Method for loading a sample of a target compound into a nanospray emitter tube for analysis by nanospray ionization mass spectrometry, wherein a cartridge having a fluid container, an inlet and an outlet is mounted onto a nanospray emitter tube on a nanospray emitter mount to form a nanospray emitter tube assembly, the assembly is mounted on a micro-centrifuge tube, a volume of the sample to be analyzed is loaded into the fluid container and the micro-centrifuge tube is spun on a centrifuge to transfer the sample into the nanospray emitter tube.