The present invention proposes a liquid chromatographmass spectrometer constructed to present a maximized or almost maximized ion-producing efficiency of APCI, irrespective of whether positive or negative ions are produced. A fuel tank can be used to supply fuel to an engine, compressor or the like such as when the tank is used to operate an engine or air compressor. Engagement of the first and second shield members with each other and engagement of first and second core connection members with each other may be by means of push-fit inter-engagement.