Photochemical Vapor Generation for Colorimetric Speciation of Inorganic Selenium

Selenium in Photochemical Vapor Generation: Mechanism Study and Potential Nonchromatographic Speciation Analysis

The mechanism of selenium in the UV photochemical vapor generation (PVG) process was investigated by the use of multiple analytical methods. It was found that the UV-induced photooxidation trapping of the generated volatile SeH2 should be responsible for the previous opinion of relative inertness of Se(VI) in PVG with formic acid. Furthermore, the formation of Se(IV) was found during the PVG process, and the comproportionation of Se(IV) with SeH2 and the photooxidation of Se(IV) into Se(VI) were investigated. Then, a preliminary model was proposed for the PVG process of Se(VI) and Se(IV) with low-molecular-weight organic acids. Then, a novel, simple, and green photocontrolled method without any photocatalyst was thus proposed for the nonchromatographic speciation analysis of Se(IV) and Se(VI), with a limit of detection of 0.2 and 5 ng/mL, respectively.

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.

Detection of trace antimony by vanadium (IV) ion assisted photochemical vapor generation with inductively coupled plasma mass spectrometry measurement

In this work, a method for sensitive detection of trace antimony (Sb) was developed by inductively coupled plasma mass spectrometry (ICP MS) coupled with photochemical vapor generation (PVG). V(IV) ions were used as new "sensitizers" for improving the PVG efficiency of Sb. Factors influenced the PVG and the detection of Sb by ICP MS were investigated, including the type and concentration of low molecular weight organic acids, the UV irradiation time, the concentration of V(IV) ions, the air-liquid interface, the flow rate of Ar carrier gas, and interferences from co-existing ions. It was found that efficient reduction of Sb was obtained in the medium of 10% (v/v) formic acid (FA), 10% (v/v) acetic acid (AA), and 80 mg L^-1 of V(IV) with 100 s UV irradiation. Under the selected conditions, there was no significant difference in analytical sensitivity between Sb(III) and Sb(V). The limit of detection (LOD, 3σ) was 4.7 ng L^-1 for Sb with ICP MS measurement. Compared to traditional direct solution nebulization, the analytical sensitivity obtained in this work was enhanced about 19-fold. Relative standard deviations (RSDs, n = 7) were 1.9% and 2.3% for replicate measurement of 0.5 μg L^-1 Sb(III) and Sb(V) standard solutions, respectively. The proposed method was applied for the determination of trace Sb in water samples and two certified reference materials (CRMs) of sediments with satisfactory results. Moreover, the generated volatile species of Sb in this work was found to be (CH₃)₃Sb.

DNA-functionalized gold nanoparticles: Modification, characterization, and biomedical applications

With the development of technologies based on gold nanoparticles (AuNPs), bare AuNPs cannot meet the increasing requirements of biomedical applications. Modifications with different functional ligands are usually needed. DNA is not only the main genetic material, but also a good biological material, which has excellent biocompatibility, facile design, and accurate identification. DNA is a perfect ligand candidate for AuNPs, which can make up for the shortcoming of bare AuNPs. DNA-modified AuNPs (DNA-AuNPs) have exciting features and bright prospects in many fields, which have been intensively investigated in the past decade. In this review, we summarize the various approaches for the immobilization of DNA strands on the surface of AuNPs. Representative studies for biomedical applications based on DNA-AuNPs are also discussed. Finally, we present the challenges and future directions.

Fabrication of functional group-rich monoliths for magnetic field-assisted in-tube solid phase microextraction of inorganic selenium species in water samples followed by online chromatographic determination

Efficient separation and enrichment is a crucial step in the analysis of Se(IV) and Se(VI). In the present study, for the first time, online monolith-based magnetic field-assisted in-tube solid phase microextraction (MFA/IT-SPME) was applied to capture inorganic selenium species in water samples. To this aim, porous monoliths mixed with magnetic nanoparticles were synthesized in a silica capillary and employed as a microextraction column (MEC) for MFA/IT-SPME. After that, a magnetic coil utilized to induce variable magnetic fields in adsorption and desorption steps was entwined around the MEC. Se(IV) was coordinated with o-phenylenediamine to form a coordination compound that was infused onto the MEC to be captured. Results evidenced that application of magnetic field during the extraction procedure assisted the capture of the Se(IV)-OPA complex, with an enhancement in the extraction efficiency from 83% to 97%. Under the optimized conditions, MFA/IT-SPME was online combined with HPLC equipped with a diode array detector (DAD) to perform quantification of Se(IV) and Se(VI) in environmental water samples. Total inorganic Se was quantified after pre-reduction of Se(VI) to Se(IV) prior to applying the established approach, and a subtraction method was adopted to calculate the Se(VI) and Se(IV) contents. The limit of detection for Se(IV) was as low as 0.012 μg L^-1. The reliability of the suggested method was investigated by assaying Se(IV) and Se(VI) species in real-life water samples with satisfactory recoveries (81.1%-116%) and repeatability (RSDs below 9%).

Efficient entrapment of inorganic Se species in water and beer samples with functional groups-rich monolith-based adsorbent

An efficient multiple fibers solid phase microextraction method based on porous monolith was established for Se(IV) and Se(VI) analysis. Poly (4-vinylphenylboronic acid/styrene-co-ethylene dimethacrylate/divinylbenzene) monolith was fabricated and employed as the extraction phase for efficient entrapment of Se(IV) complexed with o-phenylenediamine, followed by elution with a methanol/FA (99/1.0, v/v) mixture and quantification by high performance liquid chromatography with diode array detector. The Se(VI) species was measured by the difference between total inorganic Se and Se(IV) after pre-reduction. Different characterization techniques were employed to inspect the structure and morphology of prepared adsorbent. A series of key extraction factors were optimized so as to achieve the expected extraction performance. Under the optimized separation and capture parameters, the linear range and limit of detection for Se(IV) in water sample were 0.050-200 μg/L and 0.013 μg/L, respectively. For beer sample, the corresponding values were 0.010-300 μg/L and 0.032 μg/L. The developed microextraction approach was successfully utilized to detect trace Se(IV) and Se(VI) in environmental water and beer samples with satisfactory fortified recovery and repeatability. Results well reveal the attractive merits of the established method in the analysis of Se species, including simple preparation of adsorbent, convenient extraction procedure, good sensitivity, high cost-effectiveness and eco-friendliness. This article is protected by copyright. All rights reserved.

Elemental Speciation Analysis in Environmental Studies: Latest Trends and Ecological Impact

Speciation analysis is a key aspect of modern analytical chemistry, as the toxicity, environmental mobility, and bioavailability of elemental analytes are known to depend strongly on an element’s chemical species. Henceforth, great efforts have been made in recent years to develop methods that allow not only the determination of elements as a whole, but also each of its separate species. Environmental analytical chemistry has not ignored this trend, and this review aims to summarize the latest methods and techniques developed with this purpose. From the perspective of each relevant element and highlighting the importance of their speciation analysis, different sample treatment methods are introduced and described, with the spotlight on the use of modern nanomaterials and novel solvents in solid phase and liquid-liquid microextractions. In addition, an in-depth discussion of instrumental techniques aimed both at the separation and quantification of metal and metalloid species is presented, ranging from chromatographic separations to electro-chemical speciation analysis. Special emphasis is made throughout this work on the greenness of these developments, considering their alignment with the precepts of the Green Chemistry concept and critically reviewing their environmental impact.

N-compounds speciation analysis in environmental samples using ultrasound-assisted solid-liquid extraction and non-chromatographic techniques

A fast, efficient, and non-chromatographic method was presented in this study for nitrite, nitrate, and p-nitrophenol (N-compounds) extraction and speciation analysis of environmental samples. By applying ultrasound-assisted solid-liquid extraction (USLE), analytes were efficiently extracted from water, soil, or sediment collected in areas of environmental disaster. These analytes were selectively converted to NO_(g) through UV photolysis (NO₃^-), H₂O₂/UV photocatalysis (PNP), and direct conversion (NO₂^-). Following conversion, NO_(g) was separated from the liquid phase and determined by high-resolution continuum source molecular absorption spectrometry (HR-CS MAS). The LODs obtained were 0.097 ± 0.004 mg L^-1 for nitrite, 0.119 ± 0.004 mg L^-1 for nitrate, and 0.090 ± 0.006 mg L^-1 for p-nitrophenol. On applying this speciation method to environmental samples, concentrations were found to be up to 0.99 ± 0.03 mg L^-1 (NO₂^-), 49.80 ± 2.5 mg L^-1 (NO₃^-), and 0.10 ± 0.02 mg L^-1 (PNP). Finally, addition/recovery study of real water, soil, and sediment samples showed 101 ± 2% recovery for NO₂^-, 100 ± 1% for NO₃^-, and 96 ± 5% for PNP.

Impact of Gas-Liquid Interface on Photochemical Vapor Generation

Interfacial effect has attracted increasing interest as the inherent asymmetric environment of a gas-liquid interface leads to different chemical and physical properties between this region and the bulk phase, resulting in enhanced chemical processes, specific reactions, and mass transfer at the interface. Photochemical vapor generation (PVG) is regarded as a simple and green sample introduction method in atomic spectrometry. However, the photochemical behavior of elements with the interface is not known. Herein, we report the PVG of elements at the gas-liquid interface along with a possible mechanism investigated for the first time. Enhancement and/or suppression effects from the gas-liquid interface were observed on the PVG of 17 elements, which was correlated with the properties of analytes and the generated intermediate substances/products of PVG and the applied conditions. Enhancement from 1.1- to 7.3-fold in analytical sensitivity was found for 12 elements in the system with gas-liquid interface(s) compared to the results obtained in previous reports of PVG using traditional flow injection with inductively coupled plasma mass spectrometry measurement. The introduction of gas-liquid interface(s) and the resultant elevated temperature inside the PVG reactor likely facilitated the generation of radicals, the subsequent radical-based reactions, and the separation/transport/detection of volatile species of elements. In contrast, intermediate substances/products generated in PVG with poor thermostability will readily decompose at elevated temperatures, leading to a decreased signal response of analytes. The finding is helpful to understand the transport of elements under UV irradiation in the environment and has potential for analysis of trace elements in environmental and biological samples.