Cryoscopic Osmometer for Measurement of Osmolality

Osmometer Based on Freezing Point Depression
Osmometer Based on Freezing Point Depression

Osmolality measurements using an osmometer, are regularly carried out in the pharmaceutical industry and research labs to establish the isotonicity of intravenous solutions, injection, nasal and eye drops. Preparations which are hypertonic or hypotonic can cause severe irritation when injected into the bloodstream or tissue or when applied to mucous membranes like cornea and wounds.

Normal ranges of osmolality

The osmolality of blood, measured using osmometer,  ranges from 250 to 350 mOsm/kg and the normal osmolarity of body fluids given in medical books ranges from 275 to 295 mOsm/kg, but normal values usually fall in an even narrower range of 286±4 mOsm/kg. Parenteral preparations are developed to closely match the values to reduce the irritation caused by them

Pharmacopoeia Requirement

Osmolality measurement using osmometer is a pharmacopeia requirement for numerous products. The United States Pharmacopoeia (USP) gives the option of using either vapor pressure based osmometer or a cryoscopic (depression increasing point based) osmometer for the measurement of osmolarity. Whereas the Indian Pharmacopoeia (IP) only describes the cryoscopic osmometer for the measurement of osmolarity.

Features of osmometer installed at Arbro

Arbro has recently installed an osmometer based on freezing point depression in our state of the art testing lab in New Delhi. The system has numerous advantages such as –

  • Automated calibration
  • A short measurement time of 1 min
  • Automated measurement and calculation
  • The low sample volume of only 50 µl
  • Built-in printer and
  • Three-point calibration
  • Reproducibility of less than ±0.5% for 50 µm samples
  • A large measuring range of up to 3000 mOsm/kg
  • A resolution of 1 mOsm/kg over the entire measuring range

The system has been installed and duly qualified as per our internal quality systems which are accredited by NABL to ISO/IEC 17025 and is now ready for service for our customers in various industries.

Introduction to basic principles of osmometry –

Osmosis is defined as the passage of solvent into a solution through a semi-permeable membrane. This process eventually leads to equilibrium and the tendency of the solvent to move from one side of the membrane to the other can be measured by the closely related colligative property called osmotic pressure.

Osmotic pressure is classically given in terms of atmospheres, but in clinical practice, it is expressed in terms of osmoles (Osm) or milliosmols (mOsm). 1-osmolal solution is defined as the solution containing one mole of a non-ionising substance in 1 kg of water. It is a measure of the total number of particles dissolve in a kilogram of water and depends on the electrolytic nature of the solute, an ionic solute will dissociate in water to form ions or particles. The apparent number of particles in solution is measured using an osmometer.

Osmolarity is used more frequently than osmolality in the labeling of parenteral solutions in, pharmaceutical manufacturing,  hospitals, and pharmacies. But osmolarity cannot be measured and must be calculated experimentally by data mining the osmolality of a solution.

For near ideal solutions, osmolarity different from osmolality only by 1 or 2 %, but as you go towards more concentrated solutions of polyvalent electrolyte together with buffers,  preservatives, and other ions these differences become larger.

For accuracy in the preparation and labeling of parenteral solutions, osmolality should be measured carefully with the vapor pressure or freezing point based osmometer rather than being calculated based on the concentrations of ingredients added.

Contact us today!

If you require the measurement of osmolality of any of your products, contact us today using the Quick Query Form on the right or call us now on +91-11-45754575.

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