A method for semi-continuous measurement of dissolved elemental mercury in industrial and natural waters

ABSTRACT

Mercury in aqueous systems can be present in different chemical forms. Of these, dissolved elemental Hg(0) (DEM) is of great importance because it can readily be partitioned between air and water. Analytical methods used for determining DEM are conventionally based on removal of Hg(0) by purging, pre-concentration on gold and detection by either cold vapour atomic absorption (CV-AAS) or atomic fluorescence spectrophotometry (CV-AFS). At present, there is no agreed protocol for the measurement of DEM in aqueous samples. A new method is described here, which is based on continuous stripping of DEM by mercury-free nitrogen in a flow injection mode and detection by CV-AAS. The partitioning of DEM between aqueous and gas phases is largely dependent on the composition of the former. Moreover, calibration using the standard addition method is not possible due to the reactivity of DEM introduced from calibration solutions. Calibration is therefore done by reference measurements using a manual method for DEM involving quantitative removal and CV-AFS detection. DEM is then determined in the water sample by applying the partitioning factor. The optimised method is precise, sensitive and linear over a wide concentration range. It has provided comparable results with the manual method when applied on board a research vessel in the Mediterranean Sea (0.02–0.05 ng L⁻¹) and during a pilot laboratory-scale experiment on industrial aqueous media from wet flue gas desulphurisation (WFGD) equipment (2–300 ng L⁻¹).

KEYWORDS:

• Dissolved elemental mercury
• water
• manual method
• semi-continuous method

Acknowledgements

This work was supported by the Slovenian Research Agency (ARRS) in the framework of the P-0143 project and the EURAMET EMRP MeTra project. The Department of Inorganic Chemistry and Technology at the Jozef Stefan Institute is acknowledged for help in implementing the method in the laboratory-scale WFGD pilot plant. In addition, special thanks go to the Italian National Research Council (CNR) for organising the research expedition in the Mediterranean Basin and to the research crew for unconditional help.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Slovenian Research Agency (ARRS) in the framework of the P-0143 project and the EURAMET EMRP MeTra project.