bring to volume mark before or after ultrasonication?

[moonchips]

Greeting,
I noticed that volume actually change a lot after sonication. Why is that?

Shall I bring to volume mark before or after the ultrasonication?

thanks a lot

[zokitano]

Dear moonchips,

There are two factors that can change the volume of a solution during sonication:

1. Decreasing the solubility of gases during sonication can alter the total volume. During sonication you can see gas bubbles escaping out of the solution. So the total mass and volume of the system liquid (solution) + dissolved gas in it will change after sonication and

2. During sonication additional energy is introduced in the system (solution/solvent), which may cause increase of the system temperature. The change in temperature will also affect the total volume, because the volume of the liquids (and not only for liquids) is temperature dependent.

So, I'd suggest you not to bring the volume to the mark before sonication. Firstly, sonicate the solution (until everything is completely dissolved) and then let the solution to stand at prescribed working temperature (room temperature, for example). Wait until it cools down and then you could bring the volume to the mark.

Hope this helps

[Bruce Hamilton]

The purpose of sonication is usually to dissolve solids. Consequently the volume of solid + clean solvent will usually decrease as the solid dissolves.

The effect of temperature is also significant and unpredictable, most solutions will heat up, but if you are dissolving a lot of salts, you may get cooling.

I've never seen an situation where any volume change due to removal of dissolved gases was obvious, which isn't surprising given the small mass of gases..

My advice is similar to that above, add sufficient solvent to the solids to make ~ 95-98% of final volume, ultrasonicate to dissolve all solids, remove, allow to come to room temperature. make up to the mark, and mix well.

The only exception to this procedure would be when methods specify that samples should be " dissolved in xx.xx mL of solvent ". In which case, accurately add the xx.xx volume to your solids and dissolve.

Please keep having fun,

Bruce Hamilton

[DR]

Pragmatically speaking, there are 2 rules

1) Sonicate until you're working with a solution (not a suspension).

2) When you take your aliquot for further dilution, it has to be at the mark. In other words, it doesn't matter if you QS before or after you sonicate so long as you're at the correct volume when you stick your pipet into the flask. (of course, I'm assuming that you will only need to do this once - if you lack such confidence, go with "after" and make sure the temp. has stabilized - before works almost as well, but more slowly).