Column Length?

[Troubleshooter]

Hi,

I have a confusion regarding GC Capillary column. Actually there was co-elution of two compounds having difference in retention time of just 0.4 min. We were installing new column and got broken during that and after installation of new broken column last compound's peak was not shown in chromatogram but when we installed old one it also got broken almost of same length but both required peaks were there. What are the possible reasons?

Regards,
Kashif

[Troubleshooter]

I am surprised to see nobody is here to answer me even Chromatographer1 also?????????

[skunked_once]

Perhaps we are not sure what your question is but I will try to provide some input. It would help to have more information. Are you asking why you see two peaks on the old column and only one peak on the new column? Are both columns the same (length, diamater, phase, etc.)? How much of each column was broken off? If both columns are the same, the activity of the old column may be different than a brand new column which could account for some differences in sample retention times. In any case, please give more information and restate your question.

[Troubleshooter]

Both Columns were ditto except the life but old one even after being broken shown both peaks while new one was unable to show second peak.
What could be the possible reasons??????

[JGK]

Was the old column used only for the current assay method?

If not, previous methods may have affected the column characteristics slightly to give you the separation you see where the new column doesn't.

I haven't seen this effect with GC but have many times using "old" LC and new LC columns (particularly when IP reagents are used).

[Willy]

Hi there,

By the term you saw only one peak with the new column do you mean that even by heating or extending the time of the analysis you didnt see the second peak on the new column? I have 2 answers:


1-Ive experienced one time a problem with old-new columns. We did validation of a method with 2 columns. One was relatively old and the other was new. Depending on the solvent analysed some of them tends to elute faster on old columns and later on new one. ( ill will not explain but they are few reasons this could happen with old column). So we needed to extend our analysis time to be able to see the second peak from the newer column.

2-From what you say ( 0.4 minutes in retention time difference) the possible problem would be that they might co-elute. If one of them is giving a high respond and the other gives a small peak that could be the problem. Check if the peak is well shape in the new column. One of my post was about that, i couldnt separate Heptane from TEA on one column and was well separated on another column from the same type-length.....

Im betting on my second answer!

Please give feedback

Hope that will help!

Willy the GC