Pressure fluctuations? Effects on chromatography?

[dkreller]

Hi,

I work with a Waters 600 system, but I am confident that this is a sufficiently general chromatography question that even users of different pump brands will be able to relate to it and perhaps respond.

Of course, pump pressure is never going to be 100% stable. The 600 system has two reciprocating rods and there are two check valves per pump head. The pressure is always going to have some fluctuations that will be tied to the mechanical periodicities in the system. I am not a perfectionist; I know that pressure fluctuations will never be totally avoided.

Typically, I am packing my own columns with relative large particles (around 200 microns) and the backpressures from these columns are low. I have a flow restrictor between the pump and A/S to increases pressure at the pump. With flow restrictor backpressure is around 800 psi at my typical flow rate, which is 0.5 mL minute. On good days, the pressure fluctations are within 5% of this. Today, I'm look at pressure fluctuations around the average of about +/-12%

In your opinion/experience when do you feel that pressure variations become problematic?
What are the impacts on chromatography of overly large pressure fluctuations?

Thanks,

Dave

[sepscientologist]

There isn't a particular value to be concerned about. If 12% works for you then you are fine. When buying a new pump I would expect
the pressure fluctuation to be around 1%. The problem is usually with detection. Even if you are isocratic a slight change in pressure
produces a slight change in refractive index which will change the amount of UV passing through your flowcell. Depending on your conditions
you may or may not notice the effect. For gradient, depending on your pump config (binary ternary etc) and how absorbing your two solutions
are you can run into additional noise from the transient up/down conc. of the two different components.

[HW Mueller]

What would cause pressure changes in the UV detector cell?

[unmgvar]

maybe the pump needs servicing?
how long since you changed the seals or pistons?

[remesquaddie]

I have a LOT of experience on the 600E series over many years. It has an inlet at the back so you can connect HELIUM for sparging any or all solvent lines.
I would strongly recommend that.

I work with a Waters 600 system, but I am confident that this is a sufficiently general chromatography question that even users of different pump brands will be able to relate to it and perhaps respond.

Of course, pump pressure is never going to be 100% stable. The 600 system has two reciprocating rods and there are two check valves per pump head. The pressure is always going to have some fluctuations that will be tied to the mechanical periodicities in the system. I am not a perfectionist; I know that pressure fluctuations will never be totally avoided.

Typically, I am packing my own columns with relative large particles (around 200 microns) and the backpressures from these columns are low. I have a flow restrictor between the pump and A/S to increases pressure at the pump. With flow restrictor backpressure is around 800 psi at my typical flow rate, which is 0.5 mL minute. On good days, the pressure fluctations are within 5% of this. Today, I'm look at pressure fluctuations around the average of about +/-12%

In your opinion/experience when do you feel that pressure variations become problematic?
What are the impacts on chromatography of overly large pressure fluctuations?

Thanks,

Dave[/quote]