Osmolality Testing

Osmolality is a test used to measure the concentration of solute particles dissolved in a solution, expressed as Osmoles (Osm) or milliOsmoles (mOsm) per kilogram of solvent (Osm or mOsm/kg H2O)[1]. A common methodology for measuring this is USP <785>[2]. It is a useful test in various scientific and medical applications, including assessing the solute content in solutions, bodily fluid analysis, and diagnosing medical conditions. The concentration of substances within biotechnology require accuracy to ensure results, and osmolality testing provides capability of ensuring this quality standard.

History of Osmolality Testing

The concept of osmolarity and osmolality has a long history in the fields of chemistry and biology, with roots in the late 19th century when scientists began studying the behavior of solute particles in solutions. Over time, the understanding of osmolality and its importance in biological systems has grown, leading to the development of accurate measurement techniques and instruments. This testing is essential for the study of how much solute is present in a solvent, and is often used in blood and fluid tests within the medical field to assess electrolyte composition. More specifically, urine and serum osmolality can be measured together to assess if any human diseases are affecting internal solute concentrations[2]. Due to the nature of osmotic pressure, water movement between human plasma and cells is heavily reliant on solute concentration gradients between both compartments, typically moving toward high solute concentrations via semi-permeable membranes. Changes in osmolality on either side of the interaction may result in detrimental effects in humans, including severe dehydration[3].

Importance of Testing with Reagents

Osmolality determination is essential for buffers, reagents, and media which play a significant role in biological and chemical experiments and processes. They can contain various solute particles that impact the osmolality of the resulting experimental solution, making osmolality testing critical in ensuring the desired concentrations are achieved. Osmolality readings can often highlight if formulations are made correctly, even if other specifications are in-range.

What Osmolality Test is Used at Boston BioProducts?

Osmolality testing at Boston BioProducts is conducted using specialized equipment, such as an osmometer, like the Micro-Osmette Automatic Osmometer, and the OsmoTECH XT Single-Sample Micro-Osmometer. These devices supercool an aqueous solution of interest to a low temperature (around -7°C) and then seeds it to initiate crystallization. As the solution crystallizes, heat is released, causing a plateau in the cooling curve. The decrease in freezing point compared to pure water is measured using a highly sensitive thermistor in a "Wheatstone Bridge" circuit. This measurement allows the determination of osmolality[1].


Image 1 : Preparation and use of in-lab osmolality meter for reagent quality control testing.

Considerations and Limitations of Osmolality Testing

Dilute concentrated samples High concentrations of salts, detergents, sugars, and glycerol may require a 10X sample dilution from a 1X dilution before accurate osmolality determination.
Ensure sample is uniform Sample bubbles or incorrect volumes may cause output errors, along with solutions that aren't uniform upon formulation. This will affect the freezing temperatures in which the solutions will be analyzed and may cause errors in on the osmolality meter.
Ensure proper sample preparation Proper sample preparation and handling is essential for reliable results in osmolality testing. Any risks of contamination during the samples formulation, or errors in component makeup may result in the incorrect osmolality reading.

In addition to Osmolality Testing, Boston BioProducts provides a comprehensive set of QC tests for custom reagents. Learn more about custom reagent development services.