A reliable method to determine methylmercury and ethylmercury simultaneously in foods by gas chromatography with inductively coupled plasma mass spectrometry after enzymatic and acid digestion

A reliable and sensitive method for determination simultaneously of monomethylmercury (MeHg) and monoethylmercury (EtHg) in various types of foods by gas chromatography inductively coupled plasma mass spectrometry (GC-ICP/MS) was developed and validated. Samples were digested with pancreatin and then hydrochloric acid. MeHg and EtHg in the extract were derivatized in an aqueous buffer with sodium tetraphenylborate. After phase separation, the extract was directly transferred to analysis. The analyses were conducted by GC-ICP/MS with monopropylmercury chloride (PrHgCl) as surrogate standard. Concentrations of 254 ± 5.1, 13.7 ± 0.69 and 162 ± 6.2 μg Hg kg−1 (one standard deviation, n = 3) were obtained for MeHg in NIST SRM 1947 (Superior Lake fish), SRM 1566b (oyster tissue) and NRC Tort-2 (lobster Hepatopancreas), respectively. These are in good agreement with the certified values of 233 ± 10, 13.2 ± 0.7 and 152 ± 13 μg Hg kg−1 (as 95% confidence interval), respectively. The method detection limits (3σ) for MeHg and EtHg are 0.3 μg Hg kg−1. The method detection limit was estimated by using a 0.5 g of subsample, sufficiently low for the risk assessment of MeHg and EtHg in foods. The spiked recoveries of MeHg and EtHg in different food matrices were between 87 and 117% and the RSDs were less than 15%. When isotopic dilution mass spectrometry (IDMS) analysis was performed with a commercial available 201Hg-enriched monomethylmercury (Me201Hg) solution as internal standard, concentrations of 244 ± 13.4, 13.9 ± 0.25 and 161 ± 1.3 μg Hg kg−1 were obtained for MeHg in NIST SRM 1947, SRM 1566b and NRC Tort-2, respectively. It shown clearly that IDMS analysis got improvement in precision and accuracy, however, EtHg cannot be analyze simultaneously and the cost of analysis is higher.