It is not column bleeding since it shows these peaks for just one special sample. In the attached file, all of the big peaks are detected as hexadecamethyl heptasiloxane!
hello
refer the following conversation
https://www.researchgate.net/post/Why_are_so_many_different_peaks_found_in_the_Gas-Chromatography_result_of_one_pure_sample
it may help you
What column you are using? Are you using a non-polar column? Most of the non-polar columns like DB-1, DB-5 etc are having a silica backbone. These columns are fairly stable and have a high MOT(maximum operating temperature). Even then, at high temperature small amounts of the stationary phase comes out and these are invariably detected as siloxane compounds. First thing you can do is to take a blank run after conditioning the column well. Then you can inject the solvent you have used to dilute the sample. If you get a clean base line with a blank run or only the solvent peak with the solvent, then the system and the column is OK. Do not excessively raise the temperature. If you are using a polar column like wax column, then you have to use still lower temperature. Another important step is to use low bleed septas and clean glass liners in the injector. With all these precautions, I think you can sort out the problem.
What kind of pre-treatment do you use (eg. extraction, clean-up etc)? It looks a lot like some kind of membrane peaks which may come from the extraction - especially since it is only found in one sample. If the membrane used ind the reactor/container is compromised, then that is likely the cause. I have seen a lot of these in my time - usually it means starting over unless you can still get the required data from the spectrum and disregard the membrane contamination.
There are 3 basic sources of siloxanes in GCs: columns, injector liners and septa. They are all affected heavily by the type of sample that you are injecting. If your sample has dissolved water and is acidic or basic you could easily see this type of chromatogram and not see it when you run a method blank. You could, as previously mentioned, also pick up these types of compounds from sample prep steps, especially if you are using deactivated glassware.
Since you don't see the peaks in blanks (I am assuming from your comment) then you have to consider what is different between this sample and other injections. In my experience, when you get these peaks it is typically due to either the septum (or small pieces of septum in the liner) or from glass wool in the liner. You can check the liner by pulling out the glass wool if you have any and by examining it for small pieces of septum material, which comes from a septum that is being cored by the needle upon injection.
Maybe a little late, but I had this recently and found it to be caused by the vial septum of the blank (hexane), which I re-used during a couple of days. Apparently the silicone septum doesn't withstand organic solvents very well, so better prepare a new blank for each sequence. The attached image shows the old blank (black) compared to a fresh one (blue), in which all the peaks are gone.
The m/z spectra can help to distinguish between column or GC-septum or vial-septum bleed, which is very nicely explained here: https://blog.restek.com/?p=10706
My attached example reflects those findings quite well - the denoted fragments are therefore typical for silicone compounds used in vial septa. Column bleed, on the other hand, consists of more lightweight siloxanes (~ 3-4 "units"), and will generally show as a rise in the baseline.
Sample preparation protocol needs to be checked properly in addition to frequently use of new blank for every set of analysis. There is always a clear departure from the baseline for column bleeding
- Badges
- Science topic
- Similar topics
- Analytical Chemistry
- Column