12 So, let’s get sampling!

Analysing a standard sample

First you will run the GC–MS of a standard sample containing a mixture of pesticides and their metabolites, and use a pesticide library to identify the organic compound that elutes at each retention time.

• Go to the GC-MS laboratory and click on ”Enter experiment” [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] (open this link in a new window, so you can get back to the instructions easily, you may wish to sign up for this site).
• Click on the ‘Reference’ tab to run the GC–MS spectrum of the standard mixture, following the instructions on screen.
• Note the retention time of each peak in your notebook. You may find it helpful to draw a table for this. Alternatively, you could copy the data values from the output, and paste them into a spreadsheet.
• Click on the number above a peak in order to see the mass spectrum of this pesticide. A library of spectra from known pesticides will also open. Use this pesticide library to identify which pesticide/metabolite is present at that particular retention time and make a note of this in your notebook. Repeat this process until you have identified all the peaks in the standard.