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‰.     

Mercury determination and speciation analysis in surface waters

A sorbent L-cysteine grafted silica gel has been evaluated for separation and enrichment of dissolved inorganic i-Hg(II) and methylmercury CH₃Hg(I) from surface waters at sub-μg L⁻¹ concentrations. Chemical parameters for mercury species enrichment and separation have been optimized. Analytical schemes for the determination of Hg species, using selective column solid phase extraction (SPE) with continuous flow chemical vapor generation atomic absorption spectrometry (CF-CVG-AAS) or inductively coupled plasma-mass spectrometry (ICP-MS) were developed. Possibilities for on-site SPE enrichment were demonstrated as well. The limits of quantification were 1.5 and 5 ng L⁻¹ for dissolved i-Hg(II) and CH₃Hg(I) by CF-CVG-AAS and 1 and 2.5 ng L⁻¹ by ICP-MS with relative standard deviations between 7–12% and 7–14%, respectively. The chemically modified SPE sorbent has demonstrated high regeneration ability, chemical and mechanical stability, acceptable capacity and good enrichment factors. Results for total dissolved mercury were in reasonable agreement with those from independent analyses by direct ICP-MS determinations for river waters and for estuarine water certified reference material.      

Determination of mercury in environmental and biological samples by cold vapour atomic absorption spectrometry

A continuously operating monitoring method for total mercury at sub-ng/ml level in environmental and biological samples by cold vapour atomic-absorption spectrometry with NaBH₄ as a reductant was developed. The mercury vapour generator and absorption cell closed-end by quartz were used in this study. The detection limit (S/N = 3) and relative standard deviation of 12 determinations of 10 ng/ml Hg(II) were 0.11 ng/ml and 1.1%, respectively. The range of standard calibration curve was 0–50 ng/ml Hg, The proposed method was successfully applied to the completely continuous monitoring of total mercury in waste water, sediments and pork liver.     

Chelating resin preconcentration and Hg(II) assisted elution followed by differential-pulse anodic stripping voltammetry for the determination of Cd, Cu, and Pb in seawater

A new and efficient Hg(II) back-elution method for the desorption of Cd, Cu, and Pb from Chelex-100 chelating resin was developed. A smaller eluent volume and shorter elution time can be achieved using an Hg(II) containing eluent rather than pure nitric acid. Owing to the remaining Hg(II) ion in the effluent, a mercury thin-film electrode is formed in-situ during the anodic stripping voltammetric determination without any further addition of Hg(II). The results indicate that all the analytes in seawater matrix can be completely adsorbed on Chelex-100 resin from the sample at pH 6.5, and subsequently eluted from the resin with an acid solution of 5 × 10^–4 mol/L Hg²⁺ + 1 mol/L HClO₄. The detection limits obtained from the differential-pulse anodic (μg L^–1 to ng L^–1) stripping voltammetry are at sub-ppb to ppt (μg L^–1 to ng L^–1) levels permitting to determine Cd, Cu and Pb traces in seawater. The analytical reliability was confirmed by the analysis of the certified reference material CASS-II (open ocean seawater). Received: 22 April 1997 / Revised: 5 August 1997 / Accepted: 7 August 1997     

Determination of bromine and iodine in biological and environmental materials using epithermal neutron activation analysis

Epithermal neutron activation analysis (ENAA) was applied to the determination of the contents of bromine and iodine in 40 biological and environmental standard reference materials and Chinese diets. Boron nitride (BN) for solid samples and BN+Cd for liquid samples were adopted as shield material. Irradiation was carried out in inner and outer irradiation sites in a Miniature Source Reactor (MNSR) for solid and liquid samples, respectively. The 443 keV photopeak of ¹²⁸I and the 616 keV photopeak of ⁸⁰Br were used. The precision of measurement (relative standard deviation) is 2∼6% for contents of iodine of more than 100 ng/g and 8∼12% in the 20∼100 ng/g range in solid samples, and 12∼18% at less than 100 ng/ml in liquid samples. For bromine, the precision of measurement is 2–8% for solid samples and lower than 13% for liquid samples. The detection limits under experimental conditions varied between 10∼30 ng/g, 55∼95 ng/g and 25∼68 ng/g for iodine and 50∼150 ng/g, 200∼450 ng/g and 100∼300 ng/g for bromine in ENAA with BN shield in inner irradiation sites, with Cd shield and BN+Cd shield in outer irradiation sites, respectively. Received: 13 June 1996 / Revised: 2 September 1996 / Accepted: 19 September 1996     

A novel preconcentration technique using crosslinked chitosan for the determination of mercury by CVAAS

A novel crosslinked chitosan (CCTS) has been synthesized by the reaction of water-soluble chitosan with epoxy chloropropane. In the presence of the chelating EDTA and in the pH range between 4–10, CCTS selectively adsorbed trace inorganic Hg in water samples with enrichment factors of 100. Inorganic Hg could be directly reduced using KBH₄ without preceding elution and determined by CVAAS. Accordingly, the total mercury could be determined after all species of mercury in water samples were transformed into Hg²⁺. The detection limit (3σ) for mercury was 12 ng L^–1 and the relative standard deviation less than 5% at the 50 ng L^–1 level. Beer’s law was obeyed over the range 30–400 ng L^–1 of mercury and the preconcentration method was applied to environmental water samples with the recoveries between 92–96%.     

LC-MS/MS quantitative analysis of reducing carbohydrates in soil solutions extracted from crop rhizospheres

A simple, sensitive, and specific analytical method has been developed for the quantitative determination of 15 reducing carbohydrates in the soil solution of crop rhizosphere. Reducing carbohydrates were derivatized with 1-phenyl-3-methyl-5-pyrazolone, separated by reversed-phase high-performance liquid chromatography and detected by electrospray ionization tandem mass spectrometry. Lower limits of quantitation of 2 ng/mL were achieved for all carbohydrates. Quantitation was performed using peak area ratios (analyte/internal standard) and a calibration curve spiked in water with glucose-d₂ as the internal standard. Calibration curves showed excellent linearity over the range 2–100 ng/mL (10–1,000 ng/mL for glucose). The method has been tested with quality control samples spiked in water and soil solution samples obtained from the rhizosphere of wheat and canola and has been found to provide accurate and precise results.     

On-line preconcentration and determination of mercury in biological samples by flow injection vapour generation inductively coupled plasma atomic emission spectrometry

An FI-ICP-AES method for the determination of trace levels of mercury in biological samples has been described, which is based on the extraction of the mercury complex with 1,5-bis (di-2-pyridyl)methylene thiocarbonohydrazide (DPTH) on-line into isobuthyl-methyl ketone (IBMK). The organic phase (containing the complex) has been mixed on-line with SnCl₂ in N,N-dimethylformamide. Thus, mercury vapour can be generated directly from the organic phase and separated in a gas-liquid separation device. The detection limit for mercury is 4 ng/ml and the calibration curve is linear at least from 10 to 2500 ng/ml. The relative standard deviation for 10 replicate measurements is ±1% for 100 ng/ml of Hg(II). Results from the analysis of some certified biological reference materials are given.     

Selenium and mercury determination in biological samples using gamma–gamma coincidence and Compton suppression

Biological materials containing trace amounts of mercury and selenium were examined using neutron activation analysis. They were analyzed using Compton suppression and γ–γ coincidence counting. The 279 keV photopeak of activated mercury (²⁰³Hg) was analyzed in order to observe the mercury content in these samples. Selenium, an element found in many biological samples, interferes with the analysis of ²⁰³Hg when activated (⁷⁵Se). Because the selenium interference comes from a cascading emission, Compton suppression was utilized to reduce this interference. In order to fully characterize the selenium content in the samples, γ–γ coincidence was used which reduced the background and eliminated bremsstrahlung interference produced from neutron activated phosphorous through the ³¹P(n, γ)³²P reaction which is a pure beta emitter. As a result, we determined the mercury and selenium concentrations in three standard reference materials, which contain varying ratios of mercury to selenium concentrations. This study also showed that these types of concentrations can be determined from small (<500 mg) sample masses. Further work needs to be done on wet samples that require dehydration, as mercury can be lost through this process.     

Separation and Removal of Mercury(II) from Water Samples Using (Acetylacetone)‐2‐Thiol‐Phenyleneimine Immobilized on Anion‐Exchange Resin Prior to Determination by Cold Vapor Inductively Coupled Plasma Atomic Emission Spectroscopy

Abstract

(Acetylacetone)‐2‐thiol‐phenyleneimine (H₂L) immobilized on an anion‐exchange resin (Dowex) was used for separation and removal of mercury from natural water samples and for preconcentration prior to its determination by cold vapor inductively coupled plasma atomic emission spectroscopy. The metal was eluted from the column using a solution of 10% thiourea in 0.1 M HCl. The modified resin is higly selective with an exchange capacity of 1.60 mmol g^?1. Various parameters like pH, column flow rate, and desorbing agents are optimized. The proposed method has a linear calibration range of 15–1000 ng/ml Hg(II), with a relative standard deviation at the 15 ng/ml level of 3.5%. The precision of the method (evaluated as the relative standard deviation obtained after analyzing six series of five replicates) was ±4.2% at the 50 ng/ml level of Hg(II). The method has been used for routine determination of trace levels of mercury species in natural waters. The potential application of modified resin for the removal of mercury(II) from two natural water samples (top water and lake water) spiked with 50 ng/ml of mercury (II) was studied by ICP‐AES, and the results proved that excellent percent extraction of mercury(II) from both natural water samples was obtained by column method using modified resin.     

Development of an accurate,sensitive, and robust isotope dilution laser ablation ICP-MS method for simultaneous multi-element analysis (chlorine,sulfur, and heavy metals) in coal samples

A method for the direct multi-element determination of Cl, S, Hg, Pb, Cd, U, Br, Cr, Cu, Fe, and Zn in powdered coal samples has been developed by applying inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) with laser-assisted introduction into the plasma. A sector-field ICP-MS with a mass resolution of 4,000 and a high-ablation rate laser ablation system provided significantly better sensitivity, detection limits, and accuracy compared to a conventional laser ablation system coupled with a quadrupole ICP-MS. The sensitivity ranges from about 590 cps for ³⁵Cl⁺ to more than 6 × 10⁵ cps for ²³⁸U⁺ for 1 μg of trace element per gram of coal sample. Detection limits vary from 450 ng g⁻¹ for chlorine and 18 ng g⁻¹ for sulfur to 9.5 pg g⁻¹ for mercury and 0.3 pg g⁻¹ for uranium. Analyses of minor and trace elements in four certified reference materials (BCR-180 Gas Coal, BCR-331 Steam Coal, SRM 1632c Trace Elements in Coal, SRM 1635 Trace Elements in Coal) yielded good agreement of usually not more than 5% deviation from the certified values and precisions of less than 10% relative standard deviation for most elements. Higher relative standard deviations were found for particular elements such as Hg and Cd caused by inhomogeneities due to associations of these elements within micro-inclusions in coal which was demonstrated for Hg in SRM 1635, SRM 1632c, and another standard reference material (SRM 2682b, Sulfur and Mercury in Coal). The developed LA-ICP-IDMS method with its simple sample pretreatment opens the possibility for accurate, fast, and highly sensitive determinations of environmentally critical contaminants in coal as well as of trace impurities in similar sample materials like graphite powder and activated charcoal on a routine basis. Figure LA-ICP-IDMS allows direct multi-element determination in powdered coal samples     

Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

 Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples. Received: 5 July 1996/Accepted: 7 August 1996     

Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

 Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples. Received: 5 July 1996/Accepted: 7 August 1996     

Identification and quantification of pesticides and polycyclic aromatic hydrocarbons in water and food by gas chromatography-mass spectrometry

Chances are examined for the identification and determination of pesticides of different types and polycyclic aromatic hydrocarbons, 46 items, in water and food by means of gas chromatography with time-of-flight mass spectrometry detection. The detection limits make from 0.01 to 0.5 mg/L if the injected volume of samples is 1 μL; the analytical range is 0.02–10 mg/L. In the mode of selective ion registration and preliminary preconcentration by liquid and solid-phase extraction, the detection limits of analytes make from 2 to 100 ng/L in water and from 0.2 to 10 μg/kg for solid samples.     

On-line solid-phase extraction-gas chromatography-ion trap tandem mass spectrometric detection for the nanogram per liter analysis of trace pollutants in aqueous samples

Summary On-line solid-phase extraction-gas chromatographyion-trap tandem mass spectrometry (SPE-GC-MS/MS) has been used for the trace-level determination of polar and apolar pesticides. The SPE-GC interface, an Autoloop 2000, was operated at an injection temperature of 90°C which permitted the determination of thermolabile pesticides such as carbofuran and carbaryl. Rectilinear calibration curves were obtained for the analytes tested over a range of 0.1–500 ng L⁻¹, using a sample volume of 10–100 mL for enrichment on an SPE cartridge packed with styrene-divinylbenzene copolymer. The detection limits for the pesticides were in the 0.01–4 ng L⁻¹ range. For a number of pesticides acceptable tandem mass spectra were obtained at levels as low as 0.1 ng L⁻¹ level in real-life water samples. As a demonstration of the applicability of this technique for inorganic anions, bromide and nitrite were converted into 4-bromoacetanilide and 2-phenylphenol, respectively. The reaction products were pooled and subjected to simultaneous analysis by the present method using full-scan mass spectrometric detection. The detection limits were 0.3 and 2 ng L⁻¹, respectively.     

Determination of chloramphenicol in milk by a fluorescence polarization immunoassay

A procedure for the determination of the drug chloramphenicol using a fluorescence polarization immunoassay (FPIA) was proposed. The optimum pairs of antibodies and antigens labeled with fluorescein were chosen, and the analytical characteristics of the procedure were determined. A rapid procedure for milk sample preparation with the use of a saturated solution of ammonium sulfate was optimized. The total time of sample preparation and determination of chloramphenicol in milk was no longer than 10 min. The detection limits of chloramphenicol in water and milk were 10 ng/mL and 20 μg/kg, respectively. The procedure developed for the determination of chloramphenicol was tested in the analysis of model and real milk samples. It was found that some milk samples contained chloramphenicol in concentrations of 38–41 μg/kg, which are several times higher than the maximum permissible concentration (MPC) (10 μg/kg).     

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%.     

In-situ concentration and determination of mercury by graphite furnace atomic absorption spectrometry with Pd-Rh as the chemical modifier

A method has been proposed for the determination of mercury by cold vapor generation graphite furnace atomic absorption spectrometry (CV-GFAAS) with Pd-Rh as coating and chemical modifier. The trapping efficiency for mercury with Pd-Rh was higher than with Pd alone. The characteristic mass of the method, which gives an integrated absorbance of 0.0044 s, was found to be 55 pg and the absolute detection limit (3 σ) of 37 pg was obtained with the proposed modifier. The method was successfully applied to the determination of mercury in standard reference water samples, wastewater samples and cosmetics with a recovery range of 95–104%. Received: 10 April 1998 / Revised: 20 August 1998 / Accepted: 23 September 1998     

In-situ concentration and determination of mercury by graphite furnace atomic absorption spectrometry with Pd-Rh as the chemical modifier

A method has been proposed for the determination of mercury by cold vapor generation graphite furnace atomic absorption spectrometry (CV-GFAAS) with Pd-Rh as coating and chemical modifier. The trapping efficiency for mercury with Pd-Rh was higher than with Pd alone. The characteristic mass of the method, which gives an integrated absorbance of 0.0044 s, was found to be 55 pg and the absolute detection limit (3 σ) of 37 pg was obtained with the proposed modifier. The method was successfully applied to the determination of mercury in standard reference water samples, wastewater samples and cosmetics with a recovery range of 95–104%. Received: 10 April 1998 / Revised: 20 August 1998 / Accepted: 23 September 1998     

Instrumental neutron activation analysis of prehistoric and ancient bone remains

Instrumental neutron activation analysis (INAA) was used to study the element contents in bones of prehistoric dinosaurs and bones of an ancient bear and an archantrop (ancient person), which were found on the territory of Uzbekistan. Concentrations of more than 25 elements were in the range of 0.043–3600 mg/kg. Multielement analyses of bone and soil samples were carried out by INAA using the WWR-SM research nuclear reactor. Results of measurements have shown that in the dinosaurs bones the concentration of the rare earth elements (REEs) were within 280–3200 mg/kg; the uranium content reached a very high value, up to 180 mg/kg, while in soils coating the dinosaurs bones this content was 4.2 mg/kg; in the bones of the archantrop it was 1.53 mg/kg and in the bones of a standard person its amount is less than 0.016 mg/kg.