The changing pressure of Quaternary Pumps

Are you running different methods in different worklists, or are the worklists all running the same method? I assume the same method across worklists, but this is not clear in your question.

Does this change in pressure lead to a change in your quality of chromatography, peak shape or retention times and detection and quantitation of your analytes of interest? You don't state what effect (if any) these pressure differences are making to the quality of your results.

Is the difference in backpressure you are noticing due to the position of the stream selection valve going direct to waste when you are stabilizing your LC system, compared to the increase in backpressure when the LC stream is being sent through the tubing and nebulizer? In other words, more plumbing and capillaries introduced to the flow path when the MS in the flow path = more backpressure? We would need more information on the differences in the system configuration (if any) when comparing 270, 330, and 280 bar pressure readings. If there are no differences in the flow path or the condition of the column, then I would be running a pressure test on my LC system using a blank nut and Lab Advisor SW and also a leak test (see attached doc) on your quaternary pump's Multi-channel gradient valve to see if there are any leaks or intermittent proportioning valve control issues that might explain the pressure differences worklist to worklist.

Are compounds being flushed off the column efficiently, or do certain samples lead to a build-up in the column over time that leads to a pressure increase? Does the system back pressure slowly increase over a worklist, or does it say steady during a worklist and then change suddenly when the new worklist starts?

There are many potential reasons why the observed pressure differences could be happening in your system, you need to logically t-shoot the issue and eliminate any variable that does not contribute to pressure differences in your system, to narrow down the list of candidates for pressure variablity. This is generalized advice, for more specific advice based on your method and specific system configuration I would suggest logging a Service Request with your local Agilent support representative.

 DOCX

Are you running different methods in different worklists, or are the worklists all running the same method? I assume the same method across worklists, but this is not clear in your question.

Does this change in pressure lead to a change in your quality of chromatography, peak shape or retention times and detection and quantitation of your analytes of interest? You don't state what effect (if any) these pressure differences are making to the quality of your results.

Is the difference in backpressure you are noticing due to the position of the stream selection valve going direct to waste when you are stabilizing your LC system, compared to the increase in backpressure when the LC stream is being sent through the tubing and nebulizer? In other words, more plumbing and capillaries introduced to the flow path when the MS in the flow path = more backpressure? We would need more information on the differences in the system configuration (if any) when comparing 270, 330, and 280 bar pressure readings. If there are no differences in the flow path or the condition of the column, then I would be running a pressure test on my LC system using a blank nut and Lab Advisor SW and also a leak test (see attached doc) on your quaternary pump's Multi-channel gradient valve to see if there are any leaks or intermittent proportioning valve control issues that might explain the pressure differences worklist to worklist.

Are compounds being flushed off the column efficiently, or do certain samples lead to a build-up in the column over time that leads to a pressure increase? Does the system back pressure slowly increase over a worklist, or does it say steady during a worklist and then change suddenly when the new worklist starts?

There are many potential reasons why the observed pressure differences could be happening in your system, you need to logically t-shoot the issue and eliminate any variable that does not contribute to pressure differences in your system, to narrow down the list of candidates for pressure variablity. This is generalized advice, for more specific advice based on your method and specific system configuration I would suggest logging a Service Request with your local Agilent support representative.

 DOCX