Speciation of Mercury in Microalgae by Isotope Dilution-inductively Coupled Plasma Mass Spectrometry

Species-specific stable isotope dilution in combination with gold trap- or gas chromatography (GC)-inductively coupled plasma mass spectrometry (ICP-MS) is reported for the determination of inorganic mercury and methylmercury in diatoms (Chaetoceros curvisetus). The optimum conditions for the separation parameters were established. The isotope dilution analysis was performed using ¹⁹⁹Hg-enriched Hg²⁺ and laboratory-synthesized ²⁰¹Hg-enriched methylmercury. The absolute detection limits obtained with isotope dilution-ICP-MS were 9 pg for total mercury and 0.6 pg for methylmercury. The relative error of 7 Hg isotopic abundances based on the peak area measurements was better than 2.0% for 20 pg of methylmercury (as Hg) and 250 pg of inorganic mercury. The accuracy of the method was validated with a biological certified reference material. The developed method was then applied to investigate the uptake of inorganic mercury and methylmercury by C. curvisetus. Continuous uptake of inorganic mercury and methylmercury was observed during 5 days of incubation.     

Cold vapour atomic fluorescence spectrometry and gas chromatography-pyrolysis-atomic fluorescence spectrometry for routine determination of total and organometallic mercury in food samples

Two procedures have been investigated for the quantification of the different forms of mercury in food. A two-stage procedure has been developed to determine firstly total inorganic and organometallic species, and then the full separation of all organomercury species. The procedure involves solubilisation of the samples using alkaline extractions or enzymolysis, followed by the extraction of organic mercury in an organic solvent, preferably a mixture of dichloromethane and hexane (3:2). For the total organic mercury determination, the organic extract is analysed for "total" mercury after nitric acid/peroxide digestion, evaporation of the solvent and detection by cold vapour-atomic fluorescence spectrometry. Full organomercury speciation requires a clean-up step before analysis of the final extract in dichloromethane by gas chromatography coupled to a pyrolyser and an atomic fluorescence detector (GC-pyro-AFS). A detection limit of 6 ng l-1, and reproducibility of 2% was achieved for the CV-AFS method; GC-pyro-AFS yielded 200 ng l-1 and 5% for detection limit and coefficient of variation, respectively. Both procedures were validated with the use of various certified reference materials over a wide range of mercury concentrations, and by spiking experiments. The validated methods were tested successfully on a wide range of commercially available food samples.     

On-line hyphenation of capillary electrophoresis with flame-heated furnace atomic absorption spectrometry for trace mercury speciation

Capillary electrophoresis (CE) was directly interfaced to flame-heated furnace atomic absorption spectrometry (FHF-AAS) via a laboratory-made thermospray interface for nanoliter trace element speciation. The CE-FHF-AAS interface integrated the superiorities of stable CE separation, complete sample introduction, and continuous vaporization for AAS detection without the need of extra external heat sources and any post-column derivation steps. To demonstrate the usefulness of the developed hybrid technique for speciation analysis, three environmentally significant and toxic forms of methylmercury (MeHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) were taken as model analytes. Baseline separation of the three mercury species was achieved by CE in a 60 cm long x 75 microm inner diameter fused-silica capillary at 20 kV and using a mixture of 100 mM boric acid and 10% v/v methanol (pH 8.30) as running electrolyte. The precision (relative standard deviation, RSD, n = 7) of migration time, peak area and peak height for the mercury species at 500 microg x L(-1) (as Hg) level were in the range of 0.9-1.2%, 1.5-1.9%, and 1.4-2.0%, respectively. The detection limit (S/N = 3) of three mercury species was 3.0 +/- 0.15 pg (as Hg), corresponding to 50.8 +/- 2.4 microg x L(-1) (as Hg) for 60 nL sample injection, which was almost independent on specific mercury species. The developed hybrid technique was successfully applied to the speciation analysis of mercury in a certified reference material (DORM-2, dogfish muscle).     

Speciation analysis for mercury in gas condensates by capillary gas chromatography with inductively coupled plasma mass spectrometric detection

A method allowing species-selective determination of atomic mercury, non-polar dialkylated mercury compounds,polar monoalkylated species and inorganic mercury complexes in natural gas condensates was developed. Inductively coupled plasma mass spectrometry was employed as a detection method for capillary gas chromatography and compared with microwave induced plasma atomic emission detection for the analysis of hydrocarbon-rich matrices. The method was based on two consecutive injections allowing comprehensive speciation analysis. First a sample aliquot was diluted with toluene and analysed for Hg0 and individual dialkylmercury compounds. Then, another aliquot was butylated with a Grignard reagent for the species specific determination of Hg(II) and monoalkylated mercury species. The detection limits were down to 0.08 pg level.     

Determination of mercurial species in fish by inductively coupled plasma mass spectrometry with anion exchange chromatographic separation

This work demonstrated the feasibility of mercury speciation analysis by anion exchange chromatographic separation with inductively coupled plasma mass spectrometry detection. For the first time, by complexing with the mobile phase containing 3-mercapto-1-propanesulfonate into negatively charged complexes, fast separation of inorganic mercury (Hg²⁺), monomethylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) was achieved within 5 min on a 12.5-mm strong anion exchange column. The detection limits for Hg²⁺, MeHg, EtHg and PhHg were 0.008, 0.024, 0.029 and 0.034 μg L⁻¹, respectively. The relative standard deviations of peak height and peak area (5.0 μg L⁻¹ for each Hg species) were all below 3%. The determined contents of Hg²⁺, MeHg and total Hg in a certified reference material of fish tissue by the proposed method were in good accordance with the certified values with satisfactory recoveries. The relative errors for determining MeHg and total mercury were −2.4% and −1.2%, respectively, with an acceptable range for spike recoveries of 94–101%. Mercury speciation in 11 fish samples were then analyzed after the pretreated procedure. The mercury contents in all fish samples analyzed were found compliant with the criteria of the National Standards of China.     

Gas chromatographic determination of organomercury following aqueous derivatization with sodium tetraethylborate and sodium tetraphenylborate. Comparative study of gas chromatography coupled with atomic fluorescence spectrometry, atomic emission spectrometry and mass spectrometry

Several hyphenated analytical techniques, including gas chromatography (GC) coupled with atomic fluorescence spectrometry (AFS), microwave-induced plasma atomic emission spectrometry (AES), and mass spectrometry (MS), have been evaluated for methylmercury and ethylmercury analysis following aqueous derivatization with both sodium tetraethylborate and sodium tetraphenylborate. Both GC-AFS and GC-AES were shown to be excellent techniques with detection limits in the range of sub-picogram levels (0.02-0.04 pg as Hg). Both techniques have wide linear ranges, although setting of the AFS sensitivity has to be selected manually based on the concentration of mercury in the sample. Phenylation seems to be more favorable in this study because of its capability of distinguishing between ethylmercury and inorganic mercury, and low cost compared to ethylation. Although sensitivity of GC-MS is poor with detection limits ranging from 30 to 50 pg as Hg, it is an essential technique for confirmation of the derivatization products.     

Comparison of different analytical methods for speciation of seven gadolinium-based magnetic resonance imaging contrast agents and the applications in wastewater and whole blood

Three methods, high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry, high-performance liquid chromatography-tandem mass spectrometry, and ion chromatography, were compared for simultaneous speciation of seven commercial gadolinium-based contrast agents for magnetic resonance imaging. Optimizations of experimental conditions for individual method were conducted, respectively. Methods of high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry and high-performance liquid chromatography-tandem mass spectrometry showed the capability of speciation for all seven target compounds, whereas ion chromatography was only suitable for three of them when using electronic conductivity detector. The limits of detection and limits of qualification by the three methods were compared, and high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry was found to be the most sensitive one. The limits of detection for seven target compounds by high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry were in the range of 0.15–0.55 pg. Thus, high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry was chosen as the final method and successfully applied to speciation analysis of seven gadolinium-based contrast agents in wastewater and whole blood. Compounds of gadoxetic acid disodium, gadobenate dimeglumine, gadodiamide, and gadobentetate dimeglumine were found in wastewater.     

Speciation analysis of mercury by solid-phase microextraction and multicapillary gas chromatography hyphenated to inductively coupled plasma-time-of-flight-mass spectrometry

This paper reports the development of an analytical approach for speciation analysis of mercury at ultra-trace levels on the basis of solid-phase microextraction and multicapillary gas chromatography hyphenated to inductively coupled plasma-time-of-flight mass spectrometry. Headspace solid-phase microextraction with a carboxen/polydimethylsyloxane fiber is used for extraction/preconcentration of mercury species after derivatization with sodium tetraethylborate and subsequent volatilization. Isothermal separation of methylmercury (MeHg), inorganic mercury (Hg2+) and propylmercury (PrHg) used as internal standard is achieved within a chromatographic run below 45 s without the introduction of spectral skew. Method detection limits (3 x standard deviation criteria) calculated for 10 successive injections of the analytical reagent blank are 0.027 pg g(-1) (as metal) for MeHg and 0.27 pg g(-1) for Hg2+. The repeatability (R.S.D., %) is 3.3% for MeHg and 3.8% for Hg2+ for 10 successive injections of a standard mixture of 10pg. The method accuracy for MeHg and total mercury is validated through the analysis of marine and estuarine sediment reference materials. A comparison of the sediment data with those obtained by a purge-and-trap injection (PTI) method is also addressed. The analytical procedure is illustrated with some results for the ultra-trace level analysis of ice from Antarctica for which the accuracy is assessed by spike recovery experiments.     

Determination of organometallic compounds by capillar gas chromatography – inductively coupled plasma mass spectrometry

The separation and detection of volatile organometallic compounds containing tin, iron, and nickel has been achieved using capillary GC–inductively coupled plasma–mass spectrometry (capillary GC-ICP-MS). Detection limits range from 3.0 to 7.0 pg/s. The presence of volatile organotin compounds in a harbor sediment has been confirmed. The retention range of the organometallic compounds analyzed by capillary GC-ICP-MS has been extended considerably beyond that possible in earlier studies (retention indices up to 3400).     

Speciation of butyltin compounds in environmental and biological samples using headspace single drop microextraction coupled with gas chromatography-inductively coupled plasma mass spectrometry

A method based on headspace single drop microextraction (HS-SDME) in combination with gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS) was proposed for the speciation analysis of butyltin compounds in environmental and biological samples. The sodium tetraethylborate (NaBEt4) and sodium tetrahydroborate (NaBH4) were used as the derivatizing reagent for in situ derivatization of the butyltins. For the two derivatizations, the HS-SDME parameters such as organic solvent, drop volume, sample pH, stirring rate, temperature, extraction time and the ionic strength were examined systematically. The analytical performance including the linearity ranges, limits of detection (LODs) and reproducibilities of the two derivatizations were compared under the respective optimized conditions. Derivatization with NaBEt(4) proved to be more sensitive and robust than that with NaBH4, leading to the LODs of 1.4 ng/L for MBT, 1.8 ng/L for DBT and 0.8 ng/L for TBT. The reproducibilities, expressed as relative standard deviations (RSDs), were in the range of 1.1-5.3% (c=1 microg/L, n=3). With tripropyltin (TPrT) as internal standard, HS-SDME-GC-ICP-MS with NaBEt(4) derivatization was applied for the speciation analysis of butyltins in real seawater and shellfish samples. The butyltins found in the real-world samples are 31ng/L MBT, 79 ng/L DBT and 32 ng/L TBT for seawater, and 11.6-30.4 ng/g MBT, 11.8-8.9 ng/g DBT and 12.8-52.6 ng/g TBT for different shellfish samples. For validation, the developed method was also employed for the speciation analysis of butyltins in certified reference material (CRM) of PACS-2 sediment, and the determined values are in a good agreement with the certified values. The developed method is simple, rapid, sensitive, and cost-effective and provides an attractive alternative for butyltins speciation in biological and environmental samples with complex matrix.     

Development of a species-specific isotope dilution GC-ICP-MS method for the determination of thiophene derivates in petroleum products

A species-specific isotope dilution technique for accurate determination of sulfur species in low- and high-boiling petroleum products was developed by coupling capillary gas chromatography with quadrupole ICP-MS (GC-ICP-IDMS). For the isotope dilution step ³⁴S-labeled thiophene, dibenzothiophene, and mixed dibenzothiophene/4-methyldibenzothiophene spike compounds were synthesized on the milligram scale from elemental ³⁴S-enriched sulfur. Thiophene was determined in gasoline, ‘sulfur-free’ gasoline, and naphtha. By analyzing reference material NIST SRM 2296, the accuracy of species-specific GC-ICP-IDMS was demonstrated by an excellent agreement with the certified value. The detection limit is always limited by the background noise of the isotope chromatograms and was determined for thiophene to be 7 pg absolute, which corresponds to 7 ng sulfur/g sample under the experimental conditions used. Dibenzothiophene and 4-methyldibenzothiophene were determined in different high-boiling petroleum products like gas oil, diesel fuel, and heating oil. In this case a large concentration range from about < 0.04 to more than 2,000 μg g⁻¹ was covered for both sulfur species. By parallel GC-ICP-MS and GC-EI-MS experiments (EI-MS electron impact ionization mass spectrometry) the substantial influence of co-eluting hydrocarbons on the ICP-MS sulfur signal was demonstrated, which can significantly affect results obtained by external calibration but not those by the isotope dilution technique.     

Evaluation of various sample pre-treatment methods for total and inorganic mercury determination in biological certified reference materials by CVAAS technique

Sample preparation methods for non-separation cold vapor atomic absorption spectrometry (CVAAS) sequential inorganic mercury speciation in biological certified reference materials (CRMs) were investigated. The methylmercury concentration was calculated as the difference between total and inorganic mercury. Microwave-assisted decomposition method, and three ultrasonic extraction procedures based on acid leaching with HCl and HCOOH and solubilization with TMAH were employed as sample preparation methods. The replacement of a sample decomposition procedure by extraction prior to analysis by CVAAS, as well as the aspect of speciation analysis is discussed. The limits of detection in the sample were determined as 50 and 10 ng L⁻¹ for inorganic and total mercury, which corresponds to absolute detection limits of 40 and 8 ng g⁻¹ for inorganic and total mercury, respectively. The results were in good agreement with the 95% confidence level t-test of the certified values for total and inorganic mercury in the reference materials investigated. From the analysis of the CRMs, it was evident that the difference between the total and inorganic mercury concentrations agrees with the methylmercury concentration. The relative standard deviation was better than 11% for most of the samples.      

Optimization of congener-specific analysis of 40 polybrominated diphenyl ethers by gas chromatography/mass spectrometry

The analysis by gas chromatography coupled with mass spectrometry (GC/MS) of 40 different congeners of polybrominated diphenyl ethers (PBDEs) containing 1-7 bromine atoms is described. Two different MS approaches were used, negative chemical ionization (NCI-MS) and electron ionization (EI-MS). Operating parameters such as electron energy and source temperature were optimized in order to obtain the maximum sensitivity in the EI-MS study. For NCI-MS analyses, the effects of the moderating gas (methane or ammonia), source temperature and system pressure were studied. The quality parameters of the two approaches tested were compared. NCI-MS gave detection limits between 30 fg and 1.72 pg, whereas EI-MS gave detection limits between 0.53 and 32.09 pg. The main advantage of EI-MS is that it provides better structural information. Moreover, the use of EI-MS allowed the use of an isotope dilution method for quantification, making the analysis more reliable at trace levels.     

Speciation analysis of organoarsenical compounds in biological matrices by coupling ion chromatography to atomic fluorescence spectrometry with on-line photooxidation and hydride generation

The optimisation of an on-line decomposition based on UV photooxidation for the analysis of organoarsenic species by coupling cation-exchange chromatography and atomic fluorescence spectrometry with hydride generation, is described. In this study, special consideration is given to the compatibility of mobile phases with post-column treatments. Results show that the most commonly used mobile phase, aqueous pyridine solutions, decreases species conversion efficiency, leading to a significant loss of sensitivity. New fully-compatible chromatographic conditions are proposed to separate arsenobetaine, arsenocholine, trimethylarsine oxide and tetramethylarsonium ion within 20 min. The very low absolute limits of detection, 4-12 pg(As), allow speciation at trace levels. Analysis of a certified reference fish tissue (DORM-2) and other seafood samples (French and Chilean oysters and mussel) highlights the robustness and the accuracy of the optimised system.     

Multicapillary gas chromatography coupled to inductively coupled plasma-time-of-flight mass spectrometry for rapid mercury speciation analysis

A simple, rapid and accurate method on the basis of multicapillary gas chromatography (MCGC) combined with inductively coupled plasma-time-of-flight mass spectrometry (ICP-TOFMS) was developed for speciation analysis of methylmercury (MeHg⁺) and inorganic mercury (Hg²⁺). The potential of the ICP-TOFMS for transient multi-isotope detection of very short signals (peak width of 0.4 s at half peak height) was evaluated. Two injection systems (purge-and-trap (PTI) and split (SI) injections) were compared in terms of species separation resolution and transient signal profile. Using purge-and-trap injection, after in situ derivatization of the ionic mercury species with sodium tetraethylborate, a baseline separation of MeHg⁺ and Hg²⁺ was achieved within a chromatographic run of <35 s. To correct for matrix-induced ion signal variation and instrumental drift, propylmercury (PrHg⁺) was used as internal standard. Detection limits of 16 and 257 fg g⁻¹ for MeHg⁺ (as Hg) and Hg²⁺, respectively, were achieved. The analytical precision (R.S.D. (%)) for 10 successive injections of a standard mixture containing 10 pg MeHg⁺ (as Hg) and Hg²⁺ was 1.2% for MeHg⁺ and 4.1% for Hg²⁺. The method was validated by analysis of two biological certified reference materials (CRM): a dogfish muscle (DORM-2) and a freeze-dried tuna fish (CRM 464).     

Mercury speciation by HPLC-cold-vapour radiofrequency glow-discharge optical-emission spectrometry with on-line microwave oxidation

Hollow-cathode (HC) radiofrequency glow-discharge (rf-GD) optical-emission spectrometry (OES) has been used as detector for the determination of inorganic mercury by cold-vapour (CV) generation in a flow-injection (FI) system. Both NaBH4 and SnCl2 were evaluated as reducing reagents for production of mercury CV. The conditions governing the discharge (pressure, He flow rate, and delivered power) and Hg CV generation (NaBH4 or SnCl2 concentration and reagent flow rate) were optimized using both reducing agents. The analytical performance characteristics of FI-CV-rf-GD-OES for mercury detection were evaluated at the 253.6 nm emission mercury line. Detection limits (DL) of 0.2 ng mL(-1) using SnCl2 and 1.8 ng mL(-1) using NaBH4 were obtained (100 microliter sample injections were used). When the optimized experimental conditions using SnCl2 had been determined, the analytical potential of this CV-rf-GD-OES method was investigated as on-line detector for high-performance liquid chromatographic (HPLC) speciation of mercury (Hg(II) and methylmercury). The HPLC-CV-rf-GD-OES detection limits for 100 microliter sample injections were found to be 1.2 and 1.8 ng mL(-1) (as mercury) of inorganic mercury and methylmercury, respectively. The reproducibility observed was below +/- 8% for both species. Finally, the HPLC-CV-rf-GD-OES system developed was successfully applied to the determination of methylmercury (speciation) in two certified reference materials, Dorm-2 and Dolt-2.     

Chromium(III)-imprinted silica gel for speciation analysis of chromium in environmental water samples with ICP-MS detection

A new chromium(III)-imprinted 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS)-functionalized silica gel sorbent was synthesized by a surface imprinting technique and was employed as a selective solid-phase extraction material for speciation analysis of chromium in environmental water samples prior to its determination by inductively coupled plasma mass spectrometry (ICP-MS). The prepared Cr(III)-imprinted silica gel shows the selectivity coefficient of more than 700 for Cr(III) in the presence of Mn(II). The static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Cr(III) were 30.5 mg g(-1) and 13.4 mg g(-1). It was also found that Cr(VI) could be adsorbed at low pH by the prepared imprinted silica gel, and this finding makes it feasible to enrich and determine Cr(VI) at low pH without adding reducing reagents. The imprinted silica gel sorbent offered a fast kinetics for the adsorption and desorption of both chromium species. Under the optimized conditions, the detection limits of 4.43 pg mL(-1) and 8.30 pg mL(-1) with the relative standard deviations (R.S.D.s) of 4.44% and 4.41% (C=0.5 ng mL(-1), n=7) for Cr(III) and Cr(VI) were obtained, respectively. The proposed method was successfully applied to the speciation of trace chromium in environmental water samples. To validate the proposed method, two certified reference materials were analyzed and the determined values were in a good agreement with the certified values. The developed method is rapid, selective, sensitive and applicable for the speciation of trace chromium in environmental water samples.     

Capillary electrophoresis inductively coupled plasma mass spectrometry

Chemical speciation (extraction of elemental information and identification of molecular environment for an analyte in a complex sample) has been a long sought after goal for analytical chemists. Recently, because of successful developments in more sensitive element-specific detectors and gentle separation schemes, which preserve the true chemical information in a real sample, routine speciation experiments are becoming a common occurrence in the scientific literature. For many reasons, the combination of capillary electrophoresis (for separation of different chemical species) with inductively coupled plasma mass spectrometry (for element and isotope specific detection) has emerged as the method of choice for these analyses. In this article the basic principles of capillary electrophoresis inductively coupled plasma mass spectrometry are discussed. Design consideration for instrument interface, anticipated difficulties with speciation experiments and applications for specific matrices and analytes are also presented in this article.     

Two methods for the speciation analysis of mercury in fish involving microwave-assisted digestion and gas chromatography-atomic emission spectrometry

In this paper a novel approach for the speciation analysis of mercury (methyl mercury and mercury II) in fish tissue using gas chromatography-microwave induced plasma atomic emission spectromertry is described. Focused microwave-assisted digestion which has been used previously in speciation analysis only for the determination of organotin and organoselenium compounds, was applied for sample preparation, a technique which enables mild, quick and complete dissolution of the sample. The important parameters for the digestion of fish tissues were optimised for the given analytical problem. Since no experience was available for the further treatment of the produced sample solution two different derivatisation/injection procedures were examined:

1. (1) ethylation with sodium tetraethylborate, extraction into hexane and injection with a cooled injection system and

2. (2) hydride generation with sodium tetrahydroborate together with purge-and-trap injection. The latter reaction has not been used previously for the determination of mercury species in fish samples.

The optimum parameters for both procedures were evaluated and the methods were validated by analysis of a standard reference material (CRM 464). The 3σ detection limits were (1) 3.0 pg g⁻¹ and (2) 12.5 pg g⁻¹.