Comparison of Two Analytical Methods for the Analysis of Methylmercury in Fish

In this study, we compared a high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS) method and an isotope dilution gas chromatography mass spectrometry (ID-GC-MS) method for the analysis of methylmercury (MeHg) in fish samples. Using HPLC-ICP-MS, the limit of detection (LOD) was 2.0 ngHg · g −1 for inorganic Hg and was 5.0 ngHg · g −1 for MeHg. In comparison, the LOD for MeHg was 3.4 ngHg · g −1 for using ID-GC-MS. Certified reference material (CRM) results agreed well with certified values for both methods. The mean recovery for analysis of CRM BCR 463 by HPLC-ICP-MS was 99 ± 2.1 % for MeHg and was 103 ± 2.1 % for total Hg. Two CRMs, BCR 463 and CRM DORM2, were analyzed by ID-GC-MS, the mean recovery of MeHg was 87 ± 1.9 % for BCR 463, and the mean recovery of MeHg was 102 ± 2.9 % for CRM DORM2. Matrix samples spiked with Hg or MeHg at various concentrations were analyzed by two methods. For HPLC-ICP-MS method, the mean recovery for MeHg spiked samples was 93 ± 4.2 %. For ID-GC-MS method, the mean recovery for MeHg spiked samples was 91 ± 5.2 %. A total of 19 predatory fish and 54 tuna fish samples were analyzed using both methods. No significant difference was observed between the MeHg data generated from both methods. The average relative standard deviation (RSD) between the two datasets for 19 predatory fish samples was 8.8 %. The average RSD between two datasets for 54 tuna fish samples was 4.4 %.The HPLC-ICP-MS method offers substantial advantages over the method of ID-GC-MS because the former method can determine the total mercury (Hg) and MeHg in a single chromatographic run and the analysis time is much shorter. The latter method is time consuming due to overnight digestion and having to conduct presample analysis for signal-matched isotope dilution spiking and requires more expensive isotope labeled reagents.