Opening chemicals under nitrogen
Today was a research day. Usually I TA gen chem on Thursday afternoons, but we don’t have labs the first week of classes. Today’s task seems like a simple and quick one, but in reality took the better part of my afternoon. My task? Open a bottle and put a different lid on it.
So, some chemicals cannot be exposed to air without all kinds of undesirable results. In this case, the bottle contained the liquid sodium deuteroxide (NaOD). This chemical is similar to the very common strong base, sodium hydroxide (NaOH), but for my NMR research purposes has the hydrogen replaced with deuterium. (Without going into detail, this keeps the hydrogen on the base from showing up in the samples I make, while still allowing me to adjust the pH of the sample.) NaOD, however, is highly hygroscopic. This means that the chemical will absorb water from the air. The problem with this is that water continuously undergoes self-ionization (reacts with itself and will also exchange protons, H, with chemicals) and so will form NaOH (bad!) from the NaOD in the container. Adding NaOH to samples really messes up my results, so the amount of air that the liquid is exposed to has to be minimized.
Thus, in producing and distributing the chemical, the manufacturers keep the liquid under inert (stable and not prone to reacting) nitrogen gas. Unfortunately the company did not deem it necessary to also put a sure seal on the container, which is a lid under the seal that needles can be stuck through to withdraw liquid, without ever opening the container and exposing it to the atmospheric air. So, in many more words, I needed to open the bottle so that atmospheric air would not get into it, and put a new seal on it.
Instead of the more expensive glove box, our labs have what is more or less a huge giant plastic bag, designed for this purpose, with tubing from a nitrogen tank and tubing to a vacuum pump attached. All the materials that are going to be needed are placed in the bag (in this case the bottle and a couple possible rubber septum to acts as lids). The bag is then sealed by wrapping one end around a ruler, and clipping together the rolled plastic. A vacuum is then pulled, evacuating the bag of the atmospheric air, followed by nitrogen gas being pumped into the bag. It takes about ten to fifteen minutes to complete the cycle once. This process has to be done a minimum of three times (not just once!) to insure that the atmospheric air has been replaced. Simply because the purity of the NaOD is highly important in my research, I found it necessary to repeat the process five times.
The bag, ready to begin the process
Finally, an hour and a half later, I can open the bottle! The bag was gloves that reach into the bag on either side, easing the process of handling the chemicals and materials placed inside earlier. Finding the best septa to fit into the container opening once the lid was removed, folding down the sides and twisting a copper wire around it took ten minutes at most. Success! And now I can begin using the NaOD to make samples…
Phew, that was quite an explanation. Hopefully I didn’t make the explanation too confusing – in any case I decided to use the first photo as my picture for the day. Today was rather disappointing, so now I’m off to watch the third Lord of the Rings to finish my marathon. Hopefully tomorrow, and the weekend, proves to be better