Chromatography Forum

I am operating a GC-MS in NCI mode for analysis of PBDEs. Major peak tailing was observed after cleaning the source (no other maintenance performed). The source is normally operated at 150C; at source temp 250 and 300, the peak shape dramatically improves. At source 150, the peak shape for the molecular ion is great, while monitoring sequential mass fragments in the same injection, the peak shape will deteriorate. This was sudden and cannot be explained. A second, new source was installed with no improvement. An identical instrument in the same lab has no problems operating at 150 under these conditions.

Not sure what your question is

It seems that either

- You baked out your source by going to 250-300. It's not a bad idea, especially after cleaning, to approach the upper temperatures of your source for at least a couple of hours.

- The ionization of these molecules is just better at higher temperatures.

I don't work with NCI, but for instance for PAHs with GC-EI-MS, i notice a significant improvement in peak shape for the heavy ones going from 200 °C source temperature to 280 °C.

Welcome to the forum.

Are you asking about chromatographic peaks, or mass spectrum peaks ?

Peter