Chromatography Forum

dear all...
we keep discussing stable back pressure ..
but how stable is stable ...?
in our c18 column,300mm, 5 micron particle size, 93:7 water:ACN ..0.5ml flow rate we get aback pressure of 95bar and it fluctuates by +/- 1bar.
however at 1.0 flow rate .. we get 210bar with +/- 5bar .. is this fluctuation accepted ...?

with best wishes

Start with checking your pump specification for appropriate pressure parameter.

As per operational qualification at install date.Then, if you establish other limits in you performance qualification/system suitability, use those.

The first HPLC I used 20 years ago from Waters said in the manual if you had less than 200psi fluctuation you had acceptable results, that is +/- 7bar. On our new Agilent systems I usually get less than 1 bar fluctuation.

Pressure fluctuation will usually cause baseline instability, so I guess the pressure fluctuation you can get by with is what still produces acceptable baseline fluctuation.

Just remember the more stable the easier it is on the column packing.