Determination of methyl mercury and inorganic mercury in natural waters at the pgL⁻¹ level: Intercomparison between PT-GC-Pyr-AFS and GC-ICP-MS using Ethylation or Propylation derivatization

Laboratoire de Chimie Analytique Bio-Inorganique et Environnement (LCABIE), Institut des Sciences Analytiques et de Physico-Chimie pour l’Environnement et les Matériaux (IPREM), UMR 5254 CNRS- Université de Pau et des Pays de l’Adour, Hélioparc 2, av P Angot, 64053 Pau Cedex 9, France

^a a.sharif@etud.univ-pau.fr
^b david.amouroux@univ-pau.fr

Abstract

Mercury speciation analysis of both inorganic and methyl Hg in ultrapure and natural waters by purge-and-trap gas chromatography pyrolysis atomic florescence spectrometry (PT-GC-Pyr-AFS, MERX-M, Brooks Rand) was performed. This automated analytical setup was also compared with gas chromatography inductively coupled plasma mass spectrometry (GC-ICPMS, X Serie 2 ThermoFisher). In addition, a reagent cleaning step of the buffer solution and derivatizing reagents (NaBEt₄ and NaBPr₄) was evaluated to improve the detection limit of the method. PT-GC-Pyr-AFS experiments analyzing Milli-Q and Deionized water (Millipore) using cleaned reagents and quantifying by external calibration led to MeHg⁺ and Hg²⁺ concentration values significantly lower than those obtained using uncleaned reagents. The limit of detections (LODs) after cleaning was found significantly low using both NaBEt₄ and NaBPr₄. However, the lowest LODs were obtained when using cleaned NaBPr₄ (range: 1–2 pgL^–1 for MeHg⁺ and 9-10 pgL^–1 for Hg²⁺). Matrix effects have been finally investigated using both PT-GC-Pyr-AFS and GC-ICPMS to characterize and quantify potential interferences in natural water samples with different salinities and organic matter contents, including coastal water reference material (CRM) certified for total mercury concentration (IRMMBCR-579).