Osmometers – Principle, Types & Uses | Advanced Instruments

Osmometers – Principle, Types & Uses

An osmometer is a device for measuring the osmolality of aqueous samples: the concentration of solutes in a liquid solution.

Applications of Osmometers

Osmometers are used in a broad spectrum of applications in biopharmaceutical and clinical labs.

Biopharmaceutical labs benefit from routine osmolality testing in the development and manufacturing of biologic drugs. The use of osmometers offers more confidence in the process by enabling better control over titer, yield, quality and purity.

Clinical labs use osmometers to test osmolality of body fluids including but not limited to plasma, serum and urine for diagnostic purposes and for monitoring treatment responses. They help clinicians make more timely diagnoses, institute more appropriate patient care and reduce healthcare costs for medical institutions of any size, in any setting.

Types of Osmometers and their operating principle

Most modern osmometers share a common principle: They measure the osmolality of a liquid sample by comparing a particular parameter of the solution, such as its freezing point, to the same parameter of the pure solvent (e.g. water).

There are two major types of osmometers commercially available, each leveraging a particular parameter to achieve their analytical results:

  1. Freezing Point Osmometers monitor how a sample’s freezing point changes according to its solute concentration. With a precisely linear correlation between a sample’s freezing point and its osmolality, freezing point osmometry offers the most accurate assessment of osmotic concentration.
  2. Vapor Pressure Osmometers determine the concentration of osmotically active particles that reduce the vapor pressure of the solution. Thereby they use the relationship between boiling point and vapor pressure to measure solute concentration.

Freezing Point Depression vs. Vapor Pressure

Whereas both types of osmometers perform rapid and inexpensive measurements and require only small sample sizes, freezing point osmometers are the industry-preferred solution in pharmaceutical operations, clinical chemistry and quality control labs. There are a number of reasons for this.

  1. Osmometers using freezing point depression deliver the most rapid and accurate results with only small sample sizes.
  2. Vapor pressure osmometers are unable to test high molality or colloidal solutions. High quality osmometers using freezing point depression are perfectly able to address those sample types.
  3. Freezing point depression is the only acceptable method for measuring osmolality when a physician suspects a patient has ingested a volatile (i.e., alcohol). Vapor pressure osmometers, on the other hand, do not detect volatiles. This is a major drawback in the clinical chemistry lab setting as it may impact cost and quality of care by depriving the physician of important information needed to treat the patient.

Conclusion: Freezing point osmometers combine all of the advantages while showing none of the disadvantages of other forms of osmometry such as longer testing time or inability to test high molality or colloidal solutions. They have been commercially available for over 50 years and are the most widely referenced technology for osmolality testing.

Learn about the operating principle of freezing-point depression in this video: