Comparison of gas chromatographic hyphenated techniques for mercury speciation analysis

In this study, we evaluate advantages and disadvantages of three hyphenated techniques for mercury speciation analysis in different sample matrices using gas chromatography (GC) with mass spectrometry (GC–MS), inductively coupled plasma mass spectrometry (GC–ICP-MS) and pyrolysis atomic fluorescence (GC-pyro-AFS) detection. Aqueous ethylation with NaBEt4 was required in all cases. All systems were validated with respect to precision, with repeatability and reproducibility <5% RSD, confirmed by the Snedecor F-test. All methods proved to be robust according to a Plackett–Burnham design for 7 factors and 15 experiments, and calculations were carried out using the procedures described by Youden and Steiner. In order to evaluate accuracy, certified reference materials (DORM-2 and DOLT-3) were analyzed after closed-vessel microwave extraction with tetramethylammonium hydroxide (TMAH). No statistically significant differences were found to the certified values (p = 0.05). The suitability for water samples analysis with different organic matter and chloride contents was evaluated by recovery experiments in synthetic spiked waters. Absolute detection and quantification limits were in the range of 2–6 pg for GC-pyro-AFS, 1–4 pg for GC–MS, with 0.05–0.21 pg for GC–ICP-MS showing the best limits of detection for the three systems employed. However, all systems are sufficiently sensitive for mercury speciation in environmental samples, with GC–MS and GC–ICP-MS offering isotope analysis capabilities for the use of species-specific isotope dilution analysis, and GC-pyro-AFS being the most cost effective alternative.