Chromatography Forum

Dear All,
i am working on the WATER ACUITY UPLC BEH C18 ( 100 x 2.1mm, 1.7um) along with the mobile phase NH4OH buffer of pH 10.4 and Acetonitrile with gradient method. Column oven is having the temp. 45 Degree centigrade.
my compound of interest is actually basic in nature and also having Toluene as solvent.
I am facing the issue of column back pressure after some (approx. 20-30) injections as well as peak distortation.
Suddenly we observing that the column back pressure goes more than 1000 MPa (15000 to 16000 psi)
After so much cleaning with almost all the procedure we are not able to get the column in its lower pressure. If anyone is having some solution for this one column please suggest.

My first guess would be that something from your sample is precipitating at the head of the column (the presence of toluene in the dluent suggests that something in there is not very soluble in a high-aqueous medium). If that's the case, the easiest (*not* the cheapest!) fix is to use a guard cartridge and change it frequently.

Try backfluching with 50/50 MeOH/Water to remove anthing that previpped oat head of column. Use pre column filter

As an aside, you may get better peak shapes with that high pH buffer using an acquity CSH C18 column, they give better peak shape at high pH @10 with basic analytes than a regular C18, not sure if you can change the method though.

Reverse flush the column as suggested but be sure to run it to a waste beaker for an hour or so, not in the detector. As suggested, use a guard column whose job is to protect the 3-5X more expensive analytical column.
Column temp is inversely proportional to pressure. Be sure your TCC temp is holding correctly.
Swap column with a union to determine your LC system pressure "without the column" at your desired TCC temp and normal flowrate. Then add the column and determine the pressure difference, this will give you your column pressure contribution, make a daily log of your pressure to stay on top of the inevitable pressure increases.

Is it really safe to back flush this column? I have been told that it is vital to never flush solvents backwards with this column as the packing material will be damagrd. I have never tested my self so dont know how important the advise is.