Direct coupling of solid phase microextraction and quartz tube-atomic absorption spectrometry for selective and sensitive determination of methylmercury in seafood: an assessment of chloride and hydride generation

Abstract

The direct coupling between headspace solid phase microextraction and quartz tube-atomic absorption spectrometry detection has been evaluated for speciation of methylmercury in seafood after volatilization of its hydride or chloride derivative. Following variable optimisation in both procedures, a critical influence of the fibre sorbent material was observed. Liquid-phase coatings such as polydimethylsiloxane (PDMS) and 'solid' phase coatings such as polydimethylsiloxane-divinylbenzene (PDMS/DVB) or fused silica were compared. Best LODs were provided by the silica fibre for CH 3 HgH (0.4 ng mL 21 ) and by the PDMS/DVB fibre for CH 3 HgCl (0.06 ng mL 21 ). In general, repeatability was about 6% for the preconcentration of both Hg derivatives in the different fibre coatings. The affinity to sorption of CH 3 HgH was slightly improved when using silica fibres loaded with L-cysteine or palladium nitrate. Sorption/desorption studies with fused silica fibres allowed us to hypothesise that CH 3 HgH formed upon reaction of MeHg 1 with NaBH 4 -NaOH suffered from decomposition onto the fibre to yield Hg 0 like direct reaction between Hg 21 and NaBH 4 -NaOH. Generation of the chloride derivative showed an enhanced selectivity as compared with generation of the hydride. Nevertheless, experimental evidence of decomposition of the chloride derivative upon heating is also given. For methylmercury determination in seafood, hydride or chloride generation and headspace SPME were applied after ultrasound assisted extraction of methylmercury in 2 mol dm 23 HCl. Validation was carried out against CRM DORM-2 (dogfish muscle) and CRM 464 (Tuna fish), demonstrating good trueness of the methods proposed. A better LOD of MeHg 1 is obtained as compared with other SPME couplings described in the literature.

Immersed single-drop microextraction–electrothermal vaporization atomic absorption spectroscopy for the trace determination of mercury in water samples

“…Trapping of the hydrides onto the drop does not rely on their partitioning among the gas phase and the solvent phase, as typically developed for organic compounds, but on their catalytic decomposition onto the Pd(0) formed in the drop as a result of the hydrogen evolved during the derivatisation reaction. A faster mass transfer was observed for the methyl mercury hydride from the headspace to the drop in comparison with SPME, which allowed equilibrium to be reached in a significantly shorter time [19].…”

Cold vapor-solid phase microextraction using amalgamation in different Pd-based substrates combined with direct thermal desorption in a modified absorption cell for the determination of Hg by atomic absorption spectrometry

“…Considering the high toxicity of mercury and its wide distribution in the biosphere, analytical procedures providing high sensitivity for the determination of this pollutant have been developed. Studies performed on the determination of mercury using SPME for preconcentration generally have relied on fibers such as polydimethylsiloxane [33][34][35][36][37][38][39], polydimethylsiloxane/divinylbenzene [33] or carboxen/polydimethylsiloxane [39].…”

Non-chromatographic atomic spectrometric methods in speciation analysis: A review

“…A tubeshaped system showed the best analytical characteristics and it was chosen for the determination of tetraethyllead in gasoline and water samples and also methylmercury in seafood [90] after volatilization of its chloride derivative. Sub-ppb detection limits were obtained for both analytes.…”

“…Also, the determination of volatile metals (As, Sn, Hg and Pb) from the headspace above solids using SPME sampling and thermal desorption with ICP-TOF-MS detection was developed [89]. The direct coupling between headspace solid phase microextraction and quartz tubeatomic absorption spectrometry detection has been evaluated by Fragueiro et al [90] for speciation of methylmercury in seafood after volatilization of its hydride or chloride derivative. Liquid-phase coatings such as polydimethylsiloxane (PDMS) and 'solid' phase coatings such as polydimethylsiloxane-divinylbenzene (PDMS/DVB) or fused silica were compared.…”