Online solid phase extraction-HPLC-ICP-MS system for mercury and methylmercury preconcentration using functionalised carbon nanotubes for their determination in dietary supplements†
A hyphenated system was developed for Hg(II) and methylmercury (MeHg) preconcentration and speciation analysis by the online coupling of solid phase extraction (SPE), high performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS). Both analytes, Hg(II) and MeHg, were preconcentrated on a microcolumn filled with multiwalled carbon nanotubes (MWCNTs) functionalised with poly-L-methionine (polymet-MWCNTs). During the method development the sorbent material was carefully studied and the solid phase extraction conditions were optimised. An enrichment factor of 190 for Hg(II) and MeHg was obtained when 20 mL of sample was passed through the microcolumn. For the chromatographic separation, a mobile phase composed of a ternary mixture of 0.5% formic acid + 0.2% 2-mercaptoethanol + 20% methanol was used. Separation of both mercurial species was accomplished in ∼10 min on a 250 mm C18 column. The detection limits of the SPE-HPLC-ICP-MS method were 15 ng L−1 for Hg(II) and 17 ng L−1 for MeHg. The relative standard deviations of peak area for 5 ng L−1 of each Hg species were below 5%. Recoveries of Hg(II) and MeHg were never less than 93%. For checking the accuracy, BCR 643-tuna fish and TORT-3 lobster hepatopancreas certificate reference materials were analysed. Mercury species were determined in spiked fish oil-based dietary supplements and Antarctic water.