The impact of technological developments
on solvent evaporation .. a review
Steve Knight*
This article reviews the technological developments introduced by Genevac Ltd. that have most impacted the way that scientists and engineers efficiently and effectively remove solvent from their samples.
Decreasing operational downtime
The need to defrost frozen solvent from an evaporation system's refrigerated condenser can result in significant downtime at the end of each run. To remove this problem, Genevac developed and introduced a continuous running option for use with all its evaporation systems. The VCT Series continuous running condensers feature two vacuum condenser chambers. While one is running under vacuum refrigerated, the other is defrosting, ready for instant draining and refrigerated vacuum duty at the end of the run. An automatic or simple manual switchover and waste solvent pumping facility eliminates downtime and allows uninterrupted processing of samples.
Smoother operation
During the evaporation process, samples in a centrifugal evaporation system can become imbalanced and cause excessive vibration, system shutdown and possible system damage. This is most noticeable and severe in HPLC applications. The variety of aqueous/organic solvent mixtures used in HPLC causes problems of imbalance within conventional centrifugal evaporation systems due to the uneven drying rate of the fractions. In order to resolve such problems, Genevac has launched an auto-balancing option for their evaporation systems. The auto-balancing mechanism (ABM) allows samples to be loaded and unloaded without the requirement for balancing sample loads by mass. In addition, samples in solvents with differing volatility can be dried simultaneously. The auto-balancing system continuously compensates for any variations in rotor balance that may occur as a result of imbalanced rotor loads or varying rates of evaporation in fractions. The systems can operate with minimal vibration with up to 250 grams or more imbalance in the HT systems and up to 800 grams imbalance in the MEGA systems.
Increasing flexibility ..
Designed as an integral part of an "open access" LC-MS purification system for medicinal chemistry, Genevac developed an open access evaporator that allowed purified fractions to be loaded and unloaded without balancing loads opposite each other in the sample rotor. As a result, the whole system (the Model HT-4X) runs more efficiently because chemists can process their purified fractions without the delay caused by waiting for a full batch of samples. At any time, additional samples can be loaded into available spaces in the sample rotor or, if the rotor is full, replace dry samples that are ready for removal. The system incorporates a temperature control system and pressure control to ensure a safe sample temperature limit and rapid evaporation of water. At every stage in the process, the fractions can be easily identified.
Protecting samples from solvent bumping
Solvent bumping is caused by a variety of factors and is unpredictable. Although centrifugal evaporation systems prevent it in most cases by applying up to 300G force, it can still occur with certain solvents or solvent mixtures. For example, most conventional evaporation systems cannot prevent bumping with solvent combination of dichloromethane / methanol, or with very volatile or gassy solvents such as ammonia solutions. The Genevac VacRamp 11 system was specifically developed to solve bumping problems. Designed to be built-in to Genevac evaporation systems, VacRamp 11 prevents bumping by applying the vacuum gently without heat, and using a more powerful drive motor to increase rotor speeds and centrifugal force. As a result, the risk of sample loss or cross contamination is eliminated.
Actual temperature control for faster evaporation
Conventional temperature monitoring systems for centrifugal evaporation display the temperature of the radiant heat source (chamber wall) or the outside wall of the sample vessel. However, the solvents cooled by vacuum evaporation will be at a significantly lower temperature than the external wall. In order to achieve the fastest possible rate of evaporation without exceeding the maximum sample temperature, accurate temperature monitoring and control is essential. In order to ensure this, Genevac introduced SampleGuard. This is an actual sample temperature transmitter and controller that is housed in a glass-PTFE casing in the evaporation chamber with PTFE coated thermocouple probes placed directly in the sample and aluminium sample holder prior to starting the drying run. The SampleGuard system allows rapid, safe drying times with all solvents and sample formats, eliminating the need to carry out detailed test runs and saving scientist's valuable time. It also protects samples from overheating, ensuring compound temperature protection even in the event of serious failure.
What developments next ?
Looking ahead centrifugal evaporation technology is gaining acceptance as a useful tool in many new markets and applications for which further developments will be required.
For the many scientists faced with removing solvents from their samples, Solvent Removal Online a technical e-newsletter from Genevac Ltd. downloadable from their website ( ) offers a valuable source of information relating to the latest technical and applications advances, troubleshooting tips, news and new product introductions in this expanding technology area.
The Author:
Steve Knight the marketing manager of Genevac Ltd., Farthing Road, IPSWICH, IP1 5AP, UK tel. 01473-240000 email
Genevacarticle2003i.doc (817 words)