The period of time that the analytical instument accumlates the signal. In sequential ICP-MS (e.g. quadrupole systems) the dwell time is characterizing the time spent for acquiring data at each of the channels which make up a peak in the mass spectrum. The length of time is measured in fractions of a millisecond, and will ultimately affect the frequency with which data is acquired at each mass. This will have a bearing on the final precision of the isotope ratio because of the influence of various sources of noise on the analytical signal.

During SIM, the length of time allocated for measuring a particular ion or ions. It can be adjusted so that specified ions can be measured for longer periods, increasing the sensitivity of detection. The term is also used in MRM to describe the time taken to analyse a particular transition. In an ion trap CID experiment, the dwell time is adjusted to increase or decrease the collision time with the added gas.