2 Agilent 1200 - 2 pressure profiles

[annaand]

Hi,
We have 2 HPLC Agilent 1200 instruments in 2 labs. One of them is much older and has a quaternary pump, the other is younger with binary pump (working perfectly). I have a problem with Agilent 1200 Quaternary Pump which seems to give me too low pressure + very strange pressure profiles. Honestly, I don't even know if it is a problem since I have compared drug purity analysis on this fault instrument and mine (perfectly working). The chromatograms are very similar, retention times are very alike. The method is isocratic lasting 60min.
The only difference is totally different pressure profiles which doesn't seem to be constant as it should be when the instrument with quaternary pump is used. Actually it is 100Ba smaller there. I can't figure out why such a big difference in pressure and does it really matter if the chromatograms look almost the same? Which means that flow rate is the same (1mL/min).
Confused,
Anna

[R13]

Difference of 100 Ba is quite big, on the other hand You can not directly compare retention times/pressures on different HPLC systems (even if the same column piece is used). Generally You might have different length/diameter connecting capillaries (pump- autosampler-column-detector) on the different HPLC systems, some fritts can be partially cloged.

In this particular case also pumps have different internal construction (including mixing principle) and internal tubing length (dead volume).

Somewhat confusing is "pressure profile" You are mentioning. Is the pressure changing during the run? It should be constant since the run is isocratic (with exception of pressure swing during the injection).
It is important if You are using "premixed" mobile phase or mix it in the HPLC pump, also what kinds of solvents are mixed in the pump.

Then the pressure sensor simply might be faulty. We had one Agilent 1100 system which was showing 39 Ba when not pumping....