Hacks for Septa

August 4th, 2013

The Sure/Seal (TM) septa on top of Aldrich bottles are anything but. As soon as you pierce one of those puppies to extract some anhydrous solvent, you can be certain that subsequent aliquots will be of dubious dryness. I cannot count the number of times I’ve pulled a Sure/Seal bottle from a stockroom only to open the red plastic top and find a gaping hole staring back at me. At that point, why even bother leaving the septum on?

During one of my first-year rotations in grad school, the PI of the lab had a specific policy for using Sure/Seal bottles. Before any solvent was dispensed, you had to:

1) Find a 24/40 natural rubber septum
2) Invert the septum and pull it over the mouth of the bottle
3) Secure the prophylactic septum with a copper wire

Sure-Seal Septum Upgrade

Extraction of the solvent would then take place by puncturing both the Sure/Seal and the outer septum. Since the outer septum was made of natural rubber, it would re-seal more tightly than the firm Sure/Seal. (Of course, over long periods of storage, the rubber dries out crystallizes and the outer septum disintegrates—see comments.)

After you were done setting up the reaction, you were supposed to take one of those yellow plastic 14/20 stoppers and bung it in the hole of the outer septum. Finally, the entire apparatus at the top of the bottle would be wrapped with parafilm.

While the whole process was time consuming, I liked to think that it offered at least some added protection from atmospheric moisture. Milkshake prefers to tape the tops of his Sure/Seals after use, and that seems like a simple alternative. I’d love to see someone run a comparison test of these (and other) methods.

23 Responses to “Hacks for Septa”

  1. John Spevacek Says:

    “Of course, over long periods of storage, the outer septum dries out.” I think what you meant to say is “Natural rubber, over long periods of storage, crystallizes and loses its elasticity.” (Dries out? Dries out of what?)

  2. jb Says:

    We had a similar practice in my grad school lab. Problem is the Aldrich sure-seal hardens over time and it becomes impossible to puncture it with the septum above it as you can’t see anything. I ended up either putting a triple folded piece of parafilm over the puncture hole or putting silicone grease over it.

  3. Ian Says:

    I hate sureseal bottles in general.

    Our lab policy is either 1.) leave them in the glovebox and use them there or 2.) cannulate the entire contents of the bottle into an airfree storage flask such as http://www.chemglass.com/product_view.asp?pnr=AF-0522

    Once it’s in the storage flask, it’s much easier to work with on the Schlenk line AND you don’t have to worry about seals degrading over time. This is especially useful if you have enormous bottles of things like BuLi that you are going to use over and over again.

    This probably wouldn’t be cost effective if you had hundreds of these… but we have enough airfree storage space in the gloveboxs that option #1 takes care of the majority of sureseals.

  4. Hap Says:

    I assumed that natural rubber was oxidized by air over time and that that caused the cracks and degradation in the rubber, and thus the loss of elasticity/powder formation. I take it that’s not correct?

  5. Paul Says:

    @John: Thanks for that correction. First off, I shall note that John is an expert on polymers. I said “dries out” without thinking because the result looks like the rubber has dried out. My assumption was that there were natural oils in the rubber that dried out or oxidized over time, but I guess that is wrong? One observation I’ve made is that septa left in hoods or benchtops corrode faster than those left in a sealed plastic bag in a drawer. Am I imagining things, or does this observation play into the crystallization explanation?

  6. Steve Says:

    I always preferred the Acros type bottles for things like BuLi – seemed to last much longer and reseal better than Aldrich’s sureseal.

  7. John Spevacek Says:

    Hap and Paul,

    Oxidation reduces the chain length making it easier for the crystallization to occur. Ozone is a real nightmare too. I would expect the bottles in the hood to be exposed to everything imaginable.

    Natural rubber crystallization is pretty fascinating. The kinetics tell Arrhenius to go take a leap of the St. Louis Arch and show a peak with temperature, coincidentally at RT. Below RT, you get the normal rate vs. exp(1/T) behavior, but at higher temperatures, there is enough energy for the nucleating crystals to remelt.

    Stretching the rubber accelerates the crystallization as well. (Strain-induced crystallization)

  8. Robin Says:

    This would be the “unsure” seal, and was what everyone used “back in the old days” when you got a bottle of nBuLi with a naked screw cap. Do not defeat the purpose of the Sure Seal, which seals the bottle between the plastic screw cap and the metal cap holding the septa. You can, however, make it better by closing the hole in the septa.

    I recommend a “booger seal” made of a small bit of parafilm, just large enough to seal the hole in the septa, but not large enough to overfill the little space between the plastic cap and the septa, ringed by the metal sure seal. You roll the bit of parafilm around between your thumb and index finger until it becomes very soft.

    Generally speaking, there should be two holes in your septa— one for your syringe or cannula, and one for your argon line. As the argon line comes out, the “booger” goes on. The “sure seal” works just fine, but it does not replace the need for proper “modified Schlenk technique.”

  9. Reverend J Says:

    I always would wrap the top of the bottle in parafilm then put the septum on that then wrap it again with parafilm made it easier to get the septum off if I needed to. Or if I was being lazy I’d just cover it with parafilm then put the cap back on then wrap with parafilm after purging with argon.

  10. Ken Says:

    You would figure as scientists that at some point someone would do a little experiment on something we all have encountered. For example, “We stored bottles of X chemical with a primary sureseal cap but then with secondary variable tapes/caps. Here’s how the chemical holds up with time for the various options.”

    I’ve always been in the “crossing strips of teflon tape over the sureseal held in place by parafilm, then positive pressure of inert gas when in use, followed by quick replacement of teflon tape and parafilm for storage” camp, but I have absolutely no evidence to show that’s better than any other method.

  11. Paul Says:

    I just caught these comments on septa from Milkshake in the recent ingenol thread on Open Flask:

    @orgprepdaily: 2) You seem to be using smooth 24/40 septa for vacuum work- we had noticed that (depending on the manufacturer) sometimes the large 24/40 septa do not hold vacuum nearly as good so we prefer serrated SubaSeal white septa for highvac applications

    @orgprepdaily: Its not just about getting good vacuum – more concern is the oxygen and the moisture that gets sucked in. (With 0.01 Torr vacuum the pressure differential against atmosphere is about 760 Torr. At 200 Torr the pressure differential against atmosphere is about 560 Torr.) The best sealing SubaSeal are from Fisher, catalog # FB-686-90, pack of 10 costs about $30. (Aldrich similar Suba septa product is not nearly as air-tight)

  12. Dr. Mel Says:

    We would have group meetings about this. It was my opinion that the grad students were using needles with too large a bore and were charging the bottles with too much argon so that reagent removal would be easier. Once you have decomposed reagent in the puncture it prevents the seal from reforming. I am with Ian, thinking that you can keep an air sensitive reagent pure behind a sureseal cap is delusional especially if you keep the lab fridge 20 C below the ambient lab temperature. The pressure differential when the reagent is re-cooled will simply suck lab “air” into the bottle. After the first puncture the reagent degrades, your real issue is what is the acceptable level of decomposition before you start the next bottle. We bought lots of small bottles rather than “save” money by buying in bulk and discarding in bulk.

  13. Dave Says:

    In the lab I did my graduate work in, we would either: 1) Buy small sureseal bottles and cover up the seal with parafilm after the first use, then parafilm the cap as well to keep moisture and oxygen out as best as possible. 2) Keep the bottle in the glovebox. 3) Make our own fresh reagent in situ or in the glovebox in a Schlenk flask and bring it out, stored under nitrogen.

  14. Cowtipper Says:

    Aldrich now sells n-BuLi in 4 X 25mL bottles for only slightly more than 1 X 100mL ($49 vs $42). Well worth the small extra cost, in my opinion.

  15. PMP Says:

    I agree with Ken above – this is an issue that should be tested in the lab. We might br interested in carrying out this exepriment, but I would like to have some feedback on what would be the best way of conducting the study. I was thinking of using suresealed bottles of anhyd THF and to do a Karl-Fischer titrations on samples receiving different treatment. An alternative would be small bottles of nBuLi.

    In my own experience, however, indicates that the septa hacking method advocated by Paul does not work, at least not for organometallic reagents.

    The Aldrich instructions for handling SureSeals include the recommendation of replacing the cap after use. The teflon lining inside the cap should form a tight seal against the metal cap. The plastic cap should be much tighter than the septum.

    I believe the largest culprit in degrading reagents and solvents is the slow influx of moisture and air over prolonged periods of time. What happens during the short period when you actually open the cap and insert the Ar or N2 source is irrelevant compared to the long periods of time in storage.

    Finally, we always keep opened BuLi bottles in a desiccator, never in the fridge. I thinn atmospheric moisture is a bigger killer than beta-elimination. Again, this should be verified.

  16. Free Radical Says:

    Quick fix: cover holes of sure seal with Teflon tape, then cap, then para film cap.

    More robust: septum trick you described, capping with either yellow cap or with i perforated septum, then para film.

  17. Canadian Chemist Says:

    Any hacks for nasty reagents like BF3-OEt2 or BBr3? These come from Aldrich with SureSeals that are surely gone after the first puncture. I’ve never understood why they sell BBr3 as a solution… the concentration must change so rapidly as I watch the fumes pour out…

  18. Canadian Chemist Says:

    Ian, once you transfer into those types of storage Schlenk flasks, what’s the best way to get your reagent out again? I’ve always found getting a needle around the corners to be quite challenging…

  19. Ian Says:

    The key is that you want to transfer through the vertical metering valve, not through the bent sidearm.

    You put the ground glass joint sidearm under positive N2/Ar pressure (hook it up to your Schlenk line), and then remove the teflon valve and quickly put a septum on it (typically, the inside of a 24/40 subaseal septum fits snugly over the outside of a 4mm Kontes valve or CG valve. depending on your septum brand, you may need to experiment to find a good fit).

    Then, you can syringe or cannula through the septum into your desired flask. When you are done, just quickly switch out the septum for the teflon valve, seal it, and you’re good to go.

    We’re currently putting together our lab manual but I don’t think we have any pictures or written protocols for this just yet (we’re still working on more basic stuff like “how to use a rotovap” currently). At some point in time this will make it on our lab website.

  20. Canadian Chemist Says:

    The quick switch is what I was missing but makes more sense. Thanks!

  21. labmonkey Says:

    I’m not convinced putting teflon tape or parafilm does anything to prolong the life of the reagent. Does it really improve the seal between the cap and metal? Have you noticed the circular impression you get in the teflon cap – seems like a reasonable seal to me. A lot of the time students/postdocs have put too much parafilm or teflon tape and it has distorted the cap preventing what you wanted in the first place. I think the major culprit is as discussed above – taking in and out of storage in the fridge. Also, unpurged lines and needles would probably not help the cause.

  22. Matt Says:

    PMP: You are correct, n-BuLi shouldn’t be frozen, unlike s- and t-BuLi. The beta elimination rate is only significant at room temp over the course of years in the absence of air and moisture. All you do is suck in wet air.

  23. z Says:

    I realize I’m a late-comer to this thread, but my question is: When repeatedly using a sureseal bottle, do you try to puncture it in the same places each time? So, ideally, you would always have two holes present and never any more than two. Or do you puncture it in different places each time? I’ve heard different people favoring each option. In the former case, there are less holes, but they tend to widen out and stop healing after repeated puncture in the same place. In the latter case, you end up lots of holes, but they are very small and the septum might heal more effectively.

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