Evaluation of Suspension
Suspension is a coarse dispersion in which insoluble particles of a specified diameter (1 micrometer) are dispersed in a liquid medium that is generally aqueous.Read more - Suspension Meaning in Hindi.
For the evaluation of suspensions, the following types of tests are being carried out;
(a) Sedimentation Method
For the determination of sedimentation, two parameters are studied, which are;(i) Sedimentation volume
(ii) Degree of flocculation
(i) Sedimentation Volume
The volume of sedimentation is measured with the help of a measuring cylinder.A 50 ml suspension formulation is poured into a 100 ml measuring cylinder and put aside.
Now, read the sedimentation volume after 1, 2, 3, and 7 days. Then, read it for up to 12 weeks at weekly intervals.
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For each formulation, at least three results are obtained.
The sedimentation volume is calculated as per the equation given.
F = sedimentation volume
Vu = the ultimate height of sediment
V0 = the initial height of the total suspension
β = F/ F∞ = Floculated suspension sedimentation volume / Defloculated suspension
For each formulation, at least three results are obtained.
The sedimentation volume is calculated as per the equation given.
F = Vu / V0
Where, F = sedimentation volume
Vu = the ultimate height of sediment
V0 = the initial height of the total suspension
(ii) Degree of Flocculation (β)
The ratio of sedimentation of the volume of the flocculated suspension (F), and the sedimentation volume of the deflocculated suspension (F∞) is known as the degree of flocculation (β).β = F/ F∞ = Floculated suspension sedimentation volume / Defloculated suspension
sedimentation volume
The value of F ranges from less than one to greater than one
Normally, F < 1.
When F < 1 --- V₁ <Vo
When F = 1 --- Vu <Vo
The system is in flocculated equilibrium and shows no clear supernatant on standing.
When F >1 --- V >Vo
The value of F ranges from less than one to greater than one
Normally, F < 1.
When F < 1 --- V₁ <Vo
When F = 1 --- Vu <Vo
The system is in flocculated equilibrium and shows no clear supernatant on standing.
When F >1 --- V >Vo
The higher the value, the higher the stability.
It is known that due to sedimentation and formation of cake, the suspension has lesser physical stability among all the dosage forms.
When the viscosity of the dispersion medium is increased, the terminal settling velocity decreases because of this the dispersed phase settles at a slower rate, and it remains dispersed for a longer period, which yields higher stability for the suspension.
In the same way that the viscosity of the suspension increases, the durability of the suspension decreases, which becomes an inconvenience to the patients, increasing the doses.
If the suspension’s viscosity increases, then the pourability of the suspension decreases, which becomes very inconvenient to the patients when increasing the dose.
Hence, to get stable and easily pourable suspensions, the viscosity of the suspension should be maintained within the optimum or desired range.
A Brookfield viscometer that is mounted on a helipath stand is used in the rheological method.
For descending slowly into the suspension, a T-bar spindle is made, and then the resistance that the spindle shows at various levels in sediment is measured in a viscometer reading dial.
The different samples that were stored for a very long period show whether the required changes are needed or not. This measurement is done on undisturbed samples that are of different ages. The results show that with time how the particles settle over time.
In the study of screening, if the suspension is of good quality, then it shows a lower rate on the dial reading with the turns of a spindle, that is, the curve will be horizontal for a longer period.
(b) Rheological method
For the stability as well as pourability of suspensions, it is very important to prepare a suspension with the desired viscosity.It is known that due to sedimentation and formation of cake, the suspension has lesser physical stability among all the dosage forms.
When the viscosity of the dispersion medium is increased, the terminal settling velocity decreases because of this the dispersed phase settles at a slower rate, and it remains dispersed for a longer period, which yields higher stability for the suspension.
In the same way that the viscosity of the suspension increases, the durability of the suspension decreases, which becomes an inconvenience to the patients, increasing the doses.
If the suspension’s viscosity increases, then the pourability of the suspension decreases, which becomes very inconvenient to the patients when increasing the dose.
Hence, to get stable and easily pourable suspensions, the viscosity of the suspension should be maintained within the optimum or desired range.
A Brookfield viscometer that is mounted on a helipath stand is used in the rheological method.
For descending slowly into the suspension, a T-bar spindle is made, and then the resistance that the spindle shows at various levels in sediment is measured in a viscometer reading dial.
The different samples that were stored for a very long period show whether the required changes are needed or not. This measurement is done on undisturbed samples that are of different ages. The results show that with time how the particles settle over time.
In the study of screening, if the suspension is of good quality, then it shows a lower rate on the dial reading with the turns of a spindle, that is, the curve will be horizontal for a longer period.
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(c) Electro Kinetic Method
In the electrokinetic method, the zeta potential is measured with the help of the microelectrophoresis apparatus and zeta plus. Because of this, the stability of the dispersed system is obtained.Example - Micro-electrophoresis apparatus MK-1
Zeta Potential
With the help of zeta, the zeta potential of the prepared suspension is measured.By using the pipette, approximately 1ml of suspension is transferred into a plastic cuvette and diluted with distilled water.
For the measurement of zeta potential, the Brookhaven zeta potential software is used.
At a temperature of 25°C, all the parameters are set, and the refractive index should be 1.33.
Now, the zeta potential of the preparation is measured on day 0, day 7, day 14, day 21, and day 28 of the post-formulation.
(d) Micromeritic Method
The particle size of the dispersed phase is determined by the stability of the suspension.If there are any changes in particle size over time that will give beneficial information about the stability of the suspension.
The change in the particle size distribution, as well as the crystal habit, may be studied with the help of a microscope and with the help of the Coulter counter method.
Photo Microscopy Method
To estimate and determine the changes in particle size distribution and crystal form, the microscope may be used.By attaching the Polaroid camera to the piece of the monomolecular microscope, the fast processing of photomicrographs is increased.
With the help of photomicrographs, you can determine the stability as well as changes in the physical properties of the suspension.
(e) Freeze-Thaw Test
The Freeze-thaw test determines the tendency of the suspension to form crystallization or color.Freeze-thaw tests the sample is placed in the freezer for up to 18 hours, and after that, placed at room temperature for up to 4 to 6 hours.
Then repeat this freeze-thaw cycle up to 10 times.
(f) pH Measurement
In quality control testing, the measurement of pH as well as the maintenance of pH is one of the important steps.There are mainly two types of methods that are used in the measurement of pH.
Methods for pH measurement
For the measurement of pH, dip a piece of pH paper into the sample and match the color of the pH paper to the table specified on the table. This is one of the simplest and cheapest methods that is used in the measurement of pH.(g) Visual Inspection
By visual inspection, the ingredients and the final products were examined very carefully.The visual inspection determines the purity and appearance of the final products.
The physical appearance of the products is very important for the patients because if the physical appearance of the products is not good, then it will hamper patient adherence, and patient compliance becomes critical, so it should be:
- Looking good and,
- Appearance should be elegant
Evaluation of Suspension Tutorial Video
Conclusion
I hope that you have liked the article on the evaluation of suspension. If you did not understand any point, ask in the comments.
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