A mass spectrometry method comprises: introducing a first portion of a sample of ions including precursor ions comprising a first precursor-ion mass-to-charge (m/z) ratio into a first mass analyzer; transmitting the precursor ions from the first mass analyzer to a reaction or fragmentation cell such that a first population of product ions are continuously accumulated therein over a first accumulation time duration; initiating release of the accumulated first population of product ions from the reaction or fragmentation cell; continuously transmitting the released first population of product ions from the reaction cell to a second mass analyzer; transmitting a portion of the released first population of product ions comprising a first product-ion m/z ratio from the second mass analyzer to a detector; and detecting a varying quantity of the product ions having the first product-ion m/z ratio for a predetermined data-acquisition time period after the initiation of the release.