HPLC trouble shooting regarding

During calibration HPLC found some problems, please help me to solve.

  1. Injector precision- carried this test and injected 5injection and then calculated the injection volume for per injection but it shows 16ul instead of 20ul. Please tell me how to solve this issue.
  2. Quaternary gradient accuracy test- please tell me, here we have to remove column during test?
    And also tell me what sample should be keep in sample tray to perform this this?. Water or any other solvent?

Waiting for early reply

Waiting for the reply sir.
Please suggest

Open think link you will get information about Quaternary gradient test