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Topic: Evaporation condensation Q  (Read 494 times)

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Offline SHH

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Evaporation condensation Q
« on: January 31, 2020, 09:09:39 PM »
Hi all,
I'm using small 0.2mL push-cap tubes to hold aqueous solutions (standards).  There is only 25uL in each vial, and the tube is tightly sealed.  Just wondering if I should be more concerned about evaporation or condensation with such a low volume.  Obviously both will affect the concentration of analyte in the low volume of solution.
Some tubes are stored at RT, others are stored fridge.
If you have any comments I'd appreciate them :)
Regards
SH

Offline Borek

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Re: Evaporation condensation Q
« Reply #1 on: February 01, 2020, 04:07:07 AM »
If they are properly sealed they should not evaporate.

Besides - if you are using entire sample each time change in volume/concentration doesn't have to be a problem, as the amount of the solute remains constant.
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Offline SHH

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Re: Evaporation condensation Q
« Reply #2 on: February 01, 2020, 05:18:42 AM »
Besides - if you are using entire sample each time change in volume/concentration doesn't have to be a problem, as the amount of the solute remains constant.

But if there is evaporation or condensation the concentration of that solute will change (unless I'm missing something) which is what I'm concerned about.

All the tubes were tightly sealed, but I did see a small amount of condensation on the inside of the cap...

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Re: Evaporation condensation Q
« Reply #3 on: February 01, 2020, 09:39:14 AM »
Swirl before opening. Of course, there will be some evaporation until the headspace is saturated but it will not constitute a significant quantity of the liquid unless the headspace volume is really large.
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Offline SHH

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Re: Evaporation condensation Q
« Reply #4 on: February 01, 2020, 05:11:51 PM »
It's a 0.2mL tube with 25uL inside, so the headspace is about 175uL.  There was definite condensation on the inside of the cap- I considered swirling the sample but prefer not to for a few reasons.  When I tested the samples I found the concentration  of my analyte increased faster during storage in the fridge as opposed to at RT.  That seemed odd because I expected more evaporation in the tubes stored at RT.  Does that make sense?  Just trying to rationalise why analyte concentration seemed to deteriorate (increase) faster in tubes stored in the fridge, not at RT.

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