Chromatography Forum

After finishing a run of sample, I tried a blank run (no samples inject) and it shows some ‎peaks. I thought some component remain in column due to sample so extend run time of ‎sample and also temperature of programming method. But the problem didn’t solve. I ‎rinsed the column with solvent and condition again over night and run a blank run before ‎any sample. The same problem exists again. I don’t know what could be a reason of ‎pollution. is it possible it related to injector? Column is CP-CIL 5 CB, 25 m, 0.32 d and ‎‎0.53 film thickness

The problem could easily be the syringe or the injector. What type of inlet and inlet liner are you using and what is the injection volume?

How often do you change liners? And, have you changed liners since you discovered this problem?

Assuming that in your blank runs you did no injection at all, then the two most likely culpurits are a dirty inlet or dirty carrier gas. First do full inlet maintenance (which is quick and cheap) and if that does not work add scrubbers to your carrier gas lines, which you need to have in any case.

Peter

I understood this as carryover, not ghosting. We just had something similar, do you also use a syringe?

I agree with Peter. An easy test for the carrier gas is to let the system sit idle for a few hours. Then do 2 no injection runs back to back. If the first run has more and bigger peaks than the second suspect the carrier gas.
Not to sound condesending, but is the system plumbed with GC grade tubing? If no that can be a source of "crud". Been there, done that! It can be rectified by rinsng the tubing with methylene chloride and drying.

Are the peaks you see the same as in your sample? If yes, it can be carry over. Sometimes too much is injected and via back flash the sample may get in the gas lines. Make sure that the liner can take he sample volume (in gas-state)

To clean injector: you can replace seals, liner, septum, but I would also do the following before you replace the parts.
Connect a short piece of fused silica (1 meter) from an old column) and set this up with a high flow, also have a high flow through septum purge and splitter linw. Then heat the injector to high temperature 350C or so, and bake it for a few hours.

cool down ; replace the parts and start the analysis again.

Thank you for all reply. I worked for that problem in different ways. Finally I used liner without glass wool and it seems ok up to now. I know the glass wool used in the liner is silinaized and therefore it shouldn’t have showed any peak. What could be reason of peaks with liner included glass wool?

Hi
Ingectol liner new or "old"? If "Old"
Open ingector and go out liner. Its broun or black ? This product ermal degradation ulvolature sustancies in you sample...

I sometimes get the same problem that after running samples (especially dirty samples) appears peaks in blank runs. In common, this is caused by liner that glass cotton inside it is dirty. And my solution is replacing glass cotton or liner. After that, all are ok.

The deactivation on most glass wool can be hydolysed to yield siloxanes that then appear as chromatographic peaks. This problem is worse with samples that contain water (even in traces), especially if they are also high in acids or bases.

Peter

It is important to remember that a dirty liner will cause all kinds of bad things - like cary-over or degredation of samples. And, depending on your samples, you may be able to run hundreds of samples through a liner and still keep going - or one injection can make a liner dirty.

I had one set of samples that would foul a liner in five injections or less. To complete the project, I changed the liner for each injection. (There is an autosampler that can chage out liners for you - I did not have one for this project.)