I tried different analytical reverse phase columns ,different mobile phases with different time programs , different needle wash solutions . But I could not solve the problem. Adding low concentration of Ammonium acetate in mobile phase completely solved the carry over issue. What could be the reason for this?
It could be scratches inside rotor seal in autosampler, or scratches on autosampler needle/needle seat assembly.
sometimes by changing the system also not gives the solution carryover.
It could be remnants of samples left in the injection port, especially if high amount of samples are used. The septum id another possibility. When the needle is pulled out after injection in a rapid manner, the sample remnant may be left and contaminate the septum, which may be pushed in again by the next injection. If silica wool in used in the injection port, it should be heated to a high temperature after every injection to avoid contamination.
Sorry, I made a mistake thinking that it is in GCMS. Please ignore my comment and suggestion. Sorry.
You may consider try to add DMSO into your system, which was recently proved to improve the overall LC-MS signal, and could even resolve your glove. It might kill the carry over.
try with lower concentration samples and also low injection volume might be resolved ur problem....
Try different injection loops, and programs (loop overfill etc.)
You changed the solubility of the mobile phase solution by using Ammonium acetate. Before that, the sample was precipitating out of solution and contaminating your injector and flow path.
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