Carryover with extended needle seat sample loop

I have a 1290-I system with G4226A, have an 80uL needle seat sample loop installed for injecting 50uL as prescribed by the Pharmacopeia method. 


With the sample loop installed, we observed sample carryover, which disappeared after an injection of a blank solution.


Carryover is not observed when the sample run is done with 40uL without the sample loop installed, which I assume that my needle cleaning through the flush port is sufficient to remove most contaminants on the outside of the needle.


To my understanding, the ferrule of both needle seat capillary and the sample loop capillary are by default fixed at the time of manufacturing, in this case, will it be possible that there exists a small dead volume in either of both junctions that resulted in my observation?

  • Hi,


    it is possible that there is a dead volume between the union and the needle seat or the union and the needle seat extension of 80 uL. If you have other needle seats, you can try to swap it and see if it comes from the connection between the union and needle seat or if it looks to be more on the extension side of things.


    Also, by carry over, I assume you did an injection of a sample and then you injected your solvent and still found your peaks. That you did that process with and without the multi-draw. 

  • Yes, precisely what you said. So the question now is, is dead volume an unavoidable issue when I have to deal with large volume injection on systems I have?


    As for your second statement, I'm not too clear. The syringe on 1290 injector only has 40uL syringe, I couldn't avoid multi-draw right.

  • So I talked to my colleague and a new seat was tried but the same issue. So the issue now is:


    1. Either the issue with the extension itself or seats on my hand.

    2. The connections were not appropriately tightened enough resulting in dead volumes.


    I'm not sure 800 number is available at my location, but I do have a scheduled visit by FSE tomorrow so I guess it's best to consult his advice and see how we can proceed from there.


    Thanks for your help all along.

  • It is the first time I hear about a needle seat extension creating this kind of issue. So if you have another needle seat, I would try to swap to that one and see if the issue is still there. 


    If there is no difference in the injections (like if you use the same injector program or if you do not use one for with/without), then maybe your needle extension has an issue, I am not too sure. I would call our 800 number and try to talk to someone on how to proceed with getting a replacement and what is the process for that if you can.

  • If you have someone going onsite tomorrow and he is trained on the systems, I would ask the question at least to see with him. If he has couple minutes, maybe he will have time to help out.


    Have a good day!

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