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

摘要

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 (NaBEt_4 and NaBPr_4) was evaluated to improve the detection limit of the method. PT-GC-Pyr-AFS experiments analyzing Milli-Q and Deiofiized water (Millipore) using cleaned reagents and quantifying by external calibration led to MeHg~+ and Hg~(2+) concentration values significantly lower than those obtained using uncleaned reagents. The limit of detections (LODs) after cleaning was found significantly low using both NaBEt_4 and NaBPr_4. However, the lowest LODs were obtained when using cleaned NaBPr_4 (range: 1-2 pgL~(-1) for MeHg+ and 9-10 pgL~(-1) for Hg~(2+)). 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 (IRMM BCR-579).