Zwitterion-functionalized polymer microspheres-based solid phase extraction method on-line combined with HPLC–ICP-MS for mercury speciation

Towards a better understanding of ethylmercury in the environment: Addressing propylation derivatization artifact and verifying its occurrence in Chinese wetlands

Ethylmercury (EtHg), similar to methylmercury (MeHg), is highly neurotoxic and bioaccumulative. Although recent studies suggested its occurrence in natural soils and sediments, the common propylation derivatization for EtHg analysis might generate EtHg artifacts, potentially leading to its overestimation in environmental samples. Furthermore, the extensive environmental prevalence of EtHg remains unverified, keeping its importance largely uncertain. This study investigated the formation of EtHg artifacts during propylation derivatization, evaluating artifacts formation and recoveries under different extraction methods with real samples, and confirmed the widespread occurrence of EtHg in Chinese wetlands. EtHg artifacts were obviously present during the propylation derivatization and strongly dependent on the levels of Hg2+ (0.1-10 ng) in the derivatization solution (R² = 0.99), accounting for 1.38-2.14% of Hg2+. CuSO4-HNO3CH2Cl2 extraction (effectively removing Hg2+) combined with propylation derivatization offers excellent recovery (81-86%) and low artifacts (< LOD: 1.98 × 10-4 ng/g) for EtHg measurement in soils/sediments, with results aligning with those from online solid phase extraction-high performance liquid chromatography-inductively coupled plasma mass spectrometry (R2 = 0.99). Additionally, we observed the occurrence of EtHg in soil and sediment samples across 14 Chinese wetlands, with concentrations varying from 6.08 to 171 pg/g, similar to MeHg concentrations at some sites. EtHg positively correlates with MeHg, total Hg, and total organic carbon across all samples, indicating a possible biological formation. These findings help better understand and predict the prevalence of EtHg in wetlands and its key role in environmental Hg cycle.

Polymeric Materials in Speciation Analysis Based on Solid-Phase Extraction

Speciation analysis is a relevant topic since the (eco)toxicity, bioavailability, bio (geo)chemical cycles, and mobility of a given element depend on its chemical forms (oxidation state, organic ligands, etc.). The reliability of analytical results for chemical species of elements depends mostly on the maintaining of their stability during the sample pretreatment step and on the selectivity of further separation step. Solid-phase extraction (SPE) is a matter of choice as the most suitable and widely used procedure for both enrichment of chemical species of elements and their separation. The features of sorbent material are of great importance to ensure extraction efficiency from one side and selectivity from the other side of the SPE procedure. This review presents an update on the application of polymeric materials in solid-phase extraction used in nonchromatographic methods for speciation analysis.

Miniaturized point discharge optical emission spectrometry coupling with solid phase extraction: A robust approach for sensitive quantification of total mercury in mung bean sprout growth

In this work, a portable chemical vapor generation point discharge optical emission spectrometry (CVG-PD-OES) system was designed for trace Hg²⁺ monitoring in mung bean sprout samples. The system incorporated selective solid phase extraction (SPE) to enhance the detection sensitivity. Gold nanoparticles (AuNPs) were prepared and utilized to extract trace amounts of Hg²⁺ by forming gold amalgam. Subsequently, the amalgam was desorbed using 5% HCl and introduced into a low-power PD-OES system analysis via CVG. A low limit of detection (LOD) of 0.16 ng mL^-1 was obtained with a linear range of 0.5-6 ng mL^-1. The well-designed system was successfully utilized for monitoring trace Hg²⁺ in the growth of mung beans. The results indicated that the Hg²⁺ in mung bean sprouts was continuously decreased during growth based on the metabolism. Furthermore, the risk assessment conducted implied a negligible hazard quotient, suggesting that the observed levels of exposure posed minimal risk.

Strategies for mercury speciation with single and multi-element approaches by HPLC-ICP-MS

Mercury (Hg) and its compounds are highly toxic for humans and ecosystems, and their chemical forms determine both their behavior and transportation as well as their potential toxicity for human beings. Determining the various species of an element is therefore more crucial than understanding its overall concentration in samples. For this reason, several studies focus on the development of new analytical techniques for the identification, characterization, and quantification of Hg compounds. Commercially available, hyphenated technology, such as HPLC-ICP-MS, supports the rapid growth of speciation analysis. This review aims to summarize and critically examine different approaches for the quantification of mercury species in different samples using HPLC-ICP-MS. The steps preceding the quantification of the analyte, namely sampling and pretreatment, will also be addressed. The scenarios evaluated comprehend single and multi-element speciation analysis to create a complete guide about mercury content quantification.

Ultratrace mercury speciation analysis in rice by in-line solid phase extraction - liquid chromatography - atomic fluorescence spectrometry

For the first time, Hg²⁺ and methylmercury speciation analysis was accomplished by in-line SPE-LC-AFS. After modification with 0.1 mL of 0.001% (m:v) sodium diethyldithiocarbamate, a C₁₈ microcolumn retained Hg²⁺ and MetHg in rice extract within 3 min; the captured Hg species were separated within 12 min in 0.25% (v:v) 2-mercaptoethanol + 60 mmol L^-1 (m:v) ammonium acetate + 4% (v:v) acetonitrile. Under optimized conditions, the detection limits were 0.3 ng L^-1 for Hg²⁺ and 0.2 ng L^-1 for MetHg, respectively, with 10 mL injection vs. 0.1 mL eluent; in-line SPE achieved ∼ 100x enrichment. Method precision and accuracy were satisfactory at < 2% relative standard deviations (RSDs) for 20 ng L^-1 of Hg²⁺ and MetHg and 95-102% recoveries for real rice samples. In-line SPE obviated human involvement and avoided invalid transportation between interfaces, rendering this SPE-LC-AFS method easy, compact, robust, yet sensitive in mercury speciation analysis to uphold food safety.

Algal-based system for removal of emerging pollutants from wastewater: A review

The bioremediation of emerging pollutants in wastewater via algal biotechnology has been emerging as a cost-effective and low-energy input technological solution. However, the algal bioremediation technology is still not fully developed at a commercial level. The development of different technologies and new strategies to cater specific needs have been studied. The existence of multiple emerging pollutants and the selection of microalgal species is a major concern. The rate of algal bioremediation is influenced by various factors, including accidental contaminations and operational conditions in the pilot-scale studies. Algal-bioremediation can be combined with existing treatment technologies for efficient removal of emerging pollutants from wastewater. This review mainly focuses on algal-bioremediation systems for wastewater treatment and pollutant removal, the impact of emerging pollutants in the environment, selection of potential microalgal species, mechanisms involved, and challenges in removing emerging pollutants using algal-bioremediation systems.

Study of an adsorption method for trace mercury based on Bacillus subtilis

In order to decrease the difficulty in trace mercury determination, an adsorption method for trace mercury based on Bacillus subtilis cells was proposed in this article. The adsorption process was characterized by optical microscopy and SEM. The adsorption mechanism was analyzed by IR. The adsorption performance was studied by measuring the concentration of supernate and calculating the adsorption efficiency. When adsorbing Hg2+, Bacillus subtilis cells gathered and their structure turned coarse. The IR results illustrated that functional groups bound with Hg for complexation during adsorption. Bacillus subtilis completed adsorption for trace Hg2+ in 15 min. The adsorption efficiency was maintained above 80% under low Hg2+ concentrations (<200 µg/L). The proposed study illustrates that Bacillus subtilis cells are highly efficient and easily obtained material for the adsorption of trace mercury, which shows potential to be further used in the pretreatment of trace Hg2+ detection.

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.

A Microfluidic Aptamer-Based Sensor for Detection of Mercury(II) and Lead(II) Ions in Water

Heavy metal contaminants have serious consequences for the environment and human health. Consequently, effective methods for detecting their presence, particularly in water and food, are urgently required. Accordingly, the present study proposes a sensor capable of detecting mercury Hg(II) and lead Pb(II) ions simultaneously, using graphene oxide (GO) as a quenching agent and an aptamer solution as a reagent. In the proposed device, the aptamer sequences are labeled by FAM and HEX fluorescent dyes, respectively, and are mixed well with 500 ppm GO solution before injection into one inlet of the microchannel, and the heavy metal sample solution is injected into another inlet. The presence of Hg(II) and Pb(II) ions is then detected by measuring the change in the fluorescence intensity of the GO/aptamer suspension as the aptamer molecules undergo fluorescence resonance energy transfer (FRET). The selectivity of these two ions is also shown to be clear among other mixed heavy metal ions. The experimental results show that the aptamer sensors have a linear range of 10~250 nM (i.e., 2.0~50 ppb) for Hg(II) ions and 10~100 nM (i.e., 2.1~20.7 ppb) for Pb(II) ions. Furthermore, the limit of detection is around 0.70 ppb and 0.53 ppb for Hg(II) and Pb(II), respectively, which is lower than the maximum limits of 6 ppb and 10 ppb prescribed by the World Health Organization (WHO) for Hg(II) and Pb(II) in drinking water, respectively.

Techniques for the detection and quantification of emerging contaminants

In recent years, the diverse industrial practices and human inputs widely disseminated emerging contaminants (ECs) throughout environmental matrices, which is of great concern. Even at low concentrations, ECs pose major ecological problems and threaten human health and the environment’s biota. Consequently, people’s interest and concerns on the widespread dissemination of environmentally connected ECs of great concern as developed due to their scientific understanding, technical innovation, and socioeconomic awareness. Increased detection of contaminants may occur from climatic, socioeconomic, and demographic changes and the growing sensitivity of analytical techniques. Hence, this article reviews the determination of ECs in ecological specimens, from aquatic setup (river water, marine water, and wastewater), sludge, soil, sediment, and air. Sample collection and the quality measures are summarized. The preparation of samples, including extraction and cleanup and the subsequent instrumental analysis of ECs, are all covered. Traditional and recent extraction and cleanup applications to analyze ECs in samples are reviewed here in this paper. The detection and quantification of ECs using gas chromatography (GC) and liquid chromatography (LC) linked with various detectors, particularly mass spectrometry (MS), is also summarized and explored, as are other possible techniques. This study aims to give readers a more excellent knowledge of how new and improved approaches are being developed and serve as a resource for researchers looking for the best method for detecting ECs in their studies.

Sensitive Mercury Speciation Analysis in Water by High-Performance Liquid Chromatography-Atomic Fluorescence Spectrometry Coupling with Solid-Phase Extraction

An efficient method based on high-performance liquid chromatography coupled with atomic fluorescence spectrometry (HPLC-AFS) was successfully developed for the simultaneous determination of four mercury species including Hg²⁺, methylmercury (MeHg), ethylmercury (EtHg), and phenylmercury (PhHg) in water. Samples were enriched and cleaned up with a solid-phase extraction (SPE) pretreatment using a thiol cartridge. Some key parameters including the selection of a SPE cartridge, eluent type, eluent volume, and interference factors were systematically investigated. Chromatographic separation was achieved on a C₁₈ column using a mobile phase consisting of methanol and 60 mmol L^-1 ammonium acetate with 10 mmol L^-1 L-cysteine by gradient elution. Under the optimized conditions, good linearity (r ≥ 0.9991) was observed between 0.20 to 10.0 μg L^-1. The limits of detection were in the range of 0.001 - 0.002 μg L^-1. High recoveries (87.2 to 111%) and good reproducibility (1.1 - 6.5%) were obtained. Such a method is sensitive, selective and accurate, which can be applied to the quantification of mercury species in water samples.

Ultrasound-assisted dual-cloud point extraction with high-performance liquid chromatography-hydride generation atomic fluorescence spectrometry for mercury speciation analysis in environmental water and soil samples

A method for simultaneous preconcentration and determination of mercury species in water and soil samples was established using high-performance liquid chromatography with hydride generation atomic fluorescence spectrometry after ultrasound-assisted dual-cloud point extraction. The extraction process was divided into two steps. In the first cloud point extraction, inorganic mercury and methylmercury formed chelates with sodium diethyldithiocarbamate and were extracted into Triton X-114 micelles. In the second stage, a displacement reaction between sodium diethyldithiocarbamate-inorganic mercury/methylmercury and l-cysteine occurred, and the analytes entered the l-cysteine aqueous solution under ultrasonication. This aqueous solution was directly introduced to the high-performance liquid chromatography with hydride generation atomic fluorescence spectrometry and the detection was completed within 6 min. Under the optimum experimental conditions, the linear range was 0.10-5.0 μg/L (r ≥0.9993) for inorganic mercury and methylmercury, and the enhancement factors were 15.7 for inorganic mercury and 6.35 for methylmercury. The limits of detection for inorganic mercury and methylmercury were 0.004 and 0.016 μg/L, respectively. The approach was successfully applied to the determination of trace inorganic mercury and methylmercury in water and soil samples with good recoveries (85.3-110%). This method solved the problem of peak fusion of the two analytes and was successfully applied to the speciation analysis of mercury.

Preparation of environmental samples for chemical speciation of metal/metalloids: A review of extraction techniques

Chemical speciation is a relevant topic in environmental chemistry since the (eco)toxicity, bio (geo)chemical cycles, and mobility of a given element depend on its chemical forms (oxidation state, organic ligands, etc.). Maintaining the chemical stability of the species and avoiding equilibrium disruptions during the sample treatment is one of the biggest challenges in chemical speciation, especially in environmental matrices where the level of concomitants/interferents is normally high. To achieve this task, strategies based on chemical properties of the species can be carried out and pre-concentration techniques are often needed due to the low concentration ranges of many species (μg L^-1 - ng L^-1). Due to the significance of the topic and the lack of reviews dealing with sample preparation of metal (loid)s (usually, sample preparation reviews focus on the total metal content), this work is presented. This review gives an up-to-date overview of the most common sample preparation techniques for environmental samples (water, soil, and sediments), with a focus on speciation of metal/metalloids and determination by spectrometric techniques. Description of the methods is given, and the most recent applications (last 10 years) are presented.

Simultaneous enrichment of inorganic and organic species of lead and mercury in pg L-1 levels by solid phase extraction online combined with high performance liquid chromatography and inductively coupled plasma mass spectrometry

Quantification of ultra-trace inorganic and organic species of lead and mercury in unpolluted environmental water is crucial to estimate the mobility, toxicity and bioavailability and interactions. Simultaneous pre-concentration of Pb and Hg species in pg L^-1 levels followed by multi-elemental speciation analysis makes great sense to a large set of unstable samples because of time advantages. Herein simultaneous enrichment and speciation analysis of ultra-trace lead and mercury in water was developed by online solid-phase extraction coupled with high performance liquid chromatography and inductively coupled plasma mass spectrometry (SPE-HPLC-ICP-MS) for this aim. Pb(II), trimethyl lead (TML), triethyl lead (TEL), Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) were baseline separated in 11 min under gradient elution using 5 mM l-cysteine (Cys) at pH 2.5 in the 0-1 and 4-15 min and 5 mM Cys + 0.5 mM tetrabutyl ammonium hydroxide solution at pH 2.5 in the 1-4 min. Lead and mercury species in 10 mL intact water samples were adsorbed on a 1 cm C₁₈ enrichment column pre-conditioned with 10 mL of 1 mM 2-mercaptoethanol at 10 mL min^-1, and then directly desorbed by the mobile phases. High enrichment factors (459 for Pb(II), 1248 for TML, 1627 for TEL, 2485 for Hg(II), 1984 for MeHg and 1866 for EtHg) were obtained with good relative standard deviations (<5%), leading to low LODs (0.001-0.011 ng L^-1) and LOQs (0.004-0.036 ng L^-1). Good accuracy of this method was validated by two certified reference materials of total lead in water (GBW08601) and total mercury in water (GBW08603) along with spiked recoveries (89-93%). The method was applied to analyze trace lead and mercury species in river, lake, tap and rain water, and purified and mineral water. Inorganic lead of 13-68 ng L^-1 and inorganic mercury of 21-49 ng L^-1 were measured in the nine water samples whereas TML, TEL and MeHg were not detected with 2-5 ng L^-1 EtHg presented only in one river water and tap water.

Improving the Voltammetric Determination of Hg(II): A Comparison Between Ligand-Modified Glassy Carbon and Electrochemically Reduced Graphene Oxide Electrodes

A new thiosemicarbazone ligand was immobilized through a Cu(I)-catalyzed click reaction on the surface of glassy carbon (GC) and electrochemically reduced graphene oxide (GC-ERGO) electrodes grafted with phenylethynyl groups. Using the accumulation at open circuit followed by anodic stripping voltammetry, the modified electrodes showed a significant selectivity and sensibility for Hg(II) ions. A detection limit of 7 nM was achieved with the GC modified electrodes. Remarkably, GC-ERGO modified electrodes showed a significantly improved detection limit (0.8 nM), sensitivity, and linear range, which we attribute to an increased number of surface binding sites and better electron transfer properties. Both GC and GC-ERGO modified electrodes proved their applicability for the analysis of real water samples.

Speciation Analysis of Trace Arsenic, Mercury, Selenium and Antimony in Environmental and Biological Samples Based on Hyphenated Techniques

In order to obtain a well understanding of the toxicity and ecological effects of trace elements in the environment, it is necessary to determine not only the total amount, but also their existing species. Speciation analysis has become increasingly important in making risk assessments of toxic elements since the toxicity and bioavailability strongly depend on their chemical forms. Effective separation of different species in combination with highly sensitive detectors to quantify these particular species is indispensable to meet this requirement. In this paper, we present the recent progresses on the speciation analysis of trace arsenic, mercury, selenium and antimony in environmental and biological samples with an emphasis on the separation and detection techniques, especially the recent applications of high performance liquid chromatography (HPLC) hyphenated to atomic spectrometry or mass spectrometry.