Powders: Powder sampling and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector Exam

Powders: Powder sampling and MCQs for GPAT, NIPER, Pharmacist and Drug Inspector Exam

When powders are poured into a pile, segregation occurs. Particles with small size (fine particles) will stay in the center of the pile, and coarser particles tend to concentrate at the periphery. Size segregation is unavoidable, during powder transportation, storage, or packing. Therefore, powder sampling is important for the quality control of the final product.

Table no. 1 – Summary of sampling methods

Apparatus Type of sampler Method of sampling Scale Advantages Disadvantages
Sample thief Manual Tubular steel retains a core
sample when inserted into
powder
Large
and small
Good for free-flowing powders Additional weight at bottom of bag may vary sample size;
Can be hard to push into powder; Fines may lodge between
tubes; Particles can fracture; Fines compact, impeding
flow; Segregation may occur as fines percolate into sample
more easily than coarse particles; A plug of powder can be
pushed ahead of thief and surface material contaminates
sample; Personal preference introduces bias for the area
sample
Hand scoop Manual Cross-sectional sample from
moving stream, bags, or
barrels
Large Simple and cheap Thin layer may remain on belt, leading to bias; Overfilling can
lead to an excess of fines.
Shovel Manual Pits are drug in the powder
bed and a shovelful taken
from bottoms and sides
Large, up
to several
tons
Simple and cheap Cannot be used with particles of more than 5 cm diameter
Cross-cut
sampling
Manual/
semiautomatic/
automatic
Material is shovelled from the
conveyor belt
Large Simple Can leave a layer on the belt and result in bias
Pneumatic
lance
Semiautomatic Air flow used on entry and
exit of lance from powder
bed
Large Disturbance of powder minimized
over sample thief; Porous plate
prevents too many fines due to
strong air current
Personal preference may bias sample.
Vacuum probe
sampler
Semiautomatic Powder extracted by vacuum Large Simple Difficult to sample below surface without contamination;
Personal preference leads to bias; Fines more easily
extracted than coarse particles.
Gravity-flow
auger sampler
Semiautomatic Slotted tube in flowing
powder rotates and worm
screw carries out material
Large
and small
Easy to use Bias is still a problem here; Difficult to sample all of powder
stream, therefore bias.
Sampling
from a moving
stream
Manual/
automatic
Powder is sampled as it falls
off the conveyor
Large If carried out properly can be very
good sampling technique; easily
designed into a new plant.
If overfilled, a greater number of fines than coarse particles
are collected; Difficult and expensive to fit into an existing
plant; Obtaining a fixed sample is difficult; Difficult to prevent
dust escaping.
Full-stream
trough
sampler
Automatic Powder is sampled as it falls
off the conveyor
Large Can be used to sample dusty
material
Must not overfill; Difficult and expensive to install into
existing plant.
Arc path
cutter
Automatic Chute moves through powder
stream, and collects sample
Large No operator bias Difficult to take more than one sample size; Must cover the
whole of the stream to avoid bias.
Straight path
cutter
Automatic Rectangular chute moves
through powder stream
Large Different sample sizes can be
taken easily
Must cover the whole of the stream to avoid bias
Moving-flap
sample divide
Automatic A flap in the streamsamples
powder or allows it to be
stored depending on its
position
Large Efficient as covers the whole of
the stream when sampling
Resultant sample is large and subsampling needed. Bias
may be introduced here; Bias is present due to one side
being sampled more than the other.
Integrated
automatic
sampling plant
Automatic Primary sample is selected
and repeatedly screened,
resulting in the final sample
Large Quick Variations in materials can cause problems
Chute splitter Sub-sampler A series of chutes split
sample repeatedly
Large Can be repeated until desired
sample size is achieved
If segregation occurs the result can be misleading; Prone to
operator bias.
Cone and
quartering
Sub-sampler Powder poured through cone
and divided into four equal
parts. This is repeated until
the desired sample size is
reached
Small Simple Prone to operator bias as fine particles remain in the center
of the cone; Symmetry is difficult to achieve but essential for
accuracy.
Spinning riffler Sub-sampler A steady stream of powder
flows into a rotating basket of
containers
Large/
small
Good for sub-sampling large
samples; Good for powders with
good flow properties; Minimal
bias; More efficient than other
samplers tested.
Air currents may displace fines but can be avoided with
a slower rotation speed; Expensive; Time-consuming;
Segregation may be a problem.
Free-fall
tumbler mixer
Sub-sampler A ladle in the lid of the
mixer collects a good
representative sample
Large/
small
Can be used with fines present;
Representative sample produced
in a short time period.
Hopper
sample divider
Sub-sampler Hoppers oscillates and powder
falls into two containers. Only
one of the contents is kept.
Small Sample size can be controlled
by monitoring time over each
container
Large number of increments needed for accuracy
Table sampler Sub-sampler Powder flows down inclined
plane and prisms and holes
split the powder
Small Simple Very low accuracy; After each separation should be a
complete mix to avoid errors.

 Multiple choice questions:

1.When powders are poured into a pile _____ occurs.

a)segregation

b)agglomeration

c)sticking

d)all of these

2.Size segregation is unavoidable, during

a)powder transportation

b)storage

c)packing

d)all of these

3.Tubular steel retains a core sample when inserted into powder in which of the following?

a)Sample thief

b)Straight path cutter

c)Free-fall tumbler mixer

d)Table sampler

4.Which of the following is/are advantage of sample thief?

a)Good for free-flowing powders

b)Efficient as covers the whole of the stream when sampling

c)Can be used to sample dusty material

d)Simple

5.In Hand apparatus which of the following sampling methods are used?

a)Cross-sectional sample from moving stream

b)Cross-sectional sample bags

c)Cross-sectional sample from barrels

d)all of these

6.Which of the following is/are disadvantages of hand scoop method of sampling?

a)Thin layer may remain on belt, leading to bias

b)Overfilling can lead to an excess of fines

c)both of these

d)only b

7.Shovel apparatus is

a)automatic

b)manual

c)semi automatic

d)sub sampler

8.Cross-cut sampling apparatus is

a)automatic

b)manual

c)semi automatic

d)all of these

9.Which of the following is/are disadvantages of Pneumatic lance?

a)Large number of increments needed for accuracy

b)Very low accuracy

c)After each separation should be a complete mix to avoid errors

d)Personal preference may bias sample

10.Vacuum probe sampler have following advantage

a)Good for free-flowing powders

b)Efficient as covers the whole of the stream when sampling

c)Can be used to sample dusty material

d)Simple

11.Arc path cutter is based on which of the following sampling methods?

a)Chute moves through powder stream, and collects sample

b)A steady stream of powder flows into a rotating basket of containers

c)A ladle in the lid of the mixer collects a good representative sample

d)Powder flows down inclined plane and prisms and holes split the powder

12.In which of the following rectangular chute moves through powder stream?

a)Arc path cutter

b)Straight path cutter

c)Chute splitter

d)all of these

13.Cone and quartering apparatus is

a)automatic

b)semi automatic

c)manual

d)sub sampler

14.Which of the following is/are advantages of  Free-fall tumbler mixer?

a)Can be used with fines present

b)Representative sample produced in a short time period

c)Both of these

d)None of these

15.Powder flows down inclined plane and prisms and holes split the powder in which of the following apparatus?

a)Table sampler

b)Hopper sample divider

c)Spinning riffler

d)Integrated automatic sampling plant

Solutions:

  1. a)segregation
  2. d)all of these
  3. a)Sample thief
  4. a)Good for free-flowing powders
  5. d)all of these
  6. c)both of these
  7. b)manual
  8. d)all of these
  9. d)Personal preference may bias sample
  10. d)Simple
  11. a)Chute moves through powder stream, and collects sample
  12. b)Straight path cutter
  13. d)sub sampler
  14. c)Both of these
  15. a)Table sampler

 References:

  1. Remington Essentials of Pharmaceutics, 1st edition 2013, page no. 429-431.

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