It sounds to me like you may have fractured or compressed the resin. We do
not find it necessary to sonicate resins when packing in capillary columns
and we pack capillary columns at flow rates about twice the flow rate that
we will be using them. What were you using as a frit?
Also, we do not use 0.1% TFA in LC/MS, because it suppresses the signal.
If you must use TFA, try a lower dilution (I've used 0.025% with reasonable
success). Better is to use 0.1% formic acid.
Its important to filter the solvents and use in-line filters to keep junk
out of the lines. That can also increase your column pressure.
Katheryn Resing
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