Evaluation and applications of a gaseous mercuric chloride source

In this study, a diffusion-type device for generating gaseous mercuric chloride (HgCl₂) was systematically evaluated and applied to validate the annular denuder method for sampling gaseous HgCl₂ species in a synthetic gas stream. The results show that it takes at least 48 h for the system to reach a steady-state condition after the diffusion cell reaches the temperature set-point and the carrier gas is activated. The primary Hg species from the source was proven to be HgCl₂. In the temperature range from –5.00 to 11.80 °C, the Hg emission rates from the source vary from 1.8 to 14.2 pg min^–1. It is shown that, under the experimental conditions examined, KCl-coated annular quartz denuders designed for ambient reactive gaseous mercury (RGM) collection could quantitatively collect HgCl₂. It is also demonstrated that the impactors used to remove coarse airborne particulate matter could lead to a loss of up to one third of the HgCl₂ in the gas stream.     

High-precision measurement of mercury isotope ratios in sediments using cold-vapor generation multi-collector inductively coupled plasma mass spectrometry

An on-line Hg reduction technique using stannous chloride as the reductant was applied for accurate and precise mercury isotope ratio determinations by multi-collector (MC)-ICP/MS. Special attention has been paid to ensure optimal conditions (such as acquisition time and mercury concentration) allowing precision measurements good enough to be able to significantly detect the anticipated small differences in Hg isotope ratios in nature. Typically, internal precision was better than 0.002% (1 RSE) on all Hg ratios investigated as long as approximately 20 ng of Hg was measured with a 10-min acquisition time. Introducing higher amounts of mercury (50 ng Hg) improved the internal precision to <0.001%. Instrumental mass bias was corrected using ²⁰⁵Tl/²⁰³Tl correction coupled to a standard-sample bracketing approach. The large number of data acquired allowed us to validate the consistency of our measurements over a one-year period. On average, the short-term uncertainty determined by repeated runs of NIST SRM 1641d Hg standard during a single day was <0.006% (1 RSD) for all isotope pairs investigated (²⁰²Hg/¹⁹⁸Hg, ²⁰²Hg/¹⁹⁹Hg, ²⁰²Hg/²⁰⁰Hg, and ²⁰²Hg/²⁰¹Hg). The precision fell to <0.01% if the long-term reproducibility, taken over 11 months (over 100 measurements), was considered. The extent of fractionation has been investigated in a series of sediments subject to various Hg sources from different locations worldwide. The ratio ²⁰²Hg/¹⁹⁸Hg expressed as δ values (per mil deviations relative to NIST SRM 1641d Hg standard solution) displayed differences from +0.74 to −4.00‰. The magnitude of the Hg fractionation per amu was constant within one type of sample and did not exceed 1.00‰. Considering all results (the reproducibility of Hg standard solutions, reference sediment samples, and the examination of natural samples), the analytical error of our δ values for the overall method was within ±0.28‰ (1 SD), which was an order of magnitude lower than the extent of fractionation (4.74‰) observed in sediments. This study confirmed that analytical techniques have reached a level of long-term precision and accuracy that is sufficiently sensitive to detect even small differences in Hg isotope ratios that occur within one type of samples (e.g., between different sediments) and so far have unequivocally shown that Hg isotope ratios in sediments vary within approximately 5‰.     

Isotopic fractionation of mercury induced by reduction and ethylation

Isotope ratio measurements characterizing ²⁰²Hg/²⁰⁰Hg in NIST SRM 3133 Mercury Standard Solution were undertaken by multicollector inductively coupled plasma mass spectrometry employing NIST SRM 997 Tl for mass bias correction by use of the slope and the intercept obtained from a natural logarithmic plot of each session of measurements of ²⁰²Hg/²⁰⁰Hg against ²⁰⁵Tl/²⁰³Tl. The calculated value of 1.285333 ± 0.000192 (mean and one standard deviation, n = 40) for the mass bias corrected ²⁰²Hg/²⁰⁰Hg was then used for mass bias correction of other Hg isotope pairs. Ratios of 0.015337 ± 0.000011, 1.68770 ± 0.00054, 2.3056 ± 0.0015, 1.3129 ± 0.0013, 2.9634 ± 0.0038, and 0.67937 ± 0.0013 (expanded uncertainty, k = 2) were obtained for ¹⁹⁶Hg/¹⁹⁸Hg, ¹⁹⁹Hg/¹⁹⁸Hg, ²⁰⁰Hg/¹⁹⁸Hg, ²⁰¹Hg/¹⁹⁸Hg, ²⁰²Hg/¹⁹⁸Hg, and ²⁰⁴Hg/¹⁹⁸Hg, respectively. Reduction of Hg(II) to Hg⁰ in solutions of SRM 3133 was then undertaken using SnCl₂, NaBH₄, UV photolysis in the presence of formic acid, and ethylation of Hg(II) using NaBEt_4. These reactions induced significant isotope fractionation with maximum values of 1.17 ± 0.07, 1.08 ± 0.09, 1.34 ± 0.07, and 3.59 ± 0.09‰ (one standard deviation, 1SD, n = 5) for δ ^202/198Hg relative to the initial isotopic composition in the solution following 85–90% reduction of the Hg by SnCl₂, NaBH₄, UV photolysis, and ethylation with NaBEt₄, respectively. Mass-dependent fractionation was found to be dominant for all reduction processes. Figure Mass dependence of fractionation for all samples from Hg fractionation experiments using NaBEt₄. Solid lines are the theoretically predicted MDF based on δ′ ^202/198 Hg using equation 7. Error bars displayed are one standard deviation of the mean of 5 measurements of each sample     

Development of pre-concentration procedure for the determination of Hg isotope ratios in seawater samples

Hg concentrations in seawater are usually too low to allow direct (without pre-concentration and removal of salt matrix) measurement of its isotope ratios with multicollector-inductively coupled plasma mass spectrometry (MC-ICP-MS). Therefore, a new method for the pre-concentration of Hg from large volumes of seawater was developed. The final method allows for relatively fast (about 2.5 L h⁻¹) and quantitative pre-concentration of Hg from seawater samples with an average Hg recovery of 98 ± 6%. Using this newly developed method we determined Hg isotope ratios in seawater. Reference seawater samples were compared to samples potentially impacted by anthropogenic activity. The results show negative mass dependent fractionation relative to the NIST 3133 Hg standard with δ²⁰²Hg values in the range from −0.50‰ to −1.50‰. In addition, positive mass independent fractionation of ²⁰⁰Hg was observed for samples from reference sites, while impacted sites did not show significant Δ²⁰⁰Hg values. Although the influence of the impacted sediments is limited to the seawater and particulate matter in very close proximity to the sediment, this observation may raise the possibility of using Δ²⁰⁰Hg to distinguish between samples from impacted and reference sites.     

Hg stable isotope analysis by the double-spike method

Recent publications suggest great potential for analysis of Hg stable isotope abundances to elucidate sources and/or chemical processes that control the environmental impact of mercury. We have developed a new MC-ICP-MS method for analysis of mercury isotope ratios using the double-spike approach, in which a solution containing enriched ¹⁹⁶Hg and ²⁰⁴Hg is mixed with samples and provides a means to correct for instrumental mass bias and most isotopic fractionation that may occur during sample preparation and introduction into the instrument. Large amounts of isotopic fractionation induced by sample preparation and introduction into the instrument (e.g., by batch reactors) are corrected for. This may greatly enhance various Hg pre-concentration methods by correcting for minor fractionation that may occur during preparation and removing the need to demonstrate 100% recovery. Current precision, when ratios are normalized to the daily average, is 0.06‰, 0.06‰, 0.05‰, and 0.05‰ (2σ) for ²⁰²Hg/¹⁹⁸Hg, ²⁰¹Hg/¹⁹⁸Hg, ²⁰⁰Hg/¹⁹⁸Hg, and ¹⁹⁹Hg/¹⁹⁸Hg, respectively. This is slightly better than previously published methods. Additionally, this precision was attained despite the presence of large amounts of other Hg isotopes (e.g., 5.0% atom percent ¹⁹⁸Hg) in the spike solution; substantially better precision could be achieved if purer ¹⁹⁶Hg were used.     

A fluorescent chemical sensor for Hg(II) based on a corrole derivative in a PVC matrix

A fluorescent chemical sensor for Hg(II) using 5,10,15-tris(pentafluorophenyl)corrole (H₃(tpfc)) as fluorophore is described in this paper. The response of the sensor is based on the fluorescence quenching of H₃(tpfc) by coordination with Hg(II). H₃(tpfc) based sensor shows a linear response towards Hg(II) in the concentration range from 1.2 × 10⁻⁷ to 1.0 × 10⁻⁴ M, with a working pH range from 5.0 to 8.0. The response time for Hg(II) concentration ≤1.0 × 10⁻⁵ M is less than 5 min. The sensor shows good selectivity for Hg(II) over alkali, and alkaline earth, and most of transition metal cations. The effect of the composition of the sensor membrane has been studied and the experimental conditions optimized. The corrole based sensor membrane can be easily regenerated just by washing with blank buffer solution after each measurement. The sensor has been used for determination of Hg(II) in water samples with satisfactory results.     

A functionalized gold nanoparticles and Rhodamine 6G based fluorescent sensor for high sensitive and selective detection of mercury(II) in environmental water samples

A gold-nanoparticles (Au NPs)-Rhodamine 6G (Rh6G) based fluorescent sensor for detecting Hg (II) in aqueous solution has been developed. Water-soluble and monodisperse gold nanoparticles (Au NPs) has been prepared facilely and further modified with thioglycolic acid (TGA). Free Rh6G dye was strongly fluorescent in bulk solution. The sensor system composing of Rh6G and Au NPs fluoresce weakly as result of fluorescence resonance energy transfer (FRET) and collision. The fluorescence of Rh6G and Au NPs based sensor was gradually recovered due to Rh6G units departed from the surface of functionalized Au NPs in the presence of Hg(II). Based on the modulation of fluorescence quenching efficiency of Rh6G-Au NPs by Hg(II) at pH 9.0 of teraborate buffer solution, a simple, rapid, reliable and specific turn-on fluorescent assay for Hg(II) was proposed. Under the optimum conditions, the fluorescence intensity of sensor is proportional to the concentration of Hg(II). The calibration graphs are linear over the range of 5.0 × 10⁻¹⁰ to 3.55 × 10⁻⁸ mol L⁻¹, and the corresponding limit of detection (LOD) is low as 6.0 × 10⁻¹¹ mol L⁻¹. The relative standard deviation of 10 replicate measurements is 1.5% for 2.0 × 10⁻⁹ mol L⁻¹ Hg(II). In comparison with conventional fluorimetric methods for detection of mercury ion, the present nanosensor endowed with higher sensitivity and selectivity for Hg(II) in aqueous solution. Mercury(II) of real environmental water samples was determined by our proposed method with satisfactory results that were obtained by atomic absorption spectroscopy (AAS).     

Determination of mercury in airborne particulate matter collected on glass fiber filters using high-resolution continuum source graphite furnace atomic absorption spectrometry and direct solid sampling

A study has been undertaken to assess the capability of high-resolution continuum source graphite furnace atomic absorption spectrometry for the determination of mercury in airborne particulate matter (APM) collected on glass fiber filters using direct solid sampling. The main Hg absorption line at 253.652 nm was used for all determinations. The certified reference material NIST SRM 1648 (Urban Particulate Matter) was used to check the accuracy of the method, and good agreement was obtained between published and determined values. The characteristic mass was 22 pg Hg. The limit of detection (3σ), based on ten atomizations of an unexposed filter, was 40 ng g^− 1, corresponding to 0.12 ng m^− 3 in the air for a typical air volume of 1440 m³ collected within 24 h. The limit of quantification was 150 ng g⁻¹, equivalent to 0.41 ng m⁻³ in the air. The repeatability of measurements was better than 17% RSD (n = 5). Mercury concentrations found in filter samples loaded with APM collected in Buenos Aires, Argentina, were between < 40 ng g⁻¹ and 381 ± 24 ng g⁻¹. These values correspond to a mercury concentration in the air between < 0.12 ng m⁻³ and 1.47 ± 0.09 ng m⁻³. The proposed procedure was found to be simple, fast and reliable, and suitable as a screening procedure for the determination of mercury in APM samples.     

31P-NMR and X-Ray Studies of the Complexes [HgX2 (1)]. (1=2, 11-bis (diphenylphosphinomethyl)benzo [c]phenanthrene,X=Cl,I)

The ³¹P{¹H}-NMR characteristics of the complexes [HgX₂( 1 )] and [HgX₂-(PPh₂Bz)₂] (X = NO₃, Cl, Br, I, SCN, CN) and the solid state structures of the complexes [HgCl₂( 1 )] and [HgI₂( 1 )] ( 1 = 2,11-bis (diphenylphosphinomethyl)benzo-[c]phenanthrene) have been determined. The ¹J(¹⁹⁹Hg, ³¹P) values increase in the order CN < I < SCN < Br < Cl < NO₃. The two molecular structures show a distorted tetrahedral geometry about mercury. Pertinent bond lengths and bond angles from the X-ray analysis are as follows: Hg? P = 2.485(7) Å and 2.509 (8) Å, Hg? Cl = 2.525 (8) Å and 2.505 (10) Å, P? Hg? P = 125.6(3)°, Cl? Hg? Cl = 97.0(3)° for [HgCl₂( 1 )] and Hg? P = 2.491 (10) Å and 2.500(11) Å, Hg? I = 2.858(5) Å and 2.832(3) Å, P? Hg? P = 146.0(4)°, I? Hg? I = 116.9(1)° for [HgI₂( 1 )]. The equation, derived previously, relating ¹J(¹⁹⁹Hg, ³¹P) and the angles P? Hg? P and X? Hg? X is shown to be valid for 1 .     

Sequential cloud point extraction for the speciation of mercury in seafood by inductively coupled plasma optical emission spectrometry

A novel nonchromatographic speciation technique for the speciation of mercury by sequential cloud point extraction (CPE) combined with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed. The method based on Hg²⁺ was complexed with I⁻ to form HgI₄²⁻, and the HgI₄²⁻ reacted with the methyl green (MG) cation to form hydrophobic ion-associated complex, and the ion-associated complex was then extracted into the surfactant-rich phase of the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114), which are subsequently separated from methylmercury (MeHg⁺) in the initial solution by centrifugation. The surfactant-rich phase containing Hg(II) was diluted with 0.5 mol L^− 1 HNO₃ for ICP-OES determination. The supernatant is also subjected to the similar CPE procedure for the preconcentration of MeHg⁺ by the addition of a chelating agent, ammonium pyrrolidine dithiocarbamate (APDC), in order to form water-insolvable complex with MeHg⁺. The MeHg⁺ in the micelles was directly analyzed after disposal as describe above. Under the optimized conditions, the extraction efficiency was 93.5% for Hg(II) and 51.5% for MeHg⁺ with the enrichment factor of 18.7 for Hg(II) and 10.3 for MeHg⁺, respectively. The limits of detection (LODs) were 56.3 ng L^− 1 for Hg(II) and 94.6 ng L^− 1 for MeHg⁺ (as Hg) with the relative standard deviations (RSDs) of 3.6% for Hg(II) and 4.5% for MeHg⁺ (C = 10 μg L⁻¹, n = 7), respectively. The developed technique was applied to the speciation of mercury in real seafood samples and the recoveries for spiked samples were found to be in the range of 93.2–108.7%. For validation, a certified reference material of DORM-2 (dogfish muscle) was analyzed and the determined values are in good agreement with the certified values.     

Determination of Hg(II) in waters by on-line preconcentration using Cyanex 923 as a sorbent — Cold vapor atomic absorption spectrometry

Using a solid phase extraction mini-column home-made from a neutral extractant Cyanex 923, inorganic Hg could be on-line preconcentrated and simultaneously separated from methyl mercury. The preconcentrated Hg (II) was then eluted with 10% HNO₃ and subsequently reduced by NaBH₄ to form Hg vapor before determination by cold vapor atomic absorption spectrometry (CVAAS). Optimal conditions for and interferences on the Hg preconcentration and measurement were at 1% HCl, for a 25 mL sample uptake volume and a 10 mL min^− 1 sample loading rate. The detection limit was 0.2 ng L^− 1 and much lower than that of conventional method (around 15.8 ng L^− 1). The relative standard deviation (RSD) is 1.8% for measurements of 40 ng L^− 1 of Hg and the linear working curve is from 20 to 2000 ng L^− 1 (with a correlation coefficient of 0.9996). The method was applied in determination of inorganic Hg in city lake and deep well water (from Changchun, Jilin, China), and recovery test results for both samples were satisfactory.     

Determination of methylmercury and estimation of total mercury in seafood using high performance liquid chromatography (HPLC) and inductively coupled plasma-mass spectrometry (ICP-MS): Method development and validation

A method was developed for determination of methylmercury and estimation of total mercury in seafood. Mercury (Hg) compounds were extracted from 0.5 g edible seafood or 0.2 g lyophilized reference material by adding 50 ml aqueous 1% w/v l-cysteine·HCl·H₂O and heating 120 min at 60 °C in glass vials. Hg compounds in 50 μl of filtered extract were separated by reversed-phase high performance liquid chromatography using a C-18 column and aqueous 0.1% w/v l-cysteine·HCl·H₂O + 0.1% w/v l-cysteine mobile phase at room temperature and were detected by inductively coupled plasma-mass spectrometry at mass-to-charge ratio 202. Total Hg was calculated as the mathematical sum of methyl and inorganic Hg determined in extracts. For seafoods containing 0.055-2.78 mg kg⁻¹ methylmercury and 0.014-0.137 mg kg⁻¹ inorganic Hg, precision of analyses was ≤5% relative standard deviation (R.S.D.) for methylmercury and ≤9% R.S.D. for inorganic Hg. Recovery of added analyte was 94% for methylmercury and 98% for inorganic Hg. Methyl and total Hg results for reference materials agreed with certified values. Limits of quantitation were 0.007 mg kg⁻¹ methylmercury and 0.005 mg kg⁻¹ inorganic Hg in edible seafood and 0.017 mg kg⁻¹ methylmercury and 0.012 mg kg⁻¹ inorganic Hg in lyophilized reference materials. Evaluation of analyte stability demonstrated that l-cysteine both stabilized and de-alkylated methylmercury, depending on holding time and cysteine concentration. Polypropylene adversely affected methylmercury stability. Total Hg results determined by this method were equivalent to results determined independently by cold vapour-atomic absorption spectrometry. Methylmercury was the predominant form of Hg in finfish. Ratios of methylmercury/total Hg determined by this method were 93-98% for finfish and 38-48% for mollusks.     

Metal–organic frameworks of zeolitic imidazolate framework-7 and zeolitic imidazolate framework-60 for fast mercury and methylmercury speciation analysis

A fluorescence sensing platform based on metal–organic frameworks (MOFs) nanoparticles (NPs) of both zeolitic imidazolate framework-7 (ZIF-7) and zeolitic imidazolate framework-60 (ZIF-60) was developed for speciation analysis of inorganic Hg [Hg(II)] and methylmercury (MeHg⁺). Microwave-ultrasound assisted synthesis was employed for the preparation of ZIF-7 and ZIF-60 NPs, with short reaction time, easy procedure, and small particle size obtained. Based on strict cavity confinement of the ZIF-7 and ZIF-60 structures, the proposed method exhibited excellent selectivity for both Hg(II) and MeHg⁺, even in the presence of the other Hg species or various cations or anions with the concentration of 50 times high. Effect of pH and ionic strength on sensing behaviour of the ZIF MOF was studied as well. The calculated detection limit is 3 ng mL⁻¹ and 6 ng mL⁻¹ for Hg(II) and MeHg⁺, respectively. Furthermore, the application of the developed method to the analysis of local drinking water was demonstrated to be feasible, and the obtained recovery was 102% and 96.2% for Hg(II) and MeHg⁺, respectively.     

Messung von Isotopenverhältnissen des Quecksilbers im Breich Seiner Natürlichen Häufigkeit Durch Photonenaktivierungsanalyse

By irradiation of mercury with 15 MeV bremsstrahlung the radionuclides²⁰³Hg,^199mHg and^197mHg were generated. This method is suitable for determination of the isotopic relations¹⁹⁸Hg/²⁰⁴Hg and²⁰⁰Hg/²⁰⁴Hg. From mercury of natural isotopic content and of mercury enriched in²⁰⁴Hg were prepared samples with defined isotopic relations and these irradiated for two hours at the Mikrotron (23–25 μA) of the Joint Institute of Nuclear Research Dubna. The estimated standard deviation of the measured activation relations is approximately 2% (rel.), those of the mass-spectrometric method approximately 1% (rel.)      

Preparation, characterization and evaluation of water-soluble l-cysteine-capped-CdS nanoparticles as fluorescence probe for detection of Hg(II) in aqueous solution

Water-soluble l-cysteine-capped-CdS nanoparticles were prepared in aqueous solution at room temperature through a straightforward one-pot process by using safe and low-cost inorganic salts as precursors, and characterized by transmission electron microscopy, X-ray diffraction spectrometry, Fourier transform infrared spectrometry, spectrofluorometry and ultraviolet-visible spectrometry. The prepared l-cysteine-capped-CdS nanoparticles were evaluated as fluorescence probe for Hg(II) detection. The fluorescence quenching of the l-cysteine-capped-CdS nanoparticles depended on the concentration and pH of Hg(II) solution. Maximum fluorescence quenching was observed at pH 7.4 with the excitation and emission wavelengths of 360 nm and 495 nm, respectively. Quenching of its fluorescence due to Hg(II) at the 20 nmol l⁻¹level was unaffected by the presence of 5 × 10⁶-fold excesses of Na(I) and K(I), 5 × 10⁵-fold excesses of Mg(II), 5 × 10⁴-fold excesses of Ca(II), 500-fold excesses of Al(III), 91-fold excesses of Mn(II), 23.5-fold excesses of Pb(II), 25-fold excesses of Fe(III), 25-fold excesses of Ag(I), 8.5-fold excesses of Ni(II) and 5-fold excesses of Cu(II). Under optimal conditions, the quenched fluorescence intensity increased linearly with the concentration of Hg(II) ranging from 16 nmol l⁻¹ to 112 nmol l⁻¹. The limit of detection for Hg(II) was 2.4 nmol l⁻¹. The developed method was applied to the detection of trace Hg(II) in aqueous solutions.     

Density functional study of substituted (–SH, –S, –OH, –Cl) hydrated ions of Hg<Superscript>2+</Superscript>

Abstract  

The electronic structure of Hg(II) ions, [Hg(L) _n (H₂O) _m ] ^q (L = HO⁻, Cl⁻, HS⁻, S²⁻) has been studied. Geometries were fully optimized. The B3LYP and PBE functionals give structures in good agreement with available experimental data. Calculated stretching frequencies generally correlate well with bond lengths. The role of the water molecule(s) in the solvated Hg(II) complexes has been investigated. The solvent can act as nucleophile, as hydrogen bond acceptor or as a spectator. The trans-effect results in lengthening of the Hg–L bond length. It can be understood as a competition between ligands in trans positions for the ability to donate their electron density to the 6s AO of Hg(II). The effect of the presence of water molecules on the Hg–L bond length depends on whether or not the water molecules form a direct coordination bond with Hg(II); it will not guarantee an increase in the stability of the complexes. The interaction energy, which represents the interaction between Hg(II) and ligand L and excludes all other interactions, is nucleophilicity-dependent. The interaction energy and the strength of the ligand nucleophilicity follow the order: S²⁻ > HS⁻ > HO⁻ > Cl⁻ > H₂O. The charge transfer, ΔN, is an indication for the type and strength of the interaction between ligand and Hg(II). Increasing the positive and negative value of ΔN will decrease and increase the Hg(II) total NBO charge, respectively, while decreasing the electrophilicity of Hg(II) will decrease its charge and the charge transfer, ΔN.     

Analysis of inorganic mercury species associated with airborne particulate matter/aerosols: method development

This paper describes a method for speciation of Hg associated with airborne particulate matter. This method uses a mini-sampler for sample collection and analysis, thermal desorption for separating Hg species, and inductively coupled plasma mass spectrometry (ICP–MS) for identification and quantification of Hg. Coal fly ash spiked with different Hg compounds (e.g. Hg⁰, HgCl₂, HgO, and HgS) was used for qualitative calibration. A standard reference material with a certified value for Hg concentration was used to evaluate the method. When the temperature of the furnace was programmed at a linear rate of increase of 50° min^–1, different Hg compounds could clearly be separated. Three airborne particulate matter samples were collected in parallel in Toronto, ON, Canada and analyzed using this method. Reproducible results were obtained and Hg⁰, HgCl₂, HgO, and HgS species from these samples were detected.     

Simultaneous trace-levels determination of Hg(II) and Pb(II) ions in various samples using a modified carbon paste electrode based on multi-walled carbon nanotubes and a new synthesized Schiff base

A modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and 3-(4-methoxybenzylideneamino)-2-thioxothiazolodin-4-one as a new synthesized Schiff base was constructed for the simultaneous determination of trace amounts of Hg(II) and Pb(II) by square wave anodic stripping voltammetry. The modified electrode showed an excellent selectivity and stability for Hg(II) and Pb(II) determinations and for accelerated electron transfer between the electrode and the analytes. The electrochemical properties and applications of the modified electrode were studied. Operational parameters such as pH, deposition potential and deposition time were optimized for the purpose of determination of traces of metal ions at pH 3.0. Under optimal conditions the limits of detection, based on three times the background noise, were 9.0 × 10⁻⁴ and 6.0 × 10⁻⁴ μmol L⁻¹ for Hg(II) and Pb(II) with a 90 s preconcentration, respectively. In addition, the modified electrode displayed a good reproducibility and selectivity, making it suitable for the simultaneous determination of Hg(II) and Pb(II) in real samples such as sea water, waste water, tobacco, marine and human teeth samples.     

Sensitive detection of biothiols and histidine based on the recovered fluorescence of the carbon quantum dots–Hg(II) system

In this paper, we presented a novel, rapid and highly sensitive sensor for glutathione (GSH), cysteine (Cys) and histidine (His) based on the recovered fluorescence of the carbon quantum dots (CQDs)–Hg(II) system. The CQDs were synthesized by microwave-assisted approach in one pot according to our previous report. The fluorescence of CQDs could be quenched in the presence of Hg(II) due to the coordination occurring between Hg(II) and functional groups on the surface of CQDs. Subsequently, the fluorescence of the CQDs–Hg(II) system was recovered gradually with the addition of GSH, Cys or His due to their stronger affinity with Hg(II). A good linear relationship was obtained from 0.10 to 20 μmol L⁻¹ for GSH, from 0.20 to 45 μmol L⁻¹ for Cys and from 0.50 to 60 μmol L⁻¹ for His, respectively. This method has been successfully applied to the trace detection of GSH, Cys or His in human serum samples with satisfactory results. The proposed method was simple in design and fast in operation, which demonstrated great potential in bio-sensing fields.     

Evaluation and application of argon and helium microstrip plasma for the determination of mercury by the cold vapor technique and optical emission spectrometry

The suitability of a 2.45-GHz atmospheric pressure, low-power microwave microstrip plasma (MSP) operated with Ar and He for the determination of Hg by continuous-flow cold vapor (CV) generation, using SnCl₂/HCl as the reducing agent, and optical emission spectrometry (OES) using a small CCD spectrometer was studied. The areas of stability for a discharge in the Ar and in the He MSP enclosed in a cylindrical channel in a quartz wafer were investigated. The excitation temperatures as measured for discharge gas atoms (Ar I, He I), and the electron number densities at 35–40 W and 15–400 mL min⁻¹ were found to be at the order of 3,200–5,500 K and 0.8 × 10¹⁴–1.6 × 10¹⁴ cm⁻³, respectively. The relative intensity of the Hg I 253.6-nm line and the signal-to-background ratio as a function of the forward power (35–40 W) as well as of the flow rate of the working gas (15–400 mL min⁻¹) were evaluated and discussed. For the selected measurement conditions, the Ar MSP was established to have the lower detection limit for Hg (0.6 ng mL⁻¹) compared with the He MSP. The linearity range is up to 300 ng mL⁻¹ and the precision is on the order of 1–3%. With the optimized CV Ar MSP-OES method a determination of Hg in spiked domestic and natural waters at concentration levels of 20–100 μg L⁻¹ and an accuracy of 1–4% could be performed. In an NIST domestic sludge standard reference material, Hg (3.64 μg g⁻¹) could be determined with a relative standard deviation of 4% and an agreement better than 4%.