Measurements of tonicity can be assessed by measuring osmolality or osmolarity, which indicate the concentration of solute particles in a solution.
Two common methods for measuring osmolality, and subsequently assessing tonicity, are the haemolytic method and the cryoscopic method.
1. Haemolytic Method:
A biological technique that assesses the tonicity of a solution by observing its effect on red blood cells (RBCs).
Procedure:
RBCs are exposed to the test solution, and the degree of haemolysis (rupture of RBCs) is monitored.
In an isotonic solution, RBCs maintain their normal shape with no net water movement.
In a hypotonic solution, water enters the RBCs, causing them to swell and burst.
In a hypertonic solution, water leaves the RBCs, causing them to shrink and crenate (shrink).
Conclusion:
By comparing the haemolysis in the test solution with known solutions, you can determine the tonicity of the test solution.
2.Cryoscopic Method:
Also known as freezing point depression osmometry, this method measures the decrease in freezing point of a solution relative to pure solvent.
Procedure:
The freezing point of a solution is lower than that of a pure solvent due to the presence of solute particles.
The amount of freezing point depression correlates with the osmolality of the solution.
Conclusion:
By calculating the osmolality and comparing it with the osmolality of a reference solution (e.g., blood plasma), the tonicity can be determined.
Isotonic solutions have similar osmolality to the reference, hypotonic solutions have lower osmolality, and hypertonic solutions have higher osmolality.