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SPI-DRY™ Critical Point Dryers

The most widely installed CPD unit in the world!



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Introduction to the technique of critical point drying:
The technique of critical point drying is not new; it has been around for some number of years and certainly has been a part of the light and electron microscopy and microanalysis field since around 1970 when it became clear that the air drying of many types of samples, primarily biological, but not solely, would produce intolerable drying artifacts.

For many years, the conventional wisdom of the field was that the exchange of liquids should be done without agitation, and without turbulence, and that laminar flow of the exchange liquids while in the chamber was the most desirable.

And because a critical point dryer, in essence, is a "pressure bomb", there is, and correctly so, a great concern about safety and many have felt more comfortable with a system that was not electrically heated (and had the potential for overheating) and was heated only with warm water, thereby limiting the kind of situation that could exist to an over pressurization of the pressure chamber.

And with the passage of time, there has emerged a new body of end users who believe that sometimes agitation is "good" for the samples and there has emerged designs of chambers that permit gentle agitation during the exchanging of the fluids. However, we still are "old fashioned" when it comes to the agitation of fragile samples; there is just too much possibility for the disappearance of fine structures when the exchange of liquids is not done under laminar flow conditions.

CPD
SPI # 13200-AB Manual CPD




SPI-DRY™ CPD Available Regular and Jumbo Sizes
This is the sometimes called "manual" style unit which is heated with hot water and features a large viewing glass to monitor visually the most fragile of samples. And the entire unit is designed for the exchanging of fluids under laminar flow conditions. The "Jumbo" size unit is the largest chambers available in a laboratory CPD unit anywhere.
Choice of CO2:
Carbon dioxide is offered by most gas suppliers in at least two different grades: a) research grade and b) standard grade. There is a large difference in price when comparing the two grades. We have never found any indication that use of the much more expensive "research grade" results in any kind of a better result than the cheaper "standard" grade. Therefore we advice use of the lower cost "standard" grade which in the USA is typically under $10 per regular size tank (without delivery charges).

Storage of critical point dried samples:
Samples that have been critical point dried are highly hydroscopic, and will very readily absorb moisture from the atmosphere. That is why we recommend that critical point dried samples be stored either in a desiccator cabinet or a SPI-DRY™ Sample Preserver Capsule.

For the budget-minded, CPD-dried samples can be safely stored in one of our SPI SEM Mount Storage Boxes.


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Tuesday February 09, 2010
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