29 Centrifugal Vacuum Evaporation
Centrifugal evaporators induce solvent boiling under vacuum and so the samples are cold. Centrifugal evaporators use cold traps to recover the vaporised solvent. Centrifugation ensures that solvent boils from the sample surface downwards, thereby eliminating boiling over, foaming and solvent bumping and so preventing sample loss and cross-contamination. Solvent at the liquid surface is at the pressure of the equipment, whereas solvent below this level is at a higher pressure due to the extra weight of solvent multiplied by the g force exerted by the centrifuge rotor. Systems with very high rotor
speeds generating 500g or more are proven to prevent solvent bumping. The centrifugal evaporation technique accommodates a wide range of solvents and can concentrate, dry to a fi lm or freeze dry samples. Controls on the system permit hands free operation, with the most advanced systems having automatic detection for the end of the method built in.
Results of Evaluation
The systems were tested for their suitability for use in the sample preparation process, with particular attention to cross-contamination / bumping / foaming, solvent recovery and degree of user intervention. The results are shown below in Figure 2.
Bumping / Foaming
Vortexing System
Samples foam
resulting in sample loss
Blow Down No foaming or bumping
Solvent Recovery
External solvent
condenser, like rotary evaporator
None Must
continually adjust gas jet height above liquid
Centrifugal Evaporation
No foaming or bumping
Built in solvent
condenser Figure 2. Results of solvent evaporation system evaluation None required Low Medium Fast
Centrifugal Evaporation
Slow User
Attention None
required References
Vass, Hruska & Franek. 2008. Nitrofuran Antibiotics: a review on the application, prohibition and residual analysis. Veterinarni Medicina, 53, 2008 (9), pp 269-500.
About the Authors
A. Kaufmann, K. Maden und S. Walker are working at the offi cial food control authority of the canton of Zurich (Kantonales Labor Zurich). The group focuses on the analysis of veterinary drug residues in animal based food products. Commonly uses analytical techniques are Liquid chromatography coupled to high resolution mass spectrometry and liquid chromatography coupled to tandem quadrupole mass spectrometry.
Read, Share and Comment on this Article, visit:
www.labmate-online.com/articles The Perfect Response for Accelerated Oxidative Stability Testing
The Velp Scientifica (Italy) OXITEST is the perfect response for accelerated oxidative stability testing, both on raw materials and finished products. The determination of the oxidative stability is performed directly on the whole sample be it solid, liquid or doughy, with no need for preliminary fat separation, ensuring representative results.
The sample is weighed in the titanium sample holder, placed into one of the two independent titanium chambers and submitted to oxygen over-pressure of pure oxygen and high constant temperature. These two conditions drastically reduce the analysis time. The OXITEST measures the absolute pressure change inside two independent, closed and thermostatted chambers, monitoring the oxygen uptake by reactive components present in the sample.
Results are expressed through an oxidation curve, characterised by an induction period (IP), that is the time required to reach the starting point of oxidation, corresponding to either a level of detectable rancidity or a sudden change in the rate of oxidation. The longer the induction period, the higher the stability against oxidation over time. The OXITEST can be used on various sample types, being the optimal solution especially designed for R&D, Product Development and Quality Control labs in food, cosmetic and petrochemical industries.
28111pr@reply-direct.com Applications for Comprehensive QC of Edible Fats and Oils
Metrohm is pleased to publish an Application Bulletin (AB 141) presenting applications for the determination of key parameters in QC of edible oils and fats. AB 141 can be downloaded free from the company webpage
metrohm.com AB 141 describes the following analytical methods for edible fats and oils: Water content according to Karl Fischer; Oxidation stability, Rancimat method; Iodine value; Peroxide value; Saponification value; Acid value, free fatty acids (FFA); Hydroxyl value; Nickel traces, using polarography.
Special care was taken to avoid chlorinated solvents in these methods. Also as many methods as possible were automated.
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Risk of Cross Contamination
High
Evaporation Time
Slow Conclusions
Working with the rotary evaporator, a batch consisting of a total of 20 samples (reference solutions, samples and spikes) would require approximately 1.5 hours (evaporation time) for the fi rst evaporation step and another 2.5 – 3 hours for the second evaporation. A total of 4 – 4.5 hours spent where the operator has to keep an eye on the evaporator and change the samples every few minutes.
The centrifugal evaporator would require for the same batch up to 3 hours for both evaporation steps. In that time, the operator is free to do other work.
The centrifugal evaporator can take a total of 48 nitrofuran samples. These 48 samples would require approximately one hour more to evaporate (both steps) than a batch of 20. This would be an estimated 2 – 3 hours saved in comparison to working with a rotary evaporator.
Overall the installation of the EZ-2 Envi evaporator (Genevac Ltd, Ipswich, UK. Shown in fi gure 3) at KLZH is estimated to save the laboratory 2-3 hours per day that previously was spent on evaporation tasks. The instrument enabled the processing of larger sample series within a given day. It signifi cantly reduced the contamination (carry-over) issue. Previously, the frequent false positive fi ndings were the reason for re-analysis of affected sample or whole sample series. Very important is also the fact that the EZ-2 Envi operates unattended in a fully automatic manner.
Figure 3. EZ-2 Envi Evaporator
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