Magnetic dispersive micro solid-phase extraction for trace mercury pre-concentration and determination in water, hemodialysis solution and fish samples

Excellent capture of Pb(II) and Cu(II) by hierarchical nanoadsorbent Fe3O4@SiO2@PAA-SO3H: A combined experimental and theoretical study

A novel magnetic nanoadsorbent (Fe₃O₄@SiO₂@PAA-SO₃H) was synthesized by grafting acrylic acid and sulfonic group to Fe₃O₄@SiO₂ using a facile cross-link technology. The adsorbent presented water-stability and biocompatibility in wastewater, which exhibited high-selectivity capture for Pb(II) and Cu(II) of 182.5 mg/g and 250.7 mg/g, respectively, at pH 6.0. Furthermore, the adsorption-desorption processes show that nanoadsorbent still retains high uptake capacity after 6 cycles, revealing structural stability and advanced recycling. Effects from other ions existed weak interference in removal of Pb(II) and Cu(II). Meanwhile, the mechanism was further analyzed from both electrostatic potential (ESP) and average local ionization energy (ALIE) based on the density functional theory (DFT). The results indicate that interaction among nanoadsorbent and heavy metal ions is bridged by oxygen active sites. As the Fe₃O₄@SiO₂@PAA-SO₃H adsorbent is a hierarchical, highly water-dispersible and biocompatible adsorbent, it is a potential new treatment option for wastewater.

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.

Magnetic Dispersive Solid Phase Extraction Using Recycled-graphite for GO-Fe3O4-dithizone Composite Combined with FAAS for Determination of Lead in Environmental Samples

Magnetic dispersive solid phase extraction (MdSPE) was developed to determine the concentration of lead (Pb) in real water samples, while graphene oxide-magnetite-dithizone (GO-Fe₃O₄-DTZ) from the used graphite tubes (recycled graphite) of electrothermal technique was simply employed as a new sorbent to improve extraction efficiency, separated by external magnetic field and analyzed with FAAS. The synthesized sorbent was evaluated for its surface property, functional group and surface morphology by Zeta potential, Fourier transform infrared spectrophotometer (FTIR), and scanning electron microscope (SEM), respectively. The relevant measurement parameters, such as pH, extraction time, type and concentration of eluent, sample volume and reusability, were optimized. Under the optimal conditions, preconcentration factor was 13.33. The limit of detection (LOD) and limit of quantitation (LOQ) obtained were 0.070 and 0.23 mg/L, respectively. The relative standard deviation (%RSD) was 3.41%. Recovery values were 90.1 - 123%. In addition, the robustness of the method was affirmed in terms of tolerance limit obtained from interference studies.

Use of 2-Hydrazinobenzothiazole-Modified Copolymer(s) as Potential Chelating Agent for Sensitive and Selective Determination of Low Levels of Mercury in Seafood by Ultrasound-Assisted Cloud-Point Extraction Combined with Spectrophotometry

In this study, a new method was developed for the pre-concentration of trace mercury from seafood samples prior to analysis by spectrophotometry. The method is based on the complexation between 2-hydrazinobenzothiazole (2-HBT)-modified copolymer(s) and Hg(II) in the presence of an ionic surfactant, cetyltrimethylammonium bromide (CTAB), as sensitivity enhancer at pH 4.5 and the extraction of the complex into the surfactant-rich phase of polyethylene glycol tert-octylphenyl ether (Triton X-114) as the extractant. The variables affecting extraction efficiency were evaluated and optimized. Due to the observation that the modified copolymers are 2.5-fold more sensitive and selective to the Hg²⁺ ions than the CH₃Hg⁺, the amounts of free Hg²⁺ and total Hg were determined at 325 nm by spectrophotometric detection of free Hg²⁺ and total Hg in the pre-treated and extracted fish samples using dilute acid mixture containing Triton X-114 and K₂Cr₂O₇, before and after oxidation of CH₃Hg⁺ to Hg²⁺ with mixture of KBr and KBrO₃ in the acidic media. The amount of CH₃Hg⁺ was calculated from the difference between total Hg and free Hg²⁺ amounts. The accuracy was tested by analysis of two certified samples. The results were statistically in good agreement with the certified values, and the precision was lower than 6.4%. The limits of detection were 1.40 (1.58) and 1.91 (2.11) μg L^-1 for Hg²⁺ from the two calibration solutions spiked before the pre-treatment, respectively. It has been observed that there is no significant matrix effect by comparison of slopes of the calibration curves. The method was applied to seafood samples for speciation analysis of free Hg²⁺ and CH₃Hg⁺. In terms of speciation, while total Hg is detected in the range of 12.6-143.8 μg kg^-1, the distribution of mercury in seafood was in the range of 7.4-53.3 μg kg^-1 for CH₃Hg⁺ and in 8.3-90.5 μg kg^-1 for free Hg²⁺.

Reliable quantification of mercury in natural waters using surface modified magnetite nanoparticles

Reliable determination of mercury (Hg) in natural waters is a major analytical challenge due to its low concentration and to the risk of Hg losses or contamination during sampling, storage and pre-treatment of samples. The present work proposes a simple, efficient, sensitive and easy-handling methodology for extraction, pre-concentration and quantification of total dissolved mercury in natural waters, using iron oxide nanoparticles (NPs) coated with silica shells functionalized with dithiocarbamate groups (Fe₃O₄@SiO₂SiDTC). Ten mg L^-1 of these NPs were sufficient to remove 83-97% of 500 to 10 ng L^-1 of Hg in ultra-pure water and artificial seawater, used as model Hg solutions, within 24 h. Mercury sorbed to the NPs was then measured directly by thermal decomposition atomic absorption spectrometry with gold amalgamation. The detection limit of approximately 1.8 ng L^-1 is lower than the values reported in dispersive solid phase extraction for other magnetic sorbents. As a proof-of-concept, the proposed methodology was successfully tested in real samples of fresh and saline waters and more than 91% of Hg was recovered. With this methodology the extraction and pre-concentration steps may be carried out in situ decreasing the risk of Hg losses or contamination during sampling, storage and pre-treatment of water samples.

Selective magnetic mercury(ii) ion capturing ligand-doped silica gel for water analysis

This study demonstrates a simplified method for the synthesis of a magnetic adsorbent, which is selective towards the adsorption of mercury(ii) ions (Hg²⁺).