Drying Temperature; Drying Time; Sample Preparation - OHAUS MB23 Instruction Manual

MB23 / MB25
Performing a Trial Test
Prior to actual testing, a test run can be performed with these suggested settings:
(1) Temperature = 120
(2) Time = AUTO
(3) Sample = 3g of water. Place a glass fiber pad (included with the Analyzer) on the test pan, place on Pan Support. 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 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).
Sample Weight
0.5g
1g
2g
5g
10g
Repeatability
±1.0%
±0.6%
±0.3%
±0.12%
±0.06%
EN-5