Hollow fiber based liquid-phase microextraction for the determination of mercury traces in water samples by electrothermal atomic absorption spectrometry

Ionic Organic Network-based C3-symmetric@Triazine core as a selective Hg+2 sensor

The C3-symmetry ionic polymer PPyTri has been designed with multi-walled carbon nanotubes (MWCNTs) or graphene nanoplatelets (GNPs) and studied as an ultrasensitive electrochemical sensor for trace Hg(II) detection. The synthesis approach incorporated attaching three pyridinium cationic components with chloride anions to the triazine core. The precursors, BPy, were synthesized using a condensation process involving 4-pyridine carboxaldehyde and focused nicotinic hydrazide. The polymer PPyTri was further modified with either MWCNTs or GNPs. The resulting ionic polymer PPyTri and its fabricated nanocomposites were characterized using infrared (IR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and powder X-ray diffraction (XRD). The analysis revealed that both the polymer and its nanocomposites have semi-crystalline structures. The electroactivity of the designed nanocomposites toward Hg + 2 ions revealed that among the nanocomposites and bare copolymer, the glassy carbon electrode (GCE) adapted with the PPyTri GNPs-5% exhibited the greatest current response over a wide range of Hg + 2 concentrations. The nanocomposite-modified electrode presented an excellent sensitivity of 83.33 µAµM - 1 cm - 2, a low detection limit of 0.033 nM, and a linear dynamic range of 0.1 nM to 0.01 mM (R2 = 0.9945).

Determination of Hg(II) and Methylmercury by Electrothermal Atomic Absorption Spectrometry after Dispersive Solid-Phase Microextraction with a Graphene Oxide Magnetic Material

The toxicity of all species of mercury makes it necessary to implement analytical procedures capable of quantifying the different forms this element presents in the environment, even at very low concentrations. In addition, due to the assorted environmental and health consequences caused by each mercury species, it is desirable that the procedures are able to distinguish these forms. In nature, mercury is mainly found as Hg⁰, Hg²⁺ and methylmercury (MeHg), with the latter being rapidly assimilated by living organisms in the aquatic environment and biomagnified through the food chain. In this work, a dispersive solid-phase microextraction of Hg²⁺ and MeHg is proposed using as the adsorbent a magnetic hybrid material formed by graphene oxide and ferrite (Fe₃O₄@GO), along with a subsequent determination by electrothermal atomic absorption spectrometry (ETAAS). On the one hand, when dithizone at a pH = 5 is used as an auxiliary agent, both Hg(II) and MeHg are retained on the adsorbent. Next, for the determination of both species, the solid collected by the means of a magnet is suspended in a mixture of 50 µL of HNO₃ (8% v/v) and 50 µL of H₂O₂ at 30% v/v by heating for 10 min in an ultrasound thermostatic bath at 80 °C. On the other hand, when the sample is set at a pH = 9, Hg(II) and MeHg are also retained, but if the solid collected is washed with N-acetyl-L-cysteine only, then the Hg(II) remains on the adsorbent, and can be determined as indicated above. The proposed procedure exhibits an enrichment factor of 49 and the determination presents a linear range between 0.1 and 10 µg L^-1 of mercury. The procedure has been applied to the determination of mercury in water samples from different sources.

A Critical Study of the Effect of Polymeric Fibers on the Performance of Supported Liquid Membranes in Sample Microextraction for Metals Analysis

Popularity of hollow fiber-supported liquid membranes (HF-SLM) for liquid-phase microextraction (HF-LPME) has increased in the last decades. In particular, HF-SLM are applied for sample treatment in the determination and speciation of metals. Up to the date, optimization of preconcentration systems has been focused on chemical conditions. However, criteria about fiber selection are not reflected in published works. HFs differ in pore size, porosity, wall thickness, etc., which can affect efficiency and/or selectivity of chemical systems in extraction of metals. In this work, Ag+ transport using tri-isobutylphosphine sulfide (TIBPS) has been used as a model to evaluate differences in metal transport due to the properties of three different fibers. Accurel PP 50/280 fibers, with a higher effective surface and smaller wall thickness, showed the highest efficiency for metal transport. Accurel PP Q3/2 exhibited intermediate efficiency but easier handling and, finally, Accurel PP S6/2 fibers, with a higher wall thickness, offered poorer efficiency but the highest stability and capability for metal speciation. Summarizing, selection of the polymeric support of HF-SLM is a key factor in their applicability of LPME for metals in natural waters.

A handling-free methodology for rapid determination of Cu species in seawater based on direct solid micro-samplers analysis by high-resolution continuum source graphite furnace atomic absorption spectrometry

A very simple, sensible and advanced new methodology for the determination of copper species in seawater has been developed. The method consisted of two steps: first a separation/preconcentration of copper species by using liquid phase microextraction-based solvent bars followed by the direct analysis of these solid polymeric micro-samplers in an atomic absorption spectrometer provided with a device for direct analysis. For liquid microextraction, di-2-pyridylketone benzoylhydrazone (dPKBH) dissolved in octan-1-ol was selected as the extracting agent due to its ability to transport inorganic Cu species from seawater samples. The optimum chemical and physical conditions for copper micro-extraction were sample pH 8, a dPKBH concentration of 0.010 mol L^-1, a stirring speed of 800 rpm and an extraction time of 10 min. A graphite furnace temperature program was optimised to assure the complete elimination of the solvent bar matrix, and the atomisation step took place at 2200 °C. The method exhibited a limit of detection of 0.026 μg L^-1 of copper and a linear range up to 1.50 μg L^-1, showing great repeatability and reproducibility (4.07% and 4.43%, respectively). Suitability of the method was confirmed by analysing a certified reference material (CASS-4) under optimum conditions, being the first time ever that a direct solid analysis-based method has been used for the determination of total dissolved copper concentration in seawater. Furthermore, the method was applied to the determination of the operationally defined transportable Cu fraction in seawater samples at natural conditions and the results were compared with theoretical data provided by Visual MINTEQ® 3.1 software. A mathematical model that permits to estimate total dissolved copper concentration was obtained, and the non-transportable copper fraction was calculated by difference.

Ratiometric fluorometric determination of mercury(II) by exploiting its quenching effect on glutathione-stabilized and tetraphenylporphyrin modified gold nanoclusters

A ratiometric fluorometric assay for mercury(II) ion is described. It is making use of glutathione-stabilized gold nanoclusters (GSH-AuNCs) modified with tetraphenylporphyrin tetrasulfonic acid (TPPS). The resultant GSH-AuNC/TPPS nanocomposite displays dual emission (at 572 and 664 nm) under a single excitation wavelength of 365 nm. Mercury(II) ion intensively quenches the yellow fluorescence of GSH-AuNCs (peaking at 572 nm) but has a negligible effect on the red fluorescence of TPPS (at 664 nm). The ratio of fluorescence intensities at 572 and 664 nm drops linearly with Hg(II) ion concentration in the 0.02-2.0 μmol·L^-1 range, and the detection limit is 7 nmol·L^-1 (3s_b/S). The relative standard deviation (RSD) of the assay is 2.0% at a 0.5 μmol·L^-1 concentration level (n = 11). The method was successfully applied to the determination of Hg(II) ion in spiked water samples, with recoveries within the range of 87.5-107.5%. Graphical abstract Ratiometric fluorescence detection of mercury(II).

A simple gold nanoplasmonic SERS method for trace Hg2+ based on aptamer-regulating graphene oxide catalysis

The as-prepared graphene oxide (GO) exhibited a strong catalytic effect on reduction of HAuCl₄ by trisodium citrate to form gold nanoplasmons (AuNPs) with a strong surface-enhanced Raman scattering (SERS) effect at 1615 cm^-1 in the presence of molecular probe Victoria blue 4R (VB4r). SERS intensity increased with nanocatalyst GO concentration due to the formation of more AuNP substrates. The aptamer (Apt) of Hg²⁺ can bind to GO to form Apt-GO complexes, which can strongly inhibit nanocatalysis. When target Hg²⁺ is present, the formed stable Hg²⁺ -Apt complexes are separated from the GO surface, which leads to GO catalysis recovery. The enhanced SERS signal was linear to Hg²⁺ concentration in the range 0.25-10 nmol/L, with a detection limit of 0.08 nmol/L Hg²⁺ . Thus, a new gold nanoplasmon molecular spectral analysis platform was established for detecting Hg²⁺ , based on Apt regulation of GO nanocatalysis.

Colorimetric detection of Hg(II) by measurement the color alterations from the "before" and "after" RGB images of etched triangular silver nanoplates

It is shown that triangular silver nanoplates (TAgNPs) are viable colorimetric probes for the fast, sensitive and selective detection of Hg(II). Detection is accomplished by reducing Hg(II) ions to elemental Hg so that an Ag/Hg amalgam is formed on the surface of the TAgNPs. This leads to the inhibition of the etching TAgNPs by chloride ions. Correspondingly, a distinct color transition can be observed that goes from yellow to brown, purple, and blue. The color alterations extracted from the red, green, and blue part of digital (RGB) images can be applied to the determination of Hg(II). The relationship between the Euclidean distances (EDs), i.e. the square roots of the sums of the squares of the ΔRGB values, vary in the 5 nM to 100 nM Hg(II) concentration range, and the limit of detection is as low as 0.35 nM. The color changes also allow for a visual estimation of the concentrations of Hg(II). The method is simple in that it only requires a digital camera for data acquisition and a Photoshop software for extracting RGB variations and data processing. Graphical abstract Hg²⁺ detection was achieved by anti-etching of TAgNPs caused by the formation of silver amalgam, along with vivid multicolor variations from yellow to brown, purple, and eventually to be blue.

Mercaptosuccinic acid-coated NIR-emitting gold nanoparticles for the sensitive and selective detection of Hg2

A sensitive fluorescent detection platform for Hg²⁺ was constructed based on mercaptosuccinic acid (MSA) coated near-infrared (NIR)-emitting gold nanoparticles (AuNPs). The thiolated mercaptosuccinic acid was employed as both reducing agent and surface coating ligand in a one-step synthesis of NIR-emitting AuNPs (MSA-AuNPs), which exhibited stable fluorescence with the maximum wavelength at 800nm and a wide range of excitation (220-650nm) with the maxima at 413nm. The MSA coated NIR-emitting AuNPs showed a rapid fluorescence quenching toward Hg²⁺ over other metal ions with a limit of detection (LOD, 3δ) as low as 4.8nM. The sensing mechanism investigation revealed that the AuNPs formed aggregation due to the "recognition" of Hg²⁺ from the MSA, and the resultant strong coupling interaction between Hg²⁺ and Au (I) to further quench the fluorescence of the AuNPs, which synergistically resulted in a highly sensitive and selective fluorescence response toward Hg²⁺. This proposed strategy was also demonstrated the possibility to be used for Hg²⁺ detection in water samples.

Synthesis of novel AIEE active pyridopyrazines and their applications as chromogenic and fluorogenic probes for Hg2+ detection in aqueous media

A series of AIEE active novel pyridopyrazine derivatives showing selective and sensitive detection of Hg²⁺ in aqueous media is reported.

Development of paper-based chemosensor for the detection of mercury ions using mono- and tetra-sulfur bearing phenanthridines

A new sulfur-bearing phenanthridine probes were synthesized and examined for their cation recognition abilities towards different cations in aqueous ACN solution and paper strips.

A New Microextraction Technique for the Assay of Alkaloids in Chinese Compound Formula-Based Polyether Sulfone Membrane Fiber Decorated by TiO2 Nanoparticles

A new nanocomposite membrane was used to clean up impurities from complex samples and the obvious synergy was obtained in this paper. The nanocomposite membrane was prepared by dispersing TiO2 nanoparticles in chloroform and filled in the pores and lumen of polyether sulfone membrane fiber. The novel microextraction method showed the ideal selective extraction effect for alkaloids in the formulae composed of Rhizoma coptidis and the excellent clean-up efficiency compared with the single membrane method. The optimum extraction conditions were as follows: chloroform as accepted phase; the number of nanocomposite membrane fiber bars, 7; extraction time, 30 min; pH of the sample solution, 10.55; desorption solvent, methanol. The limit of detection for the described alkaloids was estimated at 0.122 μg mL-1. The recovery of the four alkaloids in complex samples ranged from 93.24% to 97.94% with relative standard deviation of <4.99 (n = 5). The validated method had been successfully applied to study the transfer rate of alkaloids in the producing process of Qihuang capsule and the ideal transfer rate of alkaloids was obtained in this paper.

Application of hollow fiber liquid phase microextraction and dispersive liquid–liquid microextraction techniques in analytical toxicology

The recent developments in hollow fiber liquid phase microextraction and dispersive liquid –liquid microextraction are reviewed. Applications of these newly emerging developments in extraction and preconcentration of a vast category of compounds including heavy metals, pesticides, pharmaceuticals and abused drugs in complex matrices (environmental and biological matrices) are reviewed and discussed. The new developments in these techniques including the use of solvents lighter than water, ionic liquids and supramolecular solvents are also considered. Applications of these new solvents reduce the use of toxic solvents and eliminate the centrifugation step, which reduces the extraction time.

Ionic-liquid-based hollow-fiber liquid-phase microextraction method combined with hybrid artificial neural network-genetic algorithm for speciation and optimized determination of ferro and ferric in environmental water samples

A novel and environmentally friendly ionic-liquid-based hollow-fiber liquid-phase microextraction method combined with a hybrid artificial neural network (ANN)-genetic algorithm (GA) strategy was developed for ferro and ferric ions speciation as model analytes. Different parameters such as type and volume of extraction solvent, amounts of chelating agent, volume and pH of sample, ionic strength, stirring rate, and extraction time were investigated. Much more effective parameters were firstly examined based on one-variable-at-a-time design, and obtained results were used to construct an independent model for each parameter. The models were then applied to achieve the best and minimum numbers of candidate points as inputs for the ANN process. The maximum extraction efficiencies were achieved after 9 min using 22.0 μL of 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6MIM][PF6]) as the acceptor phase and 10 mL of sample at pH = 7.0 containing 64.0 μg L(-1) of benzohydroxamic acid (BHA) as the complexing agent, after the GA process. Once optimized, analytical performance of the method was studied in terms of linearity (1.3-316 μg L(-1), R (2) = 0.999), accuracy (recovery = 90.1-92.3%), and precision (relative standard deviation (RSD) <3.1). Finally, the method was successfully applied to speciate the iron species in the environmental and wastewater samples.

Mercury(II) determination in commercial cosmetics and local Thai traditional medicines by flow injection spectrophotometry

OBJECTIVE

The proposed method was developed for the enhancement of sensitivity for Hg(II) determination using dithizone by adding SDS in the presence of ascorbic acid in sulphuric acid medium.

METHOD

The method was based on the reaction between Hg(II) and 1,5-diphenylthiocarbazone (dithizone), in the presence of sodium dodecyl sulphate (SDS) as an anionic surfactant (to avoid solvent extraction) and ascorbic acid in a slightly acidic medium resulting in a soluble orange coloured Hg(II)-dithizone complex which gave the maximum absorption at 490 nm. No extraction system was required in this method.

RESULT

Under the optimum conditions, a linear calibration graph was obtained over the concentration range of 0.05-1.50 μg mL(-1). The method was characterized by a limit of detection (LOD, defined as 3σ) and limit of quantification (LOQ, defined as 10σ) of 0.03 and 0.14 μg mL(-1), respectively. The relative standard deviations for replicate injection were 1.32 and 0.78% (n = 11) for 0.05 and 0.20 μg mL(-1) of Hg(II) standard solutions, respectively. The developed method has been satisfactorily applied for Hg(II) determination in commercial cosmetics and local Thai traditional medicines. Results obtained by the proposed method are compared favourably with those analysed by ICP-MS.

CONCLUSION

Enhancement of sensitivity and rapidity for Hg(II) assay by FIA could be achieved by adding SDS in ascorbic acid. The method would be useful for routine analysis of Hg(II) in real samples.