Solid-phase extraction–gas chromatography–mass spectrometry using a fullerene sorbent for the determination of inorganic mercury(II), methylmercury(I) and ethylmercury(I) in surface waters at sub-ng/ml levels

Photo-generation of mercury cold vapor mediated by graphene quantum dots/TiO2 nanocomposite: On line time-resolved speciation at ultra-trace levels

Mercury speciation was achieved using a nanocomposite, consisting of graphene quantum dots (GQDs) and TiO₂ nanoparticles, to mediate photo-degradation of mercurial species into the Hg cold vapor detected by atomic spectrometry. Sample solution (containing Hg²⁺, CH₃CH₂Hg, and CH₃Hg at hundreds of ng L^-1) was placed in quartz tube containing formic acid solution (2% v/v) and microliter aliquot of GQDs/TiO₂ nanocomposite dispersion (0.6 mg of nanocomposite). The tube was placed inside a photochemical reactor then, adapted to the mercury-dedicated spectrometer. Quantitative speciation was achieved taking advantage of the differences in UV photodegradation kinetics: Hg²⁺ (5 min), CH₃CH₂Hg (9 min) and CH₃Hg (13 min). Gas-chromatography cold vapor atomic fluorescence spectrometry was used to confirm the evolution of the reactions over time during photo-reaction. The limits of detection were 10 ng L^-1 for CH₃CH₂Hg and 7 ng L^-1 for Hg²⁺ and CH₃Hg.

Application of l-cystine modified zeolite for preconcentration and determination of ultra-trace levels of cadmium by flame atomic absorption spectrometry

A very convenient, sensitive and precise solid phase extraction (SPE) system was developed for enrichment and determination of ultra-trace of cadmium ion in water and plant samples. This method was based on the retention of cadmium(II) ions by l-cystine adsorbed in Y-zeolite and carry out in a packed mini-column. The retained cadmium ions then were eluted and determined by flame atomic absorption spectrometry. The scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy techniques were applied for the characterization of cystine modified zeolite (CMZ). Some experimental conditions affecting the analytical performance such as pH, eluent type, concentration of sample, eluent flow rate and also the presence of interfering ions were investigated. The calibration graph was linear within the range of 0.1-7.5ngmL(-1) and limit of detection was obtained 0.04ngmL(-1) with the preconcentration factor of 400. The relative standard deviation (RSD) was obtained 1.4%, indicating the excellent reproducibility of this method. The proposed method was successfully applied for the extraction and determination of cadmium(II) ion in black tea, cigarette's tobacco and also various water samples.

In vitro study of thimerosal reactions in human whole blood and plasma surrogate samples

Because of its bactericidal and fungicidal properties, thimerosal is used as a preservative in drugs and vaccines and is thus deliberately injected into the human body. In aqueous environment, it decomposes into thiosalicylic acid and the ethylmercury cation. This organomercury fragment is a potent neurotoxin and is suspected to have similar toxicity and bioavailability like the methylmercury cation. In this work, human whole blood and physiological simulation solutions were incubated with thimerosal to investigate its behaviour and binding partners in the blood stream. Inductively coupled plasma with optical emission spectrometry (ICP-OES) was used for total mercury determination in different blood fractions, while liquid chromatography (LC) coupled to electrospray ionisation time-of-flight (ESI-TOF) and inductively coupled plasma-mass spectrometry (ICP-MS) provided information on the individual mercury species in plasma surrogate samples. Analogous behaviour of methylmercury and ethylmercury species in human blood was shown and an ethylmercury-glutathione adduct was identified.

New solid-phase-nanoscavenger for the analytical enrichment of mercury from water

A nanoscavenger of mercaptopropyl-modified silica microparticles has been developed for the determination of trace levels of mercury(II) in water. The synthesis of silica microparticles nanoscavengers is carried out by modification of pre-formed silica particles with mercaptopropyltrimethoxysilane or by incorporating the thiol modification agent during the growth of the silica particles. The silica nanoscavengers were characterized by SEM, TGA, particle analyzer, IR and the parameters influencing the extraction and recovery phases of the preconcentration process were performed by AAS. The results show that careful choice of particle size and surface characteristics produce a new mercapto-silica-nanoscavenger that disperses in water as a quasi-stable sol. This permits the facile recovery of the mercury-loaded nanoscavenger particles. No agitation is required during the mercury extraction as the dispersion is maintained by Brownian motion and slow gravitational sedimentation. The technique overcomes a number of problems, such as cross-contamination and decreases in mercury concentration during sample transportation to the laboratory. Recovery achieved reaches >97 ± 4% over a wide range of preconcentration factors. At a preconcentration factor of 50 the limit of detection (3σ) was 0.19 ng mL(-1). The method is environmentally friendly as only 300 mg of mercapto-nanoscavenger is used, no organic solvent is required for the extraction and the experiment is performed without the need for manual or mechanical agitation.

Analytical potential of hybrid nanoparticles

The growing use of nanoparticles in the analytical process in recent years has set a new trend towards the simplification of analytical methods and improvement of their performance. Miniaturization and nanotechnology have allowed new analytical challenges to be met. Hybrid nanoparticles in particular possess exceptional properties enabling further improvement of analytical methods. Despite the continuous developments in their synthesis and characterization, hybrid nanomaterials have scarcely been used in analytical chemistry, however. This paper discusses the analytical potential of hybrid nanoparticles in terms of their special characteristics and properties, and describes their analytical applications.

Simultaneous speciation of monomethylmercury and monoethylmercury by aqueous phenylation and purge-and-trap preconcentration followed by atomic spectrometry detection

A new method for the detection of trace levels of organomercury species has been developed by combining the high enrichment capacity of purge and trap with aqueous phenylation derivatization. Phenylation products of monomethylmercury (MeHg) and monoethylmercury (EtHg) were first separated by capillary gas chromatography and then detected by atomic fluorescence spectrometry (AFS) or inductively coupled plasma mass spectrometry (ICPMS). This combination made it possible to simultaneously quantify trace or ultratrace level of MeHg and EtHg in environmental samples. Method detection limits were 0.03 ng/L for both MeHg and EtHg when AFS was used as the detector and 0.02 and 0.01 ng/L for MeHg and EtHg with ICPMS, respectively. Certified reference materials, IAEA-405 and DORM-2, were analyzed and the results were in accordance with certified values. Both MeHg and EtHg were detected in sediment samples collected from the Florida Everglades and a Canadian wetland. This new method has been validated for the direct detection of trace organomercury species in freshwater samples and has the additional benefits of being free from interference by Cl (-) and dissolved organic matter.

Surfactant coated fullerenes C60 as pseudostationary phase in electrokinetic chromatography

In the present paper, surfactant coated fullerenes C(60) (SC-C(60)) have been proposed as a novedous pseudostationary phase to improve separation of different aromatic compounds. The target analytes were beta-lactams antibiotics, non-steroidal anti-inflammatory drugs and amphenicols. In all cases, the analytes interacted with the pseudostationary phase producing an important enhancement on resolution. The results were compared with those obtained with surfactant coated carbon nanotubes (single-walled and multi-walled nanotubes), showing that in the proposed conditions, fullerenes C(60) were advantageous as interactions between the analytes and the pseudostationary phase were more effective. Finally, the procedure was applied to pharmaceuticals and urine samples, with satisfactory results.

Application of Carbon Sorbents for the Concentration and Separation of Metal Ions

Solid-phase extraction is an attractive approach in the preparation of many kinds of samples prior to analysis; highly selective sorbents are desirable for this purpose. The objective of this review is to provide updated information about carbon-based sorbents, their interaction modes and potential application for the concentration and separation of metal ions from environmental samples prior to their determination. New selective phases such as fullerenes and carbon nanotubes are described. Selected examples illustrate the potential of these sorbents.

Method optimization for the determination of four mercury species by micro-liquid chromatography–inductively coupled plasma mass spectrometry coupling in environmental water samples

A method based on the coupling microHPLC-microneb-ICPMS has been developed for Hg(II), MeHg+, EtHg+ and PhHg+ species. Gradient elution using methanol and l-cysteine at pH 3.0 allowed the chromatographic separation of all species in less than 13 min (total analysis time 15 min). The direct coupling of microLC to ICPMS through a Micromist nebulizer permits the analysis of environmental water without sample pretreatment and derivatization steps. Nebulizer type, organic modifier and column length were the main parameters tested. The methanol content and pH of the mobile phase greatly affected the retention time and sensitivity of the method. Key factors to obtain high signal to noise ratio, at concentrations below 1 microg L(-1), were found to be the nebulization step and traces of Hg present in the complexing agent. A detailed optimization of carrier and make up gas flow rates have enabled the nebulization of the methanol gradient elution with good mass transport efficiency, low organic solvent loading into the plasma and excellent precision. The performance of the microHPLC-microneb-ICPMS method developed was evaluated on a surface water sample filtered (0.22 microm) and spiked with 0.5 microg L(-1) (as Hg) of each species. Precision (R.S.D., n=6) for all species of Hg varied from 0.5 to 2.1%. Detection limit, defined as three times the standard deviation (n=6), ranged from 8 ng L(-1) for EtHg+ to 32 ng L(-1) for PhHg+ and was noticeably lower than those reported in previous LC-based methods. Accuracy was suitable with recoveries ranging from 85 to 100% when tested at two levels (0.5 and 10 microg L(-1)) in groundwater samples. Recovery was matrix affected when water samples of high salinity (depurated wastewater and seawater) were used.

Adsorption Characteristics of a Nanodiamond for Oxoacid Anions and Their Application to the Selective Preconcentration of Tungstate in Water Samples

A nanodiamond with a mean particle size of 4 nm, which was prepared by the detonation of a nanodiamond, has been characterized and used as a collector for tungstate in water samples. An aqueous solution of nanodiamond was found to be stable over the pH range from 3 to 10. Coagulation of the nanodiamond could be brought about by adding an electrolyte solution. The adsorption characteristics of nanodiamond have been elucidated to be attributable to amino groups on its surface by the elemental-analysis data and the zeta potential measured in weak acid media. The unique adsorption properties of the nanodiamond for oxoacid anions were applied to a selective preconcentration method for tungstate in water samples. An appropriate amount of nanodiamond was added to a sample solution at pH 5 and a calcium chloride solution was added to aggregate nanodiamond. The sample solution was then allowed to stand for 2 h and centrifuged. The nanodiamond was transferred onto a membrane filter, washed with a diluted calcium chloride solution and treated in advance of an ICP-AES measurement by either of the following procedures: (a) redispersion of the nanodiamond into dilute nitric acid with an ultrasonic washer and (b) ashing of the membrane filter and the coagulated nanodiamond at 700 degrees C, followed by a treatment of the ash with hydrochloric and tartaric acids. The average recovery of tungstate from 100-ml artificial river-water was found to be 99% at the 0.25 ppm level with an RSD of 2.2% (n = 3). The concentration factor at present is 10.

UV Irradiation Controlled Cold Vapor Generation Using SnCl2 as Reductant for Mercury Speciation

A simple and ultrasensitive method, which was based on cold vapor generation (CVG) coupled to atomic fluorescence spectrometry (AFS), was proposed for speciation analysis of inorganic mercury (Hg2+) and methylmercury (MeHg) in water samples. In the presence of UV irradiation, all the mercury (MeHg+Hg2+) in a sample solution can be reduced to Hg0 by SnCl2; without UV irradiation, only Hg2+ species can be determined. So the concentration of MeHg can be obtained from the difference of the total mercury and Hg2+ concentration; thus, speciation analysis of Hg2+ and MeHg was simply achieved without chromatographic separation. Under the optimized experimental conditions, the limits of detection were 0.01 ng mL-1 for both Hg2+ and MeHg. The sensitivity and limit of detection were not dependent on the mercury species, and a simple Hg2+ aqueous standard series can be used for the determination of both Hg2+ and MeHg.

Speciation of Organometallic Compounds in Environmetal Samples by Gas Chromatography after Flow Preconcentration on Fullerenes and Nanotubes

The development of a simple speciation method for the determination of lead (trimethyllead(I), dimethyllead(II), triethyllead(I), and diethyllead(II)), mercury (methylmercury(I), ethylmercury(I), mercury(II)), and tin (n-butyltin(III), di-n-butyltin(II), tri-n-butyltin(I), tin(IV)) compounds in environmental samples was described. The potential of C70 fullerenes and multiwalled carbon nanotubes (MWNTs) as sorbents was investigated for the first time; this study revealed that there are no significant differences between them in terms of sensitivity, selectivity, precision, and reusability. Comparative studies showed that MWNTs and C60 and C70 fullerenes were superior to graphitized carbon black and RP-C18 for the extraction of the 11 compounds studied. The accuracy of the MWNT method was evaluated from recovery values with two standard reference coastal sediments, and good concordance in the results were obtained. Detection limits of 0.5-2 pg/mL were obtained when using a sorbent column containing 160 mg of MWNTs (sample breakthrough, 50 mL of water). The method was successfully applied to the determination of lead, mercury, and tin compounds in water and coastal sediment samples with satisfactory results.