Trapping ions in an ion trapping assembly is described. In one aspect, this is implemented by introducing ions into the ion trapping assembly, applying a first RF trapping amplitude to the ion trapping assembly so as to trap introduced ions which have m/z ratios within a first range of m/z ratios, and cooling the trapped ions. In some aspects, also performed is reducing the RF trapping amplitude from the first RF trapping amplitude to a second, lower, RF trapping amplitude so as to reduce the low mass cut-off of the ion trapping assembly and trapping, at the second, lower RF trapping amplitude, introduced ions having m/z ratios within a second range of m/z ratios. A lower mass limit of the second range of m/z ratios is below the low mass cut-off of the ion trapping assembly when the first RF trapping amplitude is applied.