Two-step one-pot speciation of chromium as Cr-APDC-and-NaEDTA complexes followed by ETA-AAS analysis

Abstract

A two-step preconcentration method involving solid-and-liquid-phase extraction procedures has been proposed for the speciation of chromium in a one-pot system. The method used sodium ethylenediaminetetraacetic acid (NaEDTA) and ammonium pyrrolidinedithiocarbamate (APDC). The Cr(VI)-APDC was extracted with ethyl acetate and digested with nitric acid. while the Cr(III)-EDTA complex ion was adsorbed onto Al2O3 (neutral grade) with the aid of a tetrabutylammonium bromide (TBAB) pairing agent and desorbed with a hydrochloric acid solution. Sample splitting was not required. The ZEEnit 650P, electrothermal atomization atomic absorption spectrometer, (ETA-AAS) was employed for the analysis. The concentration of the chromium (III) in the samples ranged from 1.83±0.00 µg L−1 to 106.28±0.21 µg L−1, while <LOD to 19.85±0.12 µg L−1 was the range of Cr(VI) concentration in the samples. Recovery from spiked samples was between 83% and 117% Cr(III) and 79% and 99% Cr(VI). Precision (n = 6), was 1.87% for Cr(III) and 7.67% for Cr(VI). The limits of detection (LODs), calculated by the Aspect LS software (3σ, n = 11) were 0.42 µg L−1 and 0.62 µg L−1 for Cr(III) and Cr(VI) respectively. The mean total chromium (n = 3), from the certified reference material (CRM), LGC6019 was 0.74±0.61 µg L−1, (certified value = 0.78±0.20 µg L−1). The preconcentration factor: ratio of the Cr(III) content of CRM before and after preconcentration was 3.57. Parameters such as pH, time, temperature, and the amount of adsorbent were optimized by the isolation method. The method was validated and applied for the speciation analysis of chromium in water samples.