Thermal ionisation mass spectrometry, multi-collector ICP-MS, mass bias কী?

In thermal ionisation mass spectrometry (TIMS), a purified element is loaded on a thin metal ribbon and ionised by heating it under vacuum; the ions are accelerated across a potential of up to $10\,\mathrm{kV}$, separated by mass in a magnetic sector and collected. In multi-collector ICP-MS the ions come from an inductively coupled plasma, which ionises elements that are hard to ionise thermally, and several collectors measure the beams of different masses at the same time. The mass bias of a measurement is the departure of a measured isotope ratio from the true ratio of the sample caused by the instrument, which transmits or ionises one mass more readily than another.