Separation of chemical forms of analyte on-site - the right concept of speciation analysis for advanced water monitoring.

Advanced water monitoring should be expanded to include speciation analysis, with additional steps: separation, stabilization, and further analysis of suspension as well as the separation of the most unstable forms of the analyte from the dissolved phase directly at the sampling site. In the case of large-scale monitoring, the preservation of primary speciation immediately after sampling is necessary. Otherwise, knowledge about the true speciation in the studied water reservoir will be lost or erroneous. In this paper, we discuss, based on literature data and our own experience, ways to minimize changes in the original speciation during sample collection and preparation for analysis in the laboratory. Attention is focused on the speciation equilibria of As, Cr, Te, and Tl - elements with a high degree of mobility in water ecosystems and high toxicity potential depending on their chemical form. The solid-phase extraction technique is highlighted as the most suitable method for preserving speciation in solution after filtration, along with the necessity of suspension analysis. Sources of possible errors appearing during sample collection are discussed, and the necessity of preserving primary speciation immediately after sampling is emphasized.