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Choosing an Osmometer

What is an Osmometer?

An osmometer measures osmolality from the concentration of a substance in a solution. A freezing point osmometer, as designed and manufactured by Precision Systems, determines concentration of a solution by measuring the freezing point of the solution, as freezing point is directly correlated to concentration.
Freezing Point vs. Vapor Pressure
There are osmometers that measure concentration by measuring vapor pressure. Vapor pressure osmometers may miss certain volatiles that are in the solution, such as CO2, ammonia and alcohol. Using a freezing point osmometer provides the most accurate and reliable results for many applications.
Because of the very straightforward nature of this freezing point measurement as a way to determine concentration, or, osmolality, there are myriad applications for an osmometer. Some of the more common ones include:

  •     Clinical lab use
  •     Manufacturing and QC of Pharmaceuticals
  •     Reagents
  •     Beverages
  •     Eye solutions
  •     Research

How do I determine the appropriate Osmometer for my application?
Generally speaking, all osmometers perform the same function. Most of them operate over the same range of osmolalities. Therefore, the difference in osmometers depends on the following factors:

  •     Sample size
  •     Range
  •     Number of samples run at a given time
  •     Need for hard copy print-out of results
  •     Automation of the calibration function
  •     Type of cooling
  •     Cost

Sample Size
Where sample size is greatly limited, in such applications as veterinary, neonatal, or geriatric, the OSMETTE II and III allow for the smallest sample on the market at 10uL. A popular choice for small samples is also the Micro-OSMETTE at 50 uL.
For the majority of freezing point osmometer applications, osmolalities tend to fall in the range of 0 to 2000 mOsm/kg H2O. All Precision Systems osmometers operate over this range.
The Micro-OSMETTE, OSMETTE A and OSMETTE XL, as well as the Multi-OSMETTE purchased with the extended range option have a range of 0 to 3000 mOsm/kg H2O.
Number of samples run at a given time
If you are running many samples in a day, or at a time, the Multi-OSMETTE, a completely automated turntable osmometer with 30 uL samples can run up to 23 samples in approximately 30 minutes.
All other osmometers offered by Precision Systems are single sample.
Need for hard copy print-out of results
If records of results are needed, the OSMETTE XL, the Multi-OSMETTE and the OSMETTE III all have built-in thermal printers. They also have the ability to connect to an external printer or computer through an RS-232 port.
Automation of the calibration function
General operating procedure for optimal results with an osmometer suggests regular calibration, the frequency of which depends upon the frequency of osmometer usage. With semi-automatic calibration, a user runs a set of standards at two end-points that bracket the desired operating range, and adjusts the reading to reflect the value of the standard. With Automatic Calibration, when a user runs a set of standards, the osmometer automatically recognizes the standard's value and makes an internal adjustment to reflect that value as a calibration point.
The OSMETTE XL, the Multi-OSMETTE, and the OSMETTE II and III all have auto-calibration.
Type of Cooling
Large sample instruments require a bath or liquid cooling to attain fast sample reading. The uniform cooling, and the ability to stir large samples allows for twice the accuracy that that of non-bath osmometers. Smaller sample instruments achieve clinical accuracy, while eliminating the bath, and the associated maintenance. They also allow for samples to be run within 5 minutes of plugging in the instrument.
The OSMETTE A and the OSMETTE XL are our large sample (highest accuracy) offerings.
Each of our instruments enjoys the lowest total cost in it's marketplace. While our instrument cost is competitive, our consumable costs are often half that of comparable osmometers. In addition, we offer the best warranty, with 3 years on the cooling module, and have designed our instrumentation for highest reliability, keeping them simple with a minimum of moving parts.