Comparison of GC-ICP-MS, GC-EI-MS and GC-EI-MS/MS for the determination of methylmercury, ethylmercury and inorganic mercury in biological samples by triple spike species-specific isotope dilution mass spectrometry†
We present here the determination of Hg species in complicated matrices by three different mass spectrometric techniques coupled to gas chromatography to evaluate if ionization suppression or spectral interferences are limiting factors to provide accurate and precise determinations, particularly when using the electron ionization source. GC-ICP-MS, GC-EI-MS and GC-EI-MS/MS are compared for the determination of Hg(II), methylmercury and ethylmercury by triple spiking isotope dilution mass spectrometry in the certified matrix reference materials DOLT-4 (dogfish liver), IAEA-085 (human hair), IAEA-086 (human hair) and SRM-955c (caprine blood). The analytical figures of merit such as accuracy and precision and detection limits were compared. Overall, GC-ICP-MS has demonstrated its superiority in terms of accuracy, precision, detection limits and matrix tolerance while GC-EI-MS provided results in agreement with the certified values for hair and dogfish liver reference materials. GC-ICP-MS provided three times lower detection limits for Hg(II) and MeHg than GC-EI-MS and between 4 to 10 times lower than GC-EI-MS/MS. The analysis of more complicated matrices at lower concentration levels, such as caprine blood, has shown important limitations of molecular MS to provide accurate and precise determinations. The higher selectivity offered by GC-EI-MS/MS in the selective reaction monitoring mode does not result in improved analytical characteristics due to lower yield in the formation of in-cell product ions for propylated Hg species.