Food analysis: N-benzyl-N-methyl thiourea immobilized on multi-walled carbon nanotubes for speciation of chromium in food and water samples using ultrasound-assisted heterogeneous suspension IL-micro-solid-phase extraction.

A novel ultrasound-assisted heterogeneous suspension ionic-liquid micro-solid-phase extraction (USA-HSIL-μ-SPE) method based on N-benzyl-N-methyl thiourea immobilized on multi-walled carbon nanotubes (NB-NMT@MWCNTs) was developed for the speciation and determination of Cr(III) and Cr(VI) in water and food samples. The proposed method is based on the selective extraction of chromium species via sulfur-containing functional groups, followed by analysis using atomic trapping flame atomic absorption spectrometry (AT-FAAS). The adsorbent demonstrated a high chromium adsorption capacity of 199.5 mg/g. Under optimized conditions, the method achieved a mean enrichment factor of 48.5, a low detection limit of 0.15 μg/L, a wide linear range of 0.5-330 μg/L, and good precision with an RSD of 2.02% (n = 10). The accuracy and reliability of this method were confirmed through analysis of certified reference materials, comparison with IC-ICP-MS, and recovery studies on spiked samples. The proposed approach is simple, sensitive, and suitable for chromium speciation in food samples.