Solid phase extraction based on modified multi-walled carbon nanotubes packed column for enrichment of copper and lead on-line incorporated with flame atomic absorption spectrometry

A simple and rapid solid phase extraction-flow injection procedure is developed for on-line trace determination of Cu(II) and Pb(II) by flame atomic absorption spectrometry (FAAS). Multi-walled carbon nanotubes modified with a new Schiff's base, 2,2'-(1E, 1E')-(4-Methyl-1, 2-phenylene) bis (azen-1-yl-1-ylidine) bis (Methane-1-yl-1-ylidene) diphenol was used as a novel adsorbent material. Quantitative simultaneous extraction was obtained at pH 7.0. The retained metal ions were then eluted efficiently with 1.0 M HNO3 into the nebulizer of FAAS for on-line determination. Different variables affecting the preconcentration efficiency, including pH, eluent concentration, sample and eluent flow rates and sample loading time, were optimized. Using 3 min preconcentration of sample solution at flow rate of 5 mL min(-1) provided the enrichment factors of 20 and 21.5 for Cu(II) and Pb(II), respectively, at a sampling frequency of 17 h(-1). The detection limits (3 sigma) were found to be 0.80 and 1.80 mu g L-1 for Cu(II) and Pb(II), respectively; and the relative standard deviations at 0.05 mu g mL(-1) of these metal ions were 1.7 and 1.8% (n = 8), respectively. The accuracy was assessed by analysis of a certified reference material NKK-916 and the obtained results are in good agreement with certified amounts of Cu(II) and Pb(II). The proposed method was successfully applied to the determination of target analytes in different real samples.