Is 200 and 2500 the voltage on CEM? I am sure -200V must be a wrong value any way. The correct value is between 1300 to 2700 and depend on the model of CEM. If 2500 is close to the max value, it may be dangerous. Generally, higher CEM voltage will improve peak intensity on the high mass side, but less obvious on the low mass side. This is because high mass ion need high acceleration to get a velocity threshold before it can generate electron signal in the channeltron.