Deep eutectic solvent-based continuous sample drop flow microextraction combined with electrothermal atomic absorption spectrometry for speciation and determination of chromium ions in aqueous samples

Deep eutectic solvents as a green alternative for trace element analysis in food and beverage samples: Recent advances and challenges

Metals and metalloids have different effects on human health even at trace levels. Some of them are essential for living organisms while others can be toxic. Therefore, the determination of trace elements in food and beverage is highly important to understand their impact in human health. A new generation of solvents named deep eutectic solvents (DES) has emerged as a green alternative for trace element analysis, owing to their low toxicity, biodegradability, and high extraction capacity. In recent years, the application of DES in extraction techniques for trace element analysis in food and beverage samples has increased significantly. This review summarizes recent advances and challenges on the application of DES to develop microextraction techniques useful for the analysis of samples with complex matrices. The importance of the use of biodegradable substances instead of classic organic solvents, which are toxic, volatile, and flammable in methods for elemental analysis with a positive environmental impact is also highlighted. Finally, conclusions and future challenges arising from the use of DES in microextraction techniques are discussed.

Direct immersion dual-drop microextraction for simultaneous separation and enrichment of Cr(III) and Cr(IV) in food samples prior to graphite furnace atomic absorption spectrometry detection

Non-chromatographic speciation methods generally involve speciation conversion, which may cause sample contamination, analysis errors and tedious operations. In this work, a direct immersion dual-drop microextraction (DIDDME) was firstly developed for separation and preconcentration of Cr(III) and Cr(VI). In DIDDME, two organic drops on needle tips of microsyringes were concurrently immersed in a stirred sample solution. Each drop contains a chelating reagent for reacting with a specific species. Thus, Cr(III) and Cr(VI) were selectively extracted into different drops. This method afforded detection limits of 3.0 and 4.1 ng/L, quantification limitof 10 ng/L and 14 ng/L, linear range of 0.01-30 ng mL^-1 and enrichment factors of 354-fold and 326-fold for Cr(III) and Cr(VI), respectively. Precisions like repeatability and reproducibility were assessed by calculating relative standard deviations, which were lower than 5.4 % and 6.9 %, respectively. This procedure was used successfully for quantification of Cr(III) and Cr(VI) in food samples.

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%.

An eco-friendly and sensitive deep eutectic solvent-based liquid-phase microextraction procedure for extraction preconcentration of Pb (II) ions

In recent years, interest in green solvents, which are environmentally friendly, easy to prepare and biodegradable, and in their applications in chemistry has considerably increased. In the current study, a new and easy deep eutectic solvent-based liquid-phase microextraction method compatible with green chemistry principles was developed for preconcentration of Pb (II) ions. The amount of Pb (II) ions was determined with graphite furnace atomic absorption spectrometry (GFAAS). Various analytical parameters such as deep eutectic solvent (DES) ratio and amount, ligand amount, pH, sample volume were optimized and the effects of potential matrix ions on the method were investigated. The preconcentration factor of the method was found to be 160, while the limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.071 µg L^-1 and 0.236 µg L^-1, respectively. The developed procedure was performed to determine Pb (II) ions in lake and river waters, and the accuracy of the procedure was determined with certified reference wastewater (SPS-WW1) analysis.