Quantification of ZnO nanoparticles and other Zn containing colloids in natural waters using a high sensitivity single particle ICP-MS

Inductively coupled plasma mass spectrometry in single particle mode (SP-ICP-MS) is becoming a powerful tool of choice for the quantification and characterization of metallic nanoparticles (NP) at very low concentrations. Nonetheless, this technique has relatively high size detection limits for highly soluble nanoparticles (e.g. ZnO, CuO) or NP that are measured in the presence of high background concentrations of dissolved metal. In order to evaluate whether SP-ICP-MS could be used to measure a soluble NP under environmentally relevant conditions, an ion-exchange column (IEC) was coupled to a highly-sensitive sector-field ICP-MS (IEC-SP-ICP-MS) and then used to detect both spiked ZnO NP and natural Zn containing colloids in natural waters. The use of an ion exchange column, short dwell times (50 mu s) and a high sensitivity instrument gave size detection limits for the measurement of ZnO NP of ca. 8.2 nm in pure water, 14.3 nm in a river water and 17.7 nm in a rainwater. IEC-SP-ICP-MS measured ca. 4.4 x 10(5) mL(-1) zinc containing particles in a river water sample and ca. 1.0 x 10(5) ml(-1) particles in a local rainwater.