Dissolution is the process by which a solid enters a solution and forms a homogeneous mixture. There are several theories that describe the mechanisms of dissolution, including film theory, interfacial barrier models, and convective diffusion theory. In vitro dissolution testing utilizes standardized apparatus like baskets, paddles, cylinders, and flow-through cells to simulate dissolution in vivo and assess drug release from dosage forms over time according to established pharmacopeial methods.

1. Dissolution
Dr. Nilesh S. Kulkarni
PES Modern college of Pharmacy ( For Ladies) Moshi Pune
Nilesh Kulkarni

2. WHAT IS DISSOLUTION?
The process by which a solid or liquid forms a
homogeneous mixture with a solvent
OR mass transfer form solid phase to liquid phase
Tablet Dissolution is a standardised method for
measuring the rate of drug release from a dosage form
Nilesh Kulkarni

3. It all started in 1897 with the first reference to dissolution:
Noyes and Whitney publish a paper on
"The Rate of Solution of Solid Substances in Their Own
Solution.”
1904-Nernst and Brunner modified the Noyes-Whitney equation.
1931-Hixon and Crowell develop the cube-root law of diffusion.
1975-USP begins development of calibrators for dissolution
testing.
History of Dissolution testing
Nilesh Kulkarni

4. Dissolution is the process by which a solid solute enters a solution.
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5. THEORIES OF DISSOLUTION
1. Film theory or Diffusion layer model
2. Interfacial barrier model / Limited Solvation
3. Convective Diffusion theory
4. Dankwerts Model
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6. Film theory or Diffusion layer model
Dissolving Solid
Cs
C
Diffusion layer
The rate at which solid dissolve in
solvent was proposed in quantitative
terms by Noyes & Whitney Equation,
dc / dt = DS/V h (C s - C )
or
dm / dt = DS/h (C s - C )
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7. Interfacial barrier model / Limited Solvation
Cs
Cg
Dissolving Solid This model assumes that reaction at
solid surface is not instantaneous, due
to high free energy required for
solubility of solids.
G = Ki (C s – C g )
G- Dissolution rate per unit area
Ki- effective interfacial transport
constant
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8. Convective Diffusion theory
Nelson and Shah proposed theory, state that transport controlled
dissolution in a stirred liquid involves two process,
1. Molecular diffusion
2. Forced Convection
They developed a model based mathematical equation for mass
transport by diffusion and convection,
dc / dt = ( D div Grd C ) – ( V Grd C)
Where, D- diffusivity of solute
C- Concentration of Solute at time t
V- Velocity of Component
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9. Dissolving Solid Packets of solvent
Saturated Packets of solvent
Dankwert’s Model / Surface Renewal theory
It is given by equation,
Vdc / dt = A (C s – C b )
Where,
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10. In-Vitro Dissolution test Apparatus
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11. Nilesh Kulkarni

12. Apparatus 1 (Basket Apparatus)
The apparatus consists of vessel, covers (glass or other inert material), motor,
metallic drive shaft, and a cylinder basket (ss 316). Basket mesh size is # 22
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13. Apparatus 2 (Paddle Apparatus)
Apparatus consists of a paddle formed from a blade and a shaft is used as the stirring
element. A small, loose piece of nonreactive material, such as not more than a few turns
of wire helix, may be attached to dosage units that would otherwise float.
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14. Apparatus 3 – Reciprocating Cylinder
Reciprocating cylinder proposed by
Beckett and co-workers and
incorporated in USP in 1991
consists of a set of cylindrical, flat-
bottomed glass vessels; a set of glass
reciprocating cylinders
Screens designed to fit the tops and
bottoms of the reciprocating cylinders
a motor and drive assembly to
reciprocate the cylinders vertically
inside the vessels and, if desired, index
the reciprocating cylinders horizontally
to a different row of vessels. The
vessels are partially immersed in a
suitable water bath of any convenient
size. Nilesh Kulkarni

15. Nilesh Kulkarni

16. Apparatus 4 – Flow Through Cell
240 and 960 mL per hour, with standard flow rates of 4, 8, and 16 mL per
minute.
standard cell diameters are 12 and 22.6 mm;
a tablet holder is available
Nilesh Kulkarni

17. Apparatus 5 - Paddle Over Disk.
With the addition of a
stainless steel disk assembly
designed for holding the
transdermal system at the
bottom of the vessel.
The temperature is maintained
at 32 ± 0.5
Apply the transdermal
system to the disk assembly
The system may be attached
to the disk by applying a
suitable adhesive.
Nilesh Kulkarni

18. Apparatus 6 - Cylinder
Apparatus— Use the
vessel assembly from
Apparatus 1 as described
under Dissolution , except
to replace the basket and
shaft with a stainless steel
cylinder stirring element
and to maintain the
temperature at 32 ± 0.5
during the test.
Nilesh Kulkarni

19. Apparatus 7- Reciprocating holder
The assembly consists of a set of volumetrically calibrated or tarred solution
containers made of glass or other suitable inert material, a motor and drive
assembly to reciprocate the system vertically and to index the system
horizontally to a different row of vessels automatically if desired, and a set
of suitable sample holders.
Nilesh Kulkarni