This document specifies a method for the detection of nanoparticles in aqueous suspensions and the characterization of the particle number and particle mass concentrations as well as the number-based size distribution using ICP-MS in a time-resolved operating mode to determine the mass of the individual nanoparticles and ion concentrations. The procedure applies to the determination of the size of inorganic nanoparticles (e.g. metals and metal oxides such as Au, Ag, TiO2, BVO4 etc.) with size ranges from 10 nm to 100 nm (and larger particles up to 1 000 nm to 2 000 nm ) in aqueous suspensions. Metal compounds other than oxides (e.g. sulfides, etc.), metal composites, or coated particles with a metal core can be determined if the chemical composition and density are known. The particle number concentrations that can be determined in aqueous suspensions are between 106 particles / l to 109 particles / l, which is mass concentrations in the range from about 1 ng / l to 1,000 ng / l (for 60 nm Au particles ) corresponds. The actual numbers depend on the type of mass spectrometer used and the type of nanoparticles analyzed. In addition to the particle concentrations, the ion concentrations in the suspension can also be determined. The detection limits are comparable to those of conventional ICP-MS measurements. It should be noted that nanoparticles with sizes smaller than the particle size detection limit of the spICP-MS method may be quantitatively determined as ions. The method proposed in this document does not apply to the detection and characterization of organic or carbon-based nanoparticles such as encapsulated nanoparticles, fullerenes and carbon nanotubes (CNTs). In addition, it does not apply to elements other than carbon, which are difficult to determine with ICP-MS. Reference  gives an overview of the detectable elements and the minimum particle sizes that can be determined with spICP-MS.