Novel on-line sequential preconcentration system of Cr(III) and Cr(VI) hyphenated with flame atomic absorption spectrometry exploiting sorbents based on chemically modified silica

In the present study, a flow injection system using dual mini-columns, SiO2/Al2O3/TiO2 and silica gel functionalized with [3-(2-aminoethylamino)propyl] trimethoxysilane (SiO2/AAPTMS) for the sequential preconcentration of Cr(III) and Cr(VI), respectively, from water samples with FAAS detection was proposed. A two-level full factorial design (24) and desirability function were employed for the optimization of variables related to the system performance. The detection limits of 0.66 and 0.27 μg L−1 for Cr(III) and Cr(IV), respectively, were obtained under the optimized preconcentration conditions (flow rate of 7.0 mL min−1), pH 5.0, buffer concentration (acetate buffer) of 0.01 mol L−1, and eluent (2.5 mol L−1 HCl) flow rate of 5.0 mL min−1. The other parameters including preconcentration factor (PF), consumptive index (CI), and concentration efficiency (CE) were found to be 17.62/32.98, 1.13/0.6 mL, and 6.2/11.54 min−1 for Cr(III)/Cr(VI), respectively. The developed method was applied to the Cr(III) and Cr(VI) determination in water samples [tap, lake and mineral water, artificial saliva and parenteral solutions (physiological serum, water for injection, and glucose physiological solution)]. The method accuracy was checked by the analysis of standard reference materials (trace elements in water).