Pharmaceutical Manufacturing Handbook: Production and

1174 EFFECTS OF GRINDING IN PHARMACEUTICAL TABLET PRODUCTION
TABLE 2
Sampling
Flowing Stream Sampling
Devices Procedure of Sampling Application and Characteristics
Auger sampler
(Figure 6 a )
[Line sampler
for stream]
Constant - volume
sampler
(Figure 6 b )
[Point sampler
for stream]
Diverter sampler
(Figure 6 c )
[Cross -
sectional
sampler for
stream]
Full stream
sampler
(Figure 6 d )
[Cross -
sectional
sampler for
stream]
A pipe with a slot is placed
inside the process stream,
permitting easy capture of
powder through the process
stream cross section when
rotated. Samples are
subsequently then delivered
into a separate container by
gravitational forces. [6]
Sampling occurs when the stream
falls down through a pipe and a
constant - volume container is
inserted or withdrawn from the
stream system.
The whole stream is diverted by
opening a sliding cover or
pivoting an external fl ap in the
bottom of a gravity - fl ow chutes
or pipes or screw conveyors
[12] . The samples could be
removed to a low - angle laser
light-scattering instrument then
returned to the process stream
[6] .
Samples are withdrawn from
conveyors, carried out only on
the return stroke.
While this is often used for
stream sampling, it is diffi cult
to collect a representative
sample when stream is
heterogeneous [10] .
Designed to extract a constant
volume of homogeneous
granular material for
subsequent chemical analyses
and is not suitable for
withdrawing samples for
physical analyses [11] .
The process could be automated
and highly suitable method
for online particle size
measurement. [7]
Extremely useful for dusty
materials provided the trough
extends the whole length of
the stream and does not
overfi ll [6] .
mathematically; however, in most conditions, the shape of a particle is often irregular,
especially in powder technology, which makes it extremely diffi cult to measure
geometrically. Therefore, various methods have been developed to determine the
volume of particles and powders. The two most in use in both laboratory and industrial
settings are liquid and gas displacement methods. The different values of particle
density can also be expressed in a dimensionless form, as “ relative density ” (or
specifi c gravity), which is the ratio of the density of the particle to the density of
water.
The discussion that follows will give an overview of the common methods used
in particle density measurement.