Biomedical Engineering Reference
In-Depth Information
solution); 2) mixing with potential product impact (e.g., shear-sensitive prod-
uct). Undermixing (i.e., inadequate) would be a concern in both cases because
of a nonhomogeneous condition that may cause a nonrepresentative assay sam-
ple, quality, or yield impact; however, overmixing (i.e., excessive) should be
prevented for shear-sensitive products because of potential product degradation
or physical breakdown. The factors that impact mixing and could contribute
to product impact because of overmixing are power per volume, mixing time,
agitation style, temperature, product type, and concentration.
The first step in a risk-based approach is to identify mixing equipment, size
and configuration, and mixer type by the process steps. Risk analysis of the
mixing process parameters (i.e., input variables) and their impact on product
quality would then help design the mixing study to determine appropriate mixing
parameters for manufacturing operations. Figure 8.6 shows mixing behavior (i.e.,
homogeneity) in a 15,000 liter tank for solutions, where the sample was collected
from a sample port. As expected, concentration varied initially with time, but a
homogeneous condition is achieved within 6 min of time for working volumes of
2001-14,997 liters (Fig. 8.6). Sampling at various locations would have revealed
additional data on mixing dynamics at the prehomogeneous state; however, sam-
pling from the top, middle, and bottom of the tank is not required to determine
a homogenous condition. Solution samples from any location should provide the
same results (except measurement variability) once a homogeneous condition is
reached. As shown in Figure 8.6, a homogeneous condition is independent of
sample locations; hence, there is no need to create a special sampling device to
5
2001 L
4569 L
6300 L
14,997 L
4
3
2
1
0
0
1
2
3
4
5
6
7
8
9
10
−
1
Time (min)
Figure 8.6
Mixing in a 15,000 L tank. (
See insert for color representation of the figure
.)
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