Let’s start out by explaining why you may need a moisture analyzer.
Title 21 of the Code of Federal Regulations section n explains “Safe-moisture level is a level of moisture low enough to prevent the growth of undesirable microorganisms in the finished product under the intended conditions of manufacturing, storage, and distribution.
“The maximum safe moisture level for a food is based on its water activity (aw). An aw will be considered safe for a food if adequate data are available that demonstrate that the food at or below the given aw will not support the growth of undesirable microorganisms.”
The Role of the Moisture Analyzer
Moisture analyzers are widely used in meeting these standards. They go far beyond the food industry – affecting such diverse products as pharmaceuticals, plastics, paint, wood, birdseed, soybeans, fertilizer, cement, detergent, shampoo…etc.
A Moisture Analyzer Measures More than Water Activity
While Title 21 refers to “water activity” (aw), for the subject of this post, moisture is anything that evaporates on heating. Examples include fats, oils, alcohol, and solvents.
Moreover, moisture can lurk in places many folks would not suspect. Three examples of where moisture can exist include:
- On the surface of a sample. This can be defined as bulk water attracted to other substances. Even though you might not see it, it can be there, and its presence affects the weight of the substance. Surface moisture is most easily removed in a moisture analyzer.
- In pores or capillaries, where it more difficult to remove. Absorbed moisture can be inside the substance particle (think wet soil) or in tiny capillaries or crevices of roughly shaped substances. Generally evaporating this type of moisture takes more time than required to remove surface moisture.
- Water molecules that are chemically bonded with other molecules as water of crystallization or as hydrates or adhesively bound water chemically bonded to a material at the molecular level. An example is gypsum. Evaporating water of crystallization is more complex than surface and absorbed moisture because the substance may also have surface moisture as well as chemically bonded water. Removing surface moisture is one part of the process; removing water of crystallization is another and more difficult part. This is because the heat required may in some instances result in product decomposition.
OK, But Just What is a Moisture Analyzer?
A moisture analyzer, also called a moisture balance, is a programmable benchtop laboratory instrument used to measure the moisture content of small samples of products being manufactured or processed. Moisture analysis can be performed prior to, during, or after processing just before product packaging.
It combines an analytical balance with a heater to drive off moisture from products being tested.
Unlike large oven dryers performing bulk drying on production lines, a moisture analyzer is used to confirm bulk dryers are doing the job correctly, or that adjustments must be made in processing lines.
How does a Moisture Balance Operate?
Most moisture analyzers today operate on what is called the thermogravimetric principal – that is determining the lost of weight on drying (LOD). The loss represents the amount of moisture given off during the drying process while the change in weight is recorded by the analytical balance.
Testing procedures are programmed into to the moisture balance and the change in weight is continually calculated as it performs the drying operation. Because of small sample sizes the analysis can be accomplished very quickly.
Drying temperature is supplied by either infrared or halogen heaters with the latter technology being most prevalent because it can be used to determine the moisture content of virtually any substance. It is also faster than infrared drying.
Microwave drying is another technology, but these instruments are somewhat larger and significantly more expensive than halogen-heated moisture analyzers.
A popular halogen unit is the XM 60 moisture analyzer that is available from Tovatech. It serves as an example of the specifications to be considered in purchasing such units. It operates at a temperature range of 30 – 230˚C in 1˚C increments.
Researchers and QC personnel select soft (slow), standard and boost (high) heat rate drying profile management without requiring ramp programming. Report generating is simplified by pressing the Key- Select™ mode until the display shows the desired report, then releasing the key to send the report to a printer or via the RS232 output to the computer.
Moisture Analyzers for Specific Tasks
You can specify a moisture analyzer that is designed to simplify specific tasks. The XM60 mentioned above, for example, is recommended for gauging moisture content in the food industry
Companies striving to deliver superior quality injected molded products are aware that the moisture content of their resins feeds is absolutely critical to product quality. The DSC 71P moisture analyzer is excellent for testing low moisture plastics. To save you time it has a default program to test 75% of the most commonly used resins.
And as a final example, measuring moisture content in the wood, paper and pulp industries can be accomplished by several models including the portable IL 50.01 TS Moisture Analyzeror the XM 60 moisture analyzer with a 20 program memory.
Moisture Analyzers are Easy to use, but…
With their large LED displays moisture analyzers are relatively easy to use. But operators must be familiar with and follow the precise steps necessary to obtain accurate readings for the specific products being analyzed. While their operations may differ based on specific models here’s a typical analysis sequence:
- Establish the procedures for the products being tested and program the balance accordingly. Include each of these procedures in your company’s operations manual.
- Place the sample plate on the moisture balance sample plate holder then tare the balance
- Spread the recommended amount of product evenly on the sample plate and record the weight.
- Close the cover of the moisture balance to start the sequence.
- The unit’s display panel continually updates the status of the process. The analysis automatically terminates when drying is complete and the dry weight is stable, or after a fixed time specified by the operator, or manually.
At the end of the moisture weighing all relevant data concerning initial mass, residual mass, test parameters and results can be printed out via an RS-232 interface.
When the moisture analyzer is connected to a PC the data acquisition software allows the operator to produce a graph plotting results against time, providing valuable information on speed of drying and confirmation of dry weight stability.
Results of individual tests can be stored in the computer memory for subsequent comparison. All moisture analyzers offered by Tovatech meet GLP/ISO record keeping requirements.
Note that moisture analyzers must be recalibrated on a regular basis and every time they are moved from one location to another. Recalibration procedures for both weight and temperature are spelled out in the user manual.
Need More Info on Moisture Analysis?
There’s lots more to selecting, using, and maintaining a moisture analyzer. Info expanding on what is presented here can found by clicking on our article How a Moisture Analyzer Works.
Please call us for more information on selecting and operating precision moisture analyzers.