Determination of selenium species in infant formulas and dietetic supplements using liquid chromatography–hydride generation atomic fluorescence spectrometry

Selenium in selected samples of infant formulas and milk commercialized in Belgium and Brazil: Total content, speciation and estimated intake

Total selenium (Se) and Se species concentrations were determined in 50 infant formulas and milk samples commercialized in Brazil and Belgium. Infant formula categories were starter, follow-up, specialized and plant-based (soy and rice), while milk samples included whole, skimmed, semi-skimmed and plant-based products. Total Se content was determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), after microwave digestion. An enzymatic extraction method was applied to evaluate the Se species, mostly selenomethionine (SeMet), Se(IV) and Se(VI), through High Performance Liquid Chromatography coupled to ICP-MS (LC-ICP-MS). Starters and follow-up samples presented the highest total Se concentrations and values up to 30 µg/kg were observed in the reconstituted product. The lowest level (below the LOQ = 10 µg/kg) was verified in an anti-regurgitation specialized formula. The relative agreement between the measured total Se and the Se content declared on the label varied from 55 % to 317 %. Concentrations in infant formulas were not markedly different from concentrations in milk except for rice and oat milk samples that showed values below the LOQ. SeMet was the main species found in milks, while in infant formulas the species concentrations varied according to the product. The daily intake (DI) of Se via infant formula consumption was calculated and compared with the Adequate Intake (AI) value and the Dietary Reference Intake (DRI) established by the EFSA NDA Panel and ANVISA, respectively. Estimated maximum intakes of total Se obtained for reconstituted infant formula were 40.6 mg/day, corresponding to 400 % and 202 % of the DRI and AI, respectively.

Deep-eutectic-solvent-based dispersive and emulsification liquid-liquid microextraction methods for the speciation of selenium in water and determining its total content levels in milk formula and cereals

Rapid and environmentally friendly ultrasound-assisted dispersive liquid-liquid microextraction (US-DLLμE) and vortex assisted-emulsification liquid-liquid microextraction (VA-ELLμE) methods are proposed for the speciation of selenium in domestic and mineral water samples. A deep eutectic solvent (DES) prepared with different ratios of choline chloride and phenol is used as an extractant for hydrophobic tetravalent Se complexed with diethyldithiocarbamate in different water samples. The total inorganic Se species levels in water samples were determined via reducing Se(vi) to Se(iv), using sodium thiosulphate as a reducing agent. The total Se levels in formula milk and cereal samples were determined after microwave acid digestion. The different heating steps in GFAAS were also optimized. The analytical parameters for US-DLLμE and VA-ELLμE, including pH, the volume of complexing agent, the ultrasound and vortex mixing shaking times, and the volume and composition of the deep eutectic solvent, were optimized. The accuracies of both methods were confirmed based on the analysis of a certified reference material (CRM) BCR 189 (wholemeal flour). The enhancement factor (EF) and limit of detection (LOD) for Se(iv) via US-DLLμE were found to be 90.8 and 0.029 μg L^-1, respectively, whereas an EF of 81.8 and LOD of 0.036 μg L^-1 were obtained via VA-ELLμE. The % relative standard deviation (%RSD) values obtained based on the analysis of six replicate standards under the optimized conditions for US-DLLμE and VA-ELLμE were found to be 4.2 and 5.8%, respectively. The optimized methods were applied to different drinking water samples, and acid-digested milk formula and baby cereal food samples.

Radiochemical separation by liquid-liquid extraction for the determination of selenium in Mentha pulegium L.: Toxicity monitoring and health study

In Algeria, Data and studies on the non-metal trace element selenium (Se) are presently lacking, therefore, the aim of this investigation is to provide new data on (Se) element via its determination for the first time from Mentha pulegium L. plant. The plant samples were collected in summer of 2012 from Ain-Oussera region, Djelfa province, Algeria; they were dried and powdered. After the neutron irradiation, the samples were digested using high oxidative reagents including H₂SO₄, HNO₃, H₂O₂ and HCl. The end of this process gave two phases, organic and aqueous discard phase. By using a separating funnel, the organic phase was transferred into a vial in order to measure their induce radionuclide ⁷⁵Se using gamma-ray spectrometer. A non-chromatographic and sensitive analytical technique RNAA (Radiochemical Neutron Activation Analysis), was applied in this investigation due to its great significant minor systematic error. Results were determined using two distinguish calculation methods, relative-RNAA and k₀-RNAA, the findings were quite significant, whereas, the average separation yield was about 85% for both calculation methodologies. Moreover, (Se) concentration obtained from M. pulegium L., is close to the minimal FAO (Food and Agriculture Organization of the United Nations) recommended consumption.

Selenium Analysis and Speciation in Dietary Supplements Based on Next-Generation Selenium Ingredients

Selenium is essential for humans and the deficit of Se requires supplementation. In addition to traditional forms such as Se salts, amino acids, or selenium-enriched yeast supplements, next-generation selenium supplements, with lower risk for excess supplementation, are emerging. These are based on selenium forms with lower toxicity, higher bioavailability, and controlled release, such as zerovalent selenium nanoparticles (SeNPs) and selenized polysaccharides (SPs). This article aims to focus on the existing analytical systems for the next-generation Se dietary supplement, providing, at the same time, an overview of the analytical methods available for the traditional forms. The next-generation dietary supplements are evaluated in comparison with the conventional/traditional ones, as well as the analysis and speciation methods that are suitable to reveal which Se forms and species are present in a dietary supplement. Knowledge gaps and further research potential in this field are highlighted. The review indicates that the methods of analysis of next-generation selenium supplements should include a step related to chemical species separation. Such a step would allow a proper characterization of the selenium forms/species, including molecular mass/dimension, and substantiates the marketing claims related to the main advantages of these new selenium ingredients.

Application of enzymatic probe sonication for selenium speciation in animal feeds

Enzymatic probe sonication (EPS) was investigated as a novel and alternative technology for the extraction of five Se species SeCys₂, MeSeCys, Se (IV), SeMet and Se (VI) from animal feeds. The critical parameters of EPS such as enzyme types, ultrasonic power, sample/enzyme ratio, extraction time and temperature were carefully optimized. Under current conditions, one sample can be extracted in 60s, in contrast to several hours required by the conventional enzymatic methods Moreover, the extraction is performed in pure water, no further temperature control or pH adjustment is needed, and therefore the risk of species interconvertion is drastically reduced or inhibited. The Se species were separated and quantitatively determined by high-performance liquid chromatography-hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS), which allows the separation of organic and inorganic Se species in a single chromatographic run. The newly developed method was successfully applied to the determination of Se species in 18 feed samples collected from markets and local farms. Concerning the feed samples studied, the results of this work suggest that stricter measures should be taken to control the Se-enriched feed supplements in terms of Se species.

Nonchromatographic speciation of selenium in edible oils using dispersive liquid-liquid microextraction and electrothermal atomic absorption spectrometry

A methodology for the nonchromatographic separation of the main selenium species present in edible oils is presented. Dispersive liquid-liquid microextraction is used to extract inorganic selenium (iSe), seleno-L-cystine (SeCys₂), seleno-L-methionine (SeMet), and selenocystamine (SeCM) into a slightly acidic aqueous medium. The selenium total (tSe) content is measured in the extracts by electrothermal atomic absorption spectrometry. By repeating the microextraction stage using an ionic liquid instead of water, the sum of SeCys₂, SeMet, and SeCM is obtained and iSe is calculated by difference. The detection limit is 0.03 ng of Se per gram of oil. The fractionation of the edible oils by solid phase extraction followed by dispersive liquid-liquid extraction and atomic absorption measurement also permits speciation of iSe to be carried out. Data for tSe and iSe levels of 15 samples of different origin are given.

Evaluation of the inorganic selenium biotransformation in selenium-enriched yogurt by HPLC-ICP-MS

Selenium is an essential element in the human diet. Interestingly, there has been an increased consumption of dietary supplements containing this element in the form of either inorganic or organic compounds. The effect of using selenium as a dietary supplement in yogurt has been evaluated. For this purpose, different concentrations of inorganic Se (ranging from 0.2 to 5000 microg g(-1)) have been added to milk before the fermentation process. Biotransformation of inorganic Se into organic species has been carefully evaluated by ion-exchange, reversed-phase, or size-exclusion chromatography, coupled to inductively coupled plasma mass spectrometry (ICP-MS). Yogurt fermentation in the presence of up to 2 microg g(-1) of Se(IV) produces a complete incorporation of this element into proteins as has been demonstrated applying a dialysis procedure. Analysis by SEC-ICP-MS showed that most of them have a molecular mass in the range of 30-70 kDa. Species determination after enzymatic hydrolysis has allowed the identification of Se-cystine using two different chromatographic systems. The biotransformation process that takes place during yogurt fermentation is very attractive because yogurt can act as a source of selenium supplementation.

Speciation of selenium compounds by open tubular capillary electrochromatography-inductively coupled plasma mass spectrometry

We introduce a T-type interface and a crossflow nebulizer to find ways to combine CEC with inductively coupled plasma MS (ICP-MS) detection for selenium speciation. For CEC separation, we employed a macrocyclic polyamine-bonded phase capillary as the separation column and a bare fused-silica capillary filled with the make-up liquid (0.05 M HNO3). The effect of nebulizer gas flow rate, make-up liquid flow, type, concentration and pH of the mobile phase on the separation have been studied. Tris buffer of 50 mM at pH 8.50 gave the best performance for selenium speciation. The reproducibility of the retention time indicated that sample injection by electrokinetic and nebulizer gas flow was better than that by self-aspiration alone. The detection limits for selenate, selenite, selenocystine and selenomethionine were found to be 2.40, 3.53, 12.86 and 11.25 ng/mL, respectively. Due to the high sensitivity and element-specific detection, as well as the high selectivity of the bonded phase, quantitative analysis of selenium speciation in urine was also achieved.

New separation method for organic and inorganic selenium compounds based on anion exchange chromatography followed by inductively coupled plasma mass spectrometry

We describe a new method for separating the organic and inorganic selenocompounds methaneseleninic acid, selenite, selenate, methylselenocysteine, selenocystine as well as both selenomethionine and its oxidized form. The separation is performed on a Hamilton PRP-X100 column. According to the literature, the oxidized form of selenomethionine-which is easily formed-is eluted close to the dead volume when this column is used. The choice of parahydroxybenzoic acid as mobile phase enabled us to elute all of these species after this oxidized form, resulting in better identification and quantification. The factors determining separation (eluent concentration, pH, gradient) were optimized via an experimental design. Application of the method to yeast and commercial tablets showed that the principal Se compound present was selenomethionine, which was also present in its oxidized form.

Selenium speciation by high-performance anion-exchange chromatography–post-column UV irradiation coupled with atomic fluorescence spectrometry

A technique for the speciation of selenomethylcysteine (SeMeCys), selenocystine (SeCys), selenite [Se(IV)] and selenomethionine (SeMet) was established in this paper using high-performance anion-exchange chromatography coupled with atomic fluorescence spectrometry (HPAEC-AFS). Analytes were separated on an AminoPac PA10 column and then digested by on-line ultraviolet (UV) irradiation, which destroyed organic compound structure. Hydride generation was used as an available sample introduction technique for atomic fluorescence detection. The detection limits of four compounds were 1-5 microg/L (250 microL injection, 10 times of the baseline noise). The relative standard deviations (RSDs), calculated from seven consecutive injections of 100 microg/L standard mixtures, were from 2 to 4%. Selenious yeast tablet, which had been proposed as selenium supplement, and human urine collected from a volunteer were analyzed. Good spiked recoveries from 86 to 103% were obtained.

Direct amino acid analysis method for speciation of selenoamino acids using high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection

Speciation analysis of selenomethylcysteine (SeMeCys), selenomethionine (SeMet) and selenocystine (SeCys) has been performed using a direct amino acid analysis method with high-performance anion-exchange chromatography (HPAEC) coupled with integrated pulsed amperometric detection (IPAD). Three selenoamino acids could be baseline-separated from 19 amino acids using gradient elution conditions for amino acids and determined under new six-potential waveform. Detection limits for SeMeCys, SeMet and SeCys were 0.25, 1 and 20 microg/L (25 microL injection, 10 times of the baseline noise), respectively. The relative standard deviations (RSDs) of 200 microg/L SeMeCys, SeMet and SeCys were 3.1, 4.1 and 2.8%, respectively (n=9, 25 microL injection). The proposed method has been applied for determination of selenoamino acids in extracts of garlic and selenious yeast granule samples. No selenoamino acids were found in garlic. Both SeMet and SeCys were detected in selenious yeast tablet with the content of 45 and 129 microg Se/g, respectively. Selenoamino acids standards were spiked in garlic and yeast granule samples and the recovery ranged from 90 to 106%.