We are measuring fecal steroid metabolites, in the extraction process we have to evaporate to dryness 1 ml of 80/20 methanol/water solution. Some papers state that it can be done placing the opened pcr tubes overnight in a fume-hood, but after 24h in the fume hood the tubes still contains 0.2 ml of the solution. Any comments will be greatly appreciated.
Dear Pilar Solar,
U can use nitrogen evaporator (Recti-III) as steroidal compound non-reactive toward it and you apply heat up 50 degree and dry nitrogen gas upto 5 psi. so u need maximum 3 hrs as i guess.
Dear Pillar Solar,
I suggest to dry your samples in a speedvac system (centrifugal vaccum concentrator with a cold trap), which dries organic solvents or even aqueous samples (small reaction tubes 1,5 or 2ml size) very fast. It is a standard equipment in metabolomics and other laboratories; if you do not have such equipment, maybe ask other working groups of your university, someone should have it.
Otherwise also freeze-drying could be a possibility to dry your samples smooth.
You may also want to try placing the tubes so there is maximum flow of air over the top of the tubes (i.e. near the front with the sash close to the bottom), and maybe heat very gently.
En este caso, yo recomendaría que seques las muestras con una corriente de nitrógeno, es poco volumen y no te va a oxidar o dañar las muestras, es la mejor opción si se quiere evitar calentar las mismas.
Saludos
I would also recommend a speedvac system or freeze drying for drying of your samples. Another option is to dry under a steam of nitrogen if you don't have access to the previous systems. If you don't have a real N2 evaporator you can easily come up with a solution if you just have a gas tube, regulator, tubing and pipette tips.
The method you mentioned would probably not remove the water and that is why you see the residue. N2 stream is also not the best (not efficient when it comes to water). I would suggest using a speedvac as others have suggested. Alternatively, you could use a rotorvap system that would take your solvent mix off in minutes without heating the sample - if you have a synthetic chemistry lab close by, I will probably have one.
Thank you all for your time and helpful answers. We don't have the possibility of using a speedvac or a rotorvap, so we will try with the N2 stream.
If drying samples under fume hood be very careful to monitor the hood cycle especially over weekends as over time the steroid metabolites can decay and contaminated.
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