The application of gas chromatography-time-of-flight mass spectrometry to the analysis of monomethyl mercury at sub-picogram levels

The analysis of sub-picogram-range methyl mercury generally requires complicated hyphenated instrumentation combining chromatographic systems for the separation and identification of organic Hg components (by GC-MS or LC-MS) and inorganic mass spectrometric techniques for their quantification. To eliminate the complexities and possible biases associated with such complicated hyphenated systems, it is highly desirable to develop a simplified but reliable single-stage instrumental method for the analysis of methyl mercury in environmental samples. To this end, this paper presents an analytical technique based on thermal desorption (TD) - GC - time of flight (TOF) mass spectrometry (MS) for the quantitative analysis of mono-methyl mercury (MMHg) prepared in a liquid phase standard. This optimized system was calibrated using standards in the range of 18 pg to 45 ng and yielded a coefficient of correlation of R2 = 0.9996. This GC-TOF-MS system allowed very low detection limits for MMHg (MDL = 1.86 pg and LOD = 0.031 pg) with good reproducibility (RSE = 1.82%). The potential applicability of the GC-TOF-MS system is highlighted for the trace-level analysis of sub-pg-range of methyl mercury.