Is it possible to track changing retention times for a substance an use them to indicate column aging and column dead?
How is it possible, that the retention times in my chromatograms increase while the column is aging?

Thanks for your help!

In theory you will loose retention during column aging.

In practise you will always have slightly different retention times from run to run because there will be small differences in the mobile phases, column temperatures, voids, pump performance etc.

Thats why people use parameters like tailing factor and number of theoretical plates to monitor the condition of the column. These are designed for the purpose and they shouldn't be effected (not so much, atleast) from the small changes mentioned above.

In general, as noted above, you should expect to see decreasing retention time as a column ages but this depends at least in part on the analyte and the nature of the stationary phase. It's certainly conceivable that degradation of the stationary phase could produce a second retention mechanism for an analyte of interest which would result in increasing retention. On the other hand, if you are using reversed phase as your retention mechanism, pretty much the only way you could get increased retention with column aging is if you're column is slowly accumulating hydrophobic components from your sample. In this case, it's conceivable that you might see an increase in retention although, again, this is probably the rare case. In the latter case, one would expect that cleaning the column with a high concentration of a "good solvent" would return retention to normal. What retention mechanism are you using, what is your analyte and what is your sample?

Could the increase in retention be from degradaton of silica into irregular spheres, thus increasing dead volume?

If your compounds interact with silanols, the loss of the C18 will create more silanols and therefore more retention.

In my opinion, the column is only dead when it does not do my separation any more. Changes are interesting, but not necessarily important. (Of course this assumes that you do the same thing as I do most of the time - same separation over and over again day-in and day-out).

Thank your for your answers.
The accumulation of hydrophobic components might be the problem in my case.
I´m using a C18-RP-Phase and a mixture of Acetonitrile, Water and TFA. The analyte is Triclosan. But it is possible that there is a little calcium stearate in the sample matrix.
Although it is basically insoluable in ACN/Water I suspected it to be in the matrix before:
I sometimes observe a peak eluting before void-time. As far as I know this is only possible when large molecules are excluded from the solvent front.
Any other suspicions?

Thanks for your help!

Wow, Triclosan. I may have a project for quantifying triclosan in an ethanol solution next week. Currently I'm using GC/MS to detect it, but for quantification, I may have to switch to HPLC if the linearity of MSD isn't so great.

If you shared your LC method with me, I'd greatly appreciate it. thanks.

A peak eluting before the "void time" can be a salt.

Is there an standard procedure to prepare a new column for being used? How could I know if it is working well?

Easy: copy test chromatograms from manufacrurer!