Analyze the same vial but different peak in GC

[hoonee1000]

HI I'm a new worker using GC instrument and I need some help to solve my problem. The GC instrument is made by Shimadzu and Auto injector, not headspace. I've analyzed the standard solution in same vial six times for system suitability but the result is different. The peaks are same from first to forth analysis, but after then there are some unknown peaks. The unknown peaks appear continuously to six or seven vials analyzed after system suitability, and then disappear. I think the unknown peaks are affected by standard solution beacause it always shows after standard solution. I changed a syringe and rinsed a syringe before and after starting analysis but I don't know the reason why it's happend, and how to solve this problem.
Thank you for reading my writing, I'll be waiting for some help.

[tkubowicz]

Hello

If you have extra peaks after injecting the same solution I'd say that you need to adjust method because something is stays on column and comes out after few injections.
Try to increase final oven temperature (put few minutes "hold time") and check if something is coming out when temperature is going up.


Regards

Tomasz Kubowicz

[Steve Reimer]

Try changing the vial cap after each injection and see if the extra peaks go away. Otherwise, are the extra peaks broader than the normal ones? If so they may be carryover from previous injections.

[James_Ball]

It could be a combination of the two above answers also. If the peaks are late eluting silanes it could be that you are getting contamination of the solvent from septa particles from the vial, then these show up much later on.

To discover which is happening, divide up your solution into seven separate vials and inject it. If you still see the extra peaks then it is something with a high boiling point in your solution, if the peaks go away, then it is contamination from the septa.