The time needed would be "as long as it takes" (really). Removing methanol from water should be easy. However, you need to be careful you do not degrade your sample in the process. You should be able to rotovap (or "Speed vac") the sample quickly, using a small flask. *I would suggest that you obtain some formal training in how to do so (before you try your sample), read the operator's manual for the vac system and of course discuss this with your teacher or colleagues. On-site, in-person training is part of the learning process.

usually we put our sample in a small epp tube (2ml ) and then we use speed back evaporator it takes around 2-3 hours to evaporate all solvent

Thank you all

Which temperature I must set the instrument? Is 30 c appropriate?

Dear Ayman Turk,

Did you fully fill the 2ml tube or not? and If I fully fill it, does not the mixture pour out the tube? ( because of vaccume and low pressure)

Hi Ashrafi,

Actually the evaporation time depends on the gas pressure (bar), and temperature. Thouth, to evaporate 2mL, it would take quite long. To evaporate 95% of 2mL mixture, I would recommend you to perform a preliminary study using one or two samples to estimate the total evaporation time before going to the final experiment. Additionally, if there is no temperature limitation for your desiring things you can use high temperature. Basically, we use 37 C for biological samples. Hope, this would help you.

the boiling temperature is different for methanol and water. at 60 C methanol can easily removed but water will remove only at high temperature 100 C. Since you are using mixture of methanol and water initially methanol will be removed after some time water will be remove. so if you fix 80 C temperature within 45 minutes solvent will remove completely..

best regards....

I like the method of G. Dayana Jeyaleela, which is very simple and elegant. I would add marking the level on your test tube to give you an idea of your starting point and just look at where 2 mL would have evaporated, give or take an uncertainty amount.

Thank you for your comments, but I have concern about heat degredation of metabolites (at 80 C) which are present in the mixture.

Best regards,

Mohsen

There are several methods to accomplish this. The most appropriate are low temperature vacuum methods. The rate of evaporation is directly proportional to the partial pressure of the compound in the gas phase above the solution. If you pull a vacuum, that partial pressure goes to zero and the rate of evaporation hits a maximum. The problem is controlling for 'bumping' (boiling). This is where a speed vac is helpful, which spins the tube under vacuum preventing the liquid from boiling over. Another alternative is freeze-drying. If you can afford to wait, you can put the tubes in a -80C freezer, where the methanol/water will freeze (or flash freeze in liquid N2). The solution will slowly sublime in the -80C. You can speed this up by putting the frozen tubes inside a vacuum dessicator in the -80C freezer and pull a vacuum on that, but that requires getting a vacuum line inside the freezer. In this case there is no solution to boil, but what remains will be very fluffy and can get dislodged from the tube when you vent the dessicator. Of course, there is the old standby of putting the tubes open in a hood and waiting. The movement of fresh air over the tops of the tubes keeps the partial pressure of methanol low.

Dear Luke V Schneider,

Thank you for your helpful comment. According to your stats, I should not be concern about boiling of my mixture in speed vac instrument even under low pressure.

Thank you all again for your comments.

Best,

Speed Vac will work fine. No need for heat, but you can speed the process up a bit by applying some (e.g., 30-40 C). The sample will remain cold due to evaporative cooling until dry, then the heat may become a problem.

sorry for my late reply, if you are using an epp tube of 1.5 ml you should fil,l it till 600 ml or you can use 2ml epp tube then u can fill it up to 1.5 ml

The only issue is the angle that the fluid in the tube will take when you turn the speed vac on. The rotor holes are angled for that reason. The fluid should remain level with the lip of the tube when the rotor is turning, but will be level with the ground when you are loading and unloading the tubes, therefore, you can only fill the tube enough so that when you are loading the tubes the solution doesn't spill. There are a number of rotors available for the speed vac, but you want the tubes to fit snugly into the rotors (not flop around), so if you use tubes smaller than the holes in the rotor, you have to insert them inside larger tubes that fit snugly.

Thank you all again.

I removed methanol in 3 houres at 38 C, by use of speed vac and all of your comments were helpful.

If the water is causing your samples to take too long to evaporate on the SpeedVac you might consider adding about 1ml or so of 2,2-Dimethoxypropane (DMP). This compound reacts with water to form acetone and methanol which are easily evaporated away. I would recommend performing some controlled test experiments though to make sure you've added enough and are not generating any other products that could potentially interfere or compromise your analytical results.

2,2-DME is reactive with any alcohol and acid group, and probably amines, which means modification of the biomolecules themselves. Plus you have the spontaneous peroxide forming issues with ethers, which when you are evaporating to dryness, can lead to explosions.