A method for introducing samples through a boundary member partially defining a chamber at an entrance point coaxial to a sampling inlet of a mass spectrometer is described. Field-free conditions can be established in at least one region of the chamber. The sample can be introduced adjacent to the sampling inlet, and introducing at least a second sample can be introduced through at least one other entrance point in the chamber not adjacent to the sampling inlet. An apparatus having a sampling inlet and a boundary member partially defining a chamber is also described. Field-free conditions can be established in at least one region of the chamber, and there can be a first aperture in the boundary member through which a source emits sample. Related devices, uses and mass spectrometers are also described.