I apologize in advance for the length of this post but there is a lot of information. Our lab has an Acquity TQD coupled with an H-Class UPLC (Column manager-CM, sample manager-SM, and quaternary solvent manager-QSM). The column I'm using is a UPLC Phenyl Hexyl 2.5um 2.1x150mm Column.
We acquired the UPLC setup from another lab that did not take care of it. It was throwing overpressure errors constantly (>14,000psi) when trying to run anything other than water. I eventually got that figured out by replacing injector valves, the vespel seal (QSM), running an acid/base wash through the system, and sonicating everything that could be sonicated.
It seems like I fix one thing and then the next problem shows itself. After all of the above, the pressure dropped dramatically (~1000psi). According to Waters that was too low. Then we were seeing problems with inaccurate flow rate volume, i.e. 0.4ml/min x 5 min =
I'm not familiar with your system but they all have similar parts with some variations. Some questions that occurred to me.
-Are you sure its a pressure fluctuation and not a defective pressure sensor or loose wire? We had an HP system which was incredibly finicky about cable connections.
-You say its random but have you tried to watch where each piston is when the pressure changes?
-Seeing less fluctuation at 100% water suggest bubbles by the piston or check valves. An old system of ours had check valves on the top and bottom sides of the piston. Cracking the fittings going into the top check valves, maybe 1/8th or 1/4 turn with pump running got rid of some difficult bubbles.
-Does your system have a bypass valve (open when priming so you don't overpressure the column). Could be its not closing properly.
-Are you running the system with the column in place? I would remove the column and use 1 or 2 or 3 of those backpressure fittings that add psi.
-Most likely its a problem at the pump. Are you able to physically see every connection or are some buried inside the pump or other components. I would try to expose all connections so you can watch them while the system is running.
-See if you have a good local non-Waters HPLC service company like TSS. I'm in the bay area and found someone who cost $150/hour and it took 2 hours for him to find a problem we were having, pretty cheap.
I am not familiar with your system either but I can add my cent here:
Nick Chacos Gang Chen Thank you both for your suggestions. I think I've determined it is a software issue. We used Masslynx and for some reason, the system seems to think it's always in interactive mode (which allows you to change various processes in order to troubleshoot problems). When in this mode, the pressure drops dramatically and nothing is injected. I think I need to reinstall the software unless you are familiar with this software and have another suggestion?
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