In mobile phase water/acetonitrile with 0.01% HCOOH I have some response (not too good) in negative mode. I got "exponential" response with the increase in concentration of the type: 2.5, 5, 10, 20 ppm generates 1250, 5000, 20000, 80000 area count. I was expecting some ion suppression and the non-linearity to be with flattening as the concentration increases (having rather high concentrations for LC-MS). It is just the other way around. (NH4OOCH or CH3COOH in the mobile phase do not produce good signal, and nothing in positive mode). Is any way to make the response more linear?