# Column pressure

<p>I have read the discussion regarding UPLC accelerates regular HPLC column degradation. Very helpful information!</p><p></p><p>But I have another question: what is the pressure a column experiences in the UPLC system? I test my UPLC by connecting the inlet and outlet in the sample manager with a union, and run water @ 1 ml/min. The pressure reading is 1000 psi. That's the pressure comes from the resistance of the narrow tubing and the pressure regulator at the detector. Now I install a column, and get a pressure reading of 5000 psi. So the column is experiencing 4000 psi "real" pressure. Am I right? According to the column manual, my column maximum pressure should be under 4500 psi. If my assumption was correct, I can still run this column in the UPLC as the 5000 psi pressure reading is not the real pressure drop across the column.<img alt="" border="0" src="http://forums.waters.com/clearspace_community/images/emoticons/confused.gif"/> </p>

• Greetings TCheng,

Your basic logic is correct and the way you are measuring it is also appropriate. However, the column experiences the backpressure of it's own pressure drop and all tubing that is downstream (towards the detector) from the column. So, to fully evaluate the total backpressure on the column, you should take one additional measurement. You should disconnect the union (or column) and take a pressure reading. This will give you the "parasitic" pressure drop of the system prior to the column. Subtracting this reading from the system pressure, with the column installed, will yield the backpressure that the column is under.

Hope this helps,

pcb

• Your description about what the pressure contribution of the column is to the overall system pressure is correct. As you stated, you remove the column from the LC system, replace the column with a union, run the system as per your SOP and then measure the (system only) pressure. You then take this empirically determined 'system only' pressure and subtract this value from the overall system pressure with the column installed. This is how Waters column packers measure and report the 'column only' pressure that you see in paperwork in the column box or on the eCord of the UPLC column.

I see where you are going with your question about what is the 'real' pressure being applied to the column. You are wondering if the system (and column) is reading 5000 psi during normal operation, and the system itself is generating 1000 psi, are you still under the recommended Pmax for the column? I do not feel completely confident giving a yes/no answer but my gut feeling is that you are pushing things a bit. For example, if the major pressure contribution of the system is downstream of the column then you ARE subjecting the column to more pressure than the column is generating itself.

My suggestion may seem a bit wishy washy but I believe the best and only way is for you to run your SOP HPLC method under the conditions that provide you with the required resolution and throughput results. Then determine the HPLC column lifetime under these conditions and ask yourself if this is satisfactory for you and your laboratory. We often encounter cases where customers knowingly experience short column lifetimes because they need to REALLY push the pH, pressure and/or temperature envelope. However, they achieve results that meet or exceed their project/timeline objectives.