Determination of methyl mercury in humic-rich natural water samples using N2-distillation with isotope dilution and on-line purge and trap GC-ICP-MS

• Published in: Microchemical journal Vol. 112; pp. 113 - 118
• Main Authors: Pietilä, Heidi, Perämäki, Paavo, Piispanen, Juha, Majuri, Lyydia, Starr, Mike, Nieminen, Tiina, Kantola, Marjatta, Ukonmaanaho, Liisa
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2014
• Subjects: Distillation; GC-ICP-MS; Methyl mercury; Natural water sample; Purge and trap; Species-specific isotope dilution; Distillation; Species-specific isotope dilution; Methyl mercury; Natural water sample; GC-ICP-MS; Purge and trap
• ISSN: 0026-265X; 1095-9149
• DOI: 10.1016/j.microc.2013.10.002

In this study a method for the determination of low methyl mercury (CH3Hg+) concentrations in non-filtered humic-rich natural water samples using an ethylation-purge and trap with isotope dilution GC-ICP-MS was developed. Purge and trap system was connected on-line to GC which was then coupled to ICP-MS with a simple non-heated in-house made interface. Samples analyzed in this study contained high amounts of dissolved organic matter (16–83mg DOC L−1) which is known to interact strongly with mercury affecting the ethylation efficiency. Thus, prior to instrumental determination CH3Hg+ was separated from the interfering matrix using a nitrogen-assisted distillation. Isotopically enriched spike was added to samples prior to distillation to correct the incomplete analyte recovery during the whole analysis procedure. The method detection limit for a 20mL sample volume was 0.05ngL−1 (3σ). The method precision obtained by replicate analyses of natural water samples was found to be better than 10% (RSD). Since there is no certified reference material available for low-level CH3Hg+ in water, the accuracy of the method was verified by comparing the results with the results obtained with gas chromatography — cold vapor atomic fluorescence spectrometry (GC-CV-AFS) based on the EPA method 1630. The results obtained with the two different methods were in good agreement with each other (r2=0.87, n=25) and the method was successfully applied to non-filtered humic-rich natural waters. •Low CH3Hg+ concentrations in humic-rich natural water samples were determined by species specific isotope dilution GC-ICP-MS.•Nitrogen-assisted distillation was used to extract CH3Hg+ from unfiltered water sample.•CH3Hg+ concentrations were also measured with the GC-CV-AFS technique in different laboratories.