Magnetic dispersive micro-solid phase extraction coupled with dispersive liquid-liquid microextraction followed by graphite furnace atomic absorption spectrometry for quantification of Se(IV) and Se(VI) in food samples

Ultrasensitive determination of selenium in food samples and its speciation in water and beverages using thiosemicarbazide-incorporated graphene and total-reflection X-ray fluorescence spectrometry

The paper presents a new analytical procedure for the determination and speciation of trace and ultratrace selenium in water, beverages, seafood, milk, and vegetables. The developed method is based on the dispersive micro-solid phase extraction with the use of new thiosemicarbazide-incorporated graphene as a solid sorbent, in combination of the total-reflection X-ray fluorescence spectrometry (TXRF). As a result, we have created an auspicious analytical tool for fast and sensitive analysis of samples with a complex matrix. Regardless of the specimen type, the method is characterized by a very low detection limit of 1.7 pg mL-1 and high precision. The developed strategy allowed us to solve common problems associated with selenium loss during the sample preparation for the TXRF measurement and also improve its performance toward the analysis of beverages and high saline/solid samples, which may even be impossible to perform using standard sample preparation procedures for a TXRF measurement.

One-pot preparation of magnetic composite containing boronic acid groups and aminated multwalled carbon nanotubes for the speciation of Se(IV) and Se(VI) in water and milk samples by combination with chromatographic quantification

Speciation of Se(IV) and Se(VI) is essential due to their significant differences in reactivity, toxicity and bioavailability. Efficient extraction is the pivotal step in the quantification of inorganic selenium species. In this work, a new magnetic nano-composite (MNC) containing boronic acid group and aminated multwalled carbon nanotubes was facilely fabricated by means of one-pot hydrothermal strategy. The prepared MNC contained abundant functional groups and satisfactory magnetic saturation value. Combining with magnetic solid phase extraction (MSPE) format, the MNC displayed satisfactory capture performance towards the complex formed by the coordination of Se(IV) and o-phenylenediamine (OPA). Adsorption isotherm and adsorption kinetics were studied in detail to investigate the adsorption procedure of Se(IV)/OPA complex on MNC. Under the optimal preparation conditions of MNC and extraction parameters, the MNC/MSPE was connected with HPLC equipped with a diode array detector (DAD) to quantify trace Se(IV) and Se(VI) species in water and milk samples. Se(VI) was reduced to Se(IV) and then the total inorganic Se was quantified by the developed method. Subtraction method was used to measure the concentration of Se(VI). The achieved limits of detection were in the ranges of 0.0082-0.013 μg/L and 0.041-0.13 μg/kg for water and milk samples, respectively. Recoveries in actual samples spiked with different amounts of analytes varied from 81.0 % and 117 %, and the RSDs for repeatability varied from 1.0 % to 10 %. In comparison with existing studies based on MSPE, the established method presents some merits such as greenness in the preparation of magnetic adsorbent, rapid extraction procedure, low cost and satisfactory sensitivity in the speciation of inorganic Se species.

A systematic review and meta-analysis of validated analytical techniques for the determination of total selenium in foods and beverages

The intricate balance between the beneficial and harmful effects of selenium (Se) intake means that its quantification in food needs to be done correctly. Therefore, in this review, we systematized 105 articles to identify the most studied methodologies, analytical techniques, and food matrices. Among the analytical techniques employed, inductively coupled plasma mass spectrometry (ICP-MS) (n = 29) emerged as the most commonly used method. The most prevalent hydrolysis methodology to digest Se in food matrices involved the use of nitric acid combined with ultrasound, which improved both the yield and digestion time. Optimal recovery values were achieved when total Se quantification accounted for the sum of Se(IV) and Se(VI) (94.4-99.4%) and for SeCys (88-96.5%). These findings are relevant for advancing methodological approaches, and their results emphasize the importance of developing alternative, faster, and lower-cost protocols for Se quantification in foods and beverages.

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%.

In-syringe solid phase extraction and in-syringe vortex-assisted solidified floating organic drop microextraction of Sb(III) and Sb(V) in rice wines with determination by graphite furnace atomic absorption spectrometry

The current non-chromatographic speciation methods generally involve the conversion of different species by oxidation/reduction reactions, which may cause inherent problems such as contamination risk, time consumption and complex operations. In this work, in-syringe solid phase extraction (IS-SPE) was combined with in-syringe vortex-assisted solidified floating organic drop microextraction (IS-VA-SFODME) for the detection of Sb(V) and Sb(III) in rice wines by graphite furnace atomic absorption spectrometry. Firstly, IS-SPE involved the use of ZnFe₂O₄ nanotubes as the sorbent for the isolation and enrichment of Sb(V) and removal of the matrix components such as ethanol, pigment, sugars and carbohydrates. Then, IS-VA-SFODME was used for enriching Sb(III) in the original sample solution after IS-SPE. This technique exhibited good anti-interference ability and high enrichment efficiency without tedious pre-oxidation/pre-reduction and centrifugation/filtration operations, which may cause the contamination of samples. Under the selected conditions, the detection limits were 4.5 ng L^-1 and 3.2 ng L^-1 for Sb(III) and Sb(V) with relative standard deviations of 7.3% and 5.1%, respectively. This procedure was used with satisfactory results for the detection of Sb(III) and Sb(V) in rice wine samples and a certified reference material of water sample. Recoveries of spiked experiments ranged from 91.0 to 107%.