the process was skittish.Read More
When our customers tell me about the different places where CENCO and CSC Digital Moisture balances are used it always interests me.
A question we get a lot is:
“How do I determine the moisture in my product?
Of course, the answer is often “it depends”, and the method does depend on the chemical and physical composition of the product. There are several methods used to determine moisture content: Loss-on-Drying (also known as Weight Loss), Karl Fischer, NIR, and Radio Frequency.
“Why are my Moisture Test results inconsistent?”
That is an issue for many of you who test for moisture. We discussed the complexities and multiplicity of issues involved with moisture content determination in our “Loss-on Drying Moisture Analysis and other Moisture Mysteries” series.
In addition to intrinsic properties of test samples that may adversely affect moisture testing systems, automatic equipment parameter set-up, operator oversights and sample handling contribute to seemingly intractable moisture test result inaccuracies.