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

Abstract

A study was carried out to investigate the concentrations of Hg(II) in different categories of water samples at ng L1 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 g1 reaching a preconcentration factor (PF) of 150. The high adsorption capacity of this substrate allowed reaching a detection limit (3s) of 1.9 ng L1, when using a sorbent column containing only 1.0 mg of ox-CNTs. The limit of quantification (10s) resulted to be 6.3 ng L1. Precision, expressed as relative standard deviation (RSD), turned out to be 1.6% at the 0.1 mg L1 level (n ¼ 8). The system was evaluated for quantitative determination of Hg in river water, sea water and effluents.