Field determination of inorganic mercury in seawaters by a portable dual-channel and purge-and-trap system with atomic fluorescence spectrometry

ABSTRACT

An on-line flow injection mercury analyser (FIMA) for inorganic mercury (Hg) analysis in environmental waters is presented. The FIMA is a portable dual-channel and purge-and-trap system combining aqueous reduction with stannous chloride (SnCl₂), two-stage gold (Au) amalgamation, thermal desorption of Hg⁰ and final detection with cold vapour atomic fluorescence spectrometry (CVAFS). Simultaneous on-line operations of sample loading and analysis make analytical throughput and accuracy improved and contamination eliminated. Results of system optimisation and reliability regarding the determination of inorganic Hg²⁺ are described. Analytical performances of both channels were the same in terms of data reliability. Low procedural blanks were obtained from laboratory and field trip (≤5 pg, n = 30). Excellent calibrations (r² > 0.99) with a high precision and good stability (RSD <5%, n = 30) were obtained. Detection limits and reproducibility of the methods have been estimated as ≤0.05 ng L⁻¹ and <5% (0.5 ng L⁻¹, n = 30). The system was finally validated by measurements comparison of the two channels (r² > 0.98), and analysis of a certified reference material (coastal seawater BCR-579, recoveries 101 ± 4%, n = 10). Overall, a sample throughput of ~10 samples per hour with two-channel detections of FIMA can be achieved. The onboard analysis of inorganic Hg species (e.g. elemental, reactive, and total Hg) in surface seawaters of the East China Sea (ECS) are also successfully achieved. The portable FIMA is fast, easy, and robust for reliable monitoring of Hg in natural seawaters.

KEYWORDS:

• Hg species
• flow injection
• purge-and-trap
• dual Au amalgamation
• shipboard analysis
• cold vapour atomic fluorescence spectrometry

Acknowledgments

We thank S.-C. Yeh, K.-C. Li, and C.-S. Liu from Institute of Oceanography, National Taiwan University (IO-NTU), the officers and the crew of the R/V Ocean Research I. We also thank Prof. G.-C. Gong for providing cruise logistics.

Author contributions

S.J.A. performed analysis, generated figures and wrote the manuscript; Y.S.C. assisted experiment works; C.M.T. initiated the study, managed data and revised the paper; All authors helped to provide comments and interpret results.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

Support was provided by the Ministry of Science and Technology (MOST, Taiwan) through grant number MOST [104-2611-M-002-017-MY3, 107-2611-M-002-004, 108-2611-M-002-005, and 109-2611-M-002-010].