What factors affect Tailing in UPLC?

[EmpowersBane]

I'm running a reversed phase gradient method on UPLC which has never given me any hassle with Tailing (Empower 3) and I was consistently getting values of about 0.9 or 1.0 for my 3 active peaks. I took off the pre-column inline filter mixer kit to replace the tiny disc inside as the baseline was getting a little bumpy, and I normally change this once or twice a month. However, I didnt use the same inline filter kit to attach back to the column as it was misplaced as I was doing something else and I had to use a different inline filter kit by taking it off another column and putting it back on mine using a spanner to tighten it.

Problem is, now my Tailing has shot up to 1.4 for all actives and you can see a clear tail as the peaks elute off the column. There is no leak as I observed it for the duration of the injection, and no other changes took place (same mobile phase, washes, standard solution) so the only thing I can think of is the threads from the old inline column kit doesnt exactly line up with the column inlet, and there could be a tiny void somewhere in the connections. Even when i took it off and reconnected, same high tailing.

Any suggestions as to how to fix this, am I going to have to get a new column with a new inline filter kit to improve the tailing?

[DR]

Sounds like you need either a new in-line filter housing, or you need to passivate the one you have (which I'd try first). Passivation should help eliminate any active sites within the guard kit that could be causing the tailing issue.
Do not passivate your analytical column, not the insert for the guard column, just do the housing for the guard column (assuming it won't leak without the insert).

[Hollow]

I guess you already named it.

As far as I know, the guard and filter holder have non re-adjustable ferrules and collets.
So once thightened on a column it literally becomes part of that particular column. Only tne guard cartridges or filter disk should be replaced. I guess the housing can be opened without removingthe connector from thecolumn.

If reused on a different column, extra column volume effects may happen.

maybe you can make a run of a standard without guard kit to check if tailing on the main column is ok.
If it's ok, then a new (or the "original") guard-kit may be needed.
Otherwise also a new column with new guard may be necessary.