Methods of adjusting isotonicity of a solution is crucial in many medical and pharmaceutical applications to prevent cellular damage or discomfort upon administration.
The goal is to match the osmotic pressure of the solution to physiological fluids, such as blood or tears (~290 mOsmol/kg).
1) Class I Methods of adjusting isotonicity (Cryoscopic method):
Based on Freezing Point Depression:The formula used is:
Uses the formula:
ΔT = Kf * m
Where:
ΔT is the change in freezing point,
Kf is the cryoscopic constant,
m is the molality of the solute.
Adjust the molality to achieve the desired change in freezing point, which corresponds to isotonicity.
2) Class II Method (Osmotic Pressure Method):
Based on Osmotic Pressure:
Formula:
π = i M R * T
Where:
π is the osmotic pressure,
i is the van't Hoff factor (number of particles produced upon dissociation),
M is the molarity of the solute,
R is the ideal gas constant,
T is the temperature in Kelvin.
Adjust solute concentration to match the osmotic pressure of an isotonic solution.
3) White-Vincent Method:
Based on Isotonic Equivalents:
IE = (w / MW) * i
Where:
IE is the isotonic equivalent,
w is the weight of the solute in grams,
MW is the molecular weight of the solute,
i is the van't Hoff factor.
Calculate isotonic equivalents for all solutes and determine the amount of isotonicity-adjusting substance needed.
4) Sprowls Method:
Based on Equivalent Weights:
Formula:
Equivalent weight (EW)=M/100 × osmotic coefficient (φ)
Where:
EW is the equivalent weight,
M is the molecular weight of the solute,
φ is the osmotic coefficient.
Determine the total equivalent weight of solutes and adjust accordingly to achieve isotonicity.