contamination or interference

[yamani]

Dear all
i work with API 3000 and from 6 month till now a strange phonomena appears: contamination or intefrence peak appear at the same tR of my analyte even if blank sample from plasma or even solvent only the peak still appears.
when i moved to another analyte there still contamination with the new analyte.
what is strange is when i increse LLOQ the contamination peak increases

[Kostas Petritis]

If I understand exactly what you are saying it sounds like a curry over effect that might be coming from your injector, valves etc...

[JGK]

I agree with Kostas to see the same effect at the same time in two separate analyses would imply that the problem lies in the LC-MS system and not with the chromatography.