Measurement of Mercury Species in Whole Blood Using Speciated Isotope Dilution Methodology Integrated with Microwave-Enhanced Solubilization and Spike Equilibration, Headspace–Solid-Phase Microextraction, and GC-ICP-MS Analysis

A biomonitoring method was developed for the determination of inorganic-, methyl-, and ethylmercury (Hg2+, CH3Hg+, and C2H5Hg+, respectively) in whole blood by triple-spiking speciated isotope dilution mass spectrometry (SIDMS) using headspace (HS) solid-phase microextraction (SPME) in combination with gas chromatographic (GC) separation and inductively coupled plasma mass spectrometric (ICP-MS) detection. After spiking the blood sample with isotopically enriched analogues of the analytes (199Hg2+, CH3 200Hg+ and C2H5 201Hg+), the endogenous Hg species were solubilized in 2.0 mol L–1 HNO3 and equilibrated with the spikes using a microwave-enhanced protocol. The microwaved sample was treated with a 1% (w/v) aqueous solution of sodium tetrapropylborate (buffered to pH 5.2), and the propylated Hg species were sampled in the HS using a Carboxen/polydimethylsiloxane-coated SPME fiber. The extracted species were thermally desorbed from the fiber in the GC injection port and determined by GC-ICP-MS. The analytes were quantified, with simultaneous correction for their method-induced transformation, on the basis of the mathematical relationship in triple-spiking SIDMS. The method was validated using a bovine blood standard reference material (SRM 966, Level 2). Analysis of human blood samples demonstrated the accuracy and reproducibility of the method, which can detect the Hg species down to 30 pg g–1 in blood. The validity of the analytical results found for the blood samples was demonstrated using mass balance by comparing the sum of the concentrations of the individual Hg species with the total Hg in the corresponding samples; the latter was determined by isotope dilution mass spectrometry (IDMS) after decomposing the blood using EPA Method 3052 with single-spiking.