Improving Sample Preparation Workflow with Automated EvaporationAaron Kettle Thermo Fisher Scientific, Sunnyvale, CA, USA

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Executive SummaryThe Thermo Scientific Rocket Evaporator system automates the concentration process following extraction using a Thermo Scientific Dionex ASE Accelerated Solvent Extractor system or a Thermo Scientific AutoTrace 280 Solid-Phase Extraction instrument. This system can process up to 18 extracts simultaneously enabling walk-away capability for the busy analytical laboratory. The Rocket Evaporator eliminates the challenges experienced with nitrogen stream evaporation or rotary vacuum evaporation such as solvent bumping, need for a fume hood, and lack of end point detection. The Rocket Evaporator is the perfect automated solution to concentrate large volumes of extracts prior to analysis using the Thermo Scientific TRACE 1310 Gas Chromatograph, the Thermo Scientific ISQ Series Single Quadrupole GC-MS systems, the Thermo Scientific TSQ 8000 Evo Triple Quadrupole GC-MS/MS system or the Thermo Scientific Dionex UlitMate 3000 LC systems.

Introduction to EvaporationEvaporation is a sample preparation technique that is often performed following extraction. The analytes that are extracted may be in large volumes of solvent and with evaporation required to concentrate the sample prior to analysis. This is particularly true when the required detection limits are in the single parts per billion (g/L) range or below. When this occurs, an evaporation step is necessary to increase the concentration of the analytes in the extract prior to analysis and improve the limit of detection of the analytical procedure.

Evaporation techniques may present a challenge to laboratories when they are not entirely automated. The automation of extraction techniques has evolved in the last twenty years with prominent examples including the accelerated solvent extractor technique for solid samples and the Dionex AutoTrace 280 Automated SPE workstation for liquid samples. However, the automation of evaporation techniques has not kept pace with that of instruments used for extraction and therefore, will often cost the laboratory sample processing time and contribute to poor analytical results.

Evaporation TechniquesTraditional evaporation techniques include nitrogen stream evaporation or rotary vacuum evapora-tion. Nitrogen stream evaporation is used to evaporate solvent volumes between 40450 mL and when analytes are non-volatile. Solvent is vaporized by a gentle stream of nitrogen gas flowing either across the surface or through the solution. Samples are often immersed into a heated water bath to increase the rate of evaporation.

Rotary vacuum evaporators are an alternative to nitrogen stream evaporators. These systems evaporate large volumes of solvent (404,000 mL) by placing the sample into a round-bottomed flask that is rotated in a heated water bath. A water-cooled condenser is attached at the top and the

KeywordsCentrifugal Evaporation, Nitrogen Stream Evaporation, Rotary Vacuum Evaporation, Sample Concentration, Solvent Bumping, End-Point Detection, Accelerated Solvent Extraction, Dionex AutoTrace 280, GC, GC-MS/MS, GC-MS, HPLC

2 flask is rotated continually to expose maximum liquid surface for evaporation. Using a small pump or water aspirator, the pressure inside the flask is reduced. The mild warming and the lowered pressure remove the solvent efficiently, and the condensed solvent distills into a separate flask.

Centrifugal evaporators have been introduced to automate the evaporation process and combine a centrifuge with vacuum and heat to concentrate the extracted samples. The applied vacuum lowers the pressure inside of the instrument to allow applied heat to induce solvent boiling at a lower temperature. Because the solvent used to extract the analytes will have a different boiling point than the analytes of interest, the application of heat will gently boil off the solvent while preserving the analytes. The solvent vapors are collected using a cold trap and re-condensed, thereby eliminat-ing vapor exposure to the analyst.

Table 1 shows a comparison of the three evaporation techniques on the basis of factors important for evaporation. Automated evaporation end point detection occurs when the instrument can automatically evaporate the sample to dryness or concentrate to a predefined volume. Solvent boil over (or bumping) occurs as a result of superheating solvents in an attempt to increase the rate of evaporation. Bumping results in hot organic solvent being ejected from a glass or plastic sample container and can damage the laboratory and/or injure the analyst. As attempts to automate evaporation evolve, feature sets including the ability to concentrate directly into a GC autosampler vial and to store multiple evaporation methods have been introduced to instruments. After comparing the factors below, it is clear the centrifugal evaporation offers many advantages for laboratories seeking to automate their evaporation procedure.

Table 1. Comparison of sample evaporation techniques.

Figure 1. Example of a complete Thermo Scientific analytical workflow.

In an effort to automate extraction and evaporation, Thermo Scientific has added a centrifugal evaporator to the sample preparation portfolio. The Rocket Evaporator can concentrate extracts from either a Dionex ASE 150/350 system or a Dionex AutoTrace 280 SPE instrument. This system can concentrate a large range of sample volumes (20450 mL) directly into autosampler vials that can be directly transferred to the liquid autosampler of a TRACE 1310 GC system, a ISQ Series Single Quadrupole GC-MS system, a TSQ 8000 Evo Triple Quadrupole GC/MS-MS system or a UltiMate 3000 LC system. By automating the evaporation process, Thermo Scientific enables a fully automated workflow for the busy analytical laboratory.

Dionex ASE 350 System

TriPlus RSH, TRACE 1310 GC and ISQ LT Single Quadrupole GC-MS

Dionex UltiMate 3000 LCSystem

Dionex AutoTrace 280SPE Instrument

Rocket Evaporator

Centrifugal Evaporation

Nitrogen Stream Evaporation

Rotary Vacuum Evaporation

Automated End Point Detection Yes No No

Requires Fume Hood No Yes No

Prevents Bumping Yes Yes No

Concentrates into Autosampler Vials Yes No No

Preprogrammed Evaporation Methods Yes No No

3Figure 3. Automated end-point detection.

The Rocket Evaporator The Rocket Evaporator uses low-temperature boiling to concentrate samples following extraction using a Dionex ASE 150/350 system or a Dionex AutoTrace 280 SPE instrument. Boyles Law states that the boiling point of a solvent will decrease as pressure decreases and the Rocket Evaporator exploits this property to improve the rate of evaporation.

Once samples are loaded into the Rocket Evaporator, a vacuum seal is applied to reduce pressure below atmospheric and heat is applied in the form of steam. The evaporation rate ranges from 20 min for 250 mL of a low boiling point solvent (e.g. dichloromethane at 39.6 C) to 1.5 h for 250 mL of a high boiling point solvent (e.g. water at 100 C). The evaporation end point is automated and determined through a series of temperature sensors located in the solvent condenser. The temperature difference (delta T) between solvent vapor entering the condenser and solvent liquid leaving the condenser will decrease as evaporation nears completion. Once the delta T reaches a preset temperature in the evaporation method, the instrument will automatically stop the evaporation process (Figure 3).

Warm solvent vapor enters condenser

Waste solvent drain

Chilled coolant in,used coolant out.Temperature difference is T

Figure 2. The Rocket Evaporator.

4 The Rocket Evaporator uses two chambers (inner and outer) to ensure that the pressure is reduced and heat is applied to extracted samples in order to induce low temperature boiling (Figure 4). The extracted samples are loaded into rotor and a sealed lid is applied within the inner chamber. A pump is used to generate a vacuum that reduces the pressure and boiling points of the solvents. The outer chamber contains deionized water that is heated to produce steam. The outer chamber is also under vacuum to reduce the pressure and induce boiling of the water at a lower temperature. This is referred to as low-pressure steam and typically water boiling occurs at 40 C (70 mbar). Under these conditions, the Rocket Evaporator provides accurate temperature control for very fast, high energy heating.

In this system, the steam is always kept separate from the samples and is only used to heat the outside of the sample flasks. There is one vacuum condition for the outside of the flasks and another for the inside of the flasks where a different pressure is needed to boil the solvents. As the solvents in the flask boil, they cool the remaining solvent and the flask. Steam will condense on the outer surface of the cool flask delivering lots of heat energy to speed up solvent boiling. As the steam condenses, it is thrown to the sides of the chamber because the flasks are being spun in the rotor, and therefore there is never a buildup of water on the flasks. The water is then boiled again delivering more heat energy.

The green arrows in Figure 4 indicate the vapor path to the condenser. The inner chamber (insider the rotor) at point B is completely sealed from the outer chamber at point A. The pressure at point A may be 70 mbar to produce low pressure steam at 40 C whereas the pressure at point B may be only 10 mbar because methanol is being evaporatored.

Figure 5 shows the Rocket Evaporator system and the rotor with the inner lid removed. The rotor has six positions that can hold either flasks or adaptors for 60 mL Dionex ASE vials (Dionex ASE Pucks). The system includes a condenser that collects and cool solvent vapors. The condenser is chilled using a Julabo Chiller that uses antifreeze (50% ethylene glycol/50% water). The system is controlled from the front panel and stores up to 10 methods.

Figure 4. Rocket Evaporator schematic.

Figure 5. Rocket Evaporator with inner lid removed.

AB

Flasks

Rotor & InnerChamber

OuterChamber

Water

Outer Lid Seal Seal Clamp

Rotor

Sample HolderBasket

Sample Flask

Rotor with Inner Lid Removed

Inner Lid SealO-Ring

5Figure 6. SampleGenie Flask for GC vials. Figure 7. Flip Flop Vial with Dionex ASE puck.

Sample concentration is automatic when insulated sample holders are used. These insulated holders are adaptors that contain a GC autosampler vial. The system detects that evaporation has ended when the solvent is in the GC vial.

The Rocket Evaporator is able to concentrate samples directly into the GC or LC autosampler vials through two different sample holders. The first is the SampleGenie Flask for GC vials (Figure 6) which can evaporator up to 400 mL of solvent directly into autosampler vials. The Rocket Evaporator also uses a modified 60 mL Dionex ASE collection vial (Flip Flop Vial, Figure 7) that allows an adaptor containing a GC or LC autosampler vial. When using the Flip Flop Vials, extracts can be removed from a Dionex ASE 150/350 system, placed into the Rocket Evaporator, and samples will be concentrated directly into the autosampler vials. By using these two sample holders, the Rocket Evaporator is able to eliminate manual transfer steps that are normally required in between extraction and analysis.

The addition of the Rocket Evaporator to the Thermo Scientific portfolio allows analytical laboratories to fully automate their workflows. A wide variety of Dionex ASE 150/350 system and AutoTrace 280 SPE instrument applications require evaporation to meet the required detection limit or limit of quantification in the analytical method. These applications include persistent organic pollutants (POPs) such as polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), dioxins, furans, as well as fat determination in food products, and active ingredients in natural products.

6System Market Analyte(s) or Assay Determinative Step Matrix

Dionex ASE 150/350 System

Environmental Polyaromatic Hydrocarbons (PAHs) GC-MS or GC-MS/MS Soil, tissue

Polychlorinated Biphenyls (PCBs) GC-ECD or GC-MS/MS Soil, tissue

Dioxins/Furans GC-HRMSSediment, brick, dust, ash

Total Petroleum Hydrocarbons (TPH) GC-FID Soil

Base, Neutral, Acids (BNAs) GC-MS/MS Soil

Food Fat content GravimetricChocolate, meat, snack foods, infant formula

Dioxins/Furans GC-MS/MS Food/animal feed

Oil content GravimetricOil seeds (e.g. canola)

Pesticide residues GC-MS or GC-MS/MSFruits, vegetables, animal feeds

Acrylamide LC-MS Coffee, chocolate

Natural products Herbal marker compounds LC-UV Plants

Active ingredients in herbal supplements LC-UV Pills

Dionex AutoTrace 280 SPE Instrument

Environmental Semi-volatile organic compounds GC-MS or GC-MS/MS Drinking water

Active pharmaceutical ingredients GC-MS or GC-MS/MSDrinking, surface, sea water

Hormones LC-MSDrinking, surface, ground water

Dioxins/Furans GC-HRMS Surface water

Pesticides GC-ECD or GC-MS/MS Drinking water

Table 2. Complete workflow applications using automated sample preparation.

Table 2 lists applications that use the Dionex ASE 150/350 system or AutoTrace 280 SPE instrument for extraction. These applications require evaporation and the Rocket Evaporator will serve as a suitable replacement for nitrogen stream or rotary vacuum evaporation. These applications can use TRACE 1300 Series GC, the ISQ Series Single Quadrupole GC-MS systems, the TSQ 8000 Evo GC-MS/MS as well as UltiMate 3000 LC systems for the determinative step.

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www.thermoscientific.com/samplepreparation 2014 Thermo Fisher Scientific Inc. All rights reserved. ISO is a trademark of the International Standards Organization. SampleGenie Flask is a registered trademark of Genevac Inc. All other trademarks are the property of Thermo Fisher Scientific and its subsidiaries. This information is presented as an example of the capabilities of Thermo Fisher Scientific products. It is not intended to encourage use of these products in any manners that might infringe the intellectual property rights of others. Specifications, terms and pricing are subject to change. Not all products are available in all countries. Please consult your local sales representative for details.

Thermo Fisher Scientific, Sunnyvale, CA USA is ISO 9001:2008 Certified.

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Table 3. Rocket Evaporator value summary.

Conclusion The Rocket Evaporator features provide numerous benefits for laboratories that are looking to automate evaporation within their sample preparation workflow. The Rocket Evaporator improves productivity by enabling walk-away capability and improves peace of mind by providing precise automated end point detection. The manual sample transfer steps that introduce error into sample preparation procedures are eliminated and operational flexibility is introduced by allowing samples with different extraction solvents to be evaporated at the same time. Table 3 summaries the key features, benefits, and values that the Rocket Evaporator brings to the analytical laboratory.

Additional information can be found on our Sample Preparation page at thermoscientific.com/samplepreparation, which contains videos, brochures, white papers, and application notes that have combined automated sample preparation solutions with analytical techniques.

References1. Thermo Fisher Scientific. Rocket Evaporator Product Brochure. Sunnyvale, CA. [Online]

http://www.thermoscientific.com/content/dam/tfs/ATG/CMD/CMD%20Documents/Catalogs %20&%20Brochures/Chromatography/Chromatography%20Sample%20Preparation%20Equipment/BR-70315-Rocket-Evaporator-BR70315-EN.pdf (accessed July 22, 2014).

2. Genevac Inc. Genevac Rocket Evaporator User Manual. Genevac Part Number 04-6276, Gardiner, NY, 2013.

Feature Benefit Value

Centrifugal EvaporatorControllable evaporation rates that minimize sample loss from bumping

High sample recovery and increased reproducibility that improves analytical performance

Chilled CondenserSolvent vapors are automatically collected and condensed within the Rocket Evaporator

Technology that does not expose the analyst to solvent vapors (>98% vapors are condensed and trapped)

Evaporation End-Point Detection

Automatically detects when evaporation is complete though in-line temperature sensors

Enables walk-away capability so analysts can focus on other tasks

SampleGenie and Flip Flop Tubes

Concentrates extracts directly into GC or LC autosampler vials

Simplifies use by allowing direct transfer of sample to the GC or LC autosampler

Dionex ASE Pucks

Allows direct transfer of extracts from the Dionex ASE system to the Rocket Evaporator and eliminates the need for manual pipetting of samples

Increases sample processing productivity and eliminates cross contamination between samples

Preprogrammed Evaporation Methods

Evaporates solvents used by the Dionex ASE system and Dionex AutoTrace 280 SPE instrument with boiling points ranging from 36 C to 100 C

Simplifies use and increases flexibility by working with commonly used extraction solvents such as dichloromethane, methanol, and water