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Keeping moisture-sensitive chemicals dry

  1. Mar 24, 2010 #1

    MATLABdude

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    For a while, I've been stepping outside my comfort zone a bit and working with really moisture-sensitive chemicals (isothiocyanates, carbodiimides, succinimides, etc.: stuff that rapidly hydrolyzes and loses functionality). Even though we only purchased a tiny amount each time, we only used a tiny, tiny amount, leaving us with excess. That and the cost of these chemicals meant that we wanted to try to keep them around beyond one round of experiments.

    In any case, we moved up from vacuum desiccator (we felt that the moisture requirement was more important than the "keep frozen" one), to heat-sealed Ziplocs with desiccant packs (these really don't work long-term: like beyond a month or so, at least according to the humidity indicator cards) to the heat-sealed moisture barriers used for SMT electronics. Unfortunately, we don't have a very good glove box to create a high-quality inert environment in (we can nitrogen purge bottles, which we do, but not sealed bags).

    For the last while, we've just tried to squeeze out as much air out of the moisture barrier bag as possible prior to sealing with a few packets of desiccant and a humidity indicator card. In any case, I had an idea to use one of the food vacuum sealer units to even further reduce the humidity sealed in with the pouches. Does anybody have any experience with this, or know, back-of-the-envelope whether or not that's a whole lot of effort for not very much gain?

    Thank you!
     
  2. jcsd
  3. Mar 24, 2010 #2
    I'm sure sometimes you can just use oil if it is water sensitive, but I don't think taht was what you were asking.
     
  4. Mar 24, 2010 #3

    MATLABdude

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    No, I've seen that done for larger samples of alkali metals (lithium, sodium, etc.) but I don't think that'll work particularly well for my powdered compounds...
     
  5. Mar 25, 2010 #4

    Ygggdrasil

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    Most moisture sensitive compounds are moisture sensitive because they react with water. In addition to keeping moisture out, storing at low temperature (e.g. in the freezer) can slow the rate of hydrolysis. Just remember to let the bottles warm to room temperature before opening to prevent water from condensing on your compounds once you open the bottle.
     
  6. Mar 25, 2010 #5

    chemisttree

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    I would store my carbodiimides in an old empty mayo jar 1/3 full with indicating Drierite. Putting water-sensitive stuff in the freezer is asking for trouble since most of the time the environment inside is at dew point. Take it out and the entire thing is immediately coated with water... sort of like warming it under a stream of warm water. Polyethylene (ziplock) is a terrible barrier to moisture and I wouldn't trust the vacuum food bags either. They were designed to keep air out not moisture. If you want the ultimate in moisture barriers learn about storage schlenks. You can purchase them or have your glassblower make them using thick-walled round bottoms and glass stopcocks. These will last a lot longer but if you are really using small amounts, you should transfer all of your compounds into ampules when you first use them and seal them with a torch. This is done using schlenk line techniques and is suitable for even pyrophoric boranes. Purchasing those chemicals in small quantities with, for example, an Aldrich SureSeal septa is the best way to buy them but you should always be aware that these are likely stored on a shelf at your supplier's warehouse for some time before shipment. You will need to confirm activity before you begin if purity is a critical thing.
     
  7. Mar 30, 2010 #6

    MATLABdude

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    Thanks for the responses! I was hoping to use the food vacuum sealer not with the bags it comes with but rather moisture barrier bags (ones designed for electronics and which have very low moisture permeability). We have been freezing the (heat-sealed and bagged) vials after hopefully giving the desiccant time to scavenge the moisture inside. Thus far, it's worked so perhaps I'm being overly paranoid...
     
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