Importance of 10^-5 torr in high vacuum distillation
Posted: Wed Oct 30, 2013 2:11 am
Greetings! This question is directed at anyone with experience using high vacuum distillation. Personally, I have never done a vacuum distillation before. This is for GCMS sample prep.
I am looking into a technique called "solvent assisted flavour evaporation" or "safe" (original paper in 1999 by engel and schieberle) which is essentially a high vacuum distillation of an extract with some fancy workarounds for problems like condensation in the transfer tubes and reaction of analytes. Typical conditions are 40C sample to liquid nitrogen-cooled distillate, and 10^-5 torr vacuum, with ethyl acetate as the solvent. My question/call for help is about the vacuum. A good $3k rotary vane pump will get you 10^-3 torr, but all the "safe" papers I've read use either turbopumps or diffusion pumps to achieve the 10-5 torr or lower. However, looking through these papers and elsewhere, I cannot find an explanation for why the extra expense of a turbopump is necessary. It seems to me that 10^-3 torr is already plenty low to induce the evaporation of flavor compounds at 40C. Can anyone comment on what the added benefit would be so that I can decide whether to spend the extra dough?
-Nathan
I am looking into a technique called "solvent assisted flavour evaporation" or "safe" (original paper in 1999 by engel and schieberle) which is essentially a high vacuum distillation of an extract with some fancy workarounds for problems like condensation in the transfer tubes and reaction of analytes. Typical conditions are 40C sample to liquid nitrogen-cooled distillate, and 10^-5 torr vacuum, with ethyl acetate as the solvent. My question/call for help is about the vacuum. A good $3k rotary vane pump will get you 10^-3 torr, but all the "safe" papers I've read use either turbopumps or diffusion pumps to achieve the 10-5 torr or lower. However, looking through these papers and elsewhere, I cannot find an explanation for why the extra expense of a turbopump is necessary. It seems to me that 10^-3 torr is already plenty low to induce the evaporation of flavor compounds at 40C. Can anyone comment on what the added benefit would be so that I can decide whether to spend the extra dough?
-Nathan