Mass bias is the deviation of measured isotope ratios by a mass spectrometer from the "true value", due to mass discrimination that occurs in all mass spectrometers. In particular, several factors have been found to affect bias in ICP-MS, such as detector "dead time", the electrostatic ion focussing lens and the "space charge" effect occuring at the interface region. Compared with conventional ICP-MS, the hexapole ICP-MS hass high mass bias at low mass region, but lower mass bias at higher mass.