Chromatography Forum

We have recently purchased a GC-TOF-MS (Waters GCT) I am developing a testmix to assess its performance. I will be using Peak Assemetry as one factor, on Quads we use S/N in the TIC. Using the same testmix it fails the S/N of one compound, however I feel this is irrelevant for this instrument. Would the Peak Area of an Extracted Ion be more appropriate?

What the parameters have to be for a test mix, and the composition of the test mix itself, should be guided by the real analyses that you want the instrument to do. If you are doing quantitative trace analyses then LOD or LOQ (which you would probably measure as S:N for a small peak) is a useful parameter, if you are trying to "identify" trace componenets then you need to know what the smallest peak is that you can pull a full scan spectrum off. If your samples are full of acids, the shape of an amine peak might not be particualrly relevant.

Peter

In evaluating the S/N ratio a few other thoughts: If I recall correctly, the Waters GCT is an accurate mass instrument. It acquires data a bit differently than a unit mass instrument - such as the typical quadropole. If you can select the accurate mass range to be included in an ion trace, the signal to noise ratio may vary, even on an ion trace, depending on the width whether you are including a width of 1 amu or some fraction thereof.

Also consider the sampling rate of the instrument and any smoothing that happens in the software during processing.

Its for qualatative analysis of unknown samples containing phosphorous compounds.

For such a specific application you need a special test mixture - preferably one that contains compounds as close as possible in structure and properties to the ones that you are looking for.

Think of all the things that could compromise performance for the application, e.g. poor S:N, poor chromatographic resolution, poor mass accuracy and resolution, thermal degradation of sensitive compounds, and check for those.

Peter