4. ConclusionsA method for the dete

4. Conclusions
A method for the determination of low CH3Hg+ concentrations in
humic-rich natural water samples (16–83 mg DOC L−1) using an online
purge and trap GC-ICP-MS was developed in this study. Prior to
the instrumental determination, CH3Hg+ was separated from the
interfering sample matrix using N2-assisted distillation to achieve a
sufficiently low detection limit. Quantitative results were obtained
using a species-specific isotope dilution technique in which samples
were spiked with CH3
201Hg+ prior to the distillation step to correct the incomplete analyte recovery during the whole analysis procedure.
When N2-distillation is used as a pre-extraction method, methylation
of Hg2+ in organic-rich samples may exist. In this study, no artifact
formation of CH3Hg+ was observed during distillation (or during the
ethylation reaction) with humic-rich natural water samples studied.
The method detection limit was found to be 0.05 ng L−1 (3σ) for a
20 mL sample volume which is adequate for the most natural water
samples. The accuracy of the method was verified by analyzing parallel
natural water samples with GC-CV-AFS based on the EPA method 1630.
The results obtainedwith the developed and reference methodswere in
good agreement and did not differ significantly fromeach other. The N2-
distillation with isotope dilution and online purge and trap GC-ICP-MS
method developed in this study were found to be reliable for detecting
low CH3Hg+ concentrations in humic-rich natural waters.