A green analytical method for ultratrace determination of hexavalent chromium ions based on micro-solid phase extraction using amino-silanized cellulose membranes.

A new method based on the application of amino-silanized cellulose membranes for selective adsorption of hexavalent chromium ions was developed. The membranes were prepared by coating the cellulose fibers with amorphous silica modified with three amino-silanes containing different numbers of amino groups. The structure and morphology of the membranes denoted as cellulose-1N, cellulose-2N and cellulose-3N were characterized by microscopic and spectroscopic techniques. The batch adsorption experiments show that Cr(VI) can be selectively separated from Cr(III) at pH 4. The maximum adsorption capacities toward Cr(VI) differ from each other significantly and are proportional to the number of protonated amino groups present on the membrane surface: 10.2, 18.1, 34.7 mg g−1 for cellulose-1N < cellulose-2N < cellulose-3N, respectively. The membranes can be applied in the removal of Cr(VI) from aqueous solutions as well as in determination or speciation of chromium due to their selectivity toward Cr(VI) in the presence of Cr(III). In the developed method, Cr(VI) ions were adsorbed at pH 4 from 20 mL sample within 300 min. The presented approach is advantageous since the preconcentration procedures combined with other spectroscopic techniques the elution step is not required and Cr(VI) retained onto the membrane can be directly measured by EDXRF. Due to the very high enrichment factor of 650 the method is characterized by good detection limit of 0.16 ng mL−1. In addition, it is based on the use of miniaturized membranes and their direct measurement using a low-power X-ray spectrometer without gas consumption during the measurements. Therefore, the method can be treated as environmentally favorable and lies in the green analytical chemistry principles. Unlabelled Image • A new preconcentration procedure for Cr(VI) determination • Novel amino-silanized cellulose membranes for selective adsorption of Cr(VI) • Low detection limit suitable for environmental analysis • Simple, fast, inexpensive and environmental friendly method [ABSTRACT FROM AUTHOR]