TRANSFORMING RESULTS
Results from number based systems, such as microscopes or image analyzers
construct their beginning result as a number distribution. Results from laser
diffraction construct their beginning result as a volume distribution. The software for
many of these systems includes the ability to transform the results from number to
volume or vice versa. It is perfectly acceptable to transform image analysis results
from a number to volume basis. In fact the pharmaceutical industry has concluded
that it prefers results be reported on a volume basis for most applications (ref. 6).
On the other hand, converting a volume result from laser diffraction to a number
basis can lead to undefined errors and is only suggested when comparing to
results generated by microscopy. Figure 13 below shows an example where a laser
diffraction result is transformed from volume to both a number and a surface area
based distribution. Notice the large change in median from 11.58µm to 0.30µm
when converted from volume to number.
12
10
8
6
4
2
0
0.34
0.58
1.15
2.27
4.47
8.82
17.38
34.25
PARTICLE SIZE
NUMBER DISTRIBUTION
MEAN = 0.38µm
MEDIAN = 0.30µm
SA = 13467 cm²/cm³
STANDARD DEV = 0.40
NUMBER
AREA
VOLUME
VOLUME DISTRIBUTION
MEAN = 12.65µm
MEDIAN = 11.58µm
SA = 13467 cm²/cm³
STANDARD DEV = 8.29
figure 9
|
13 BEANS OF EACH SIZE
figure 10
|
THE SAME
39 BEANS PLACED
IN VOLUMETRIC CYLINDERS
figure 11
|
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