The Belly of the Beast: Inside the Mass Spectrometer

As my lab work draws to a close I realise I have learned a surprising amount about running and fixing lab instruments, such as the Delta XP mass spectrometer (mainly when things go wrong as they often do with such high precision instruments). This post is more about the inner workings of the CosTech Elemental Analyser, used for analysing my stable isotopes of Carbon and Nitrogen from feathers.

The Delta XP in the foreground. The Costec furnace (with the blue stripe) for
Carbon/Nitrogen analysis and the tall red Vecstar furnace for Hydrogen in the
background

Inside the CosTec:

Not a tube of festive decorations, but a spent
reduction column filled with copper shot.
When new all the copper was grey, as in the
bottom of the column. 

A used and new combustion column with the 
handy ruler to guide column packing.
This is the column where the sample is burned.
Note the build up of ash from the tin capsules
in the used column.
    (QW= Quartz wool)

Inside the Mass Spectrometer:

The furnace has 2 reactor columns, 1 where the burning takes place (flash pyrolysis), the other is a reduction column that scrubs out unwanted compounds from the sample gas before it is carried by helium to the mass spectrometer which "counts" the number of isotopes of different weight in the gas. Simple!

Inside the Delta XP mass spectrometer

Even deeper inside the Delta XP. The Source  -if you see this then something has
gone very wrong and the mass spec has been opened up. It takes a few days for
it to return to vacuum and for atmospheric moisture to be removed.
So seeing the source means delays in lab work. Fixing it requires a steady hand,
tweezers and a tiny screw driver. 

I have only seen the ion source (known simply as The Source) 3 times during my 4 years of mass spectrometry as a Masters and PhD student. The ion source converts the sample in to charged particles (ions) which are then passed to the magnet. The magnetic field deflects the particles by differing amounts according to their mass:charge ratio. The detector then counts the relative abundance of the different ions based on their mass:charge ratio. I am measuring the ratios of 12C:13C and 14N:15N, the heavier form being rarer. 

Iberia is dominated by C3 photosynthetic pathway plants with an average 13C of -27 parts per thousand (per mil), where as in Africa in the savannas of Senegal, most plants are C4 pathway plants with an average of -13 per mil. All living things take up these isotopic ratios through diet and they become fixed in tissues like feathers. In this way if I select a Lesser Kestrel feather likely to have been moulted in Africa I can tell from the isotopic ratios whether an individual migrated to Africa or whether it wintered in Iberia. Really fascinating science!