Automated Online SPE-ICP-MS for Ultra-Trace Determination of Mercury in Freshwaters

Abstract

Mercury (Hg) contamination in aquatic environments requires analytical methods capable of reliable ultra-trace quantification to support environmental monitoring, regulatory compliance and, ultimately, health risk assessment. Conventional approaches often involve labor-intensive preparation, derivatization steps, or insufficient sensitivity for pristine waters. To overcome these limitations, solid-phase extraction (SPE) has been increasingly employed to preconcentrate Hg prior to detection; however, existing strategies typically rely on complex, customized sorbents, offline procedures, or additional hyphenated techniques for speciation, which increase cost, time, and operational complexity. In this study, we present a fully automated online SPE-inductively coupled plasma mass spectrometry (SPE–ICP-MS) method for total Hg determination in natural waters. The method exploits thiourea-assisted complexation of inorganic and organic Hg species, enabling their simultaneous retention on a cation-exchange resin and species-independent elution with 1 M HCl. Adjustable accumulation times allow tuning between rapid analysis and enhanced sensitivity. Under optimized conditions, the method achieves a detection limit of 0.93 ng/L, a linear range up to 1600 ng/L, and accurate recoveries (96–104%) in mineral water samples. Compared with established analytical protocols, the developed system offers competitive sensitivity while enabling high-throughput and simple operation. These features make this method suitable for routine Hg monitoring.