Methylmercury speciation in fish muscle by HPLC-ICP-MS following enzymatic hydrolysis

Monomethylmercury (MeHg+ and its complexes; hereafter referred to as MeHg) in the intracellular environment is known to be predominantly bonded to thiol-containing biomolecules, but the actual identities of these target biomolecules remain unknown. While binding with glutathione acts as a detoxification mechanism for MeHg, binding with L-cysteine is thought to be the main pathway of MeHg transport across the blood-brain barrier. Here we report a HPLC-ICP-MS method that is capable of separating and analyzing MeHg-cysteine complexes (MeHgCys; charges are neglected for simplicity) and MeHg-glutathione complexes (MeHgGlu), as well as MeHgX (X = H2O, OH-, or Cl-) and inorganic HgX, with detection limits at the sub-micromolar levels. The method was successfully applied for the determination of MeHg speciation in a dogfish muscle sample after enzymatic hydrolysis with trypsin, and provided the first analytical evidence for the presence and dominance of MeHgCys in fish muscle.