This document discusses dissolution testing apparatus and methods. It defines dissolution as the process by which a solid substance enters the solvent phase to form a solution. Several theories of drug dissolution are described, including the diffusion layer theory, Danckwert's model, and the interfacial barrier model. Six common apparatus are summarized: the basket, paddle, reciprocating cylinder, flow-through cell, paddle over disk, and cylinder methods. Procedures for each apparatus are provided. Common dissolution media and factors affecting media selection are also outlined. The document provides an overview of key concepts and equipment in dissolution testing.

1. DISSOLUTION TESTING
APPARATUS
SUBMITTED BY
Y.AKHILA( Y18MPH352)
under the guidance of
M.GAYATRI RAMYA M.Pharm (ph.D)
A.N.U College of pharmaceutical sciences

2. DEFINITION
● Dissolution is the physicochemical process by which a solid sustance
enters the solvent phase to yield a solution.
● WHY DISSOLUTION STUDY:
● Estimation of amount of drug released per unit time.
● Batch to batch quality control.
● It is the rate limitimg factor for poorly soluble drugs.
● For product development.

4. Therioes of drug dissolution
● Several theories to explain drug dissolution have been
proposed. Some of the important theories are:
● 1. Diffusion layer theory
● 2. Danckwert’s model / penetration or surface renewal
theory
● 3. Interfacial barrier model / Double- barrier or Limited
solvation theorymm

5. Diffusion layer model / Film theory
● Solutions of the solid to
form a thin film or layer at
the solid /liquid interface
called as stagnant film or
diffusion layer which is
saturated with the drug.
● Diffusion of the soluble
solute from the stagnant
layer to the bulk of the
solution. This step is the
rate determing step in drug
dissolution

6. ● When the process is Diffusion – controlled and involves no
chemical reaction it ws given by Noyes and Whitney
● dC / dt = k (Cs – Cb )
● It was based on Fick’s second law of diffusion. Nernst and
Brunner incorporated Fick’s first law of diffusion and modified
the Noyes-Whitney equation to
● dC / dt = DAKW/O ( Cs – Cb ) / Vh

7. Danckwert’s model
● Danckwert did not approve of the existance of a stagnant
layer and suggested that turbalence in the dissoluion
medium exists at the solid/liquid interface. As a result, the
agitated fluid consisting of macroscopic mass of eddies or
packets reach the solute by diffusion and carry it to the
bulk of the solution.
● Such solute containind packetsare continuously replaced
with new packets of fresh solvent due to which the drug
concentration at the sold/liquid interface never reaches Cs
and has a lower limiting value of Ci. Since the solvent
packets are exposed to new solid surface each time, the
theory is called as surface renewal theory..

8. ●
●
●

9. Interfacial barrier model
• The rate determing step that control dissolution
is the mass transport.
• Solid- solution equlibrium is achieved at the
solid / liquid interface.
●
● G = Ki ( Cs – Cb )
● G = diffusion rate per unit area
● ki = effective interfacial transport constant

10. Dissolution media
● Common dissolution media used
● Purified water
● Dilution acid (0.9 N Hcl)
● Buffered aqueous solutions
● Simulated gastric fluid
● Simulated intestinal fluid
● Factors effecting selection of dissolution media:
● Dissolved gases
● Composition of dissolution media
● Ph of dissolution media
● Viscosity of dissolution media
● Surfacace

13. Apparatus 1-Basket apparatus:
● The assembly consists of the following:
● A covered vessel
● Transparent material
● A motor
● A metallic drive shaft
● A cylindrical basket the water bath permits the holding of temperature
inside the vessel at 37(+/-) 0.5 degrees centigrade
● The vessel is a cylindrical with hemispherical bottom.

14. ● The shaft is positioned so that
its axis is not more than 2mm at
any point from the vertical axis
of the vessel and rotates
smoothly.
● Use 40mm mesh cloth.
● A basket having gold coating
0.0001 inch thick may be used.
● The dosage unit is placed in a
dry basket at the beginning of
each test.
● He distance between the inside
bottom of the vessel and the
basket is maintained at 25+/-
2m.

15. Apparatus 2-Paddle apparatus
● A shaft is used as a stirring
element.
● The distance 25+/-mm between the
blade and the inside bottom of the
vessel.
● The paddle, blade and shaft may
be coated with a suitably inert
coating
● The dosage unit is allowed to sink
to the bottom of the vessel before
rotation of the blade.
● A small loose piece of nonreactive
maretial such as wire helix may be
attache to dosage units in order to
prevent floating.

16. ● Procedure :
● Place the stated volume of the
dissolution medium in the
vessel. Equilibrate the
dissolution medium to 37+/-
0.5degree centigrade.Place 1
tablet in the apparatus.
● Operate the apparatus .Within
the time interval, withdraw a
specimen from zone midway
between the surface of the
dissolution medium and the top
of the rotating basket, not less
than 1cm from the vessel wall.
● Replace equal volume of
dissolution medium at
37deg.cent.
Standard volume:
900/1000ml
Advantages:
1. easy to use
2. ph change possible
Disadvantages:
1. floating dosage forms require
sinker.
2. positioning of tablet.

17. Apparatus 3- Reciprocating cylinder
● The vessel is immersed in water
bath holding temperature at 37+/-
0.5 deg.cent.
● Standard volume: 200-
250ml/station
● Advantages:
● Easy to change the ph profile.
● Disavantage:
● Small volume[max. 250Ml]
● Limited data.

18. Procedure
● Place the stated volume of the
dissolution medium in each
vessel.
● Equilibrate the dissolution
medium to 37+/- 0.5deg.cent.
● Place 1 dosage- form unit in
each of the six reciprocating
cylinders.
● Operate the apparatus.
● During the upward and
downward stroke, the
reciprocating cylinder moves
through a total distance of 9.9 to
10.1 cm.
● Within the time interval
specified withdraw a portion of
the solution under test from a
zone midway between the
surface of the dissolution
medium and the bottom of each
vessel.
● Perform the analysis as directed
in the individual monograph.

19. Apparatus 4 – Flow through cell
• The assembly consists of a reservoir
and a pump for the dissolution
medium, a flow- through cell, a water
bath.
• The pump forces the dissolution
medium upwards through the flow –
through cell.
• The pump has a delivery rang
between 240 and 960ml per hour,
with standard flow rates of 4, 8 and
16ml per minute
Advantages
• Easy to change ph media
• Ph profile possible

20. Disadvantages
• High volumes of media
• Labor intensive
Procedure
• Place the glass beads into the
cell specified in the
monograph.
• Place 1 dosage form unit on
top of the beads.
• Assemble the filter head and
fix the parts together by means
of a suitable clamping device.
• Introduce by the pump the
dissolution medium warmed to
37 +/- 0.5 degree through the
bottom of the cell.
• Collect the eluate by fractions
at each of the times stated.
• Perform the analysis as
directed in the individual
monograph.
• Uses
• Low solubility drugs
• Micro particulates
• Implants
• Suppositories.

21. Apparatus 5- Paddle over disk
• The paddle and vessel
assembly from apparatus 2
with the addition of stainless
steel disk assembly.
Standard volume; 900 ml
Disadvantage
disk assembly restricts the patch
size

22. Procedure:
• Place the stated volume of
dissolution medium in the
vessel assemble the apparatus
without the disk assembly and
equlibrate the medium to 32
+/- 0.5 degree cent.
• Apply the transdermal system
disk assembly.
• The system may be attached to
the disk by a suitable adhesive
• Place the disk assembly flat at
the bottom of the vessel with
the release surface facing up
• and parallel to the paddle blade
and surface of the dissolution
medium.
• Operate the apparatus
• At each sampling time interval,
withdraw a sample from a zone
midway between the surface of
the dissolution medium and the
top of the blade, not less than 1
cm from the vessel wall.
• Perform the analysis on each
sampled aliquot as directed in
the monograph.

23. Apparatus 6 - Cylinder
• The dosage unit is placed on
the cylinder at the beginning of
each test.
• The distance between the
inside bottom of the vessel and
the cylinder is maintained at
25+/- 2 mm during the test.
• Procedure
Place the stated volume of the
dissolution medium in the vessel.
equilibrate the dissolution
medium to 32+/- 0.5 degree cent.

24. • Prepare the test system prior to
test as follows
• Remove the protective liner
from the system and place the
adhesive side on a piece of
cuprophan.
• Cuprophan covered side down,
on a clean surface, and apply a
suitable adhesive to the
exposed cuprophan borders.
• Dry for 1 min. press the
cuprophan covering to remove
trapped air bubbles.
• Place the cylinder in the
apparatus and immediately
rotate at the rate specified.
• Within the time interval
specified, withdraw a quantity
of dissolution medium for
analysis from a zone midway
between the surface of the
dissolution medium and the top
of the rotating cylinder, not
less than 1 cm from the vessel.

25. Apparatus 7- Reciprocating holder
• The assembly consists of a set of volumetrically calibrated or tared
solution containers.
• A motor and drive assembly to reciprocate the system vertically.
• A set of suitable sample holder.
• The solution containers are partially immersed in a suitable water
bath, inside the temperature of the container at 32+/- 0.5 degree cent.

26. REFERENCE
1.The theory and practice of industrial pharmacy by Lachman L,Liebrman.
2.www.slideshare.net