Best injection mode to prevent carryover?

<p>I have an assay that frequently exhibits carryover, and is very sensitive to the concentrations of formic acid in my mobile phases and needle washes. Between the full loop and partial loop injection mode, which is better to prevent carryover? I currently run a 5 µL injection on a 10 µL loop and sample consumption is not really an issue. More specifically, of these two types of injection modes, will one type expose the actual sample to more needle wash, or will one type wash my injection port area more thoroughly?</p><p>Thank you,</p><p>Laura</p>


  • Hi Laura

    I think that you problem does not depend on the injection mode if not of the type of wash solvents (weak and strong) you are using. You must search and try the best wash solution in order to decrease the effect of carryover. As well you must try different proportions of both weak and strong wash solvents. For example, traditionally we use a proportion of 1:3 strong:weak, then maybe you need another quantity, like for example 1:1, 1:2, etc.

    Best Regards

  • Hi Laura,

    I see very little carryover when using full loop injection mode. If sample amount is not a problem I would go for full loop. If I remember correctly, the loop is washed with 4 sample amounts in full loop mode as standard setting. I also think that in full loop mode, you will minimize the amount of wash solvent getting in contact with your sample. The best way to find out is to test it. Try it out with a 5 µL loop or if your application allows it dilute twice and inject 10 µl on your 10 µL loop. I have heard that there is an Acquity software update, that makes it posible to wash the injection valve more thoroughly during the sample run. Ask your local Waters office for more information regading this, as I am not completly sure how this works.

    Good luck.

    Best regards


  • lizh


    Thank you Rasmus, Full Loop and your other recommendations are all excellent.

    I will attach a link to our carryover web cast it does walk through a tree for troubleshooting, as even though carryover can be a instrument issue, it can be a method issue and you have to rule out all the possibilities. This webcast is about the ACQUITY I-Class, but as it has the Fixed Loop (ACQUITY UPLC) and the Flow-Through-Needle (ACQUITY UPLC H-Class) Sample Managers as options it applies all three systems.

    ACQUITY UPLC I-Class System Strategies for Exploiting Sensitivity of Modern MS Detection - LINK

    If you do isolate the carryover to the valve in the latest ACQUITY UPLC June 2011 Driver pack you can use a timed event to move the valve. This works for ACQUITY UPLC and ACQUITY UPLC I-Class fixed loop injectors. It will depend on you chromatography data software and system configurations if upgrading is appropriate. Both software and firmware are affected. If you have an Empower network then the system administrator and the IT managers would ahve to deploy. Qualification status could be affected too. However, if you ahve the software the best place would be at the end of the gradient during the hold. Here the organic is highest and the chromatography has finished. You may need to extend the time to make the event fit in.

    Hope this helps,


  • mikeSB

    The link does not work. how can I get more information about carry-over troubleshooting?

  • RD

    The contents of the link are attached.