Chromatography Forum

Hi,
we've been using a Kromasil C18 150-4.6-5µm (AIT packed) in routine analysis of synthesis crude (monitoring of Starting Material conversion + MS coupling for conformity of expected product mass). The most frequently used system is H2O-ACN, the column is used with a guard (phenomenex Secury-guard) and the column has 635 injections. The pressure is stil high, about 143bar @0.7ml/min for 30-70 ACN-H2O, despite i cahnged the pre-column and proceed a washing procedure of the column with inverted flow direction.
What can i do more ?

One last thing you can do is to change the entrance frit. There is no guarantee that the column will work again after opening it. So, don't do this until the column has so much pressure that you can no longer use it.

In the future, you may need to use a finer porosity filter when preparing your samples. You can also install an inline filter between the injector and the column and change it daily. You can also replace your guard column more frequently.

We also use Agilent column with 0.2µ frit and we never observe the same problem than for the Kromasil, is a bigger or a smaller pore size better to eliminate the problem ?

You have to flush the column with a stronger solvent. If the column gets contaminated with ACN:water or buffer as the eluent, no amount of flushing with a similar solvent will help.

Reverse the column, disconnect from detector; flush with a strong solvent(something that will dissolve your mixture); then flush with you starting eluent and reconnect.

THF is much stronger than ACN but you should examine any potential solubility problems.