Abstract: An apparatus and a method for inductively coupled plasma mass spectrometry (ICP-MS) with improved detection limits are disclosed. The ICP-MS includes apparatus for generating an inductively coupled plasma (ICP) in a gas at substantially atmospheric pressure to ionize a sample, a mass analyzer (MS) operable at a low pressure of the order of 10−2-10−4 Pa for detecting at least part of the sample ions, and an interface for transferring the sample ions from the ICP to the MS. The interface is provided with a controller for increasing the pressure in the interface from its normal pressure, for example, to 350-450 Pa. The increased pressure may reduce the sensitivity of the instrument, but can improve detection limits by selective reduction of interfering ions.