[coquim]

Hi people!
i´ve realized that after sonication, an exactly volume ( in volumetric flask) are increased or decreased depending on the kind of solution i´m using...
Only two minutes or less are necessary to cause this...
My question is what is the correct form? or what is the correct volume should i take as a real value, in order to get the more exactly result??

Thanks you all!

[Arkcon]

Volumetric glassware is very sensitive to temperature changes.  You say you've only sonicated for a short duration, so I can't be sure it's been heated, however ...

It sounds to me like your volumetric technique may be poor.  Don't feel bad, I didn't have it down smooth after I left college and for my first couplea jobs, it only became an issue for more recent, quality assurance jobs.

You should be dissolving your solids in a small amount of solvent in the volumetric, only up filling the round portion, if you even have to use that much.  Then you do what you have to do to dissolve it - mix, heat or sonicate.  Then when you're satisfied you've dissolved everything, you may have to cool the solution to the temperature it's rated for -- that's obvious if you've warmed it, but sonication can generate heat too, and in some rare cases I've heard of, your hand's heat can affect the volume.  (Usually, that was for very thin-walled glass, of very small total volume, for liquids with low heat capacity and high expansion coefficients, not a standard aqueous solution in a 25 ml volumetric.)  But still, volumetric glassware can be surprising.

Only then, do you top up to the line, for accurate volume.  If that hasn't described your procedure -- dump it out, and start over, so you don't base your results on data from a bad prep.

And yeah, going through that, all day every day, dozens of times will eat up your day.  That's what you signed up for when you picked this career.

And watch out for excessive sonication.  Ultrasound can break bonds that can't be broken thermally.  How much is excessive?   Only trial and error can tell you that.

[coquim]

THANKS!....for your help, as always...
I dont feel bad, i´m learning, and i think i may be adjust my sonication volume technique inmediatly, i´m gonna do some glassware test by the way...
i know about glassware changes by heat and other things you´ve mentioned, but i´d like to know if sonication may broke bonds not by heat, but by ultrasound per se...you know what i mean...
thanks again!!!...

[Arkcon]

Years ago, I was reading a technical journal called Biotechniques, it was a free subscription, so the boss got it.  Mostly, it contained submissions from people who were working under NIH grants, this was way back in the ancient history of human events, when we were still trying to map the human genome, and rode to work on dinosaurs, you know, a decade ago, right? 

At any rate, any new stain for gel run samples was interesting to me, we were developing an scanning device.  Then someone publishes a short article about how they over-sonicated nitrophenol (if memory serves), and developed a new fluorescent DNA gel stain, and ... well, that's it, I've never found any follow-up.  It might be real, it might have been an artifact, I don't know.  I never found any more info.