Au revoir to Liege and GC-MS basics

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The ion source of the mass spectrometer part of the GC-MS machine, with the old ion source on top waiting to be sent away for maintenance. The gas chromatograph part of the machine can be seen in the top of the photo, linked to the ion source by the part that has the ‘caution hot surface’ warning on it.

My time with CART at the University of Liege has now finished for this year! I completed all the lab work I needed to do which is great, but unfortunately the Gas Chromatography – Mass Spectrometry (GC-MS) machines are still down because of the heat. So we will have to wait to get all our pollutant results, fingers crossed things cool down in Belgium soon.

While they were trying to fix the machines during the last few days of my stay I got to see the insides of the GC-MS machines which was really interesting, they have so many intricate parts which you don’t normally get to see when they are running. The above picture is of a newly installed ion source in the mass spectrometer part of the machine (find out more technical details about ion sources here). On top of the machine is the old ion source in two bits that needs to be sent away for cleaning. In the picture below you can see the gas chromatograph part of the machine opened up to replace the column inside. The column is long and thin and looks like a coiled piece of wire (you can’t see it in this picture, its been removed but you can see where it joins to the inlet to the MS machine at the bottom right of the machine).

GC-MS machines work by coupling two detection methods together. The gas chromatography (GC) part separates out different substances in your sample by vaporising it (the gas phase) and then putting it through a column which is coated with substances (the solid phase) that interact with the vaporised sample. These interactions mean that different molecules in the sample elute, or reach the end of the column, at different times (the retention time). Substances can then be identified by how long they take to elute. However, some molecules have similar elution times under GC, called ‘co-elution’, which make telling them apart difficult from just this method. By combining the GC with mass spectrometry (MS) we can identify things with much greater accuracy.

MS works by ionising the vaporised sample eluting from the GC part of the machine by bombarding the various molecules with electrons (from the ion source, pictured above). The ions are then accelerated and deflected towards a detector, and measuring the mass-to-charge ratio of the ions enables us to identify which substances are present in a sample. Molecules that co-elute on the GC column will behave differently in the MS part of the machine, enabling us to tell them apart.

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The GC machine opened up and with the column removed for maintenance. The MS part of the machine is to the right, connected via the small, thin tube you can see in the bottom right of the GC chamber.

So I will bid ‘au revoir’ to Liege for the time being. I will hopefully return next year to analyse the new samples we will collect on the Isle of May this winter and from any seals we find moulting in the spring of 2017. When I get back to the lab I will be looking at the biochemistry of our study seals (measuring substances like glucose and free fatty acids in blood samples) and will also start preparing all the equipment we need for the big field season in October, like ordering a new CO2 incubation chamber that can be transported by boat to an island! The blog will be in hiatus until October when we’re about to set off for the Isle of May and exciting things are happening again. Expect weekly blog updates to return then…

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During the summer the Isle of May is open to visits from the public to see the huge bird colony there, but from October onwards the island is closed to protect the seals breeding there.

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