Parallel Evaporation

 

 

Definition of concentration in chemistry

 

In chemical analysis, concentration is a sample pretreatment process of separating solvent and solute by removing the solvent in the solution in order to  increase concentration of the solute. Concentration can increase the ratio of the target substance in a solution to either solvent or total solution, and reduce the factors that might effect experiment results, thus is an important part of sample pretreatment before analysis.

 

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Concentration procedure and methods

 

Concentration procedure can be described as follow:

 

1. Sampling: After homogenizing the sample, take an appropriate amount of samples according to the experimental method.
2. Extraction: Separate of target substances from mixtures and obtain extract. Common extracting methods include solid/liquid extraction, liquid/liquid extraction, solid-phase extraction (SPE), solid-phase micro-extraction (SPME), or supercritical fluid extraction, super critical fluid extraction (SFE) and immuno affinity column (IAC).
3. Purification: Use physical or chemical methods to remove impurities in the extract. The most common purification method is solid-phase extraction (SPE).
4. Concentration: Increase ratio of the target substance in a solution and sample sensitivity.
5. Reconstitution: Restore the concentrated samples into liquid state with solvents.
6. Analysis: Analyze the restored liquid sample in instruments, for example, HPLC (High Performance Liquid Chromatograph), GC (Gas Chromatograph), LC-MS/MS (Liquid Chromatograph / Tandem Mass Spectrometer) or GC-MS/MS (Gas Chromatograph / Tandem Mass Spectrometer).

 

Concentration procedure example: An LC‐MS/MS Method for the Determination of Antibiotic Residues in Distillers Grains (C-012.01), FDA

 

 

1. Sampling: Weigh 5.0 ± 0.1 g ground distillers grains into individual 50 mL tubes.
2. Extraction: Add acetate buffer and acetonitrile (ACN) for extraction. 
3. Purification: Use Solid Phase Extraction on Oasis HLB (60 mg, 3 mL) to purify the extract.
4. Concentration: Evaporate eluates at 40 oC to 50 µL.
5. Reconstitution: Reconstitute with 80:20 mixture of water ACN and filter with membrane.
6. Analysis: Analysis antibiotic residues by LC-MS/MS.

 

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Evaporation concentration

 

There are several ways of concentration, like evaporation concentration, membrane concentration and freeze concentration. Principle of evaporation concentration is solvent removal. As liquid gets vaporized to gas and removed, less volatile samples are left concentrated and solvent-free (dry).

 

Common evaporation concentration techniques

 

Common concentration techniques used in laboratories include: rotary evaporation, nitrogen evaporation, centrifugal evaporation, and vacuum-vortex evaporation.

 

Rotary evaporation

Rotary evaporation techniques promotes solvent evaporation by rotating a round bottom flask at elevated temperature and reduced pressure. To execute rotary evaporation, five components are required: heat bath, rotor, condenser, solvent trap and a vacuum pump. It’s major disadvantage is lacking of capacity of processing more than one sample per time.

 

Nitrogen blowdown evaporation

Nitrogen blowdown evaporators use thin tubes (needles) to blow continuous nitrogen gas stream onto the surface of a solvent to lower the vapor pressure and increase the surface area. Heating block or dry bath can be applied to accelerate solvent vaporization. Nitrogen evaporators are often used for small volume of samples (less than 50mL). However, because it uses open vials, risk of cross-contamination should be carefully managed. It’s also not the most ideal method of removing less volatile solvents.

 

Centrifugal evaporation

Principle of centrifugal evaporation is to reduce pressure with vacuum to induce solvent boiling. Heat energy is also applied by infrared or steam to accelerate evaporation. Centrifugation ensures that solvent boils from the sample surface downwards, therefore minimizes boiling over and solvent bumping as well as prevents sample loss and cross-contamination. Centrifugal evaporation is an ideal technique to process multiple samples in smaller volume. However it’s not possible to make any observation under process.

 

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Parallel evaporation / Vacuum-vortex evaporation

 

Parallel evaporation is to create vortex by swirling the sample tubes. The created vortex generates larger sample surface thus promotes vaporization and makes the process faster. However, g force generated to prevent bumping through vortex is insufficient as compared to centrifugal evaporation. As a result, typical vortex evaporator are prone to sample loss and cross-contamination. More advanced vortex evaporator adds vacuum pumps to reduce pressure, and heaters to increase temperature to further accelerate evaporation. Cold trap is also essential in such system to collect solvent gases. 

See how Rocker’s ConVap 150-T prevents cross-contamination with their patented cover
A complete Rocker ConVap 150-T Parallel Evaporation System includes: 

• ConVap 15/150 Parallel Evaporator: Process up to 48 samples per time.
• ConTrap 200 Cold Trap:  
  Cools down to -65 °C, collects more than 95% of vaporized solvents.
• Chemker 610 Chemical-resistant Vacuum Pump:
  Max. vacuum 7 mbar. High chemical resistance.

 

Comparison of ConVap 150 with other concentration methods

 

	Lab A		Lab B			Lab C
Test	Pesticide residues in food		Antibiotic Residues in Animals			Biochemical extraction
Sample size	48		12			12
Solvent used	1 mL ACN		50 mL Acetate buffer and acetonitrile (ACN)			1 mL sterile water
Concentration Technique	Nitrogen Concentration	ConVap 15 Parallel Evaporator	Vacuum Concentration	Nitrogen Concentration	ConVap 150 Parallel Evaporator	Centrifugal Concentration	Nitrogen Concentration	ConVap 15 Parallel Evaporator
Procedure time	40 mins	10 mins	4 hours	2 hours	1.5 hours	200 mins	65 mins	20 mins

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Comparison of evaporation technologies

 

Concentration Technologies	Vacuum Vortex Concentration/ Parallel Evaporator	Rotary Concentration	Nitrogen Blowdown Concentration	Centrifugal Concentration
Number of Sample	Multiple  (12 / 48)	1	Multiple	Multiple
Parameter Controls	Vacuum, temperature, RPM, time	Temperature,  RPM	Temperature, flow speed	Temperature, RPM, time
Cross-contamination	Risk-free	Risk-free	High risk	Low risk
Consumable parts	No	No	Nitrogen	No
Visibility	Yes	Yes	Yes	No
Tube Loading/ Unloading	Batch & single	Single	Batch & single	Single
Solvent Vapor Collection	Yes. In-room.	Yes. In-hood.	No. In-hood.	Yes. In-room.

Common Applications of Parallel Evaporator

 

• Food analysis, including veterinary medicine, pesticide residue.
• Environmental testing, including Environmental agents, Diosin.
• Sample extraction, concentration and evaporation clinical experiments, biology, chemistry….etc.

 

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References:

Centrifugal concentrators for biological applications.
Types of Solvent Evaporators – An Overview
NITROGEN EVAPORATORS (Sample Concentrators)
Introduction to Evaporation – biophara group
Evaporators – American Chemical Society
Deciding Whether or Not to Use a Fume Hood With Your Rotary Evaporator