By Jessica A on Friday, October 17, 2003 - 01:56 pm:
I am researching a GC question for a fellow student.
Why does a compound of with a 150 degrees C boiling point still elute from a column of 90 degrees?
By Anonymous on Sunday, October 19, 2003 - 09:13 pm:
In fact the inner pressure of the column is less than atomspheric pressure so this compound can boil under a lower temp.
Any other viewpoint?
By Anonymous on Monday, October 20, 2003 - 04:40 am:
Simply, it has a vapour pressure so is evaporating. Think of a puddle of water - it will dry up even though the temperature isn't at its boiling point of 100°C.
Regards,
Ralph
By Rodney on Monday, October 20, 2003 - 06:36 am:
Ralph is correct.
It is a matter of concentration of analyte in the vapor phase. Vapor leaves a liquid prior to its boiling point. My steaming hot cup of coffee is not at 100°C or my mouth would be in great pain this morning.
Benzene, for example, can be eluted from a GC column tens of degrees below its melting (not boiling) point if my memory serves me well.
Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823
814-359-5737 voice
814-359-5459 fax
rgeorge @ sial.com
By Anonymous on Monday, October 20, 2003 - 09:40 pm:
Every one,
Your discussion derived a question from here. Is a lower boiling point related to a higher vapor pressure generally?
Thank you
By Anonymous on Tuesday, October 21, 2003 - 08:30 am:
That is a good question. Not an easy generalization, perhaps, but a meaningful question.
By mahmoud on Wednesday, October 22, 2003 - 01:41 pm:
I think there is a good discussion in this regard. Normally, vapor pressure variation with temperature is a non-linear. for more info please check
http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/vappre.html
cheers,
By Russ on Saturday, October 25, 2003 - 05:49 am:
Not sure if you can readily correlate vapor pressure to boiling point. One example that immediately came to my mind is mercury, which has an appreciable vapor pressure at room temperature even though the boiling point would be very high.
By Anonymous on Monday, October 27, 2003 - 09:12 am:
For the temperature at which tha analyte moves through the GC the slope and type of curve of vapor pressure vs. temperature is important. A compound with a lower vapor pressure at room temperature will elute sooner than one with a higher vapor pressure if the vapor pressure increases more rapidly than the second.