Patent ID: 7528365

Claim:
A method for reducing chemical noise in a mass spectrometry instrument, comprising the steps of: substantially excluding ions in an ion source below a selected mass-to-charge ratio value (m/z) from entering a reaction region while transmitting at least a portion of ions from the ion source with a m/z value above a selected m/z value to the reaction region, the ions in the source comprising one or more background ions and one or more analytes of interest; changing the m/z value of one or more background ions transmitted to the reaction region by reacting the one or more background ions with a neutral organic chemical species in the reaction region; extracting from the reaction region into a mass analyzer at least a portion of the ions with a m/z value in a selected m/z range and substantially excluding from extraction into the mass analyzer ions with a m/z value outside the selected m/z range.