Separation and chromium speciation by single-wall carbon nanotubes microcolumn and inductively coupled plasma mass spectrometry

Microcolumn packed single-walled carbon nanotubes (SWCNTs) were used as solid phase extraction adsorbent for chromium speciation coupled to inductively coupled plasma mass spectrometry for detection. The effects of the experimental parameters, including pH of the solution, sample flow rate, volume and concentration of eluent, sample volume and interfering ions, on separation and determination of Cr(III) and Cr(VI) were investigated in detail. It was found that Cr(III) was selectively sorbed on the microcolumn packed with SWCNTs in the pH range from 2.0 to 4.0, while Cr(VI) remained in solution. The retained Cr(III) was subsequently eluted with 2.0 mL of 1.2 mol L⁻¹ nitric acid. Under the optimum conditions, the detection limits based on 3σ criterion were 0.01 ng mL⁻¹ and 0.024 ng mL⁻¹ for Cr(III) and Cr(VI), respectively. The relative standard deviations were less than 5.0% (n = 9, c = 1.0 ng mL⁻¹). The method was successfully applied to the speciation of chromium in real samples including natural and waste water. The recoveries of spiked samples were higher than 92.5%.