Particle size analysis final

Question 2

Why must a drug dissolve before it can be absorbed?

Answer 2

Only dissolved drug molecules can cross biological membranes and enter the bloodstream.

Question 3

What is the most important factor controlling drug dissolution rate?

Answer 3

Surface area of the particles.

Question 4

How does particle size affect dissolution?

Answer 4

Smaller particles → larger surface area → faster dissolution.

Question 5

What equation links particle size to dissolution rate?

Answer 5

Noyes–Whitney equation.

Question 6

How does particle size affect bioavailability?

Answer 6

Smaller particles dissolve faster, increasing absorption and bioavailability.

Question 7

Why might very small particles be problematic in manufacturing?

Answer 7

They clump (cohesion), causing poor powder flow.

Question 8

How does particle size affect tablet production?

Answer 8

It affects powder flow and die filling, influencing dose uniformity.

Question 9

What happens if powder flow is poor during tableting?

Answer 9

Uneven die filling → tablets contain different drug amounts.

Question 10

Why does particle size affect drug taste?

Answer 10

Smaller particles dissolve faster in saliva → stronger taste (often more bitter).

Question 11

What particle size is optimal for inhalers?

Answer 11

1–5 µm (to reach the lungs).

Question 12

What does D50 (or X50) mean?

Answer 12

The median particle diameter — 50% of particles are smaller and 50% are larger.

Question 13

What is a polydisperse powder?

Answer 13

A powder containing a range of particle sizes.

Question 14

What is a monodisperse powder?

Answer 14

A powder where particles are all approximately the same size.

Question 15

Why are pharmaceutical powders usually polydisperse?

Answer 15

Manufacturing cannot produce perfectly identical crystals.

Question 16

Why do we use “equivalent sphere diameter”?

Answer 16

Real particles are irregular shapes, so we approximate them as spheres for measurement.

Question 17

What determines the particle size value obtained?

Answer 17

The measurement method used.

Question 18

What is a frequency distribution?

Answer 18

A graph showing how many particles occur at each size.

Question 19

What is a cumulative distribution?

Answer 19

A graph showing the percentage of particles smaller than a given size.

Question 20

How do you find D50 on a cumulative graph?

Answer 20

Find 50% on the y-axis → go to the curve → drop to the x-axis.

Question 21

In a histogram, where are most particles located?

Answer 21

Around the peak (highest bar).

Question 22

What does a right-hand tail (positive skew) mean in particle size distribution?

Answer 22

Many fine particles and a few coarse particles.

Question 23

What does a left-hand tail (negative skew) mean?

Answer 23

Many coarse particles and a few fine particles.

Question 24

What is bimodal distribution?

Answer 24

A distribution with two peaks (two common particle sizes).

Question 25

What is powder segregation?

Answer 25

Separation of particles based on size during storage or vibration.

Question 26

Why do small particles move downward in a mixture?

Answer 26

They fall through gaps between larger particles.

Question 27

Why is segregation dangerous in tablets?

Answer 27

Causes non-uniform drug distribution and dose variation.

Question 28

Why should drug and excipient particles have similar size?

Answer 28

To prevent segregation and ensure dose uniformity.

Question 29

What is a micronised powder?

Answer 29

Powder with particle size <10 µm.

Question 30

Why are drugs micronised?

Answer 30

To increase dissolution rate and bioavailability.

Question 31

What happens to flow as particle size decreases?

Answer 31

Flow becomes worse.

Question 32

What happens to dissolution as particle size decreases?

Answer 32

Dissolution becomes faster.

Question 33

What particle size range is measured by sieving?

Answer 33

About 45–1000 µm.

Question 34

What is the principle of sieving?

Answer 34

Separation by mesh size.

Question 35

What is the advantage of microscopy?

Answer 35

Provides particle size and shape information.

Question 36

What does SEM show that light microscopy does not?

Answer 36

3D surface texture and morphology.

Question 37

What is sedimentation based on?

Answer 37

Larger particles settle faster (Stokes’ law).

Question 38

What does a Coulter counter measure?

Answer 38

Particle size from electrical pulses as particles pass through an aperture.

Question 39

What is the principle of laser diffraction?

Answer 39

Particle size determined from how particles scatter laser light.

Question 40

How do large particles scatter light?

Answer 40

Small angles.

Question 41

How do small particles scatter light?

Answer 41

Wide angles.

Question 42

Why must aggregates be avoided in laser diffraction?

Answer 42

Clumps are detected as one large particle, giving incorrect size.

Question 43

What does laser diffraction provide?

Answer 43

Full size distribution (D10, D50, D90).

Question 44

What technique is best for nanoparticles?

Answer 44

Dynamic light scattering.

Question 45

What technique is used for inhaler aerosols?

Answer 45

Cascade impaction.

Question 46

Histogram with bars concentrated at small sizes and a right tail — what does it mean?

Answer 46

Mostly fine particles.

Question 47

S-shaped curve — what type of graph?

Answer 47

Cumulative distribution.

Question 48

Bars/columns graph — what type?

Answer 48

Frequency distribution.

Question 49

Why is particle size analysis important clinically?

Answer 49

It affects dissolution, absorption, and drug effect.