Ohaus MB23 MOISTURE ANALYZER Manual it - Manual (Page 7)

MB23 / MB25 EN-5
Press Tare to zero the pan weight. Add 3g of water to the fiber pad.
(4) Press Start to initiate the test. A perfect result on the trial test would be: 0g, 100% moisture or 0%solids.
Results may vary slightly due to weighing errors involved with a small sample, or other experimental
errors. See also Section 4. Test Optimization.
4. TEST OPTIMIZATION
Moisture is determined from the weight loss of a sample dried by heating.
The speed and quality of the measurement process will rely on the following parameters. Experimentation will also help
ascertain the optimal setup of these parameters:
 Drying temperature
 Drying time
 Sample weight
 Sample preparation
 Type of sample
Drying Temperature
 The drying temperature exerts a controlling influence on the drying time (e.g., a low temperature can prolong the drying
time unnecessarily).
 Select a drying temperature that neither decomposes nor changes the chemical structure of the sample.
 Some samples can give off different amounts of moisture at different drying temperatures. In these cases, deviations
can be compensated by changing the drying temperature.
Drying Time
This analyzer has three methods to establish the drying time.
 Manual, where the user stops the test in progress by pressing the Stop button. The test must be longer than 30
seconds to be a valid test.
 Automatic, which ends the drying process when detecting less than 1mg loss in 60 seconds. To keep the drying time
short, select a small sample weight that still maintains the required measurement accuracy.
 Timed duration, where the test ends when the pre-set drying time elapses.
Sample Weight
The weight of a sample influences the measurement time and repeatability of the results. With large amounts of samples,
more moisture must be vaporized and the process takes longer. Generally, the sample weight should be between 3g and
20g. 3g samples give fast results with some sacrifice in accuracy. 20g samples generally give more consistent results
but require a longer test time.
Another way to determine the sample weight is to use the relation between sample weight and repeatability, as shown in
the following table. If requiring repeatability results better than ±0.3%, for example, the table indicates that a sample
weight of at least 2g will be needed.
Sample Weight Repeatability
0.5g
1g
2g
5g
10g
±1.0%
±0.6%
±0.3%
±0.12%
±0.06%
Sample Preparation
Samples must always be uniform and representative of the total amount to obtain accurate and reproducible results.
When preparing samples, it is essential to ensure thin and uniform distribution of the sample on the test pan (i.e., avoid
piling and excessive amounts).
Types of Samples
Pasty, fat containing and melting substances
Use a glass fiber filter to increase the surface area of these types of samples (e.g., butter). The moisture in these
substances is more uniformly distributed through the filter. The increased surface area results in faster and more complete
vaporization of the moisture.