Investigation of natural colloidal particles contained metals in lake water by single particle inductively coupled plasma mass spectrometry

The existence of inorganic elements in natural water is heterogeneous due to the suspended micro colloidal and nanoparticles. In this work, the signals of Fe, Cu, Cd, Pb content in natural water samples collected from a city lake were examined using the single-particle inductively coupled plasma mass spectrometry (ICP-MS) under the time resolved detection mode. Total numbers, data distributions and central values of the detected signals were obtained based on statistical analysis using the Excel and the Origin software. Both fractionation filtration (0.22, 0.45 and 3.0 mu m membranes) and centrifugation (2000, 4000, 6000 and 8000 rpm rotating speed) have a significant effect on the detection of metals coexisted in the natural colloidal particles (NCPs) in water. Notable number of single-particle signals still presents in the lake water samples even after the pretreatment of 0.22 mu m filtration or 8000 rpm centrifugation, which reveals the ubiquitous existence of micro aggregates or colloids in natural water. Sampling with online dilution is proved to be a direct, simple and effective method for the implementation of time resolved analysis of metallic micro NCPs in lake water by ICP-MS, especially for elements with high dissolved concentration. The results enhance the knowledge of how-to evaluation of the quantity and chemical stability of metal-containing aggregates, colloids and nanoparticles that may exist in natural water.