Multi-walled carbon nanotubes — Solid phase extraction for isolating marine dissolved organic matter before characterization by size exclusion chromatography
The feasibility of multi-walled carbon nanotubes (MWCNTs) for extracting dissolved organic matter (DOM) from seawater has been investigated. Solid phase extraction (SPE) operating in column and batch modes was used as an extractive technique, and the latter mode offered better performance. DOM adsorption was achieved using 60mg of MWCNTs per each 250mL of seawater subsample, working at pH 1.0 and under an orbital-horizontal shaking at 180rpm and 25°C for 4h. DOM desorption from the MWCNTs support implied an orbital–horizontal shaking (180rpm and 25°C) for 2h using 10mL of a 0.1M sodium hydroxide solution (DOM determination), or using 20mL of alkaline methanol (pH 10.0) for DOM fractionation by size exclusion chromatography (SEC) with UV detection at 205nm. A Total Organic Carbon (TOC) analyzer with wet DOM oxidation (30% (m/v) potassium peroxodisulphate in 6.0M phosphoric acid) under super critical conditions and with Non-Dispersive Infra Red (NDIR) for CO2 detection was used for DOM measurements. Calibration covered TOC concentrations within the 0.13–1000mgL−1 range. The percentage of DOM retained in the MWCNTs support was dependent on the seawater sample, and it varied from 34 to 81%. This means that only the DOM of certain molecular weights is capable to interact with the SPE support. Various SEC columns, ranging from 100 to 7000 and from 500 to 15,000Da (optimum separation range for peptides), were therefore used for DOM fractionation. Results have shown that DOM of low molecular weight is retained in the MWCNTs (fractions within the ranges of 125–1102Da and 6.88–125Da).
Juan Sánchez-González, Natalia García-Otero, Antonio Moreda-Piñeiro, Pilar Bermejo-Barrera
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