When it all goes haywire

Sometimes it all seems to go wrong at once – yesterday we needed to replace a gas regulator, replace a broken filament in the Mass Spectrometer, clean several months of dirt from the filament housing, and pump all the air out of the system to make a vacuum again.

The filament in action
The filament in action

The important thing when setting everything up again is to run a standard. This will check that the machine is functioning properly before there is a risk of wasting precious samples in faulty equipment. A standard sample will be simple enough to produce a consistent result, but complex enough to produce more than just one peak in the chromatogram.

Preparing a standard - slice a small piece of PE and insert into a glass tube
Preparing a standard – slice a small piece of PE and insert into a glass tube

We use poly-ethylene¬† as a pyrolysis standard because the long polymer chains will break into a range of sizes during the heating phase. This produces a nice series of identical peaks, which emerge from the column in the order of their chain length. As long as this run comes out clean, it’s good to go.

A Poly-ethylene Py-GC chromatogram
A Poly-ethylene Py-GC chromatogram

Perfect – now the GC is up and running again