Chromatography Forum

As we all know, ion suppression by non-volatile and co-eluting analytes on HPLC column has a significant effect on quantification of LC-MS. But I am wondering if it has a similar effect on GC-MS since the ionization is obtained by electron impact.

Thanks!!

As we all know, ion suppression by non-volatile and co-eluting analytes on HPLC column has a significant effect on quantification of LC-MS. But I am wondering if it has a similar effect on GC-MS since the ionization is obtained by electron impact.

Thanks!!

I don't think so because in GC/MS, the mobile phase is He and rarely you will have prolems of coelution, and more hardly that you have non volatile inside the ion source.

"rarely you will have prolems of coelution"

That depends what you are analysing - in trace analysis of natural materials you get a forest of peaks with lots of overlaps - optimising the separation to get the peaks of interest clean is a major part of method deveopment. That's why 2D GC is becoming so popular and why column makers develop speciality phases.

Peter

While it is not common, you can get ion supression in GC-MS. I've experienced this in GC/MS analysis of tobacco extracts. Nicotine is present at relatively high concentrations and, with a sample of sufficient concentration for analysis for trace analysis, I've see a peak attenuated about half way through - which was where the signal for nicotine rose from nothing to off the scale.

Loss of sensitivity is more of an issue in ion traps in GCMS that it is for quadrupoles. An ion trap can effectively contain only a certain number of ions, the ionization time is usually determined by a pre-scan, and if there is a trace component co-eluting with a large matrix peak the trace component can be significantly suppressed. With the continuous generation and transmission of ions this is less of a problem, although trace components under a matrix peak can still be challenging.

In GC/MS, ion suppression is more often when the ionsourse is dirty and it is very severe.
I still do not understand why when you have new filament, everything is ok but the ion source is dirty then you have very low signal or even zero.

I still do not understand why when you have new filament, everything is ok but the ion source is dirty then you have very low signal or even zero.

Don't the analytes just get stuck in the dirt ?

Peter

I still do not understand why when you have new filament, everything is ok but the ion source is dirty then you have very low signal or even zero.

Don't the analytes just get stuck in the dirt ?

Peter

OK, it may be logical. But the dirt occupies just a little space on the surface of the source. In doing the tune, if the source is dirty, the signal can degraded 10 times or more.

The function of the ion source depends on electrical field gradients. If the dirt changes those gradients, particulalry unevenly across a surface, the effectivness of the source will be changed.

I suspect that there are several possibilities as to why sensitivity falls in a dirty source. And it is somethign to ponder while polishing parts of a source...