Hello, We have HPLC Agilent 1260 the problem is that the pressure bcom very low when we use the gradient mode (The addition of water during the time with Acetonitrile) causes this problem of pressure.
What is your column and flow (relative to what)? It is typical to have a decreased pressure when you are pumping an organic solvent. In contrast water will increase your pressure since it has an increased density. As the particle size of the packing decreases the pressure will increase for the same flow rate and same mobile phase,
This is common Dr Ala, when you add water to any organic mobile phase it raises pressure. Please make sure to start your tests at low pressure and flow rate while using acetonitrile, as it will usually be higher as compared to aqueous counterpart.
on starting and according to the method, I use 60% non-acidified water and 40% acetonitrile, the pressure is 70 bar, and over time I have a decrease in water and an increase in acetonitrile (a gradient) ,pressure then reaches 1 bar at the end of analysis , (the flow rate is 1 ml / min )
Also we are using C18 ZORBAX ECLIPS PLUS column (Analytical 4.6 x 150mm ; 5-micron). Thanks to all.
Ala,
It sounds as if you are not truly pumping from the acetonitrile channel. It may be vapor locked or you may have a bad check valve(s). Take the column loose and set the flow to 100% acetonitrile and check the volumetric flow rate.
I agree with Michael, Ala. You don't have ACN flow. Typical pressure drop is on the order of 50% when going from 100% water to 100% ACN. To get a reading of 1 bar you literally have no flow.
Check the flowrate of the ACN channel at 1ml/min without a column as stated above and measure with a small cylinder to see if you have accurate flowrate.Also make sure that the channel isn't block and that there are no leaks in your system.
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