Chromatography Forum

dear forum member

I have a querry concerning: HPLC and TLC air extraction devices
Local Extraction / Venting around HPLC set, what do use usually: some Lab operators tell us that when air speed is too high that allows the solvant to evaporate; and thus mitigate results; so they dont want
Fume cupboard (https://extranet.fisher.co.uk/insight2_ ... Position=3)
they prefere Chemical hood, or Local exhaust Ventilation above the solvant / waste container:

https://extranet.fisher.co.uk/insight2_ ... osition=13

(https://extranet.fisher.co.uk/webfiles/ ... 8P1216.PDF)

https://extranet.fisher.co.uk/insight2_ ... Position=7

what will be your choice?

Thanks!

i have to admit that i fail to understand the problem.

in both of your examples i do not see how those devices can influence the chromatography, unless you do not use capped bottles for your solvents in your HPLC and you do not put a lid over your TLC tank.

can you be more detailed please.

the few times that i saw in HPLC a "problem" related to evaporation it was when too large bottles were used 5 liters-10 liters and the mobile phase was used almost entirely.
it does happen a lot that the conc. of your slovents in the gas phase is different then what you have in your liquid phase. simple thermodynamics.
then when you reach the end of your slovent in a big container the liquid phase changes dramatically because of the ratio in the gas phase.
but this in 1-2 liter bottles is close to insignificant if you keep your bottles closed.

Hello; thanks for your clear answer!
in fact, all is related to air extraction capacity:
for a simple extraction hood; count 150 m3/h; while for a fume cupboard it is 700 m3/h (for recent models, olders are at 1200m3/h) while those devices are more used for solvants preparations, some analysts wants them to handle solvants tanks during HPLC run ...

you are true when you say that a capped bottle will show little evaporation if not at all; and that capacity is important...
but french drug agency issued a statement for this and called it: "effet de bord", bottles where capped; could you tell me what will be the best choice for caps for HPLC or lid for TLC?
if we use those caps / lids, no evaporation will occur, then no need for air extraction;

have a nice day!

these days most HPLC vendors sell caps for the standard bottles used in labs. the same goes for TLC, especially for TLC. a correct TLC development should be done with a lid over the tank. by default tanks are sold with a lid, it is a must. ask your local vendors, it should not be hard to find those items.

as for your ventilation, you work in a lab, there should be some safety regualtion in France like for any EU country i believe regarding the speed rate at which the air in your lab should be changed. so in essence if you have caps for your bottles and tanks then you should only meet that regulation.
but, in order to prepare the solvents that you will use for your TLC or HPLC you will need a chemical hood. it is advisable to have your tanks in the chemical hood as well, since you still need to open and close them in order to insert or take out the plates. TLC means nasty organic solvents.

hello,
thanks for your reply, I understand better the process, it seems that the TLC is giving some of our analysts more problems than it s really should!

have a nice day,