Evaluation of Suspension - Pharmaceutics - I B. Pharma 1st Semester

Evaluation of Suspension

Learning Objectives

At the end of this lecture, student will be able to

• Enlist the instabilities in emulsions

• Recommend suitable measures for prevention of instabilities

• Explain the methods of evaluation of suspensions

Instabilities in Suspensions

1. Sedimentation

2. Cake formation

Prevention of Instabilities

1. Controlled flocculation

2. Use of right amounts of suspending / thickening agents

Evaluation of Suspension

1. Determination of rate of sedimentation

2. Determination of viscosity (Rheological method)

3. Determination of zeta potential

4. Determination of particle size change

1. Determination of rate of sedimentation

• Measurement of the sedimentation volume and ease of redispersion

Sedimentation volume = Ultimate height of sediment (Hu) / Initial height of sediment (Ho)

• Carried out in a measuring cylinder

• Larger this fraction, better is the suspendability.

• If the initial ht is 50 ml and after 1 day if the height of the sediment is 40 ml

Then S.V = 40/50 = 0.8

If the initial ht is 50 ml and after 1 day if the height of the sediment is 20 ml

Then S.V = 20/50 = 0.4

- Evaluation of redispersibility: is done using a mechanical shaking device which simulates the human arm motion during the shaking process.

2. Determination of Viscosity (Rheological method)

Determined using a Brookefield’s viscometer.

3. Determination of Zeta potential

• Zeta potential controls flocculation of the dispersed phase

• Determined by an instrument called “Zetameter”

• Measures the electrophoretic mobility of particles in suspension.

Zeta Potential

• Zeta potential is a scientific term for electrokinetic potential in colloidal dispersions. It is denoted using the Greek letter zeta (ζ), hence ζ- potential.

• ZP (ζ) is related to surface charge

• A high ζ will produce a well-dispersed suspension; this, in turn results in good sedimentation stability and solids loading capacity.

• In contrast, a low ζ results in particle association.

Effect of Zeta Potential on Suspension Properties

Zeta Potential Values

Zeta potential [mV]	Stability behavior of the colloid
from 0 to ±5,	Rapid coagulation or flocculation
from ±10 to ±30	Incipient instability
from ±30 to ±40	Moderate stability
from ±40 to ±60	Good stability
more than ±61	Excellent stability