Trace metal determination in natural waters by automated solid phase extraction system and ICP-MS: The influence of low level Mg and Ca

Highly Blue-fluorescent Carbon Quantum Dots Obtained from Medlar Seed for Hg2+ Determination in Real Water Samples

The carbon quantum dots (CQDs) have been prepared from medlar seeds with pyrolysis method in an oven at 300 °C. UV-vis absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR) spectroscopy, x-ray diffraction (XRD) technique, x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were used in the characterization of CQDs. CQDs, give a strong blue fluorescence under UV lamp (at 365 nm), have a quantum yield of 12.2%. The influence of metal ions such as K+, Mg2+, Ca2+, Be2+, Cr3+, Mn2+, Ni2+, Ag+, Hg2+, and Al3+ on the fluorescence properties of the CQDs was investigated by means of emission spectrophotometry. CQDs altering fluorescence characteristics depending on the excitation wavelength show selectivity for Hg2+ ions with outstanding fluorescence quenching among the tested metal ions. Based on these results, a new fluorimetric method has been developed for the determination of Hg2+ in real water samples. The linear range of method is 1.0 to 5.0 mgL- 1. Limit of detection and limit of quantification are 0.26 and 0.79 mgL- 1, respectively. The proposed method has been successfully used in determination of Hg2+ ions in tap, sea, and stream water samples with application of addition-recovery experiments.

Low-cost modular chromatography column rack and vial holders

Gravity-driven chromatography columns are used in scientific, engineering, medical, and industrial fields to separate desired compounds from solutions. Running multiple columns simultaneously saves time and improves procedural consistency. Though column chromatography is widely used, to meet their laboratory needs many investigators must resort to designing and fabricating custom racks for holding their chromatography columns. We have created a robust column rack design, with collection vial holders, that is easily made, inexpensive to build, and may be easily adapted to fit experimental needs. The column holder can be made to hold various sizes of columns (and can be interchanged as necessary); the height of columns above collection vials can be precisely set; and the design is modular, so the rack and vial holders can be expanded to accommodate the desired numbers of columns and the numbers and sizes of vials used to collect fractions eluted from each column. Importantly, the rack is made of inexpensive, readily-available materials and the fabrication is straightforward. Here we present details of the rack's features, a list of materials, and instructions for making it. We hope our design will help investigators who perform gravity-driven column chromatography.

Peroxidase-Mimicking DNAzymes as Receptors for Label-Free Discriminating Heavy Metal Ions by Chemiluminescence Sensor Arrays

Receptors are crucial to the analytical performance of sensor arrays. Different from the previous receptors in sensor arrays, herein, peroxidase-mimicking DNAzymes were innovatively used as receptors to develop a label-free chemiluminescence sensor array for discriminating various heavy metal ions in complex samples. The peroxidase-mimicking DNAzymes are composed of functional oligonucleotides and hemin, including G-triplex-hemin DNAzyme (G3-DNAzyme), G-quadruplex-hemin DNAzyme (G4-DNAzyme), and the dimer of G-quadruplex-hemin DNAzyme (dG4-DNAzyme). Circular dichroism (CD) spectroscopy demonstrated that different metal ions diversely affect the conformation of G-quadruplex and G-triplex, resulting in a change in the activity of peroxidase-mimicking DNAzyme. Thus, the unique fingerprints formed to easily discriminate seven kinds of heavy metal ions by principal component analysis (PCA) within 20 min. The discrimination of unknown metal ions in tap water further confirmed its ability for discriminating multiple heavy metal ions. Moreover, it will not bring water pollution due to the good biocompatibility of DNA. Therefore, it not only merely offers a label-free, rapid, environment-friendly, and cheap (1.49 $) sensor assay for discriminating metal ions but also comes up with an innovative way for developing sensor arrays.

Automated rapid solid-phase extraction system for separation and preconcentration of trace elements using carboxymethylated polyethyleneimine-type chelating resin

An automated system for the rapid separation and preconcentration of trace elements was developed. Carboxymethylated polyethyleneimine 600 (CM-PEI600), which is a partially carboxymethylated polyethyleneimine with a molecular weight of 600 Da, was used as a chelating resin to quantitatively recover trace elements under high-flow-rate conditions. For accurately and precisely determining trace elements, even with a rough control of the sample and eluent flow volumes, an internal standardization technique was employed for the solid-phase extraction and separation. A recovery test of the deionized water-based sample solution was conducted using this system, and good results, with a recovery of 92% or higher, were obtained for 11 elements (Cd, Co, Cu, Fe, Mn, Mo, Ni, Pb, Ti, V, and Zn). Eight elements present in certified groundwater and wastewater reference materials (ES-L-1 and EU-L) were separated and preconcentrated using this system. Almost all the determined values were within their tolerance intervals, and no significant differences were observed between the determined and certified values, demonstrating the validity of this method. The time required for the separation and preconcentration using approximately 100 mL of the sample solution was approximately 6.5 min, and theoretically, the system could be used to preconcentrate 17 samples in an hour because extraction and elution could be conducted simultaneously using two cartridges packed with the chelating resin. Using this system equipped with cartridges packed with CM-PEI600 resin, solid-phase extraction and the separation of multiple elements were performed simultaneously, automatically, and rapidly, enabling the accurate and precise determination of trace elements in environmental water and inorganic salts even by rapidly flowing the sample solutions using peristaltic pumps. Compared to NOBIAS Chelate PA-1, a commercially available chelating resin, the CM-PEI600 resin can recover trace elements even under an extremely high flow rate of approximately 50 mL min^-1.

A dual-channel visual sensing system for recognition of multiple metal ions

Here, we propose a simple, rapid, and effective colorimetric sensor array for discrimination of metal ions. The sensor array was constructed using two sensing channels, i.e., gold nanoparticles (AuNPs)- Tetramethylbenzidine (TMB)-H₂O₂ and AuNPs-O-phenylenediamine (OPD)-H₂O₂ reaction systems. The presence of metal ions with positive charges would lead to the corresponding surface charge change of negatively charged AuNPs, resulting in diverse catalytic performances of citrate-modified AuNPs, accompanied by a substantial colorimetric performance of oxidation products of TMB and OPD. Employing the diversity of colorimetric responses of metal ions to the two sensing channels, nine metal ions including Cr³⁺, Fe³⁺, Cu²⁺, Co²⁺, Ni²⁺, Pb²⁺, Mg²⁺, K⁺, and Cd²⁺ were well distinguished with a discrimination accuracy of 100% at a concentration as low as 50 nM. Further experiment showed that the sensor array was also capable of discriminating and quantifying metal ions at various concentrations, as well as the identification of metal ion mixtures. The feasibility of the sensor array was also verified by the successful identification of the nine metal ions in river water samples.

Carbon Quantum Dots Based Chemosensor Array for Monitoring Multiple Metal Ions

The simultaneous identification of multiple metal ions in water has attracted enormous research interest in the past few decades. We herein describe a novel method for multiple metal ion detection using a carbon quantum dots (CQDs)-based chemosensor array and the CQDs are functionalized with different amino acids (glutamine, histidine, arginine, lysine and proline), which act as sensing elements in the sensor array. Eleven metal ions are successfully identified by the designed chemosensor array, with 100% classification accuracy. Importantly, the proposed method allowed the quantitative prediction of the concentration of individual metal ions in the mixture with the aid of a support vector machine (SVM). The sensor array also enables the qualitative detection of unknown metal ions under the interference of tap water and local river water. Thus, the strategy provides a novel high-throughput approach for the identification of various analytes in complex systems.

The impact of seasonal and event-based infiltration on transition metals (Cu, Ni, Co) in tropical cave drip water

RATIONALE

The first-row transition metals Cu, Ni, and Co show a strong binding affinity to natural organic matter. Compared to dissolved elements and stable water isotopes, they may be transported rapidly through the soil and host rock into caves in response to infiltration events. This study aims to assess the potential of transition metal ratios as indicators for infiltration changes in response to the seasonal and/or event-based rainfall variation.

METHODS

We developed a protocol to analyze Cu, Ni, and Co in the cave drip water using collision cell ICP-QMS without extensive sample pretreatment. The high Ca matrix leads to significant isobaric interferences on all isotope masses. Our method includes a correction of these matrix effects and yields results with comparable accuracy and reproducibility to other published methods. We applied this protocol to drip water samples from Larga Cave (Puerto Rico) covering at least two full annual cycles between 2014 and 2019 on a bimonthly scale.

RESULTS

The analysis of external reference materials yielded a reproducibility between 4.7% and 9.2% (relative standard deviation), validating the accuracy of the matrix correction method. The limit of detection is <0.04 ppb for Cu, <0.02 ppb for Ni, and <0.008 ppb for Co. The analysis of drip water samples from Larga Cave reveals pronounced changes of several orders of magnitude in all Element (El) to Ca, Cu/Ni, and Cu/Co ratios in response to seasonal infiltration changes. In addition, we observe a partly even stronger response after major tropical storms and heavy precipitation events of the period of record, for example, tropical storm "Bertha" (2014) and the category 5 hurricanes "Irma" and "Maria" (both 2017).

CONCLUSIONS

Transition metal ratios can be accurately measured in cave drip waters with high Ca matrix. At our tropical site, these are promising tracers of infiltration changes in response to changes in the amount of rainfall, providing the first step toward tropical cyclone reconstruction using trace elements in speleothems.

Development of a fully automatic separation system coupled with online ICP-MS for measuring rare earth elements in seawater

Rare earth elements (REEs) are useful geological indicators of marine geochemistry. However, extremely low concentrations (sub-ng L⁻¹) and high-salt matrices result in inefficient measurements. A fully automatic separation system (ELSPE-2 Precon) is used in the online determination of ultra-trace REEs in seawater using inductively coupled plasma mass spectrometry. This system mainly comprises three sections: (i) an auto-sampler (eas-2A) with 120 positions; (ii) a poly(styrene-divinylbenzene) resin column (Prin-Cen Col007) with iminodiacetic and ethylenediaminetriacetic acid functional groups to eliminate the high-salt matrix (e.g., Na, Ca, K, Mg, Al, Ba, Fe, Sr, P, and S) and preserve the target REEs; and (iii) a Trp002 cleanup column for the reduction of the reagent and procedural blank values. The detection limits (3σ) were in the range 0.002 (Dy)–0.097 ng L⁻¹ (La), and the long-term reproducibility (8 h) was between 80% and 120% for all REEs in a 3.5% NaCl matrix solution. The accuracy of this method was verified using a seawater reference material (NASS-6), and the measured REE concentrations were consistent with those previously reported. The proposed online system was used to investigate coastal water samples with varying salinities from the Pearl River Estuary (Guangdong, China). Variations in the REE distribution patterns of different layers of seawater were observed, which could be due to the mixing of potentially light rare earth element-enriched bottom seawater. Moreover, a positive Gd anomaly in river water and seawater might be attributed to anthropogenic pollution from hospitals and the pharmaceutical industry.

A new fully automatic separation system coupled with online ICP-MS for measuring rare earth elements in seawater.

Determination of Rare Earth Elements in Pore Water Samples of Marine Sediments Using an Offline Preconcentration Method

The concentrations of dissolved yttrium and rare earth elements (REY) in sediment pore water provide important geochemical information. However, due to the low REY concentration, complex matrix, and limited sample volume (often only a few milliliters), analysis of the REY in pore water often is highly challenging. In this study, a method was established to determine the dissolved REY in pore water of marine sediments using an offline preconcentration step with the ethylenediaminetriacetate chelating resin, followed by inductively coupled plasma-mass spectrometry. In addition, using a commercially available automated trace-element preconcentration system, the preconcentration step can be fully automated, saving labor and providing a better control of the final elution volume. The experimental conditions (pH, elution volume, elution acid concentration, and organic complexation effect) were assessed, and the optimal conditions were chosen. In particular, the organic complexation effect was found to be negligible. The procedure blank and limit of detection were satisfactory for studying REY in pore water of marine sediments, and the method also yielded satisfactory recoveries for the REY elements (83-110%). The method was then applied to analyze the dissolved REY concentrations of pore water samples collected in a sediment core (~ 30 cm) in the central Indian Ocean. The vertical distribution, dissolved REY concentration, and the average Post Archean Australian Shale-normalized pattern of the REY showed similarities to the previously published pore water REY data. This method provides an accurate yet facile approach for the analysis of all 15 REY in marine pore water samples using the sample volume of only ~ 5 mL.

Metatranscriptomics of the bacterial community in response to atmospheric deposition in the Western North Pacific Ocean

Atmospheric deposition represents a major vector of both macro- and micro-nutrients to the oligotrophic open oceans, potentially imposing a profound impact on the functioning of the microbial community. Whereas bacterial responses to atmospheric deposition are being studied at the community level, corresponding functional changes are essentially unknown. Here we conducted a microcosm experiment coupled with metatranscriptomic analyses to elucidate taxonomic and functional profiles of the bacterial community in response to East Asian aerosols in the Western North Pacific Ocean (WNPO). While the abundance of heterotrophic bacteria showed a minor change, cyanobacterial cell count number decreased dramatically, with Prochlorococcus and Synechococcus counts reduced by 83.2% and 21.5% in the aerosol treatment in relation to the control. Expression of transcripts related with Prochlorococcus, Synechococcus, Trichodesmium and Crocosphaera both were lower in the treatment (5.7%, 2.3%, 0.5% and 0.02%, respectively) than in the control (18.6%, 2.7%, 9.8% and 0.14%, respectively). Aerosol addition led to an increase in transcripts involved in iron metabolism (tonB, feoB, irr, exbB), indicating Fe limitation. Heavy metal toxicity was evidenced by an elevated expression of resistance genes, such as czcC, czcB, czcA and a probable Co/Zn/Cd efflux protein, and a range of genes functioning against oxidative stress. Our findings provide insights into an inhibitory effect of high-flux East Asian aerosols on cyanobacteria in the WNPO likely due to Fe scavenging and heavy metal toxicity.

Separation of 44Sc from Natural Calcium Carbonate Targets for Synthesis of 44Sc-DOTATATE

The rapid increase in applications of scandium isotopes in nuclear medicine requires new efficient production routes for these radioisotopes. Recently, irradiations of calcium in cyclotrons by α, deuteron, and proton beams have been used. Therefore, effective post-irradiation separation and preconcentration of the radioactive scandium from the calcium matrix are important to obtain the pure final product in a relatively small volume. Nobias resin was used as a sorbent for effective separation of ⁴⁴Sc from calcium targets. Separation was performed at pH 3 using a column containing 10 mg of resin. Scandium was eluted with 100 μL of 2 mol L⁻¹ HCl. Particular attention was paid to the reduction of calcium concentration, presence of metallic impurities, robustness and simple automation. ⁴⁴Sc was separated with 94.9 ± 2.8% yield, with results in the range of 91.7–99.0%. Purity of the eluate was confirmed with ICP-OES determination of metallic impurities and >99% chelation efficiency with DOTATATE, followed by >36 h radiochemical stability of the complex. A wide range of optimal conditions and robustness to target variability and suspended matter facilitates the proposed method in automatic systems for scandium isotope separation and synthesis of scandium-labeled radiopharmaceuticals.

Characteristics of trace metals and phosphorus in seawaters offshore the Yangtze River

This study presents the spatial distribution of total dissolved Cu, Zn, Co, and V during an autumn survey in the East China Sea (ECS). Dissolved Fe and its organic complexation were also investigated. The present study aimed to evaluate the relationship between Cu, Zn, Co, V, D-Fe and its organic ligands and total dissolved phosphate (TDP) in the coastal waters of the ECS. A correlation analysis shows that Cu, Zn and D-Fe were nutrient-like metals, whereas Co and V were non-nutrient-like metals. A multivariate statistical analysis showed that TDP was associated with D-Fe, Cu, Zn and Co, but was not associated with V. Furthermore, TDP was observed to be positively related with D-Fe, while negatively with Fe', which indicated that the limitation of TDP decreased the uptake of Fe'. This paper improves our understanding of the association among trace metals, TDP and phytoplankton biomass in the ECS.

Effects of Trace Metal Concentrations on the Growth of the Coral Endosymbiont Symbiodinium kawagutii

Symbiodinium is an indispensable endosymbiont in corals and the most important primary producer in coral reef ecosystems. During the past decades, coral bleaching attributed to the disruption of the symbiosis has frequently occurred resulting in reduction of coral reef coverage globally. Growth and proliferation of corals require some specific trace metals that are essential components of pertinent biochemical processes, such as in photosynthetic systems and electron transport chains. In addition, trace metals are vital in the survival of corals against oxidative stress because these metals serve as enzymatic cofactors in antioxidative defense mechanisms. The basic knowledge about trace metal requirements of Symbiodinium is lacking. Here we show that the requirement of Symbiodinium kawagutii for antioxidant-associated trace metals exhibits the following order: Fe >> Cu/Zn/Mn >> Ni. In growth media with Cu, Zn, Mn, and varying Fe concentrations, we observed that Cu, Zn, and Mn cellular quotas were inversely related to Fe concentrations. In the absence of Cu, Zn, and Mn, growth rates increased with increasing inorganic Fe concentrations up to 1250 pM, indicating the relatively high Fe requirement for Symbiodinium growth and potential functional complementarity of these metals. These results demonstrate the relative importance of trace metals to sustain Symbiodinium growth and a potential metal inter replacement strategy in Symbiodinium to ensure survival of coral reefs in an oligotrophic and stressful environment.

Trace metal determination as it relates to metallosis of orthopaedic implants: Evolution and current status

In utilising metal surfaces that are in constant contact with each other, metal-on-metal (MoM) surgical implants present a unique challenge, in the sense that their necessity is accompanied by the potential risk of wear particle generation, metal ion release and subsequent patient toxicity. This is especially true of orthopaedic devices that are faulty and subject to failure, where the metal surfaces undergo atypical degradation and release even more unwanted byproducts, as was highlighted by the recent recall of orthopaedic surgical implants. The aim of this review is to examine the area of metallosis arising from the wear of MoM articulations in orthopaedic devices, including how the surgical procedures and detection methods have advanced to meet growing performance and analytical needs, respectively.

Green approach for ultratrace determination of divalent metal ions and arsenic species using total-reflection X-ray fluorescence spectrometry and mercapto-modified graphene oxide nanosheets as a novel adsorbent

A new method based on dispersive microsolid phase extraction (DMSPE) and total-reflection X-ray fluorescence spectrometry (TXRF) is proposed for multielemental ultratrace determination of heavy metal ions and arsenic species. In the developed methodology, the crucial issue is a novel adsorbent synthesized by grafting 3-mercaptopropyl trimethoxysilane on a graphene oxide (GO) surface. Mercapto-modified graphene oxide (GO-SH) can be applied in quantitative adsorption of cobalt, nickel, copper, cadmium, and lead ions. Moreover, GO-SH demonstrates selectivity toward arsenite in the presence of arsenate. Due to such features of GO-SH nanosheets as wrinkled structure and excellent dispersibility in water, GO-SH seems to be ideal for fast and simple preconcentration and determination of heavy metal ions using methodology based on DMSPE and TXRF measurement. The suspension of GO-SH was injected into an analyzed water sample; after filtration, the GO-SH nanosheets with adsorbed metal ions were redispersed in a small volume of internal standard solution and deposited onto a quartz reflector. The high enrichment factor of 150 allows obtaining detection limits of 0.11, 0.078, 0.079, 0.064, 0.054, and 0.083 ng mL(-1) for Co(II), Ni(II), Cu(II), As(III), Cd(II), and Pb(II), respectively. Such low detection limits can be obtained using a benchtop TXRF system without cooling media and gas consumption. The method is suitable for the analysis of water, including high salinity samples difficult to analyze using other spectroscopy techniques. Moreover, GO-SH can be applied to the arsenic speciation due to its selectivity toward arsenite.

An off-line automated preconcentration system with ethylenediaminetriacetate chelating resin for the determination of trace metals in seawater by high-resolution inductively coupled plasma mass spectrometry

A novel automated off-line preconcentration system for trace metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in seawater was developed by improving a commercially available solid-phase extraction system SPE-100 (Hiranuma Sangyo). The utilized chelating resin was NOBIAS Chelate-PA1 (Hitachi High-Technologies) with ethylenediaminetriacetic acid and iminodiacetic acid functional groups. Parts of the 8-way valve made of alumina and zirconia in the original SPE-100 system were replaced with parts made of polychlorotrifluoroethylene in order to reduce contamination of trace metals. The eluent pass was altered for the back flush elution of trace metals. We optimized the cleaning procedures for the chelating resin column and flow lines of the preconcentration system, and developed a preconcentration procedure, which required less labor and led to a superior performance compared to manual preconcentration (Sohrin et al.). The nine trace metals were simultaneously and quantitatively preconcentrated from ∼120 g of seawater, eluted with ∼15 g of 1M HNO3, and determined by HR-ICP-MS using the calibration curve method. The single-step preconcentration removed more than 99.998% of Na, K, Mg, Ca, and Sr from seawater. The procedural blanks and detection limits were lower than the lowest concentrations in seawater for Mn, Ni, Cu, and Pb, while they were as low as the lowest concentrations in seawater for Al, Fe, Co, Zn, and Cd. The accuracy and precision of this method were confirmed by the analysis of reference seawater samples (CASS-5, NASS-5, GEOTRACES GS, and GD) and seawater samples for vertical distribution in the western North Pacific Ocean.