I am a biologist currently doing field work where I need to quickly dry leaf samples using silica gel crystals. I use the orange indicating kind that are 2-4mm in size. The setup is like this. I stuff 1-2 leaves in a manila paper envelop which I drop in a ziplock bag containing ~1/8th cup of silica gel. Then I squeeze out most of the air before sealing the ziplock. The end goal here is to extract DNA from dried leaves when I am back in the lab.

I have had varied results in terms of drying and looking to achieve the maximum efficiency. Recently it occurred to me whether squeezing air out is actually counterproductive to fast drying.

So my question is, whether presence of sufficient air necessary for silica gel to absorb moisture from leaves? Essentially I am creating partial vacuum inside the ziplock. Is that keeping silica from doing its job?

  • $\begingroup$ Air should play no role in silica water absorption capacity. What you can do is to ensure that silica is stored in a dry condition before use. $\endgroup$
    – ACR
    Commented Jul 20, 2019 at 18:11
  • 1
    $\begingroup$ It's stored in a air tight container, so starting moisture is not a concern. If chemically speaking, air is not a concern, would proximity of beads to the sample could still play a role? For example, when you squeeze air out, it's restricts movement of beads allowing one to control their proximity to the leaves. If there is air in the ziplock, then movement is unrestricted. This is what my question is mostly coming from. $\endgroup$
    – cryptic0
    Commented Jul 20, 2019 at 19:27
  • $\begingroup$ @cryptic0 If you aim for the isolation of the DNA, assuming taxonomy in lines of "first leaves of a special tea shrub" already is done in the field, I speculate drying of the leaves might be accelerated if these were crushed / shred early there. With increased exposed surface to the air shuttling back and forth to the silicagel, the process of drying were faster than passing water all across cuticulae / stomata / epidermis. (This assumes the silica is kept in their paper bags, not in direct contact to the specimen.) $\endgroup$
    – Buttonwood
    Commented Jul 20, 2019 at 19:40
  • $\begingroup$ @Buttonwood You bring up an interesting point, one I have pondered, but not followed through with. I am going to set up an experiment, with one iteration as you describe (silica in envelope), shredded leaf in ziplock and another my regular method and see which one dries faster. Notwithstanding, the question of how much air to allow in the ziplock remains. $\endgroup$
    – cryptic0
    Commented Jul 20, 2019 at 19:56
  • $\begingroup$ I wonder if it would help to keep the manila envelop in the ziplock bag with the descant prior to putting the leaf in. The paper will pick up water. With the envelop, the water vapor has to travel through the envelop to the air in the bag to the descant. $\endgroup$
    – MaxW
    Commented Jul 20, 2019 at 20:16


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