Increasing Pressure as the run go

<p>Hi, </p><p></p><p>I'm validating a method with the following parameters</p><p></p><p>BEH C18 1.7micro 2.1*100 mm</p><p></p><p>Line A Sodium tetraborate Buffer pH 9.0 : 65%</p><p>Line B ACN : 35 %</p><p></p><p>Line C and D : 100 % MeOH for storage </p><p></p><p>Start Pressure : 7920 PSI</p><p></p><p>I went throught a lot of problems which included changing the check valve of the I2V and having to clean my flow cell with 30 % OPA in order to get the erbium shutter to go back to its place. </p><p></p><p>Every morning, I'm purging all my lines and run a RSD. </p><p></p><p>Please find attached the partern of the system pressure as I'm running it. it slowy raise at each injection.</p><p></p><p>Then at some point ( ramdomly during the run )  the pressure drop by a 1000 PSI, and I start getting what I call " blank chromatograms " ( also attached ) whatever I'm injecting as if the PDA wouldn't work at all.</p><p></p><p>Did anyone experience it ? </p><p></p><p>Would anyone have any tip of how to fix it ? </p><p></p><p>Thanks </p>


  • Hi Severine,

    I am afraid that this will be tough to resolve here. I have quite a lot of questions...

    What exactly are you injecting (and how is it dissolved?) and how much? The pressure increases at each injection and not during the run, so there must be "something"  going on there. What are your wash and purge solvents?

    What do you do when the pressure has dropped and you get your blank chromatograms? This sounds like a leak  in the FTN / Needle Seal... How do get your peaks back?

    Are you using In-Line-Filters or Guard Columns in front of your column? Are you filtering the Buffers and/or the samples? What is the buffer concentration and how do you flush the system? Does the borate buffer precipitate when you hit 100% ACN?

    I am sorry that I am not answering any questions but only adding so many new ones. Maybe you can answer some of them? This would help a lot.

    Best regards


  • Hi,

    I found out why the pressure was increasing steadily before dropping.

    The I2V was leaking and the check valve had to be replaced.

    Since then the pressure has been perfect.