Redox Preconcentration/Speciation of Chromium by Using Nanocomposites Based on Carbon Nanotubes and Functional Polymers

In this chapter, an online solid-phase extraction (SPE) system to preconcentrate/speciate Cr3 + and Cr6 + using two mini-columns individually packed with two carbon nanotubes/polymers nanocomposites was developed and coupled to flame atomic absorption spectrometry (FAAS). The nanocomposites were synthesized and characterized by Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy (TEM), and textural data. The analytical method was based on percolate 24.0 mL of Cr3 + and Cr6 + binary solutions through mini-columns packed with 50.0 mg of nanocomposites at flow rate of 6.0 mL min− 1. While Cr3 + specie is retained onto multi-walled carbon nanotube (MWCNT)-poly(methacrylic acid), the Cr6 + is eluted from MWCNT-poly(4-vinylpyridine) using 2.5 mol L− 1 HNO3 at flow rate of 4.0 mL min− 1 directly toward FAAS detector. By switching the central part of injector, the elution of Cr3 + is carried out and Cr6 + is again preconcentrated into MWCNT-poly(vinylpyridine). The effect of variables related to preconcentration and speciation method was evaluated by a full 24 factorial design. The analytical curve for Cr3 + was ranged from 1.7 to 150.0 μg L− 1 (Radj = 0.999) while the limit of detection, enrichment factor, and consumption index were found to be 0.47 μg L− 1, 31.5, and 0.76 mL, respectively. To Cr6 +, the analytical curve ranged from 5.2 to 150.0 μg L− 1 (Radj = 0.999) while the limit of detection, enrichment factor, and consumption index were found to be 1.58 μg L− 1, 9.7, and 2.48 mL, respectively. The chromium speciation in aqueous medium could be performed efficiently with analytical frequency of 14 h− 1. The method applicability of method was attested by water (mineral and potable) samples analysis, yielding recoveries from 91% to 109%, as well by analysis of certified reference material.