Autosampler leak

<p>Hello everyone!</p><p></p><p>We have an Acquity UPLC and I have a leak in the sample manager. I was doing test injections of Caffeine STD 100 ug/mL to check system precision and had several issues:</p><p></p><p>1) A couple of injections with no peak on it</p><p>2) An split peak in one injection</p><p>3) A consistent shifting of the retention time from 1.5 min to 0.8 min and less.</p><p></p><p>I thought that the split peak could be my column but after observing the retention time shifting I inspected the system during injecting and I saw liquid around the tubes where the injections happen. to explain myself better, there are two tubes at the back of the autosampler, the puncture needle goes to the vial, the sample is withdrawn and it goes to the tube on the right side to inject. Around that tube is where I saw liquid. I'm using Partial Loop with Needle Overfill so I don't know if this liquid is the "overfill" or a leak on the system. </p><p></p><p>Does anybody have information about this? Did it happen to someone before? Thanks!</p><p></p><p>De Leon </p>

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  • Accepted Answer

    Hi De Leon

    I think what you are seeing is the wash solutions coming out of the wash tube and not a leak. Are you seeing this after the injection valve has turned to inject ? If yes this is normal. When the needle is plunged into the wash station ( in PLUNO this happens after the injection) the weak wash solution is pumped up from the bottom of the wash station and the strong wash solution is pumped out through the needle and meets the weak wash. The combined solution then flows up on the outside of the needle and flows out of the wash tube at the top and then is going to the drain in the wash block. I would instead look for leaks at the injection valve itself or at the column inlet/outlet.

    You could measure the flow after the detector to see if you get the flow rate that you have set on the pump.

    best regards

    Rune

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