A Complete Lab Guide to Osmometer
A Complete Guide to Osmometer
- Hypertonic - Concentration of solutes is higher in the outside solution causing the cell to lose water.
- Hypotonic - Concentration of solutes is lower in the outside solution causing the cell to gain water. Cells without cell walls swell and burst due to excessive water intake.
- Isotonic - Concentration of solutes is same inside and outside the cell maintaining equilibrium.
- Osmolality is a measurement of the total number of solutes in a liquid solution.
- It is expressed in mOsm/kg H20.
- Osmolality, along with pH, is one critical factor while preparation of cell culture medium.
- Vapor pressure depression osmometers
- Membrane osmometers
- Freezing point depression osmometers
- Determines the concentration of osmotically active particles that reduce the vapor pressure of the solution.
- Disadvantage:- Volatile compounds exert their own vapor pressure.
- Measures osmotic pressure of a solution separated by a semi-permeable membrane.
- Disadvantage:- Lack of availability of a proper semi-permeable membrane
- Determines the osmotic strength of a solution using freezing point depression.
- Most commonly used method in clinical, pharmaceutical and quality control laboratories.
- Rapid, sensitive and accurate. Hence it is widely preferred over the other two types.
- Requires very less sample size (very few microlitres).
- Easy to use. Does not require sound technical knowledge of the instrument for handling.
- When a solute is added to a solvent, the freezing point of the solution is lower than that of the solvent.
- As the concentration of the solute increases, there is further decrease in the freezing point of the solution.
- The osmolality of the solution can be determined by measuring the freezing point of that solution.
- A cuvette containing the test solution is loaded into the cooling chamber.
- The solution is freeze below its expected freezing point with constant stirring by the wire.
- The temperature of the solution is monitored throughout the process by a thermistor connected to the wire.
- Stirring leads to the formation of ice crystals and thermal heat is generated in this process.
- As a result, an equilibrium is achieved and the temperature of the solution remains constant.
- A plateau is achieved which indicates the real freezing point of the solution.
- Calibrate the instrument with a known standard before use to ensure proper working of the instrument.
- Use clean cuvettes for freezing (preferably new).
- Wash the cuvettes properly if later use is expected.
- Keep extra cuvettes covered to avoid contact with dust.
- Never keep the freezing chamber empty.
- When not-in-use, place an empty cuvette in the freezing chamber.
- Always wipe the probe and the wire with lint-free tissue to remove traces of the previous solution.
- Check the level of heat transfer fluid at regular intervals. Change the fluid when the solution reaches its warning mark.
- Annually or six-monthly calibrate the osmometer with different ranges of standards to check the efficiency of the instrument.
- Cover the instrument when not-in-use.
Author’s name: Kalyani Koli
Kalyani Koli, a post-graduate in Biotechnology, from the University of Mumbai with extensive 8 years of experience in the field of Animal Cell Culture and Immunology. She works as a Senior Cell Culture Analyst at Department of Animal Cell Culture. She has also worked as Copy Editor for Elsevier, Williams & Wilkinson and America Online. Follow Kalyani on Facebook