0
$\begingroup$

I would like to know your opinion regarding the setup of a system for oxygen purging with nitrogen. Before ordering the necessary materials, I'd like to be sure if this setup is feasible or if it can be enhanced or even simplified, so any advice or new ideas are more than welcome.

To summarize, the experiment I'm going to perform is as follows:

-Oxidative weathering in solution of various sulfide minerals will be studied under different chemicals conditions. Some of the experiments must be performed in anoxic conditions, so all dissolved oxygen must be purged with nitrogen.

  • It is necessary to control the temperature throughout the experiment (40-42 ºC). The duration of the experiments will be 72h (non-stop). Stirring is also required. My first question: is it advisable to use a hot stirring plate together with the use of a silicon bath (or other suitable heating bath oil)? Is there any safety recommendation on the use of conventional hot plates for a prolonged period?
  • About the materials needed. As container, I've thought of using normal Erlenmeyer flasks (125 ml would be enough) but septum-sealed. The setup I have in mind is to use a small diameter Pasteur pipette inserted into a Tefzel tubing connected directly to the nitrogen tank. Then, just pass the pipette through the septum (nitrogen inlet). For the outlet and positive pressure, maybe I could use a needle tip (wide diameter). For better visualization, I include a very basic drawing with the assembly scheme I propose: enter image description here

How can I perform these experiments in series? That is, three flasks with different solutions purging, being stirred inside heating baths at the same time, but using a single tank of nitrogen.

Any advice on the assembly? Should I use another type of glassware instead of an Erlenmeyer? Are there better alternatives instead of using a Tefzel tubing (connectors, nitrogen tank adapters…)?

Do not hesitate to give your opinion. Thank you in advance.

$\endgroup$

1 Answer 1

2
$\begingroup$

If you can, join a collaboration with a group active in organic or inorganic chemistry, or catalysis possessing a Schlenk line. Its typical use in these lab aims to perform reactions without interference of oxygen and water. If you have to perform experiments of this type multiple times, consider to purchase such an installation.

The Schlenk line basically is an advanced two-tube manifold with connection to a vacuum pump, and a protection gas:

enter image description here

(image credit to https://schlenklinesurvivalguide.com/)

The principal advantage is that you evacuate the reaction flasks (round bottom flasks, but not Erlenmeyer flasks) and thus effectively replace the atmosphere in these containers by a dry inert gas e.g., nitrogen. A bit more expensive per liter is argon (the protection gas used e.g., for welding); in comparison to nitrogen, argon is of higher density than air and thus yields a good «blanket» covering your samples. Using a Schlenk line equally offers the advantage to connect to multiple (three to five) reaction vessels in parallel, which may be immersed in a bath (e.g., silicon) on top of a heating plate.

Request an on-site hands-on training session by a more senior chemist how to perform a pump-and-thaw cycle (cycling in said survival guide, one of multiple youtube video providing a demonstration) and the maneuvers you might need which are known as Schlenk techniques.


If you can't find a group to borrow access to a Schlenk line, a very much down-scaled approach would be to use multiple test tubes in lecture scale to create small compartments of controlled atmosphere. It is cheaper than a Schlenk line, but does not offer pump-thaw cycles. These test tubes may closed by a rubber stopper intentionally pierced twice for gas-in and gas-out, and are large enough to accommodate a rugby-shaped stirring bar. Though initially not set up for this purpose, you may alter the set up described recently by Johnson and West in the Journal of Chemical Education:

enter image description here

(image credit to Johnson et al.)

The very first and very last tubes in such a series would be filled partially by silicon oil to close the vessels against normal atmosphere. The inner tubes in this series (marked red) could be used to expose your hot material to oxygen with slight over pressure. (The sequence how the smaller tubes reach into the test tubes does matter as does the level of filling the liquids to prevent an accidental transfer of solution/liquid into an adjacent test tube.) The ensemble has a height of about $25\dots\pu{30 cm}$ depending on the rack used

enter image description here

(image credit to Johnson et al.)

but it equally is possible to hold the tubes housing an intentional reaction with a clamp immersed in a bath.

Reference:

Johnson, S. E.; West. J. K. A Simple, Inexpensive, Mercury-Free Bubbler Apparatus. J. Chem. Educ. 2021, 98, 2482–2485; doi 10.1021/acs.jchemed.1c00224.

$\endgroup$
3
  • $\begingroup$ Thank you very much for your reply. The proposed Schlenk line system seems very suitable. Unfortunately, it is not possible to spend funds on the purchase of this equipment, because we are not going to perform these experiments under anoxic conditions many times. However, I will ask an organic group from the other department if they have this system. In any case, I would like to know more alternatives, how I can get a good oxygen purge with a more "lab-made" configuration. $\endgroup$
    – Emmcrumun
    Feb 1, 2022 at 11:57
  • $\begingroup$ This would be a pity if a university active in chemistry has neither permanently installed Schlenk lines, nor some to borrow from the inventory. Some chemistry departments actually have a «shop» to borrow machinery (like heating plates), glass ware (like round bottom flasks) and chemicals, so it might be necessary to give the colleagues a telephone call to learn when this counter is open. $\endgroup$
    – Buttonwood
    Feb 1, 2022 at 18:06
  • 1
    $\begingroup$ The proposed new setup looks very promising. I suppose I could adapt it to my experimental purpose. Even if it's a down-scaled approach compared with the Schlenk lines, In my opinion I could get good results, I'll test the performance of the system with previous trials. Thank you so much for your explanation, the reference and for your feedback. $\endgroup$
    – Emmcrumun
    Feb 2, 2022 at 9:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.