Table of contents:
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- Methods
- Sample Size
- Batch Size
- Solvent
- Sample Type
- More Resources
Choosing the right evaporator or sample concentrator for your lab can significantly impact the efficiency and accuracy of your analysis. With various techniques available, such as rotary evaporation, Kuderna Danish evaporation, nitrogen blowdown, centrifugal evaporation, and freeze drying, it’s essential to understand which method suits your specific needs. This guide will help you navigate the selection process by posing key questions in four critical areas: sample size and starting volume, batch size, solvent removal, and sample type. Let’s dive in and determine the best approach for your lab.
Methods
Here are the concentration methods covered in this guide:
Rotary Evaporation
Uses rotation, vacuum, and heat to efficiently concentrate samples. Rotary evaporators can typically handle a wide range of sample volumes, but are limited to processing one sample at a time. When rotary evaporation is feasible, it is typically the fastest of the sample concentration methods on a per-sample basis.
Nitrogen Blowdown Evaporation
Uses a stream of nitrogen gas, with or without heat, to evaporate solvents from multiple samples simultaneously, typically in test tubes or vials. Nitrogen blowdown is often the preferred evaporation method when working with volatile analytes. It is also often the cheapest in terms of total installation cost and easiest in terms of sample setup.
Centrifugal Evaporation
Uses centrifugal force, vacuum, and heat to concentrate multiple small volume samples at once. Centrifugal evaporation is typically used to concentrate biological samples such as DNA.
Kuderna-Danish Concentration
A specialized concentration method for removing organic solvents from volatile or semi-volatile analytes, commonly used in environmental analyses.
Freeze Drying (Lyophilization)
Removes liquid by freezing samples and sublimating the ice under vacuum. Freeze dryers are ideal for drying heat sensitive biological compounds in aqueous matrices. This method is the slowest of the evaporation methods covered in this guide but results in the least thermal degradation.
Sample Size
What size are your samples? What is your starting volume?
Understanding the size and starting volume of your samples is crucial in selecting the appropriate evaporator
or sample concentrator.
Microwell Plates
Nitrogen blowdown & centrifugal evaporation are optimal for microplates, with freeze drying as a less common
alternative for water removal in heat-sensitive analytes. Specialized accessories are required for all methods.
Small Samples (1-30 mL)
Nitrogen blowdown is typically the fastest option for small samples, while centrifugal evaporation allows higher throughput. Rotary evaporation can handle small samples if properly adapted but is generally more efficient for larger volumes.
Medium Samples (30-100 mL)
Rotary evaporation is the most efficient method for medium-sized samples, offering speed and flexibility.
Nitrogen blowdown is an alternative for thermally sensitive samples, though it is slower for this volume range.
Large Samples (>100 mL)
Rotary evaporation is the gold standard for quickly processing large samples. When preserving volatile analytes is critical, Kuderna-Danish concentration may be preferred.
Batch Size
How many samples are you looking to concentrate at once?
The number of samples and batch size are critical factors in choosing the right equipment.
Single Samples
Multiple Samples
High Throughput (>1,000/day)
Rotary Evaporation
Yes
No
No
Nitrogen Blowdown
Yes
Yes
No
Centrifugal Evaporation
No
Yes
Yes
Kuderna-Danish Evaporation
Yes
Yes
No
Freeze Drying
Yes
Yes
Yes
Single Sample Processing
Rotary evaporation, nitrogen blowdown, and Kuderna-Danish concentration excel for single samples. Choose rotary evaporation for larger samples or difficult solvents; for small samples (<10 mL), nitrogen blowdown is simpler and faster.
Multiple Sample Processing
Nitrogen blowdown and centrifugal evaporation handle multiple samples efficiently. Nitrogen evaporators typically accommodate 10–100 samples, while some centrifugal systems can process up to 500 at once.
High Throughput
Labs processing over samples daily benefit from automated systems integrated into the sample preparation workflow.
Solvent
What solvents are you looking to remove?
Different evaporators are optimized for various solvents. Choosing the right one improves efficiency and safety.
Volatile Organic Solvents
High Boiling Solvents
Aqueous Solutions
Rotary Evaporation
Yes
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Less common
Less common
Nitrogen Blowdown
Yes
Less common
Less common
Centrifugal Evaporation
Yes
Less common
Yes
Kuderna-Danish Evaporation
Yes
No
No
Freeze Drying
Less common
Less common
Yes
Non-Evaporative Methods
Less common
Yes
Yes
Volatile Organic Solvents
Organic solvents are well-suited to removal via evaporation and can be evaporated using most of the methods
discussed in this guide. The exception is freeze drying; not all organic solvents can be lyophilized, and those that
can often require a specialized model.
High Boiling Solvents
Solvents with high boiling points, such as DMF, DMSO, and NMP, are typically challenging to remove through
evaporation. Common removal techniques are washing, extraction, or other non-evaporative removal methods
like chromatographic separation. These solvents can sometimes be removed under high vacuum, such as in a
rotary evaporator or other specialized vacuum concentrator. DMSO can sometimes be lyophilized. While slow,
nitrogen blowdown can also be an effective option for small volume samples.
Aqueous Solutions
Freeze drying is excellent for removing water from heat-sensitive samples while preserving their integrity. Centrifugal evaporation is another common method for evaporating water, especially when concentrating proteins or DNA. Nitrogen blowdown and rotary evaporation can be used as well, but each have challenges. Nitrogen blowdown of water is extremely slow without the application of heat, which can be an issue for solutes prone to thermal degradation. Rotary evaporation requires a relatively strong vacuum, which can lead to challenges with bumping.
Mixed Solvent Systems
Mixed organic solvents and azeotropes can typically be evaporated using the same methods as a single organic solvent. For aqueous-organic mixture, a combination of concentration techniques is typically most effective. Consider evaporating off the organic component first and then removing the remaining water in a freeze dryer, or alternatively removing the water with drying agents before evaporating the organic solvent.
Sample Type
What type of samples are you concentrating?
The nature of the sample being concentrated is a crucial consideration, especially for those sensitive to heat.
Thermally Stable Analytes
Samples with thermally stable, nonvolatile analytes are the easiest to concentrate because the solvent can simply be boiled off without concern for the analyte. Evaporation speed can be increased by applying vacuum (rotary evaporation) or a stream of nitrogen gas. Unfortunately, most analytes are either volatile or thermally unstable to some extent.
Volatile & Semi-Volatile Analytes
Nitrogen blowdown evaporation and Kuderna-Danish concentration are the leading methods for retaining volatile or semi-volatile analytes when concentrating samples. The two methods are frequently used in tandem, with large volume samples being concentrated using the Kuderna-Danish technique before being moved to a nitrogen blowdown evaporator for a final (controlled) concentration to a specific endpoint.
Heat Sensitive Samples
The best concentration method for heat-sensitive samples depends on how heat-sensitive they are. Rotary evaporation allows for efficient removal of solvents at 40-60 °C, well below the temperature that would be required to boil most common solvents. For samples that cannot be heated but that are stable at room temperature, nitrogen blowdown and centrifugal evaporation can both be operated effectively without the application of heat. For extremely heat-sensitive samples, freeze drying may be the best choice since it allows the sample to remain below room temperature during concentration. Some advanced centrifugal evaporators have a refrigeration option to achieve a similar effect.
Complex Biological Structures
Freeze drying is often preferred for complex biological samples such as proteins or cells if the molecular or cellular structure needs to be preserved.
More Resources
Conclusion
By considering the size of your samples, your batch processing needs, the solvents you aim to remove, and the type of samples you are concentrating, you can make an informed decision about the most suitable evaporator or concentrator for your laboratory. Whether it’s the versatility of rotary evaporation, the advantage of vacuum through centrifugal evaporation, the high-throughput capability and gentle nature of nitrogen blowdown, or the ability to remove water efficiently through freeze drying, each method has its strengths.
Take a moment to try out the "Which evaporation method is best for me?" tool. This quick and easy tool can further assist you in determining the best evaporation method tailored to your specific needs, helping you make the most informed decision for your lab's requirements. Optimize your lab’s evaporation and concentration processes for maximum efficiency and accuracy today.
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