troubleshooting!

[elaine.zhang]

Hi, professionals,
Now, I have a big problem with my new column, I only can see the solvent peak, when i injected the standards(there should be 4-37 compounds), what is the major reason?
thanks a lot for your support!
Elaine

[chromatographer1]

Elaine

There can be a lot of causes and no main one.

You can have the column installed incorrectly.

You split ratio could be set too high if you are using capillary.

You can have a large leak, injector septum, column connections, or at the detector.

You can have your detector electronics set at the wrong setting.

Your test sample could be wrong.

You should check out your instrument with a known sample to determine if everything is working correctly.

Your GC manual should have a test sample documented. Usually they suggest a C14-C16 hydrocarbon mix in hexane or something similar

Good luck.

Rod

[zokitano]

Are you sure that your column is adequate for your analysis?

I'll suspect on the possibility your components in the standard to elute together with the solvent or they adosorb in your system, somewhere.

Check the boiling points of your components of interest, and also see whether your oven temperature program is adequate. Maybe the highest temperature in your oven temperature program is much lower than the boiling points of the standard peaks (components). This also maybe a problem.
In that case i suggest raising the temperature of the oven and if the peaks elute after that, you are sure that your oven temperature program is not appropriate.

Best regards

[elaine.zhang]

Hi, thank you so much for so quick answer!

All the parameters are intact, which i used on the old column, I am doing the fatty acid development, with agilent GC6890, auto liquid sampler, the standard i used is the FAMEs, from the supelco.
1. with the old column, DB-23, 30m*0.25mm*0.25um,
the peaks are always fronting, some cannot be seperated well.
2. i bought the new one,DB23, 60m*0.25mm*0.15um,
at first begining, after conditioning, i inject the stadards, the peaks' shape were not well, big tailing, especially from C16:0 to C24:1, therefore, i reinstalled the column, and reconditioned, now, when i inject the stadards, i only can see the solvent, which is isooctane with butylhydroxytoluene(abbreivated as BHT 100mg/l), i can see the isooctane and the BHT, but no standards.

I and another chemist reinstalled the column, and checked the whole system, still cannot locate the problem.

any comments are very welcome,
thanks,
Elaine

[zokitano]

Did you check the possible leaking from the connecting parts (between column and injector and column and detector)?

[chromatographer1]

From your description the older column was installed correctly but was overloaded. Fronting on a capillary column indicates that you were injecting too much sample for the column to handle. The lack of resolution also indicates an overload.

I suspect that your installation of the column is incorrect. How far past the ferrule does your column extend into the inlet?

Your split ratio may be set incorrectly.

Have you replaced your septum lately? Perhaps you got a piece of septum onto your column?

Are you getting the proper amount of sample into your autosampler needle? If it isn't injected it won't be seen at the detector!

I think you may need to review the proper selection of inlet liner and its correct installation.

You also may need to change your gold seal in your injector.

I hope you find the problem. It should be solved without excessive trouble.

really !

good luck and best wishes,

Rod

[Consumer Products Guy]

As the others noted, there could be a zillion reasons for your issue. You need to start with the basics, even making sure your syringe is not plugged. You're obviously not getting all the molecules to the detector, troubleshoot logically, one thing at a time. Don't overlook the obvious. Of course, it does help to have 30 years experience....my company one sent a chemist cross-country in the late 1970s to a manufacturer to fix a GC problem, and the location had two syringes, both of which were plugged up. Now we'd investigate by phone and E-mail to help in a similar situation.

[JI2002]

One possible reason is that you are using the same parameters as for the old column. You need to adjust the oven temperature program as well as inlet pressure when a 30m column is replaced with a 60 m column. Because film thickness is 0.15 um for 60 m column, you need to inject less to avoid overloading.

[zokitano]

One possible reason is that you are using the same parameters as for the old column. You need to adjust the oven temperature program as well as inlet pressure when a 30m column is replaced with a 60 m column. Because film thickness is 0.15 um for 60 m column, you need to inject less to avoid overloading.

Yes, but in this case she doesn't get any peak from her standard. The column length and film thickness do not affect whether the peaks will come out or stay in the column. The lenght affects the time of retardation of the components in the column. However she waited and waited but the peaks do not come out. So the main problem is from other nature. The change of the parameters of the column I think wouldn't show this kind of problem.

Best regards