Agustín Londonio

On-line flow injection solid phase extraction using oxidised carbon nanotubes as the substrate for cold vapour-atomic absorption determination of Hg(II) in different kinds of water

A study was carried out to investigate the concentrations of Hg(II) in different categories of water samples at ng L−1 levels. The capabilities of oxidised carbon nanotubes (ox-CNTs) were studied to assess if this substrate serves as an efficient material for Hg(II) preconcentration using an on-line flow injection cold vapour-atomic absorption spectrometry (FI-CV-AAS) system. Carbon nanotubes are characterized by a marked tendency to aggregate, which negatively affects the retention of Hg whenever integrated in flow systems as a packed column. For this reason, the preconcentration was carried out in a microcolumn filled with a mixture of ox-CNTs and a low molecular weight polyethylene. The preparation of the microcolumn was studied in detail. Concerning column design, the best performance was achieved when packing the substrate in a microcolumn of 2.25 mm (i.d.) × 20 mm length. The effect of chemical and physical parameters including the pH of the solutions, the eluent type and the concentration was systematically examined. Mercury was retained at pH 5.0 and 15% (v/v) HCl was the best alternative for Hg(II) elution. Under optimal conditions, the adsorption capacity of the substrate was found to be 3.2 mg g−1 reaching a preconcentration factor (PF) of 150. The high adsorption capacity of this substrate allowed reaching a detection limit (3σ) of 1.9 ng L−1, when using a sorbent column containing only 1.0 mg of ox-CNTs. The limit of quantification (10σ) resulted to be 6.3 ng L−1. Precision, expressed as relative standard deviation (RSD), turned out to be 1.6% at the 0.1 μg L−1 level (n = 8). The system was evaluated for quantitative determination of Hg in river water, sea water and effluents.

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.