Determination Of Se Species Research Articles

Highly efficient natural deep eutectic solvent-based liquid-liquid microextraction and inductively coupled plasma mass spectrometry for selective determination of inorganic selenium species in nut samples

A novel method involving the use of a hydrophobic natural deep eutectic solvent (NADES) in the vortex-assisted liquid-liquid microextraction technique based on the solidification of floating NADES for inorganic Se speciation analysis was developed. In this work, Se(IV) species was selectively complexed with ammonium pyrrolidinedithiocarbamate (APDC) and extracted with 50 μL of the NADES thymol:decanoic acid (THY:DA) (1:2) followed by fast phase separation upon freezing. Se(VI) species remaining in the aqueous phase was directly determined by inductively coupled plasma mass spectrometry (ICP-MS) while total inorganic Se concentration was determined by direct analysis of the acidic extract originated from the samples. Therefore, Se(IV) was calculated by subtracting the concentration of Se(VI) from the total inorganic Se concentration. Extraction conditions such as pH, sample volume, and type and volume of NADES were optimized, yielding an extraction efficiency of 99.6% for Se(IV). Limits of detection of 0.31 μg L−1 for Se(IV) and 0.24 μg L−1 for Se(VI), relative standard deviations of 3.5% for Se(IV) and 3.0% for Se(VI) and a linear range of 0.78–1000 μg L−1 were obtained. This work reports the first application of the NADES THY:DA (1:2) for the separation and determination of Se species in complex matrix samples such as almond, hazel nut, peanut, walnut, cashew nut, pecan nut and Brazil nut.

Determination of Selenium Fractionation and Speciation in Wetland Sediments by Parallel extraction

Selenium (Se) fractionation and speciation of wetland sediments is very important in understanding the bioavailability and bioaccumulation of Se in wetland systems. Sequential extraction of Se in sediments is often used in fractionation and speciation studies. Because of the difficulty to accurately determine Se fractions and species in sediment samples containing relatively low concentrations, high light materials and high clay texture by using a sequential extraction procedure, an alternative method was developed by parallel extraction of Se in sediments with deionized (DI) water, NaOH, Na 2 SO 3 and H 2 O 2 -HCl, and determination of Se species by differences. Results showed that adsorbed Se from spiked Se in sediments during DI water extraction can be quantitatively recovered with 0.1 M NaOH and 1 M Na 2 SO 3 . Mass recovery of Se from sediments between the parallel extraction and a sequential extraction was very close, indicating that sequential extraction can be replaced by parallel extraction in Se fractionation and speciation studies. Selenite [Se(IV)], elemental Se [Se(0)], organic material-related Se (OM-Se) and organic Se were the major forms of Se, respectively accounting for 31.2, 24.4, 25.2, and 11.6% of the total Se in Tulare Lake Drainage District wetland and Stewart Lake sediments. Reduction of selenate [Se(VI)] to reduced Se [Se(IV) + Se(0)] and Se uptake by wetland organisms with incorporation of these organisms into the sediment are two major immobilization processes that accumulate Se in wetland sediments.

Reversed-phase liquid chromatography with mixed ion-pair reagents coupled with ICP-MS for the direct speciation analysis of selenium compounds in human urine

A sensitive and robust method for the determination of five inorganic and organic Se species in human urine by reversed-phase liquid chromatography with mixed ion-pair reagents coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) is described in this paper. A good separation for anionic, cationic and neutral Se species, namely selenate [Se(VI)], selenourea (SeUr), selenomethionine (SeMet), selenoethionine (SeEt), and trimethylselenonium ion (TMSe+), was achieved within 15 min on a LiChrosorb RP 18 reversed-phase column by using mixed ion-pair reagents of 2.5 mM sodium 1-butanesulfonate and 8 mM tetramethylammonium hydroxide, with isocratic elution at a flow rate of 1.0 mL min−1. The detection limits of the five Se species obtained by HPLC-ICP-MS ranged from 0.6 to 1.5 ng Se mL−1 using an injection volume of 20 µL. It is noteworthy that the urine sample can be directly injected into the analytical system without any pre-treatment, except a filtration with a 0.45 µm membrane filter, and that the determination of Se species was free from chloride-induced matrix interference. In addition, no serious deterioration in column performance or decrease in the sensitivity of ICP-MS was observed for the experimental period of three months. In Japanese urine samples, no detectable SeMet, SeUr, and SeEt could be found, even if the total Se concentration was higher than 100 ng Se mL−1. On the contrary, TMSe+ and two unknown Se species (U1 and U2) were detected in the urine. The major unknown, U1, was found in all of the measured urine samples, suggesting that it might be one of the important Se metabolites.