Looking a bit like a silver Dalek, the liquid nitrogen tank releases excess pressure as it is being filled.

By Nick Scroxton (originally posted 18th February 2012)

It’s O-week here at the university. An event that passes most post-graduates by, since we’ve already been back from the summer “break” since early January. But I thought now would be a good time to share one of my first moments in science.

In my first week at university, not so many years ago, I was walking through the corridors of my new department, moving between lectures probably, or to or from the library. On my way, I had to move to the side of the corridor, to let through a shining, gleaming beast. A giant, silver, cylindrical tank, welded onto its own trolley, with taps and handles and gauges sticking out of the top. Written large across the front was “Cryostore 90”. The scene was completed by a man in a white lab coat pushing it with an air of authority. It looked, to me anyway, incredibly futuristic and sciencey.

It was one of my first wow moments in science, I felt like I had arrived. No longer was I studying in a school classroom, I was in a famous department, where there was real science going on, real discoveries being made, all thanks to the help of fancy machines and devices like the “Cryostore 90”.

Now, a few years on, I am excited by the fact it is now me who wears the white lab coat and pushes the Cryostore 90 through the corridors of the (different) department, or at least a very similar piece of apparatus. Mine says XL240 on it, impressive, but the word cryostore is so much cooler!

The Cyrostore 90 and the XL240 are liquid nitrogen tanks. And they are vital in the running of my mass spectrometer. In the mass spectrometer, carbonate samples from my milled stalagmites (see here) are dissolved in acid and the carbon dioxide is collected. But there is also water vapour mixed in, and we don’t want that to get into the mass spectrometer – it causes all kinds of problems. So the collected gases are plunged into a bath of liquid nitrogen at -196˚C. Both the carbon dioxide and the water vapour freeze. Then the temperature of the bath is slowly raised. At -78˚C, the carbon dioxide turns to gas, whilst the water ice remains behind. The carbon dioxide gas is removed and taken on into the depths of the mass spectrometer to be analysed.

As its in the middle of a warm room, no matter how well insulated the nitrogen bath is, the liquid nitrogen slowly boils off during the process. As a consequence, about twice a week, the XL240 requires refilling and if I’m running the mass spectrometer then it is part of my job to go and refill it from a giant tank out in the courtyard. And so I get to push the XL240 through the corridors of the department, in my white lab coat. And I get a little buzz of excitement every time I do!