[GCxGC-MS] 2D chromatogram curves in one sample but not the others

Hi kalle-h, 

Has the method worked well for you in the past?  Any changes recently like column trims?  Sometimes small pieces of column can get caught inside the modulator fittings and impede flow, which has negative effects on our data.  

If your peaks are consistent along the X-axis, there probably isn't an issue in the 1st D.  This looks like a modulator or 2nd D column change.  The compounds are eluting more slowly off column 2, which is causing them to display higher in the Y-axis when the data is processed.  The intensity of peaks looks lower in sample 3 compared to sample 2, so I would say we are losing sample at the modulator so it isn't registered at the proper time on the detector.  It seems to affect the entire run, not lighter or heavier compounds specifically.  

This is the troubleshooting process I would take to figure out where the problem is:  

If you run a solvent blank, do you see peaks?  There could be carry-over in the system.  When you do a library search against the peaks that are showing up in the expected blank space of images 2 and 3, what compounds are identified?  Are they expected as part of your sample or does it look like contamination? I could speculate that the extra peaks that are showing up are the missing parts of the lower intensity compounds, but I can't say for certain.   

How consistent is your unprocessed data - not the GC Image processed version, but what comes from your data system?  Could this be a setting on GC Image that is rendering differently?  

Your modulator settings look good, we just need to make sure that the system can supply the flows the method is calling for. 

Do you have a post 2D column split between another detector and your MSD (commonly an FID)?  What does that detector chromatogram look like? Ideally you would see the exact same profile if the splitter is configured properly, but it may give us a clue.  If you have a second detector, I would recommend measuring the column flows with a flowmeter to verify the configuration is delivering the the same values as the GC setpoints.     

There are many other things to investigate, but this is where I would start.  

Let us know what you find out?

Abbey

Hi kalle-h, 

Has the method worked well for you in the past?  Any changes recently like column trims?  Sometimes small pieces of column can get caught inside the modulator fittings and impede flow, which has negative effects on our data.  

If your peaks are consistent along the X-axis, there probably isn't an issue in the 1st D.  This looks like a modulator or 2nd D column change.  The compounds are eluting more slowly off column 2, which is causing them to display higher in the Y-axis when the data is processed.  The intensity of peaks looks lower in sample 3 compared to sample 2, so I would say we are losing sample at the modulator so it isn't registered at the proper time on the detector.  It seems to affect the entire run, not lighter or heavier compounds specifically.  

This is the troubleshooting process I would take to figure out where the problem is:  

If you run a solvent blank, do you see peaks?  There could be carry-over in the system.  When you do a library search against the peaks that are showing up in the expected blank space of images 2 and 3, what compounds are identified?  Are they expected as part of your sample or does it look like contamination? I could speculate that the extra peaks that are showing up are the missing parts of the lower intensity compounds, but I can't say for certain.   

How consistent is your unprocessed data - not the GC Image processed version, but what comes from your data system?  Could this be a setting on GC Image that is rendering differently?  

Your modulator settings look good, we just need to make sure that the system can supply the flows the method is calling for. 

Do you have a post 2D column split between another detector and your MSD (commonly an FID)?  What does that detector chromatogram look like? Ideally you would see the exact same profile if the splitter is configured properly, but it may give us a clue.  If you have a second detector, I would recommend measuring the column flows with a flowmeter to verify the configuration is delivering the the same values as the GC setpoints.     

There are many other things to investigate, but this is where I would start.  

Let us know what you find out?

Abbey