Liquid membranes for quantification and speciation of trace metals in natural waters

Liquid-membrane (LM) technology, traditionally used for metals recovery in metallurgy, has attracted increasing interest in chemical analysis in recent years. As a pre-concentration tool for metals determination in natural waters, including seawater, LMs have important advantages over traditional solvent extraction (e.g., minimal risk of sample contamination, shorter analysis times – by simultaneous extraction and re-extraction – reduced generation of waste, possibility of automation, and speciation). Some of these features make LMs environmentally friendly in sample treatment. LMs also have several advantages over solid-phase extraction (e.g., low cost and tenability).We present an overview of recent developments in LMs for trace-metal speciation and determination in natural waters. Unpublished results from our own research illustrate new capabilities and applications. We discuss the most significant contributions to this field, and the advantages and the disadvantages of different LM configurations. We give several examples of using bulk or supported LM systems to focus on a wide variety of trace metals, including essential ones (e.g., copper), metals with toxicological relevance (e.g., cadmium), and industrial and urban contaminants (e.g., lead and silver).Also, taking into account the importance of heavy-metal-species distribution to understand their behavior and bioavailability in aquatic ecosystems, we also review the potential of LMs in speciation.Finally, we analyze and discuss future perspectives and trends within this field.