Nanoparticles generated in situ in the electrospray instrument were introduced on-line to the inductively coupled plasma mass spectrometry (ICP- MS) for elemental analysis and to the scanning mobility particle sizer (SMPS) for measuring the particle size. A mixture of argon and oxygen gas was optimized and applied as the carrier gas, which ensured the electronic conductivity for electrospray and permitted the measurement by the ICP- MS. Nanoparticles of MgSO4, NH4H2PO4, and Al-2(SO4)(3) were respectively produced in situ from salt solutions and analyzed.