Chromatography Forum

Hello. I have an Agilent GC model 7890B. I was wondering if there is any way to overlay chromatograms with offset retention times. I cut the column and reinserted it into the injector and detector. After making sure everything was secure, I started the GC. When I did my first two injections. the retention times were overlaying perfectly. The next day, I notice the retention times are completely off. I am not sure if this means my column is too short to compensate for my sample eluting or I need to install a new column. Is there anything to help with overlaying offset retention times? I use Agilent OpenLab for data analysis.

... When I did my first two injections. the retention times were overlaying perfectly. The next day, I notice the retention times are completely off. ...

May be a leak in the inlet causing changes in flow of carrier gas through the column resulting in retention time changes.

How do I check a leak in the inlet? I do not have a flowmeter to check for leaks.

How do I check a leak in the inlet? I do not have a flowmeter to check for leaks.

If you don't have leak detector install your column in the inlet again paying attention to do it properly. Change the inlet septum as well if it is "tired" with many injections.
What do you mean by "RT are completely off" ? Are they longer or shorter or they change randomly ?

About visual comparison:
http://unichrom.com/lnet/c-anone.html

Active chromatogram can be shifted either using shift+mouse dragging or using toolbar "Move graph" buttons.

And yes, the OpenLab .ch file can be opened.

Workbook with two chromatograms can be constructed in two ways:
1. menu Edit/Copy layer, select another workbook and Edit /Paste layer
2. menu Edit/ Collect batch

Visual comparison can help in decision - if it is inlet problem (leak or liner overflow) or artifact from another injection.