At one end of the spectrum of the moisture world is the classic Speedy Moisture Tester where you use the reaction of water with calcium carbide to cause a mini explosion resulting in a moisture measurement reading. This method is used frequently for soils, concrete, and other like materials.
Loss-On-Drying moisture analysis seemed like a simple process until, in a state of naïve bliss, I promised to look at evaporation, vapor pressure and bound water. While I was otherwise occupied with hese realities, I offered to enter the world of witchcraft and folklore; water activity.
When our customers tell me about the different places where CENCO and CSC Digital Moisture balances are used it always interests me.
The most popular was to measure include:
- Drying the material and measure the weight loss
- Using a calibration and electronic instrument
- Using a titration method such as Karl Fischer
When using these processes, we take for granted that the results will be the product's actual moisture.
Topics: Coulometric Karl Fischer, Moisture Analysis, Moisture Testing, Karl Fischer Oven, Karl Fischer, Karl Fischer Titration, Loss-On-Drying, Moisture, interfacial tension, moisture content, moisture measurement
What seems like a million words ago, I began this journey explaining the simplest approach to measuring or determining moisture: Loss-on Drying. Little did I know how involved and esoteric it would become.
This voyage has taken me down mysterious paths through spooky theories, back to age-old chemistry concepts and into the vagaries of thermodynamics related to evaporation, vapor pressure, bound water and water activity. I have come full-circle; back to explaining Loss-on Drying -- a form of drying that I had assumed would be the simplest of all.
I thought the first four topics [evaporation, vapor pressure, bound moisture, water activity] were tough, complex, confounding and less-than-obvious. Drying -- defined as “the mass-transfer process of removing water (or other solute) by evaporation from a solid, semi solid or liquid” -- seemed easy.
As is often the case, reality makes “easy” a non-operative word. Such has turned out to be so with respect to the issue of drying.
In my previous missive about Loss-On drying, we discussed Vapor Pressure -- because logically it was next. As we continue to explore moisture, we learn how vital vapor pressure is when regarding the quirky issues of free and bound water.
Topics: Evaporation, Bound Moisture, Free Moisture, Moisture Analysis, Moisture Testing, Karl Fischer Titration, Praxis Moisture Balance, Loss-On-Drying, Moisture, karl fischer moisture, water content measurement
One quiet night, I was musing over moisture analysis and how easy it is to do using loss-on drying. Little did I know what was in store.
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.