Gas Chromatography Atomic Fluorescence Spectrometry Research Articles

An improved method for rapid and safe preparation and measurement of dimethylmercury using gas chromatography-atomic fluorescence spectrometry

Transformations between dimethylmercury (DMHg) and other mercury (Hg) species have been one of the critical knowledge gaps in the Hg global biogeochemical cycle due to the lack of detailed studies. The preparation and measurement of DMHg are challenging due to the high toxicity and volatility of DMHg. In this work, we invented a new DMHg generator for successfully preparing high-purity DMHg in a highly controllable and safe way. The DMHg could be spontaneously volatilized and diffused from the original preparation solution to the solution to be studied. The parameters for generating DMHg were optimized to be the pH value of 4.0 with a MeCo/Hg2+ molar ratio of 10 at 20 °C. The following measurement method of DMHg in the presence of various species of Hg was also investigated and optimized. Hg0 and DMHg could be separated effectively with the carrier gas flow rate of 15 mL min−1 and the gas chromatography column temperature of 30 °C. The interferences of Hg0, monomethylmercury and other species were excluded by systematic control experiments. A sensitive and reliable approach for quantifying trace DMHg in water was developed. Under the optimal conditions, the limits of detection for Hg0, MMHg and DMHg were 0.03, 0.002 and 0.024 ng L−1, respectively, with the relative standard deviation below 8.2%. The developed method was validated by the determination Hg species of different natural water samples. This work is expected to provide a new and safe strategy for DMHg preparation and a verified method for DMHg measurement.

Behavior of KCl sorbent traps and KCl trapping solutions used for atmospheric mercury speciation: stability and specificity

Abstract. Atmospheric mercury speciation is of paramount importance for understanding the behavior of mercury once it is emitted into the atmosphere as gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate-bound mercury (PBM). GOM and PBM can also be formed in the atmosphere; their sampling is the most problematic step in the atmospheric mercury speciation. GOM sampling with speciation traps composed of KCl sorbent materials and KCl trapping solutions are commonly used sampling methods, although the research conducted with them at ambient air concentrations is limited. The results of the specificity test demonstrated that the KCl sorbent traps are highly specific when using new traps, while their specificity drops dramatically when they are reused. The results of the stability test indicated that the highest Hg2+ losses (up to 5.5 % of Hg2+ loss) occur when low amounts of Hg2+ (< 1 ng) are loaded, due to a reduction of Hg2+ to Hg0. KCl trapping solutions have also been considered as a selective trapping media for GOM in atmospheric samples. A dimensionless Henry law constant was experimentally derived and was used to calculate the solubility of elemental Hg in KCl solution. The degree of GEM oxidation was established by purging elemental Hg calibration gas into a KCl solution and determining the GOM trapped using aqueous-phase propylation liquid–liquid extraction and gas chromatography–atomic fluorescence spectrometry (GC-AFS) measurement. A positive GOM bias was observed due to the solubility and oxidation of GEM in KCl trapping solutions, strongly suggesting that this approach is unsuitable for atmospheric mercury speciation measurements.

Rapid determination of femtomolar methylmercury in seawater using automated GC-AFS method: Optimisation of the extraction step and method validation

Among ionic mercury species methyl mercury (MMHg) is the most toxic form present in the environment, which is known to be bio-accumulative neurotoxin in the aquatic food chain and could provide the major route of exposure for humans to mercury through consumption of marine food products. The availability of reliable analytical methods for evaluating spatial and temporal contamination trends of MMHg in the ocean is an important prerequisite for marine monitoring. Sound strategies for marine monitoring call also for measurement systems capable of producing comparable analytical results with demonstrated quality.A sensitive analytical procedure for environmental monitoring of MMHg content in seawater, based on specific extraction and Gas Chromatography Atomic Fluorescence Spectrometry validated according to the requirements of international guidelines and standards, ISO 17025 and Eurachem guidelines, is presented in this study.The entire measurement process was described by mathematical equations and all factors influencing the results were systematically investigated. Selectivity, working range, linearity, recovery (94 ± 4%), repeatability (3.3%–4.5%), intermediate precision (2.9%), limits of detection (0.0004 ng kg−1as Hg) were systematically assessed. The relative expanded uncertainties obtained were in the range from 16% to 25%, (k = 2).Modelling of the entire measurement process related obtained values for MMHg in seawater to the International System of units (Kg). The potential of this analytical procedure was tested and additionally validated via inter laboratory comparison exercise organised under the Geotraces programme. Obtained results were in excellent agreement with the assigned values.The proposed analytical procedure from the sample preparation to the measurement step combined with the high efficiency of the new generation of the automated MMHg analyzers is fit for purpose for routine monitoring studies on the dissolved MMHg in the costal and open ocean seawaters.

Atomic fluorescence spectrometric detection of methylmercury in seawater at sub ng L−1 level by UV-induced atomization of gaseous methylethylmercury after NaBEt4 derivatization with purge and trap preconcentration and gas chromatography separation

A sensitive method for methylmercury (MeHg) analysis in seawater by UV-induced atomization of methylethylmercury (MeHgEt) based on NaBEt4 derivatization with purge and trap preconcentration and gas chromatography- atomic fluorescence spectrometry (GC-AFS) detection was developed. The UV atomizer was demonstrated successfully to atomize MeHgEt to Hg0 with low temperature (<45 °C) and low consumption (11 W). The effects of UV lamp power, the quartz tube length, the GC carrier gas flow rate and the NaBEt4 concentration on MeHg determination were optimized. The relative standard deviations obtained from 0.25 ng L−1 MeHg was 3.5%. The detection limits was calculated as 0.0002 ng L−1 for MeHg, which not only reduced two orders of magnitude compared to the solid-phase extraction and cation or anion exchange column preconcentration methods, but also was comparable or even better than the thermal decomposition and dielectric barrier discharge (DBD) atomization methods after NaBEt4 or NaBPr4 derivatization with purge and trap preconcentration. In addition, compared with KBH4 as reductant without preconcentration, the detection limit of this method was nearly reduced six orders of magnitude for MeHg. The accuracy of the proposed method was also validated by analyzing a certified reference sample (GBW08675) with a satisfactory result and successfully applied to the determination of MeHg in sub ng L−1 level in different seawater samples.

Dielectric barrier discharge induced atomization of gaseous methylethylmercury after NaBEt4 derivatization with purge and trap preconcentration for methylmercury determination in seawater by GC-AFS

A novel method suitable for methylmercury (CH3Hg) analysis in seawater by gas chromatography (GC)-atomic fluorescence spectrometry (AFS) based on dielectric barrier discharge (DBD) induced atomization of gaseous methylethylmercury (CH3HgC2H5) after sodium tetraethylborate (NaBEt4) derivatization with purge and trap preconcentration was developed in this work. In the proposed method, with NaBEt4 used as derivatization reagent, the nonvolatile CH3Hg could be converted to the gaseous CH3HgC2H5 and trapped in a quartz tube with Tenax sorbent for preconcentration. A DBD atomizer was employed for the atomization of CH3HgC2H5 to Hg0 between the GC separation and AFS detection instead of the conventional thermal decomposition atomizer, which had not been reported before. The DBD atomizer not only produces a comparable atomization efficiency for CH3HgC2H5 to the thermal decomposition atomizer, but also can be operated at room temperature with low power consumption (5 W). The effects of DBD input discharge voltage, DBD discharge distance, N2 gas purge time, and thermal desorption time on CH3Hg determination were evaluated. The method provided good reproducibility (RSD, 2.0%) and low detection limits of CH3Hg (LOD, 0.0008 ng L−1). The proposed method was validated by the analysis of a certified reference material (GBW08675) and successfully applied to the determination of CH3Hg in sub ng L−1 level in different seawater samples.

Study on analytical method for methlmecury in sediment by gas chromatography-atomic fluorescence spectrometry using Grignard reagcuts for alkylation

The analytical method for methylmercury in sediment samples was performed using an hyphenated system of gas chromatograph coupled atomic fluorescence detector (GC-AFS). Methylmercury in sediment samples was leached and extracted into dichloromethane with the assistance of HNO3, KCl and CuSO4. Dichloromethane was evaporated resulting in the relocation of MeHg to the aqueous phase. MeHg was then extracted in the form of diethyldithiocarmate complex into hexane followed by the alkylation processes with Grignard reagents, butyl magnesium chloride and ethyl magnesium chloride. The alkylation reactions were optimized with respect to the mounts of Grignard reagents, the reaction temperature and time for the best alkylation yields and least extent of trans-alkylation and degradation of the alkylated products. The alkylated MeHg compounds were analyzed by GC-AFS. The analytical method for methylmercury was validated using certified reference material ERM-CC580. The instrumental limit of detection was 1.4 pg as Hg. The method limits of detection for EtMgCl and BuMgCl were 0.18 were 0.18 ng/g and 0.19 ng/g, respectively. This method can be used to analyze MeHg in sediment samples.

Determination of methylmercury in marine biota samples with advanced mercury analyzer: Method validation

In this paper, we present a simple, fast and cost-effective method for determination of methyl mercury (MeHg) in marine samples. All important parameters influencing the sample preparation process were investigated and optimized. Full validation of the method was performed in accordance to the ISO-17025 (ISO/IEC, 2005) and Eurachem guidelines. Blanks, selectivity, working range (0.09–3.0ng), recovery (92–108%), intermediate precision (1.7–4.5%), traceability, limit of detection (0.009ng), limit of quantification (0.045ng) and expanded uncertainty (15%, k=2) were assessed. Estimation of the uncertainty contribution of each parameter and the demonstration of traceability of measurement results was provided as well. Furthermore, the selectivity of the method was studied by analyzing the same sample extracts by advanced mercury analyzer (AMA) and gas chromatography–atomic fluorescence spectrometry (GC–AFS).Additional validation of the proposed procedure was effectuated by participation in the IAEA-461 worldwide inter-laboratory comparison exercises.

Determination of Methylmercury in Soil Samples with Online Purge and Trap Gas Chromatography-Atomic Fluorescence Spectrometry

Determination of Methylmercury in Soil Samples with Online Purge and Trap Gas Chromatography-Atomic Fluorescence Spectrometry

Biogeochemistry of mercury and methylmercury in sediment cores from Sundarban mangrove wetland, India—a UNESCO World Heritage Site

This study was performed to elucidate the distribution, concentration trend and possible sources of total mercury (Hg(T)) and methylmercury (MeHg) in sediment cores (<63 μm particle size; n = 75) of Sundarban mangrove wetland, northeastern part of the Bay of Bengal, India. Total mercury was determined by atomic absorption spectrometry (AAS) in a Leco AMA 254 instrument and MeHg by gas chromatography-atomic fluorescence spectrometry (GC-AFS). A wide range of variation in Hg(T) (0.032-0.196 μg g(-1) dry wt.) as well as MeHg (0.04-0.13 ng g(-1) dry wt.) concentrations revealed a slight local contamination. The prevalent low Hg(T) levels in sediments could be explained by sediment transport by the tidal Hugli (Ganges) River that would dilute the Hg(T) values via sediment mixing processes. A broader variation of MeHg proportions (%) were also observed in samples suggesting that other environmental variables such as organic carbon and microbial activity may play a major role in the methylation process. An overall elevated concentration of Hg(T) in surface layers (0-4 cm) of the core is due to remobilization of mercury from deeper sediments. Based on the index of geoaccumulation (I (geo)) and low effects-range (ER-L) values, it is considered that the sediment is less polluted by Hg(T) and there is less ecotoxicological risk. The paper provides the first information of MeHg in sediments from this wetland environment and the authors strongly recommend further examination of Hg(T) fluxes for the development of a detailed coastal MeHg model. This could provide more refine estimates of a total flux into the water column.

Application of Gas Chromatography–Atomic Fluorescence Spectrometry Hyphenated System for Speciation of Butyltin Compounds in Water Samples

ABSTRACT A laboratory-established capillary gas chromatography (GC)–atomic fluorescence spectrometry (AFS) hyphenated system was applied to butyltin speciation in water samples. Monobutyltin (MBT), dibutyltin (DBT), and tributyltin (TBT) were extracted and preconcentrated with headspace solid-phase microextraction (SPME) technique after derivatization using KBH4, and then determined by GC-AFS directly. The experimental conditions—including the flow rates of carrier gas, argon and hydrogen–and the lamp current—were optimized in detail. Under the optimum conditions, the detection limits for MBT, DBT, and TBT, calculated as three times the baseline noise, were 10, 0.2, and 0.1 ng mL−1 Sn, respectively. Good linear relationships were obtained when the concentrations of MBT, DBT, and TBT increased to 3000, 100, and 200 ng mL−1 Sn. The relative standard deviations (RSDs) of five replicates were 5.2%, 7.4%, and 7.1% for MBT, DBT, and TBT, respectively. The recoveries of MBT, DBT, and TBT in three different types of water samples (seawater, tap water, and wastewater) were between 72.1% and 97.9%, indicating that the proposed method was accurate and feasible for speciation analysis of butyltin compounds in water samples.

Mercury speciation in hair by headspace injection–gas chromatography–atomic fluorescence spectrometry (methylmercury) and combustion-atomic absorption spectrometry (total Hg)

The speciation of Hg in human hair was carried out with combustion-atomic absorption spectrometry for total Hg (THg) and headspace–gas chromatography–atomic fluorescence spectrometry (HS–GC–AFS) for methylmercury (MMHg). The determination of total Hg in hair was carried out with the AMA analyzer (Advanced Mercury Analyser 254). Accuracy and reproducibility were assessed on a Certified Reference hair sample (IAEA-086 CRM), yielding, respectively, a recovery of 97.5% and a RSD of 3.2%. Analyses of 10 blank measurements resulted in a detection limit of 1.5 ng g −1 of THg for a 20 mg sample of human hair. MMHg concentrations in hair were assessed with HS–GC–AFS in a single analysis step. Either acid or alkaline extraction can be applied because they yielded very similar results on a IAEA-086 CRM: we observed a recovery of 103% and a RSD of 7% with acid extraction and a recovery of 110% and a RSD of 9% with alkaline extraction. Optimization of the headspace vial, injection and GC parameters is described. The detection limit of the MMHg determination in human hair, which amounts to 0.04 ng g −1 for a 20 mg sample, is far below the concentrations observed in natural samples. The number of samples that can be analyzed per hour, respectively, amounts to 8 for THg and 4 for MMHg. Finally, Hg speciation in natural human hair samples was carried out by combining both AMA and HS–GC–AFS analysis methods. THg levels were at the μg g −1, level, with an average MMHg fraction of about 70%.

Improvements of reliability for methylmercury determination in environmental samples

The determination of methylmercury (MeHg) in environmental samples by ethylation derivation–gas chromatography–atomic fluorescence spectrometry (ED–GC–AFS) is associated with an intimate problem of water moisture accumulation introduced in the ethylation step, which enters the detection system and cause a spectroscopic interference. With a simple modification on the GC–AFS system, this problem was eliminated and the analytical quality of the measurements was significantly improved. The presence of dissolved sulfide in samples can also cause serious chemical interference in the ethylation step resulting in lower or total loss of the MeHg signal. It was found that a masking system of CuSO 4–Na 2C 2O 4 was able to eliminate this interference. With this system, the accurate determination of trace amount of MeHg in high dissolved sulfide containing samples was achieved. Satisfactory analytical results were obtained with the certified reference sediment IAEA405, sulfate reducing bacteria culture and sulfide containing water samples. The limit of detection and quantitation of this masking system is 0.01 and 0.04 ng L −1 respectively. Other factors affecting ethylation are also discussed.

Analytical approach for routine methylmercury determination in seafood using gas chromatography-atomic fluorescence spectrometry

Two methodologies have been developed for the analysis of mercury species in seafood by capillary gas chromatography coupled to an AFS detector via pyrolysis. The first one is based on the ethylation of both, inorganic and methylmercury species ( Method 1), in which clean-up is not necessary because a small amount of sample is required. In the second one, monoalkylated mercury species are extracted into organic phases after forming the corresponding chlorides ( Method 2). In this case the elimination of the interfering compounds from the matrix requires a clean-up step, which enables the treatment of higher quantities of sample. Both procedures can be considered complementary because the concentration range applicable for each one of them is different: 0.75–10 μg Hg g −1, in dry basis for methylmercury ( Method 1) and 6–1000 ng Hg g −1 ( Method 2). The range of application for natural samples can be easily selected by a preliminary analysis of total mercury, because most mercury in seafood is present as MeHg. Optimum parameters for both procedures have been evaluated, and the methods were validated with two standard reference materials (BCR-463 and NIST-2977). Finally, the methods have been applied to the analysis of seafood samples. Detection limits of MeHg range from 1.7 to 220 ng Hg g −1 (dry basis) depending of the methodology selected and the weight of sample. The method can be successfully applied to commercially available seafood samples, and considered for routine analysis.

Evaluation of different sample pre-treatment and extraction procedures for mercury speciation in fish samples

Investigations are described to select the most suitable drying and extraction procedures for mercury speciation in fish samples. The criteria for selection were good recovery and preservation of the original species information. Three different drying techniques were evaluated: oven-dried, microwave oven-dried and freeze-dried. Best results were obtained when oven-dried, but microwave dried or freeze-dried showed mercury losses. The four extraction methods investigated were: HCl leaching, alkaline–methanol extraction with tetramethylammonium hydroxide (TMAH) and with KOH, and sodium dodecyl sulfate (SDS) extraction. The extraction efficiency was determined by comparing the total amount of mercury in the samples after microwave digestion with the amount extracted by the different methods described. Mercury measurements were carried out by flow injection-cold vapour-atomic fluorescence spectrometry (FI-CV-AFS). Quantitative mercury extraction was only achieved with HCl leaching (97%). Species integrity after extraction was evaluated by investigating the extracts with capillary gas chromatography-atomic fluorescence spectrometry. Artificial formation of dimethylmercury occurs when TMAH is used as extractant. HCl leaching-GC-AFS was finally applied to methylmercury determination in tuna fish and swordfish samples, and gave results in the range 0.78–1.93 mg kg−1. The detection limit for monomethylmercury (MMHg) was found to be 1.2 pg.

Determination of methylmercury in sediments by steam distillation/aqueous-phase ethylation and atomic fluorescence spectrometry

A method is described for the determination of methylmercury in natural sediment samples using steam distillation followed by aqueous phase derivatisation and gas chromatography-atomic fluorescence spectrometry. Recoveries of methylmercury spikes to wet sediments were >95% except for an industrially-contaminated, sulfidic sediment (76% recovery). The method precision was typically <10% relative standard deviation for unspiked sediment samples having methylmercury concentrations ranging from 0.6 to 76 ng/g. The detection limit was approximately 0.01 ng/g for 1 g of wet sediment. The method was assessed for artefactual methylation of added inorganic mercury spikes (1–10 μg). Artefactual methylation ranged from unmeasurable to 0.05% of added inorganic mercury in one tropical lake sample. The results obtained with the proposed procedure for two reference sediment materials were significantly lower than literature reported values obtained by nitrogen-assisted distillation and were comparable with data obtained using low artifact producing solvent extraction procedures. Method throughput of the steam distillation step was four to five samples per hour which represents a considerable improvement over existing distillation methods.

Determination of methyl-and ethylmercury compounds using gas chromatography atomic fluorescence spectrometry following aqueous derivatization with sodium tetraphenylborate

An analytical procedure is described for the determination of methylmercury and ethylmercury compounds in fish and sediment samples, using gas chromatography atomic fluorescence spectrometry following aqueous phenylation with sodium tetraphenylborate. The derivatization products were identified by gas chromatography mass spectrometry. The advantages of using phenylation with sodium tetraphenylborate over ethylation with sodium tetraethylborate are discussed. The validation of the analytical procedure was performed by analyzing standard reference material (DORM-2). Applications for the analysis of fish and sediment samples were carried out and compared to other techniques.

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 AFS and ICP-MS detection coupled with gas chromatography for the determination of methylmercury in marine samples

Inductively coupled plasma mass spectrometry (ICP-MS) and atomic fluorescence spectrometry (AFS) coupled with gas chromatography (GC) have been evaluated as element specific detectors for the determination of methylmercury in marine samples. Detection limits for methylmercury chloride, obtained using ICP-MS and AFS, were 0.9 and 0.25 pg as Hg, respectively. Methylmercury was determined in marine tissue reference materials IAEA 142 and NIST 8044 mussel homogenate, and DOLT-2 dogfish liver by GC–AFS, with found values of 45±7, 26±4, and 671±41 ng g −1, compared with certified values of 47±4, 28±2, and 693±53 ng g −1. The analyses of IAEA 142 and NIST 8044 were repeated using GC–ICP-MS, with found values of 48±9 and 30±3 ng g −1, respectively. Methylmercury was determined in real samples of ringed seal and beluga whale, with found values of 801±62 and 2830±113 ng g −1, respectively.

Determination of methylmercury in fish and aqueous samples using solid-phase microextraction followed by gas chromatography-atomic fluorescence spectrometry

An analytical method is described for methylmercury determination in fish and aqueous samples using solid-phase microextraction (SPME) followed by gas chromatography–atomic fluorescence spectrometry (GC–AFS). The procedure involves aqueous-phase derivatization of methylmercury species with sodium tetraethylborate in a sample vial and subsequent extraction with a silica fiber coated with poly-­(dimethylsiloxane). The mercury derivatives are desorbed in the splitless injection port of a gas chromatograph and subsequently analyzed by GC–AFS. The headspace SPME procedure is used and parameters affecting the extraction, adsorption and desorption are evaluated. Results for methylmercury analysis in standard reference material (DORM-2) and fish samples are presented. © 1998 John Wiley & Sons, Ltd.

Evaluation of some Isolation Methods for Organomercury Determination in Soil and Fish Samples by Capillary Gas Chromatography—Atomic Fluorescence Spectrometry

Three extraction methods, acidic KBr/CuSO4 isolation-methylene chloride extraction. acidic KBr/CuSo4 isolation-methylene chloride extraction with an alkaline digestion pretreatment, and an extration method at a milder condition with citrate buffer and dithizone in chloroform, were studied for methylmercury and ethylmercury determination in soils, sediments and fish samples by the recently developed capillary gas chromatography—atomic fluorescence spectrometry system (GC-AFS). The acidic KBr/CuSO4-methylene chloride extraction and the acidic KBr/CuSO4-methylene chloride extraction with an alkaline digestion pretreatment were shown to be the effective methods for soils/sediments and fish samples analysis, respectively. The presence of ethylmercury species in soils of the Florida Everglades, observed with the acidic KBr/CuSO4 isolation and methylene chloride extraction procedure, was further confirmed with the dithizone complexation/extraction procedure. The GC-AFS analytical method offers high senstivity and selectivity for the determination of organomercury halides. The GC column maintenance, a critical step for organomercury halides analysis using GC, is also discussed.