Capillary electrophoresis on-line coupled with hydride generation-atomic fluorescence spectrometry for speciation analysis of selenium

An overview of the methods for analyzing the chemical forms of metals in plants

Currently, the occurrence of toxic levels of metals in soils is a serious environmental issue worldwide. Phytoremediation is getting much attention to control metals soil pollution because it is economic and environmentally friendly. However, the methods used to detect metals in plants are not uniform and have depicted poor comparability of the research investigations. Therefore, the present overview is designed to discuss the possible chemical forms of metals in various environmental matrixes and the detection methods employed to identify the chemical forms of metals in plants. Moreover, the in situ and indirect methods to detect metals in plants have also been discussed herein. In addition, the pros and cons of the available techniques have also been critically analyzed and discussed. Finally, key points/challenges and future perspectives of these methods have been highlighted for the scientific community.Novelty statementIn the current review, the possible chemical forms of metals in various environmental matrixes are discussed in detail. Various extraction agents and their efficiency for extracting metals from plants have been clearly illustrated. Further, all the available methods for analyzing the chemical forms of metals in plants have been compared.

Monitoring and analysis of selenium as an emerging contaminant in mining industry: A critical review

Selenium is an indispensable trace element for humans, however, its release at high concentrations becomes a major concern for terrestrial and aquatic ecosystems due to its bioaccumulation potential. Mining and metal-mineral processing are among the main sources of selenium released into the environment. Excessive levels of selenium may induce toxicity in human as selenosis, in grazing animals as alkali disease and in aquatic organisms as larval and developmental deformities and mortality. Due to the introduction of new policies for Se monitoring in the mining industry mainly setting the guidelines for selenium level in freshwaters as recommended by the Canadian Council of Ministers of Environment and Environment and climate change Canada, an improved understanding of Se occurrence, mobility, bioavailability and treatment technologies for efficient removal is timely and required. In this context, this review updated the understanding of mining-related selenium occurrence in surface water, soil and plant, with a focus on its mobility and bioavailability. Selenium uptake, translocation, accumulation, and metabolism in plants are further presented. Selenium monitoring and treatment is the key to adopt the corrective measures to mitigate highly contaminated effluent and to minimize the associated adverse health effects. Future research directions and recommendations for selenium analysis and treatment processes are also discussed.

Selenium analysis in waters. Part 2: Speciation methods

In aquatic ecosystems, there is often no correlation between the total concentration of selenium present in the water column and the toxic effects observed in that environment. This is due, in part, to the variation in the bioavailability of different selenium species to organisms at the base of the aquatic food chain. The first part of this review (Kumkrong et al., 2018) discusses regulatory framework and standard methodologies for selenium analysis in waters. In this second article, we are reviewing the state of speciation analysis and importance of speciation data for decision makers in industry and regulators. We look in detail at fractionation methods for speciation, including the popular selective sequential hydride generation. We examine advantages and limitations of these methods, in terms of achievable detection limits and interferences from other matrix species, as well as the potential to over- or under-estimate operationally-defined fractions based on the various conversion steps involved in fractionation processes. Additionally, we discuss methods of discrete speciation (through separation methods), their importance in analyzing individual selenium species, difficulties associated with their implementation, as well as ways to overcome these difficulties. We also provide a brief overview of biological treatment methods for the remediation of selenium-contaminated waters. We discuss the importance of selenium speciation in the application of these methods and their potential to actually increase the bioavailability of selenium despite decreasing its total waterborne concentration.

Sensitive, selective analysis of selenium oxoanions using microchip electrophoresis with contact conductivity detection

The common selenium oxoanions selenite (SeO3(2-)) and selenate (SeO4(2-)) are toxic at intake levels slightly below 1 mg day(-1). These anions are currently monitored by a variety of traditional analytical techniques that are time-consuming, expensive, require large sample volumes, and/or lack portability. To address the need for a fast and inexpensive analysis of selenium oxoanions, we present the first microchip capillary zone electrophoresis (MCE) separation targeting these species in the presence of chloride, sulfate, nitrate, nitrite, chlorate, sulfamate, methanesulfonate, and fluoride, which can be simultaneously monitored. The chemistry was designed to give high selectivity in nonideal matrices. Interference from common weak acids is avoided by operating near pH 4. Separation resolution from chloride was enhanced to improve tolerance of high-salinity matrices. As a result, selenate can be quantified in the presence of up to 1.5 mM NaCl, and selenite analysis is even more robust against chloride. Using contact conductivity detection, detection limits for samples with conductivity equal to the background electrolyte are 53 nM (4.2 ppb Se) and 380 nM (30 ppb) for selenate and selenite, respectively. Analysis time, including injection, is ∼2 min. The MCE method was validated against ion chromatography (IC) using spiked samples of dilute BBL broth and slightly outperformed the IC in accuracy while requiring <10% of the analysis time. The applicability of the technique to real samples was shown by monitoring the consumption of selenite by bacteria incubated in LB broth.

Efficient interface for online coupling of capillary electrophoresis with inductively coupled plasma-mass spectrometry and its application in simultaneous speciation analysis of arsenic and selenium

A simple and highly efficient online system coupling of capillary electrophoresis to inductively coupled plasma-mass spectrometry (CE-ICP-MS) for simultaneous separation and determination of arsenic and selenium compounds was developed. CE was coupled to an ICP-MS system by a sprayer with a novel direct-injection high-efficiency nebulizer (DIHEN) chamber as the interface. By using this interface, six arsenic species, including arsenite (As(III), arsenate (As(V)), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), and arsenocholine (AsC) and five selenium species (such as sodium selenite (Se(IV)), sodium selenate (Se(VI)), selenocysteine (SeCys), selenomethionine (SeMet), and Se-methylselenocysteine (MeSeCys)) were baseline-separated and determined in a single run within 9 min under the optimized conditions. Minimum dead volume, low and steady sheath flow liquid, high nebulization efficiency, and high sample transport efficiency were obtained by using this interface. Detection limits were in the range of 0.11-0.37 μg L(-1) for the six arsenic compounds (determined as (75)As at m/z 75) and 1.33-2.31 μg L(-1) for the five selenium species (determined as (82)Se at m/z 82). Repeatability expressed as the relative standard deviations (RSD, n = 6) of both migration time and peak area were better than 2.68% for arsenic compounds and 3.28% for selenium compounds, respectively. The proposed method had been successfully applied for the determination of arsenic and selenium species in the certified reference materials DORM-3, water, urine, and fish samples.

Speciation analysis of lead in marine animals by using capillary electrophoresis couple online with inductively coupled plasma mass spectrometry

We herein reported a environment-friendly microwave-assisted extraction used to extract trace lead compounds from marine animals and a ultrasensitive method for the analysis of Pb²⁺, trimethyl lead chloride (TML) and triethyl lead chloride (TEL) by using CE-ICP-MS. The extraction method is simple and has a high extracting efficiency. It can be used to completely extract both inorganic lead and organolead in marine animal samples without altering its species. The analytical method has a detection limit as low as 0.012-0.084 ng Pb/mL for Pb²⁺, TML, and TEL, and can be used to determine ultratrace Pb²⁺, TML, and TEL in marine animals directly without any preconcentration. With the help of above methods, we have successfully determined Pb²⁺, TML, and TEL in clam and oyster tissue within 20 min with a RSD (n = 6) < 5% and a recovery of 91-104%. Our results showed that Pb²⁺ was the main species of lead in clam and oyster, and organolead (TML) was only found in oyster. The proposed method provides a realistic approach for the accurate evaluation of lead pollution in seafood.

Determination of ultra-trace amounts of inorganic selenium species in natural water by ion chromatography-inductively coupled plasma-mass spectrometry coupled with nano-Al2O3 solid phase extraction

This work presents a nano-Al2O3 solid phase extraction technique for the determination of ultra-trace amounts of inorganic selenium species in aqueous systems using ion chromatography inductively coupled plasma-mass spectrometry (IC-ICP-MS). In this experiment, the inorganic selenium species were successfully extracted on a nano-Al2O3 solid phase column and then quantitative eluted with a 100 mmol L−1 NaOH solution. Extraction conditions such as solvent identity, solvent concentration, solvent volume, solvent pH and salt addition were optimized. Under the optimum extraction conditions (elute solvent: 100 mmol L−1 NaOH, solvent volume: 4 mL, pH: 7.0), low detection limits (Se (IV): 6 ng L−1, Se (VI): 11 ng L−1; RSD−1, R2 &gt; 0.999) were obtained for all of the analytes. Good spiked recoveries over the range of 80–98% were obtained by applying the proposed method on real environmental water samples. These results indicated that this method is very sensitive and reliable when monitoring trace levels of inorganic selenium species in aqueous samples.

Ultrasonic extraction of arsenic and selenium from rocks associated with mountaintop removal/valley fills coal mining: Estimation of bioaccessible concentrations

Ultrasonic extraction (UE) was used to estimate the total bioaccessible fractions of arsenic and selenium released from rocks associated with mountaintop removal/valley fill coal mining. The combined readily bioaccessible amounts of arsenic and selenium in water soluble, exchangeable and NaOH fractions can be extracted from the solid phase within a 20 or 25 min application of 200 W cm(-2) ultrasound energy in nanopure water for selenium and arsenic, respectively. Application of a two-way ANOVA predicted that there are no significant differences (p0.001, n=12) in the extracted arsenic and selenium concentrations between the combined bioaccessible and ultrasonic extracts. The mechanisms for the UE of arsenic and selenium are thought to involve the formation of secondary minerals on the particle surfaces which eventually dissolve with continued sonication. This is supported by the presence of transient Si-O stretching and OH absorption and bending ATR-FTIR peaks at 795.33 cm(-1), 696.61 cm(-1) and 910.81 cm(-1). The subsequent dissolution of secondary minerals is followed by the release of chemical species that include selenium and arsenic. Release rates decrease after the ultrasound energy elastic limit for the particles is reached. Selenium and arsenic are bound differently within the rock lattice because no selenium was detected in the acid soluble fraction and no arsenic was found in the exchangeable fraction. However, selenium was found in the exchangeable fraction and arsenic was found in the acid soluble fraction. The characterization of coal associated rocks is essential to the design of methodologies and procedures that can be used to control the release of arsenic and selenium from valley fills.

Organic and inorganic selenium speciation in environmental and biological samples by nanometer-sized materials packed dual-column separation/preconcentration on-line coupled with ICP-MS

A novel, fast, and cheap nonchromatographic method for direct speciation of dissolved inorganic and organic selenium species in environmental and biological samples was developed by flow injection (FI) dual-column preconcentration/separation on-line coupled with ICP-MS determination. In the developed technique, the first column packed with nanometer-sized Al(2)O(3) could selectively adsorb the inorganic selenium [Se(IV), Se(VI)], and the retained inorganic selenium could be eluted by 0.2 mol l(-1) NaOH, while the organic Se [selenocystine (SeCys(2)) and selenomethionine (Se-Met)] was not retained. On the other hand, the second column packed with mesoporous TiO(2) chemically modified by dimercaptosuccinic acid (DMSA) could selectively adsorb Se(IV) and SeCys(2) and barely adsorb Se(VI) and Se-Met. When the sample solution was passed through the column 1, separation of inorganic selenium and organic selenium could be achieved first. Then, the effluent from column 1 was successively introduced into the column 2 and the speciation of organic selenium could be attained due to the different adsorption behaviors of Se-Met and SeCys(2) on DMSA modified TiO(2). After that, the eluent from column 1 contained Se(IV), and Se(VI) was adjusted to desired pH and injected into column 2, and the speciation of Se(IV) and Se(VI) could also be realized thanks to their different retention on column 2. The parameters affecting the separation were investigated systematically and the optimal separation conditions were established. The detection limits obtained for Se(IV), Se(VI), Se-Met and SeCys(2) were 45-210 ng l(-1) with precisions of 3.6-9.7%. The proposed method has been successfully applied for the speciation of dissolved inorganic and organic selenium in environmental and biological samples. In order to validate the methodology, the developed method was also applied to the speciation of selenium in certified reference material of SELM-1 yeast, and the determined values were in good agreement with the certified values.

Recent trends in CE of inorganic ions: From individual to multiple elemental species analysis

The major methodological developments in CE related to inorganic analysis are overviewed. This is an update to a previous review article by the author (Timerbaev, A. R., Electrophoresis 2004, 25, 4008-4031) and it covers the review work and innovative research papers published between January 2004 and the first part of 2006. As was underlined in that review, a growing interest of analytical community in providing elemental speciation information found a sound response of the CE method developers. Presently, almost every second research paper in the field of interest deals with element species analysis, the use of inductively coupled plasma MS detection and biochemical applications being the topics of utmost research efforts. On the other hand, advances in general methodology traditionally centered on a CE system modernization for improvements in sensitivity and separation selectivity have attracted less attention over the review period. While there is no indication that inorganic ion applications would surpass by the developmental rate the more matured analysis of organic analytes, CE can now be seen as an analytical technique to be before long customary in a number of inorganic analysis arenas.

Determination of copper(I) and copper(II) ions after complexation with bicinchoninic acid by CE

A facile, sensitive, and selective method was developed for the simultaneous separation and determination of copper(I) [Cu(+)] and copper(II) [Cu(2+)] ions using CE with direct UV detection. The copper ions were complexed with a 1.5 mM bicinchoninic acid disodium salt solution at pH 8.7 prior to analysis. Acetate buffer (2 mM) was used as the CE running buffer. Parameters affecting CE separation such as sample pH, applied voltage, concentration of complexing agent, nature of the buffer solution, and interferences by other metal ions, were evaluated. The LODs for Cu(+) and Cu(2+) were 3.0 and 2.5 microg/mL (S/N = 3), respectively. The developed method allows the simultaneous determination of Cu(+) and Cu(2+) in less than 5 min with RSDs of between 5.3 and 9.5% for migration time and between 3.4 and 9.7% for peak areas, respectively. At optimum conditions, the percentage recoveries of Cu(+) and Cu(2+) were found to be 99.4 and 99.5%.

Speciation analysis of arsenic and selenium compounds in environmental and biological samples by ion chromatography-inductively coupled plasma dynamic reaction cell mass spectrometer

An inductively coupled plasma mass spectrometer (ICP-MS) was used as an ion chromatographic (IC) detector for the speciation analysis of arsenic and selenium. The arsenic and selenium species studied included arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), selenite [Se(IV)] and selenate [Se(VI)]. Gradient elution using (NH4)2CO3 and methanol at pH 9 allowed the chromatographic separation of all species in less than 12 min. Effluents from the IC column were delivered to the nebulization system of ICP-DRC-MS for the determination of arsenic and selenium. The potentially interfering 38Ar 40Ar+ and 40Ar 40Ar+ at the selenium masses m/z 78 and 80 were reduced in intensity by approximately 3 orders of magnitude by using 0.6 mL min(-1) CH4 as reactive cell gas in the DRC while an Rpq value of 0.3 was used. Meanwhile, arsenic was determined as the adduct ion 75As 12CHH+ at m/z 89, which is more sensitive than 75As. The limits of detection for arsenic and selenium were in the range of 0.002-0.01 ng mL(-1) and 0.01-0.02 ng mL(-1), respectively, based on peak height. The relative standard deviation of the peak areas for five injections of 5 ng mL(-1) As and Se mixture was in the range of 2-4%. The concentrations of arsenic and selenium species have been determined in urine samples collected locally. The major As and Se species in urines were AsB, DMA and probably selenosugar at concentration of 20-40, 15-19 and 17-31 ng mL(-1), respectively. The recoveries were in the range of 94-105% for all the determinations. This method has also been applied to determine various arsenic compounds in two fish samples. In this study, a simple and rapid microwave-assisted extraction method was used for the extraction of arsenic compounds from fish. The arsenic species were quantitatively leached with an 80% v/v methanol solution in a focused microwave field during a period of 5 min.

Speciation of inorganic selenium using capillary electrophoresis–inductively coupled plasma-atomic emission spectrometry with on-line hydride generation

A novel and simple hydride generator has been developed. The hydride generator has good stability and high gas liquid separation efficiency. The generator serves as an interface of capillary electrophoresis (CE) and inductively coupled plasma atomic emission spectrometry (ICP-AES). This device eliminates the nebulization step and overcomes the common problem of suction flow resulting from the use of nebulization gas in ICP. Selenium compounds that were separated by CE were converted into the corresponding volatile hydrides, followed by ICP-AES measurement. The effects of the concentration of the hydride generating reagents (HCl and NaBH4), the carrier gas flow rate, and heavy metal interference on Se emission intensity were discussed. The relative standard deviations (RSDs) of peak area, based on six determinations of 50 ng mL(-1) standard of Se(IV) and Se(VI), were 1.5% and 1.8%, respectively. The detection limits (3sigma) of peak area were 2.1 ng mL(-1) and 2.3 ng mL(-1) for Se(IV) and Se(VI), respectively. Speciation analysis of inorganic Se(IV) and Se(IV) species using the HG-CE-ICP-AES system was demonstrated in tap and river water samples.

On-line hyphenation of flow injection, miniaturized capillary electrophoresis and atomic fluorescence spectrometry for high-throughput speciation analysis

A hyphenated technique was developed for high-throughput speciation analysis by on-line coupling of flow injection (FI), miniaturized capillary electrophoresis (CE) and atomic fluorescence spectrometry (AFS). Two interfaces were used to couple all three systems: the first to couple FI and CE and the second to couple miniaturized CE and AFS. The first interface was a modified flow through chamber, connected to the FI valve with a piece of PTFE tube (0.1mm i.d.x 20 cm long). The capillary outlet was coupled to the AFS by using the second concentric "tube-in-tube" interface. Split sampling was achieved in the electrokinetic mode. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were taken as model analytes to demonstrate the performance of the developed hyphenated technique. A volatile species generation (VSG) technique was employed to convert the analytes from the CE effluent into their respective volatile species. Baseline separation of Hg(II) and MeHg(I) was achieved by CE in a 50 microm i.d.x 8 cm long capillary at 3.0 kV within 60s. The precisions (RSD, n=12) were in the range of 0.7-0.9% for migration time, 3.8-4.2% for peak area, and 2.1-3.5% for peak height. The detection limits were 0.1 and 0.2 microgmL(-1) (as Hg) for Hg(II) and MeHg(I) with a sample throughput of 60 samples h(-1). The recoveries of both mercury species in the water samples studied were in the range of 93-106%.

Recent advances in capillary electrophoresis and capillary electrochromatography of pollutants

Recent advances in the CE and CEC separation, detection, and sample preparation methodologies applied to the determination of a variety of compounds having current or potential environmental relevance have been overviewed. The reviewed literature has illustrated the wide range of CE applications, indicating the continuing interest in CE and CEC in the environmental field.