One property of organic INSs that differs significantly from inorganic INSs is density (Table ). Organic INSs generally have densities of 1.6 g cm -3 or less , whereas inorganic INSs have densities of 2.1 g cm -3 or greater 2023; National Center for Biotechnology Information 2023; . Here, we present a new method for separating and quantifying organic and inorganic INSs based on density gradient centrifugation, which takes advantage of these differences. This method is straightforward and uses instruments that are available in many laboratories. This method should also be compatible with INS samples collected using filters or impingers . Additionally, this method does not suffer from sampling statistics since many samples can be processed in a reasonable amount of time .