Ultrasensitive determination of selenium in water and food samples by ICP-MS: UiO-66-NH2 for preconcentration and direct slurry hydride generation.

BACKGROUND: Selenium is an indispensable microelement for humans and food is the main source of selenium intake. As one of the best techniques for the determination of selenium, inductive coupling plasma-mass spectrometry (ICP-MS) features some unique advantages, such as wide linear range and high sensitivity. Nevertheless, it still remains a challenge to achieve the accurate and high sensitivity determination of ultra-trace selenium in food samples by ICP-MS owning to the high first ionization energy of selenium and interferences from sample matrices as well as isobaric interferences. RESULTS: In this work, UiO-66-NH2 (metal organic framework, MOF) was fast synthesized by microwave method and employed for the preconcentration of ultra-trace selenium with an adsorption efficiency of nearly 100%. The selenium-adsorbed MOF was collected by filtration, and then simply converted to slurry for in situ hydride generation (HG) for sensitive detection of selenium by ICP-MS. Various factors affecting the adsorption of selenium by the MOF (including pH, adsorption time, and amount of MOF) together with main parameters of hydride generation (including concentrations of HCl and NaBH4) were carefully evaluated. Experimental results show that effective matrix separation can greatly reduce interference, with an excellent detection limit of 1 ng/L. The practicability and accuracy of this method were successfully confirmed by the determination of trace selenium in several food samples. SIGNIFICANCE: UiO-66-NH2 (MOF) was used as an effective adsorbent for the preconcentration of selenium prior to direct slurry sampling HG-ICP-MS determination. Direct slurry sampling avoided additional elution procedures and was conducive to eliminating matrix and isobaric interferences. High sensitivity and anti-interference determination were achieved for determination of ultra-trace Se in complex food samples.

Three-Dimensional Printed Dual-Mode Chemical Vapor Generation Point Discharge Optical Emission Spectrometer for Field Speciation Analyses of Mercury and Inorganic Selenium.

Due to the large size and high energy consumption of instruments, field elemental speciation analysis is still challenging so far. In this work, a portable and compact system device (230 mm length × 38 mm width × 84 mm height) was fabricated by using three-dimensional (3D) printing technology for the field speciation analyses of mercury and inorganic selenium. The device comprises a cold vapor generator, photochemical vapor generator, and miniaturized point discharge optical emission spectrometer (µPD-OES). For mercury, inorganic mercury (IHg) was selectively reduced to Hg0 by cold vapor generation, whereas the reductions of both IHg and methylmercury (MeHg) were obtained by photochemical vapor generation (PVG) in the presence of formic acid. For selenium, Se(IV) and total inorganic selenium were converted to their volatile species by PVG in the presence and the absence of nano-TiO2, respectively. The generated volatile species were consequently detected by µPD-OES. Limits of detection of MeHg, IHg, Se(IV), and Se(VI) were 0.1, 0.1, 5.2, and 3.5 µg L-1, respectively. Precision expressed as the relative standard deviations (n = 11) were better than 4.5%. The accuracy and practicality of the proposed method were evaluated by the analyses of Certified Reference Materials (DORM-4, DOLT-5, and GBW(E)080395) and several environmental water samples with satisfactory recoveries (95-103%). This work confirms that 3D printing has great potential to fabricate a simple, miniaturized, easy-to-operate, and low gas and power consuming atomic spectrometer for field elemental speciation analysis.

Enriching Mn-Doped ZnSe Quantum Dots onto Mesoporous Silica Nanoparticles for Enhanced Fluorescence/Magnetic Resonance Imaging Dual-Modal Bio-Imaging.

Multimodal imaging is more suitable for disease diagnosis because of its ability to provide more complementary and accurate information over single-mode imaging. Mn-doped quantum dots (QDs), especially Mn-doped ZnS (ZnSe) QDs, possess unique fluorescent and magnetic properties and are thus attractive for fluorescence/magnetic resonance imaging (MRI) dual-mode imaging. However, the optimal dopant (Mn2+) concentration for maximizing the fluorescence of QDs is relatively low for the MRI imaging. Herein, based on the large Stokes shift of Mn-doped ZnSe QDs, an enrichment strategy with mesoporous silica (MSN) loading was explored for constructing a highly luminescent/paramagnetism Mn-doped ZnSe QDs assembly (MSN@QDs) for improved MRI/optical dual-model imaging. After assembly, the loading density of QDs in MSNs was estimated to be 152 ± 12. Upon loading, the fluorescence of the MSN@QDs assembly was enriched along with QDs (enrichment factor of ∼143). Because of the large Stokes shift (∼200 nm), no appreciable concentration quenching was observed. Meanwhile, the T1 MR contrast was also increased both in vitro and in vivo through improved local Mn2+ concentration, realizing MRI signal enrichment. In fluorescence imaging investigations, MSN@QDs showed better performance over both single QDs and equivalent numbers of MSN-free single QD. Therefore, this enrichment strategy allowed simultaneous signal enhancement of the two imaging modes of Mn-doped ZnSe QDs.

Gold Nanoparticle-Based Colorimetric Assay for Selenium Detection via Hydride Generation.

Gold nanoparticles (AuNPs)-based colorimetric assays are of particular interest since molecular events can be easily read out with the color changes of AuNPs by the naked eye. However, the molecular recognitions occur almost exclusively in the liquid phase (i.e., the interaction between target analytes and AuNPs is always proceeded in the presence of the sample matrix). Since the aggregation of the unmodified AuNPs is prone to be influenced by the ionic strength of the solution, sample matrix will cause undesirable interference. Here, we proposed a new type of AuNP-based colorimetric assay, in which target analyte selenium was first converted to its hydride chemical vapor (H2Se) and then delivered into the solution of AuNPs to induce color change. Therefore, sample matrix (for example, high salinity) were eliminated, leading to excellent selectivity. With the aid of hydride generation, the proposed method offered a detection limit of 0.05 µM with UV-vis detection and 1 µM with the naked eye. Successful application of this method for selenium detection in biological and environmental samples was demonstrated.

Hydride Generation for Headspace Solid-Phase Extraction with CdTe Quantum Dots Immobilized on Paper for Sensitive Visual Detection of Selenium.

A low-cost, simple, and highly selective analytical method was developed for sensitive visual detection of selenium in human urine both outdoors and at home, by coupling hydride generation with headspace solid-phase extraction using quantum dots (QDs) immobilized on paper. The visible fluorescence from the CdTe QDs immobilized on paper was quenched by H2Se from hydride generation reaction and headspace solid-phase extraction. The potential mechanism was investigated by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) as well as Density Functional Theory (DFT). Potential interferences from coexisting ions, particularly Ag(+), Cu(2+), and Zn(2+), were eliminated. The selectivity was significantly increased because the selenium hydride was effectively separated from sample matrices by hydride generation. Moreover, due to the high sampling efficiency of hydride generation and headspace solid phase extraction, the sensitivity and the limit of detection (LOD) were significantly improved compared to conventional methods. A LOD of 0.1 µg L(-1) and a relative standard deviation (RSD, n = 7) of 2.4% at a concentration of 20 µg L(-1) were obtained when using a commercial spectrofluorometer as the detector. Furthermore, a visual assay based on the proposed method was developed for the detection of Se, 5 µg L(-1) of selenium in urine can be discriminated from the blank solution with the naked eye. The proposed method was validated by analysis of certified reference materials and human urine samples with satisfactory results.

Simultaneous determination of three Curcuminoids in Curcuma wenyujin Y.H.chen et C.Ling. by liquid chromatography-tandem mass spectrometry combined with pressurized liquid extraction.

A sensitive and efficient method based on pressurized liquid extraction (PLE) followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for simultaneous identification and quantification of three Curcuminoids in Curcuma wenyujin Y.H.chen et C.Ling., a well known traditional Chinese medicinal herb. PLE was performed using methanol as the extractant, and with the temperature set at 100 °C and the pressure at 1500 psi. Shorter extraction time and less solvent consumption were obtained compared to other extraction methods. LC was performed by using a Waters XBridge C18 column (150 mm × 2.1 mm i.d., 3.5 µm) and a mobile phase of acetonitrile containing 0.1% acetic acid. The operating parameters were thoroughly optimized. The recoveries ranged from 92.4% to 104.1% and relative standard deviations were lower than 3.6%. The method was applied to the determination of Curcumin, Demethoxycurcumin and Bisdemethoxycurcumin contained in Curcuma wenyujin Y.H.chen et C.Ling. samples, which provided a new analytical approach for analysis and quality assessment of traditional Chinese medicines.

UV Photochemical vapor generation sample introduction for determination of Ni, Fe, and Se in biological tissue by isotope dilution ICPMS.

A novel, sensitive method is described for the accurate determination of Ni, Se, and Fe in biological tissues by isotope dilution inductively coupled plasma mass spectrometry (ID ICPMS) based on sample introduction arising from online UV photochemical vapor generation (UV-PVG). Volatile species of Ni, Se, and Fe were liberated from a formic acid medium following exposure to a UV source. Sensitivities were enhanced 27- to 355-fold compared to those obtained using pneumatic nebulization sample introduction. Although precision was slightly degraded (a factor of 2) with ultraviolet photochemical mediated vapor generation (UV-PVG), limits of detection (LODs) of 0.18, 1.7, and 1.0 pg g(-1) for Ni, Se, and Fe, respectively, based on an external calibration, provided 28-, 150-, and 29-fold improvements over that realized with conventional pneumatic solution nebulization. Method validation was demonstrated by determination of Ni, Se, and Fe in biological tissue certified reference materials (CRMs) TORT-2 and DORM-3. Concentrations of 2.33 +/- 0.03, 5.80 +/- 0.28, and 109 +/- 2 microg g(-1) (1SD, n = 4) and 1.31 +/- 0.04, 3.35 +/- 0.18, and 353 +/- 5 microg g(-1) (1SD, n = 4) for Ni, Se, and Fe, respectively were obtained in TORT-2 and DORM-3, in good agreement with certified values.

A novel HPLC-UV/nano-TiO2-chemiluminescence system for the determination of selenocystine and selenomethionine.

Active oxygen species from the photocatalytic reaction in aqueous solution react with luminol to emit strong chemiluminescence (CL), and this can be inhibited by the UV decomposed-products of selenocystine (SeCys) or selenomethionine (SeMet). Based on this phenomenon, a novel hyphenated technique, HPLC-UV/nano-TiO(2)-CL, was established for the determination of SeCys and SeMet. The effects of pH, the UV irradiation time, the TiO(2) coated on the inner surface of the reaction tubing, and the Co(2+) catalyst concentration on the CL intensity and/or chromatographic resolution were systematically investigated. Under these optimized conditions, the inhibited CL intensity has a good linear relationship with the concentration of SeCys in the range of 0.04-10.6 microg mL(-1) or SeMet in the range of 0.05-12.4 microg mL(-1), with a limit of detection (S/N=3) of 6.4 microg L(-1) for SeCys or 12 microg L(-1) for SeMet. As an example, the method was preliminarily applied to the determination of the selenoamino acids in garlic and rabbit serum, with a recovery of 88-104%.