Nickel oxide/nickel ferrite/layered double hydroxide nanocomposite as a novel magnetic adsorbent for chromium speciation

Nickel oxide nanoparticles modified with dimethylglyoxime grafted on a cellulose surface as an efficient adsorbent for thin film microextraction of tramadol in biological fluids followed by its determination using HPLC

In the current study, nickel oxide nanoparticles (NiO NPs) modified with dimethylglyoxime (DMG) were deposited onto the cellulose surface (Ni(DMG)2-NiO-Cell) and used as an efficient adsorbent for thin film microextraction (TFME) of tramadol (TRA). The extracted TRA was determined using a high-performance liquid chromatography-ultraviolet detector (HPLC-UV). NiO NPs were synthesized by co-precipitation method on the surface of the cellulose substrate; afterward, its surface was modified by DMG to increase the extraction capability of the thin film toward TRA. The synthesized NiO-Cell and Ni(DMG)2-NiO-Cell thin films were characterized using various techniques. The effect of modification of the NiO thin film with DMG reagent on the extraction efficiency was investigated. The crucial parameters influencing the extraction efficiency, including extraction time, desorption time, desorption solvent, pH and salt content, were investigated via a one-at-a-time approach. The figures of merit for the developed method were evaluated in urine, plasma, and deionized water under the optimized extraction and desorption condition. The limits of detection and limits of quantification were in the range of 0.1 to 1 ng mL-1 and 0.3 to 3 ng mL-1, respectively, for the studied samples. The linear dynamic ranges of the developed TFME-HPLC-UV method were 0.3-1000, 1-2500, and 3-5000 ng mL-1 for the deionized water, urine, and plasma samples, respectively. The reproducibility and repeatability of the developed method was assayed in terms of intra-day, inter-day, and inter-thin film precisions by conducting six-replicate experiments at the concentration level of 0.1 and 1 μg mL-1, which were in the range of 5.9% to 8.3%. The sufficiency and applicability of the developed TFME-HPLC-UV method was investigated by determining TRA in urine and plasma samples, and the resulting relative recoveries (RR%) were 85.9% and 91.7%, respectively.

A novel separation and preconcentration methodology based on direct immersion dual-drop microextraction for speciation of inorganic chromium in environmental water samples

In this study, for the first time, a novel separation and preconcentration method of direct immersion dual-drop microextraction (DIDDME) was proposed for the species of inorganic chromium (Cr(III) and Cr(VI)) followed by graphite furnace atomic absorption spectrometry detection. The methodology is based on that two organic drops hold on the needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent, which can react with a specific species under the same pH value. Therefore, Cr(III) and Cr(VI) can be selectively extracted into different drops. This procedure did not require tedious and complicated pre-oxidation/pre-reduction and centrifugation/filtration operations, which may lead to the risk of sample contamination and analysis errors. Main parameters influencing separation, preconcentration and identification of the target species were investigated. An enrichment factor of 400-fold was obtained for Cr(III) and Cr(VI). Under the optimized conditions, detection limits for this method were 1.1 ng L^-1 and 1.4 ng L^-1 for Cr(III) and Cr(VI) with relative standard deviations of 5.1 and 6.3%, respectively. This procedure was applied for the separation, preconcentration and determination of Cr(III) and Cr(VI) in environmental water samples and certified reference materials with satisfactory results. Recoveries of spiked experiments ranged from 86.0 to 112%.