There are several different approaches a laboratory can apply to concentrate samples for further analysis, such as gas chromatography. While various evaporation techniques fill this category, there is also an approach called freeze drying or lyophilization.
As you might guess, both in and out of an organics lab, freeze drying is a popular approach for removing water (and other solvents) from a substance. Below are the general lyophilization steps using water as an example:
- The water is frozen into a solid state
- The frozen water is sublimated through the application of heat and reduced pressure. This means that the majority of the water content goes directly from being solid to vapor (commonly referred to as the primary drying step)
- The process enables the substance to be dried fully and storage-ready (commonly referred to as the secondary drying step)
Freeze drying is appealing because it provides an effective process for removing moisture from perishable materials without damaging the composition of the substance. Commonly, these samples start as liquids and become semi-solids or solids after freeze drying. In some cases, the goal might be to remove water from the sample, creating a dry product which is easy to transport. An example of this could be a juice which has been concentrated into a powder.
In the laboratory, lyophilization is a popular approach for preserving biological samples so that they do not degrade over time. Another common use case would be the extraction of botanicals or other natural extracts where again, preserving the potency over time is critical.
Solvent evaporation is most commonly a process associated with heating the sample near the solvent’s boiling point. Lyophilization on the other hand involves cooling the sample near the solvent’s freezing point to sublimate the solvent which is typically water.
Lyophilization vs. nitrogen blowdown:
- Sample composition - In general, freeze drying is able to accept a much wider variety of sample forms such as solid, liquids and gels where N2 evaporators are used to process only liquid samples
- Heat sensitivity - While the most popular freeze-drying application is the removal of water from a sample. this technique is popular in general because freezing minimizes the risk of heat-induced degradation. On the other hand, nitrogen blowdown typically involves applying heat to speed the evaporation process. An exception to this rule is that nitrogen gas can always be used at ambient temperatures to dry down the sample without the application of heat.
- Sample size and throughput - N2 blowdown excels at concentrating small millimeter samples at a wide range of bath sizes while freeze drying is better for fewer, larger samples
- Speed - nitrogen blow down is typically faster with some freeze drying processes taking several hours or days
- Equipment cost - nitrogen evaporators tend to be much more affordable than freeze dryers. While nitrogen evaporators are relatively simple, freeze dryers require both refrigeration and vacuum components.
In summary, nitrogen blow down is preferred over lyophilization when speed, throughput, and simplicity are prioritized, and when the sample is relatively small. However, lyophilization is preferred when maintaining sample integrity and working with larger volumes of samples are critical.
Check out our full list of types of laboratory evaporators to determine which is best for your lab. If you have any questions or would like to speak to our team of experts, reach out to sales@organomation.com.