Application of isotope dilution to the determination of methylmercury in fish tissue by solid-phase microextraction gas chromatography–mass spectrometry

Simple and rapid analytical method for the determination of methylmercury in fish and shellfish using solid-phase extraction and gas chromatography-mass spectrometry

Herein, we devise a method to detect methylmercury (MeHg) in fish and shellfish food samples using solid-phase extraction. We draw from the principles of the "QuEChERS" method, eliminating the need for hazardous organic solvents and employing general-purpose gas chromatography-mass spectrometry (GC-MS) equipment. The use of acetonitrile during extraction prevents emulsion formation, which could otherwise disrupt MeHg recovery. Additionally, the introduction of sulfuric acid solution during extraction dissolves sample lipids. The purification process involves solid-phase extraction instead of liquid-liquid extraction, ensuring rapid and straightforward analysis. The MeHg recovery, analyzed using reference samples and MeHg-loaded blank samples, is 86.1 %-98.3 %, and the limit of quantification is 0.02 mg/kg. The calibration curves for phenyl-derivatized MeHg exhibit exceptional linearity at 1-50 ng/mL. The intra- and inter-assay coefficients of variation validate the repeatability and intermediate precision of our method. This analytical approach is simple, and it offers high precision and accuracy, making it valuable for quantifying MeHg in fish and shellfish food samples.

Characterization of arsenic species by liquid sampling-atmospheric pressure glow discharge ionization mass spectrometry

A liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source operating at a nominal power of 30 W and solution flow rate of 30 µL min-1 and supported in a He sheath gas flow rate of 500 mL min-1 was interfaced to an Orbitrap mass spectrometer and assessed for use in rapid identification of inorganic and organic arsenic species, including As(III), As(V), monomethylarsonic acid, dimethylarsinic acid, and arsenobetaine in a 2% (v/v) nitric acid medium. Mass spectral acquisition in low-resolution mode, using only the ion trap analyzer, provided detection of protonated molecular ions for AsBet (m/z 179), DMA (m/z 139), MMA (m/z 141), and As(V) (m/z 143). As(III) is oxidized to As(V), likely due to in-source processes. Typical fragmentation of these compounds resulted in the loss of either water or methyl groups, as appropriate, i.e., introducing DMA also generated ions corresponding to MMA and As(V) as dissociation products. Structure assignments were also confirmed by high-resolution Orbitrap measurements. Spectral fingerprint assignments were based on the introduction of solutions containing 5 µg mL-1 of each arsenic compound.

Reduction in mercury bioavailability to Asian clams (Corbicula fluminea) and changes in bacterial communities in sediments with activated carbon amendment

Activated carbon (AC) amendment is considered as one of the alternatives for managing and remediating mercury (Hg) contaminated sediments because of its high sorptive capacity and potential to immobilize the contaminant. For this study, the underlying mechanisms that control the reduction of Hg bioavailability in AC-amended estuarine sediments were investigated in box microcosm set-ups with 28-day Asian clam bioassay experiments. The application of diffusive gradients in thin film technique (DGT) revealed that the total mercury and methylmercury levels in sediment pore water decreased by 60%-75% in 1%-3% AC-amended sediments. This decrease subsequently led to a linear reduction in the Hg body burden in Asian clams, even at 1% sorbent mixing. These observations implied that AC amendment reduced the net flux of Hg into the pore water and overlying water, resulting in reduced Hg bioaccumulation in benthic organisms. The addition of AC to sediment also led to reduced dissolved organic carbon and several biogeochemical indicators (HS^-, Mn, and Fe) in the pore water. Furthermore, the 16 S rRNA gene amplicon sequencing analysis revealed noticeable alterations in the microbial communities after AC amendment. The predominant phylum was Firmicutes in control sediment, Bacteroidetes in 1% AC-amended sediment, and Proteobacteria in both 2% and 3% AC-amended sediment samples. The genera-level analysis showed that the relative abundance of the Hg-methylators decreased as the level of AC amendment increased. These observations suggested that AC amendment decreased Hg bioavailability not only by physicochemical sorption but also by changing geochemical species and shifting the microbial community composition.

Dinuclear HgII tetracarbene complex-triggered aggregation-induced emission for rapid and selective sensing of Hg2+ and organomercury species

Mercury-mediated chelate ring formation and subsequent aggregation gives strong fluorescence for rapid and selective sensing of Hg²⁺ and organomercury.

Rapid, reliable and highly selective detection of mercury species, including Hg²⁺ ions and organomercury, is of significant importance for environmental protection and human health. Herein, a new fluorescent dye 1,1,2,2-tetrakis[4-(3-methyl-1H-benzimidazol-1-yl)phenyl ethylene tetraiodide (Tmbipe) with aggregation-induced emission (AIE) potential was prepared and characterized. The presence of four positively charged methylated benzimidazole groups endows Tmbipe with excellent water solubility and almost undetectable background fluorescence. However, it can coordinate with two Hg²⁺ ions or two organomercury molecules (e.g. methylmercury and phenylmercury) to form a planar dinuclear Hg^II tetracarbene complex, which can then self-aggregate to turn on AIE fluorescence. Such a fluorescence turn-on process can be completed in 3 min. In addition, synergic rigidification of the tetraphenylethylene-bridged Tmbipe molecule by mercury-mediated chelate ring formation and subsequent aggregation results in obviously higher fluorescence enhancement than that given by the single aggregation-induced one. Low background, high fluorescence enhancement and rapid response time make Tmbipe a good fluorescent probe for reliable, sensitive and highly selective quantitation of both inorganic and organic mercury species. This probe was also demonstrated to work well for identification of mercury species accumulation in living cells.

Solid phase microextraction (SPME) combined with TGA as a technique for guest analysis in crystal engineering

Guest identification using SPME – a technique for analysis of TGA off-gas that eliminates the need for direct TGA-GC/MS coupling.

Mercury and methylmercury in Korean herbal medicines and functional health foods

Total mercury (Hg) and methyl mercury (MeHg) were analysed in functional health foods (FHFs) and in Korean herbal medicines (KHMs). A total of 560 samples (FHFs, n = 511; KHMs, n = 49) were collected. The levels of total Hg in 416 samples were lower than the limit of detection. MeHg analysis was conducted in 45 samples and the ranges of MeHg levels in samples were less than the LOD of 38.92 ng g(-1). Weekly intake per body weight (WIPBW) values of total Hg in FHFs and KHMS were 0.89 and 11.77 ng kg(-1) BW, respectively. The margins of exposure (MOEs) of total Hg for FHFs and KHMS were 598,753 and 36,503, respectively. The WIPBW values of MeHg for FHFs and KHMS were 0.22 and 0.01 ng kg(-1) BW, respectively. MOE values of MeHg for FHFs and KHMS were 412,276 and 517,363, respectively.

Blood concentration of methylmercury in relation to food consumption

OBJECTIVE

Dietary fish is the main source of methylmercury (MeHg) for man, and fish consumption has been used as a measure of MeHg exposure. However, other dietary sources of exposure exist and MeHg metabolism may also be modified by nutritional factors. The aim of the present study was to examine the association between blood MeHg concentration and consumption of different foods in a Finnish population with high fish consumption.

DESIGN

Blood samples, a detailed FFQ and additional frequency data on fish consumption were collected. MeHg was analysed from whole blood by the isotope dilution method with high-resolution MS. The consumption of different foods was calculated by MeHg quartiles and tested for linear trend.

SETTING

Finnish southern and south-western coast of the Baltic Sea.

SUBJECTS

Two hundred and ninety-nine professional fishermen, their spouses and other family members.

RESULTS

Mean (range) blood MeHg concentration was 4·6 (0·21-22) μg/l among men and 2·8 (<0·15-20) μg/l among women. Fish had the strongest positive association with MeHg (P for linear trend <0·001 among both men and women). Among men, positive associations were also observed for fruit vegetables, wheat and wine. Among women, positive associations were observed for root vegetables, legumes, potato and game, but adjustment for fish consumption attenuated these trends.

CONCLUSIONS

The study shows that, besides fish, MeHg may have other dietary sources that should be taken into account in risk assessment studies. Due to the observed high blood MeHg concentration, a thorough exposure assessment among the general Finnish population is recommended.

Isotope dilution SPME GC/MS for the determination of methylmercury in tuna fish samples

The development of a rapid, precise and accurate analytical method for the determination of methylmercury in tuna fish samples is described. The method is based on the use of isotope dilution GC/MS with electron impact ionization, a widespread technique in routine testing laboratories. A certified spike containing (202)Hg-enriched methylmercury was used for the isotope dilution of the samples. After extraction of the methylmercury from the sample, methylmercury was propylated using sodium tetrapropyl borate in SPME vials and the analytes were sampled from the headspace for 15 min. For isotope measurements, the molecular ion (MePrHg(+)) was used in the SIM mode. Five molecular ions were monitored, corresponding to the (198)Hg, (199)Hg, (200)Hg, (201)Hg and (202)Hg isotopes. The detection at masses corresponding to (198)Hg was used to correct for m + 1 contributions of (13)C from the organic groups attached to the mercury atom on the (199)Hg, (200)Hg, (201)Hg and (202)Hg masses with simple mathematical equations, and the concentration of methylmercury was calculated on the basis of the corrected (200)Hg/(202)Hg isotope ratio. The (202)Hg-enriched methylmercury spike was applied, with satisfactory results, to the determination of methylmercury in the certified reference material BCR 464. The method was successfully applied to the determination of methylmercury in tuna fish samples, and the obtained results were included in the CCQM-P39 interlaboratory exercise, organized by the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium) with excellent agreement between our results and the average obtained by the other participants.

Isotope dilution GC-MS routine method for the determination of butyltin compounds in water

A standard GC-MS instrument with electron impact ionisation has been used to develop a fast, simple and reliable method for the simultaneous determination of monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in water samples. Isotope dilution analysis (IDA) is used for the determination of species, taking advantage of a commercially available spike solution containing a mixture of MBT, DBT and TBT enriched in 119Sn. Method detection limits for 100-mL samples were between 0.18 and 0.25 ng L(-1) for the three butyltin compounds with typical RSD between 2 and 4% at levels between 100 and 10 ng L(-1), respectively. Recovery of tin species in spiked samples (natural water, wastewater and seawater) was quantitative. The stability of butyltin compounds in collected seawater samples was also studied. The addition of a 1% (v/v) glacial acetic acid preserved tin species in the samples for at least 5 days at room temperature. The IDA method was finally implemented in a routine testing laboratory and it was subsequently accredited by the Spanish National Accreditation Body according to the requirements of UNE-EN ISO/IEC 17025.

Determination of Methionine and Selenomethionine in Selenium-Enriched Yeast by Species-Specific Isotope Dilution with Liquid Chromatography−Mass Spectrometry and Inductively Coupled Plasma Mass Spectrometry Detection

Selenomethionine (SeMet) and methionine (Met), liberated by acid hydrolysis of selenium-enriched yeast, were quantified by liquid chromatography-mass spectrometry (LC/MS) using standard additions calibrations as well as isotope dilution (ID) based on species-specific (13)C-enriched spikes. LC inductively coupled plasma mass spectrometry (ICPMS) was also employed for the quantification of SeMet, and (74)Se-enriched SeMet was used for ID calibration. The results were evaluated to ascertain the feasibility of using these methods in a campaign to certify selenized yeast. Good agreement was found between the methods, which, when averaged, gave concentrations of 5482.2 +/- 101 and 3256.9 +/- 217.4 microg/g for Met and SeMet, respectively. This corresponds to a 1.68:1 Met-to-SeMet ratio in the yeast. Quantification by ID LC/MS and LC ICPMS yields the most precise sets of results with relative standard deviations in the range 0.5-1.3% (n = 6). A total selenium concentration of 2064.6 +/- 45.4 microg/g was obtained for this yeast material. The extraction efficiency and a mass balance budget were determined. Acid hydrolysis liberated 81.0% of the total selenium present. SeMet comprised 79.0% of the extracted selenium and 63.9% of the total selenium present in the yeast.

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

A novel, straightforward solid-phase extraction system for the determination of inorganic mercury and organomercury compounds in water is proposed. The analytes, in a buffer medium at pH 4.5, are sorbed as diethyldithiocarbamate complexes on a C60 fullerene column an subsequently eluted and derivatized with sodium tetra-n-propylborate in ethyl acetate. Following elution, 1 microl of extract is injected into a gas chromatograph-mass spectrometer system. The proposed gas chromatography-mass spectrometry speciation method exhibits a linear range of 4-1 ng/ml, and a detection limit of 1.5 ng/l (sample volume, 50 ml). Its repeatibility, as relative standard deviation (RSD) (from 11 standards containing 50 ng/l for each analyte), is ca. 7%. No interferences from metals ions, such as Zn2+, Fe3+, Sb3+, As3+, Pb2+, Ni2+, Cu2+, Sn2+, Co2+, Mn2+ and Cd2+ were encountered at concentrations 1000 times higher than those of the mercury compounds. The method was used for the speciation of inorganic mercury, methylmercury and ethylmercury in various types of water including sea and waste water.

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.