Determination of chromium (VI) by dispersive solid-phase extraction using dissolvable Zn-Al layered double hydroxide intercalated with L-Alanine as adsorbent

In this study, a new and efficient analytical method was developed to determine hexavalent chromium, Cr (VI), in water by flame atomic absorption spectrometry (FAAS). This method consists on the simultaneous selective extraction and preconcentration of Cr (VI) in water by dispersive solid phase extraction (DSPE), using Zn-Al layered double hydroxide intercalated with L-Alanine (ZnAl-ALA-LDH) as adsorbent. Experimental parameters that influence Cr (IV) determination efficiency, such as pH, time and interfering ions were studied and optimized. After selective extraction of Cr (VI) in the presence of Cr (III) at pH 5.2, ZnAl-ALA-LDH was dissolved in H2SO4 5 mol.L-1. An interesting property of this material is its immediate dissolution at pH values below 3. The complete ZnAl-ALA-LDH dissolution after adsorption ensured that all Cr (VI) adsorbed was analyzed by FAAS, dispensing the use of eluents during the process and thus decreasing the extraction time. In addition to the selective extraction of Cr (VI), the method also allowed sensitivity increase and interference reduction by pre-concentration. Calibration was linear in the range of 20 to 700 mu g.L-1 (r(2) > 0.99). The limits of detection (LOD) and quantification (LOQ) were 7.1 mu g.L-1 and 23.6 mu g.L-1, respectively. Relative standard deviation (RSD) was 2.7% (n = 10). The method accuracy was verified by analyzing a certified water containing Cr (VI) (Cr (VI)-QC1453) and recovery studies on drinking water samples.