Experimental setup

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](https://i.stack.imgur.com/Uwhgg.png)](https://i.stack.imgur.com/Uwhgg.png)


**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.




If you can, join a collaboration with a group active in organic or inorganic chemistry, or catalysis possessing a [Schlenk line](https://en.wikipedia.org/wiki/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](https://i.stack.imgur.com/V9kyO.png)](https://i.stack.imgur.com/V9kyO.png)


(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](https://schlenklinesurvivalguide.com/cycling-onto-the-schlenk-line/) in said survival guide, one of multiple [youtube video](https://www.youtube.com/watch?v=Eov60kI7yw8) providing a demonstration) and the maneuvers you might need which are known as Schlenk techniques.




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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](https://i.stack.imgur.com/qmzcS.png)](https://i.stack.imgur.com/qmzcS.png)


(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](https://i.stack.imgur.com/5Yu3D.png)](https://i.stack.imgur.com/5Yu3D.png)


(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](https://doi.org/10.1021/acs.jchemed.1c00224).


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