An accurate and sensitive method for the determination of methylmercury in biological specimens using GC-ICP-MS with solid phase microextraction

Abstract

A highly sensitive and selective method has been developed for the determination of methylmercury in biological specimens and NIST Standard Reference Materials (SRMs). The procedure involves microwave extraction with acetic acid, followed by derivatization and headspace solid-phase microextraction (SPME) with a polydimethylsiloxane (PDMS)-coated silica fiber. Optimization of conditions including gas chromatograph injection temperature, microwave extraction power and microwave extraction time are presented. The identification and quantification (via the method of standard additions) of the extracted compounds is carried out by capillary gas chromatography with inductively coupled plasma mass spectrometric detection (GC-ICP-MS) using a unique heated interface that was designed for this work. The SPME-GC-ICP-MS method was validated for the determination of methylmercury (MeHg) concentrations in a variety of biological Standard Reference Materials (SRMs), ranging from 13.2 ng g⁻¹ in SRM 1566b Oyster Tissue, to 397 ng g⁻¹ in SRM 1946 Lake Superior Fish Tissue. Additionally, this method was applied to the determination of MeHg in seabird eggs (common murres, Uria aalge and thick-billed murres, Uria lomvia) collected from colonies on Little Diomede and Bogoslof islands in the Bering Sea and Saint Lazaria Island in the Gulf of Alaska and cryogenically banked in the Marine Environmental Specimen Bank. The results obtained demonstrate that SPME-GC-ICP-MS is a sensitive technique for the determination of methylmercury at trace and ultra-trace levels in a variety of natural matrices with high reproducibility and accuracy. In all instances, the sample-to-sample variability was typically 2% relative standard deviation (RSD) and the method detection limit for methylmercury was 4.2 pg g⁻¹ (as Hg), based on a 0.5 g tissue sample of SRM 1566b Oyster Tissue.