Pressure and ACN

[dragosb]

Just a simple question?

Is it normal for the pressure to go down when I increase the ACN concentration for example from 20% to 50%?

My pressure goes down from 130 bar to 120 bar.

Thanks

[HPLCaddict]

Simple answer: Yes
Acetonitrile has a lower viscosity than water. The higher the ACN content in your eluent, the lower the viscosity and thus the backpressure will be.
Other organic solvents might show different characteristics. Especially methanol is a different story...

[dragosb]

Thanks