A method for analyzing a sample includes trapping a first ion packet in a first segment of a multi-segment reaction cell; trapping a second ion packet in a second segment of the multi-segment reaction cell; and trapping a third ion packet in a third segment of the multi-segment reaction cell. At least one of the first, second, and third ion packets includes precursor ions, and at least another one of the first, second, and third ion packets includes reagent ions. The method further includes mixing the first, second, and third ion packets within the reaction cell to cause a reaction between the precursor ions and the reagent ions to form product ions.