multiple injections

Hello, is it possible to inject the same sample several times during a run? Our kit (uPLC-UV-MS-ELSD) has an ELSD detector that requires calibration to ensure quantification of our test samples. Currently, we calibrate the ELSD using 4 standards eluting at different retention times. However, as we are currently experiencing issues with this approach, we are wondering iwhether it would be possible to inject one single standard every few minutes during the same run. Thanks,


  • Hello,

    as long as you're using the acqutiy sample manager it is not possible - or you can alter the icop, what is very unlikely...

    But you can do this with a workaround:

    Take a high pressure switching valve, insert the smallest loop you can get (0.5 µl or lower volume) and connect this between sample manager and column inlet. You need a programmable pump, which fills the loop for some seconds with your desired standard solution after getting an event from sample manager switch 1 (programmed in the event table of the sample manager). Maybe 10 seconds later you use switch 2 to switch the loop into flow path for one or two seconds.

    Problem with this is you get with every switch a pressure drop and likely a noise in the baseline. On the other hand you can easily enhance the system to get what you want.


  • Hello

    Could you tell us a little about the issues and perhasp there could be other possible solutions.


  • If retetention time is long enough, you can inject a few times with a run time much shorter than the retention time, except for the last injection where all the peaks will come out.

    Assuming a retention time of 10 minutes, inject 3 references with a runtime of 2 minutes, then inject a fourth reference with a runtime set at 12 minutes.

    All your peaks will come out in the last run, showing a nice profile or whatever you want.


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