The determination of methylmercury in biological samples by HPLC coupled to ICP‐MS detection

Abstract

The use of high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) for the determination of methylmercury (MeHg + ) in fish tissue and hair samples is described. Analysis of these sample types is required when carrying out biomonitoring studies to determine human dietary exposure to this toxic mercurial compound. The developed method used a mobile phase containing an organic modifier and a sulfydryl compound (1 : 1 v/v methanol : water containing 0.01% v/v 2-mercaptoethanol) to limit peak tailing and aid separation. The chromatographic separation was coupled to the ICP-MS detector via a short piece of PEEK tubing, attached to the nebulizer. A cooled spraychamber and oxygen addition post-nebulization were required to limit the solvent loading on the plasma and reduce carbon build-up on the cones, respectively. The sample preparation procedure employed a drying step followed by digestion of the sample using tetramethylammonium hydroxide (TMAH) and heating in an open vessel microwave system. Two fish tissue certified reference materials (CRM), tuna fish CRM 463 and 464 (BCR, Brussels), a tuna fish proficiency test sample, IMEP-20 (IRMM, Geel, Belgium) and a hair CRM NIES no. 13 (National Institute of Environmental Science, Japan), were used to evaluate the method. The recovery of MeHg + for these four materials was between 83 and 100%, with precisions better than 6% for three separate extractions of the different materials. The limit of quantitation for MeHg + using the developed protocol was 0.5 µg Hg g −1 . The stability of MeHg + in the fish sample extracts was also assessed and losses of 14-16% were observed after storage of the extracts in a refrigerator at 5 • C, in high-density polypropylene tubes, for 6 months. The developed protocol has been used previously with atmospheric pressure ionization mass spectrometry (API-MS) to provide structural characterization and also with calibration via isotope dilution (IDMS) to provide high accuracy quantitation. Copyright forms of an element becomes apparent when considering its toxicity and environmental bioavailability. This is particularly true for the heavy metal mercury because of the acute toxicity of all the chemical species, which has resulted in a number of fatal poisoning instances throughout the world.2,3 Methylmercury (MeHg + ) is notable in this respect, because it is readily formed from inorganic mercury (Hg 2+ ) by natural environmental processes, can be absorbed across the gastrointestinal tract, cross the blood-brain barrier and can pass between mother and fetus. These characteristics can lead to an accumulation of MeHg + in fetal blood, resulting in neurological impairment of the newborn. Speciation Analysis and EnvironmentThe main source of non-acutely toxic MeHg + in the general population is the dietary intake of certain species of fish and other marine life, 5 most notably those at the top of the ecological food chain. The monitoring of mercury in the tissue of edible fish is important becau...

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