Gas Chromatography-inductively Coupled Plasma Mass Spectrometry Research Articles

GC-ICP-MS for Process and Quality Control in Semiconductor Manufacturing

Gas chromatography (GC) coupled to inductively coupled plasma–mass spectrometry (ICP-MS) is a powerful and flexible analytical solution that is well-established for measuring organometallic compounds such as organotin, organomercury, and organolead in environmental samples, foodstuffs, and consumer products. GC–ICP-MS is also used for industrial applications, such as monitoring catalyst poisons and environmental contaminant elements in petrochemical processing and plastics manufacturing. The semiconductor industry uses a range of high-purity specialty gases and volatile liquids as precursors in wafer substrate production, and for processes such as plasma etching and deposition of thin films by chemical vapor deposition (CVD). Semiconductor manufacturers are constantly developing new integrated circuit (IC) chips with smaller sizes, higher speeds, lower power consumptions, and greater transistor densities. This trend means that contaminants must be controlled at even lower levels in process chemicals and precursors. In this article, we show how GC–ICP-MS, particularly using triple quadrupole or tandem ICP-MS (ICP-MS/MS), enables determination of the lowest levels of contaminants in the specialty gases and volatile liquids used to make the most advanced electronic devices.

Patterns of fish and whale consumption in relation to methylmercury in hair among residents of Western Canadian Arctic communities

BackgroundMethylmercury contamination of the environment represents a substantial environmental health concern. Human exposure to methylmercury occurs primarily through consumption of fish and marine mammals. Heavily exposed subgroups include sport or subsistence fishers residing in Arctic communities. We aimed to estimate the association of fish/whale consumption patterns of Canadian Arctic subsistence fishers with the internal dose of methylmercury as measured in hair.MethodsThis research was conducted within ongoing community projects led by the CANHelp Working Group in Aklavik and Fort McPherson, Northwest Territories and Old Crow, Yukon. We interviewed each participant using a fish-focused food-frequency questionnaire during September–November 2016 and collected hair samples concurrently. Methylmercury was measured in the full-length of each hair sample using gas chromatography inductively-coupled plasma-mass spectrometry. Multivariable linear regression estimated beta-coefficients and 95% confidence intervals (CIs) for the effect of fish/whale consumption on hair-methylmercury concentrations.ResultsAmong 101 participants who provided hair samples and diet data, the mean number of fish/whale species eaten was 3.5 (SD:1.9). The mean hair-methylmercury concentration was 0.60 μg/g (SD:0.47). Fish/whale consumption was positively associated with hair-methylmercury concentration, after adjusting for sex, hair length and use of permanent hair treatments. Hair-methylmercury concentrations among participants who consumed the most fish/whale in each season ranged from 0.30–0.50 μg/g higher than those who consumed < 1 meal/week.ConclusionsIn this population of Canadian Arctic subsistence fishers, hair-methylmercury concentration increased with fish/whale consumption, but the maximum concentrations were below Health Canada’s 6.0 μg/g threshold for safe exposure.

Influence of Macrophyte and Gut Microbiota on Mercury Contamination in Fish: A Microcosms Study

The freshwater lakes of southwestern France are subject to the development of invasive macrophytes which are associated with mercury (Hg) contamination of the food web. The aim of this study was to determine the bioavailability of methylmercury (MeHg) produced by plant roots in aquatic ecosystems. A microcosm experiment was performed using isotopically enriched inorganic Hg at environmental concentrations (1 µg 199IHg·L−1). For all conditions, total Hg in fish as well as Hg species associated with different compartments (water, sediments, plant roots, fish) were analyzed by gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS). In addition, sediment, plants, and fish gut microbiota were studied by MiSEQ sequencing. Some strains were isolated and tested for their ability to methylate Hg. The results revealed 199MeHg production in plant roots and the presence of this form in fish (tissues and gut), highlighting a MeHg trophic transfer. Moreover, methylator bacteria were identified from the gut contents of the fish when they were in the presence of plants. Some of them were related to bacteria found in the plant roots. On the basis of these results, the transfer of MeHg and bacteria from plants to fish is highlighted; in addition, Hg methylation is strongly suspected in the fish gut, potentially increasing the Hg bioaccumulation.

Headspace In-Tube Microextraction and GC-ICP-MS Determination of Mercury Species in Petroleum Hydrocarbons

Characterization of mercury contamination in petroleum hydrocarbons (PHs) is necessary in order to assess the risk of corrosion of the processing infrastructure and to assess the level of human exposure to Hg-containing substances. Here we present an accurate and sensitive method for determination of Hg species in PHs by headspace sampling with a possibility of on-line pre-concentration using in-tube extraction (ITEX) combined with gas chromatography–inductively coupled plasma mass spectrometry (GC-ICP-MS) analysis. Mercury species were first extracted from the PHs matrix into an aqueous phase via dithizone chelation and subsequently converted with sodium tetrapropyl borate into volatile derivatives which could be sampled from the headspace prior to GC-ICP-MS analysis. For concentrations in the ng kg–1 range, the on-line ITEX method was applied, whereas the μg kg–1 range was accessible by static headspace. Quantitation of Hg species was carried out by a double isotope dilution method, with quantitative recoveries of methylmercury (MeHg, average 101 ± 5%) and inorganic mercury (InHg, average 97 ± 7%) by direct headspace injection. Average recoveries of Hg spikes after on-line ITEX pre-concentration were 95 ± 3% for MeHg and 98 ± 8% for InHg. The detection limits for MeHg and InHg were 428 and 46 ng kg–1 when measured by static headspace, and 2.4 ng kg–1 and 1.7 ng kg–1 by on-line ITEX pre-concentration. The accuracy of the pre-concentration method was demonstrated by analysis of a crude oil standard reference material (NIST 2722) certified for InHg.

Determination of polybrominated diphenyl ethers in human serum by gas chromatography – inductively coupled plasma mass spectrometry

Polybrominated diphenyl ethers (PBDEs) are flame retardants that are added to a wide range of consumer products. Due to their extensive use in the past, their presence has been documented in multiple environmental compartments and living organisms, including humans. To assess the exposure of humans to PBDEs, a new simple, reliable, and sensitive method was developed for the determination of six PBDE congeners (BDE 28, BDE 47, BDE 99, BDE 100, BDE 153, BDE 154) in human serum by gas chromatography–inductively coupled plasma mass spectrometry (GC-ICP-MS). The PBDEs were extracted from 1 mL ofserum by 30 min of mechanical shaking with formic acid. Subsequently, 2 mL of iso-octane was added and 30 min of mechanical shaking was applied. For clean-up of the extract Florisil column was applied. The analytical method was validated by analysis of human serum standard reference materials SRM 1957 (Non-Fortified Human Serum) and SRM 1958 (Fortified Human Serum). Good agreement of the determined concentrations with those certified was found. The repeatability and reproducibility of the analytical method was within 5.9% and 6.1%, respectively, whereas the limits of detection (LODs) for the PBDEs analysed were between 0.0016 and 0.0039 ng mL−1 wet weight (ww). The feasibility of the method was tested by analysing human serum samples. In this study, the determined concentrations in sera were in a range similar to that of as those reported for certain other European countries.

Development of a Common Procedure for the Determination of Methylmercury, Ethylmercury, and Inorganic Mercury in Human Whole Blood, Hair, and Urine by Triple Spike Species-Specific Isotope Dilution Mass Spectrometry.

We report the first common methodology for the simultaneous determination of methylmercury (MeHg), ethylmercury (EtHg), and inorganic mercury (Hg(II)) in human blood hair and urine. With the exception of the initial sample mass (0.15 g for blood, 0.5 g for urine, and 0.1 g for hair), the same sample preparation and gas chromatography-inductively coupled plasma mass spectrometry (GC-ICPMS) measurement conditions are employed for the three matrixes providing experimental values in agreement with the certified values in the analysis of NIST SRM 955c (Caprine Blood) Level 3 and the certified human hairs IAEA 085 and IAEA 086. Also, the method provides quantitative recoveries for the three Hg species in the analysis of fortified human urine samples at 1, 2, and 5 ng Hg g-1. Mercury species concentrations for levels 2 and 4 of SRM 955c are reported here for the first time. A systematic interconversion of EtHg into Hg(II) was obtained for all matrixes reaching values up to 95% in blood, 29% in hair, and 11% in urine. MeHg dealkylation was also observed in a lesser extent in blood and hair analyses, but it was not observed when analyzing urine samples. Hg methylation was not observed in any matrix. The amount of NaBPr4 added for derivatization has been found to be the main factor responsible for Hg species interconversion. This work demonstrates for the first time that experimental conditions optimized for SRM 955c (caprine blood) are not valid for human blood samples as the optimum initial sample amount for a real sample is more than 3 times lower than that for SRM 955c.

δ34S character of organosulfur compounds in kerogen and bitumen fractions of sedimentary rocks

Hydropyrolysis (HyPy) of S-containing oil mature rock samples from two geologic settings each produced much higher concentrations of organosulfur compounds (OSCs) compared to their free occurrence in the bitumen. The δ34S values of the most abundant OSCs from the kerogen and in the bitumen, were measured by gas chromatography inductively coupled plasma mass spectrometry (GC-ICP-MS). DBT and mDBTs from the HyPy processed kerogen fractions showed a distinct 34S depletion, with δ34S values up to 12‰ lighter than their bitumen occurrence. The different δ34S values of OSCs from the kerogen and bitumen fractions is likely reflective of differences in timing of production, reduced sulfur sources or organic sulfurisation mechanism.

The use of isotopically enriched tin tracers to follow the transformation of organotin compounds in landfill leachate

Landfill leachates are an important pool of organotin compounds (OTCs). Several studies have been performed on the occurrence of OTCs in landfill leachates, but only a few of them report degradation and biomethylation processes by bacteria. In the present study transformation of OTCs in landfill leachate was investigated under simulated landfill conditions over a time span of six months. The degradation and biomethylation processes of OTCs were followed by the use of isotopically enriched tin tracers, namely 117Sn-enriched tributyltin (TBT), 119Sn-enriched dibutyltin (DBT), 117Sn-enriched SnCl2, 117Sn-enriched SnCl4 and a 119Sn-enriched butyltin mix containing TBT, DBT and monobutyltin (MBT). Transformation of OTCs in spiked leachates was followed at m/z of the enriched spikes and at m/z 120, which allowed simultaneous observation of the transformation of OTCs in the leachate itself and of the added spike. In parallel, these processes were also monitored in a non-spiked leachate sample at m/z 120. Quantification of OTCs was performed by gas chromatography – inductively coupled plasma mass spectrometry (GC-ICP-MS). To discriminate the biotic and abiotic transformations of OTCs and inorganic tin species, sterilization of leachate was also performed and data compared to non-sterilized samples. During the course of the experiment the microbial degradation of TBT was clearly manifested in Sn-enriched spiked leachate samples, while abiotic pathway of degradation was observed for DBT. Biomethylation process was also observed in the leachate spiked with Sn-enriched Sn2+ or Sn4+, in concentrations close to those found for total tin in landfill leachates. Monomethyltin (MMeT) was formed first. Stepwise alkylation resulted in dimethyltin (DMeT) and trimethyltin (TMeT) species formation. Hydrolysis of Sn2+ and Sn4+ species was found to be a limiting factor which controlled the extent of methyltin formation. The results of the present investigation importantly contribute to a better understanding of the processes that OTCs undergo in leachates, and provide useful information to managers of landfills in taking measures necessary to prevent the release of toxic methyltin species to the nearby environment.

Species-specific isotope dilution-GC-ICP-MS for accurate and precise measurement of methylmercury in water, sediments and biological tissues

Species-specific isotope dilution (SSID) in combination with gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS) has been developed for the separation and determination of methylmercury (MeHg) in water, sediments and biological tissues. Optimum conditions for the measurement of isotope ratios on the transient chromatographic peaks have been established. SSID analysis was performed using a laboratory synthesized enriched spike of Me198Hg. Isotope ratio precision based on the peak area measurements was 1.4% RSD for 50 pg (as Hg). The absolute detection limits obtained with GC-ICP-MS were 4.3 pg for 198Hg and 8.1 pg for 202Hg, respectively. Analytical precision was typically less than 3.6% RSD over eight repeated measurements. The accuracy of the method has been compared with the method with Tl as internal standard and further validated with certified reference materials (ERM-cc580 for sediments and Tort-2 for the biological tissues). The results obtained by SSID-GC-ICP-MS were in good agreement with the certified reference values.

Comparison between GC–MS and GC–ICPMS using isotope dilution for the simultaneous monitoring of inorganic and methyl mercury, butyl and phenyl tin compounds in biological tissues

The aim of this work is to compare simultaneous isotope dilution analysis of organotin and organomercury compounds by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP/MS) on certified bivalve samples. These samples were extracted by microwave with tetramethylammonium hydroxide (TMAH). Derivatization with both NaBEt4 and NaBPr4 was evaluated, and analytical performances were compared. Two CRM materials, BCR-710 and CRM-477, were analyzed by both techniques to verify accuracy. A mixed spike containing (201)Hg-enriched methylmercury (MeHg), (199)Hg-enriched inorganic mercury (iHg), (119)Sn-enriched monobutyltin (MBT), dibutyltin (DBT), and tributyltin (TBT) as well as homemade (116)Sn-enriched monophenyltin (MPT), diphenyltin (DPT), and triphenyltin (TPT) was used for the isotope dilution analysis of samples. The two techniques studied were compared in terms of classic analytical parameters: linearity, precision or repeatability (i.e., percent relative standard deviation, RSD%), limit of detection (LOD), and limit of quantification (LOQ), showing excellent linearity, precision below 12% for all analytes, and LOQs of 0.06-1.45 pg for GC-MS and 0.02-0.27 pg for GC-ICP/MS.

Acid extraction for the determination of methyl mercury in biotissues by isotope dilution gas chromatography inductively coupled plasma-mass spectrometry

Methyl mercury (MeHg) is a common contaminant worldwide. Health authorities keep monitoring MeHg levels in biological and environmental samples to assess the corresponding exposure in the population. So far, a basic leaching has been mostly used for the MeHg extraction. In this study, it was demonstrated that methanesulfonic acid, commonly used for amino acid extraction, can be used for MeHg extraction. Species-specific isotope dilution was employed to achieve accurate results. The method was validated by analysis of dogfish liver certified reference material (DOLT-4). The derivatized extracts were then analyzed with gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS). Results obtained for MeHg in DOLT-4 are in agreement with the certified value (t-test, P = 0.05), confirming that methanesulfonic acid extraction is suitable for extraction of MeHg in biological tissues. This new procedure could be of particular interest in biological and toxicological studies where a simultaneous determination of MeHg and certain amino acids is sometimes required.

Volatile Dimethyl Polonium Produced by Aerobic Marine Microorganisms

The production of volatile polonium (Po(v)), a naturally occurring radioactive element, by pure cultures of aerobic marine tellurite-resistant microorganisms was investigated. Rhodotorula mucilaginosa, a carotogenic yeast, and a Bacillus sp. strain, a Gram-positive bacterium, generated approximately one and 2 orders of magnitude, respectively, greater amounts of Po(v) compared to the other organisms tested. Gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS) analysis identified dimethyl polonide (DMPo) as the predominant volatile Po compound in culture headspace of the yeast. This species assignment is based on the exact relation between GC retention times and boiling points of this and other Group VI B analogues (S, Se, and Te). The extent of the biotic Po(v) production correlates exponentially with elevated particulate Po (Po(p)): dissolved Po (Po(aq)) ratios in the cultures, consistent with efficient Po bioaccumulation. Further experimentation demonstrated that some abiotic Po(v) generation is possible. However, high-level Po(v) generation in these cultures is predominantly biotic.

Double Spike Isotope Dilution GC-ICP-MS for Evaluation of Mercury Species Transformation in Real Fish Samples Using Ultrasound-Assisted Extraction

Sample preparation continues being a key factor to obtain fast and reliable quantification of Hg species. Assisted procedures enhance the efficiency and reduce the extraction time; however, collateral species transformations have been observed. Moreover, differential interconversions have been observed even between similar matrixes, which introduce an important uncertainty for real sample analysis. Trying to minimize Hg species transformations, we have tested a soft ultrasound-assisted extraction procedure. Species quantification and transformations have been evaluated using double spike isotope dilution analysis (IDA) together with gas chromatography inductively coupled plasma mass spectrometry (GC-ICP-MS) for a CRM material (Tort-2) and shark and swordfish muscle samples. Optimum extraction solution and sonication time led to quantitative extraction and accurate determination of MeHg and IHg in a short time, although different behaviors regarding species preservation were observed depending on the sample. Negligible species transformations were observed in the analysis of the CRM, while a small but significant demethylation factor was observed in the case of real samples. In comparison with other extraction procedures, species transformations became smaller, and fewer differences between fish species were found. Similar results were obtained for fresh and lyophilized samples of both fish samples, which permit one to analyze the fresh sample directly and save time in the sample preparation step. The high grade of species preservation and the affordability of the extraction procedure allow one to obtain accurate determinations even for routine laboratories using quantification techniques, which do not estimate species transformations.

Mercury speciation analysis in human hair by species-specific isotope-dilution using GC–ICP–MS

We optimized a mercury (Hg) speciation extraction method for human hair in combination with species-specific isotope-dilution analysis by gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS). The method was validated on human hair reference material RM (IAEA-086), which is recommended for analysis of monomethylmercury (MMHg) and inorganic mercury (IHg). Three reagents, hydrochloric acid (HCl), nitric acid (HNO3), and tetramethylammonium hydroxide (TMAH), and three extraction procedures, at ambient temperature for 12h, microwave-assisted at 75°C for 6min, and oven heated at 80°C for 2h were tested. Extraction efficiency, recovery, and potential species transformations were evaluated for each method. The most efficient procedures, with recovery of ~90% for each species with limited demethylation (<5%) and methylation (0%), were HNO3 digestion, irrespective of temperature, and microwave-assisted TMAH extraction. Acidic extraction with HCl induces significant demethylation, with production of artifacts. To correct for potential demethylation artifacts we recommend spiking with isotopically enriched standards before the extraction step.

A reliable method to determine methylmercury and ethylmercury simultaneously in foods by gas chromatography with inductively coupled plasma mass spectrometry after enzymatic and acid digestion

A reliable and sensitive method for determination simultaneously of monomethylmercury (MeHg) and monoethylmercury (EtHg) in various types of foods by gas chromatography inductively coupled plasma mass spectrometry (GC-ICP/MS) was developed and validated. Samples were digested with pancreatin and then hydrochloric acid. MeHg and EtHg in the extract were derivatized in an aqueous buffer with sodium tetraphenylborate. After phase separation, the extract was directly transferred to analysis. The analyses were conducted by GC-ICP/MS with monopropylmercury chloride (PrHgCl) as surrogate standard. Concentrations of 254 ± 5.1, 13.7 ± 0.69 and 162 ± 6.2 μg Hg kg −1 (one standard deviation, n = 3) were obtained for MeHg in NIST SRM 1947 (Superior Lake fish), SRM 1566b (oyster tissue) and NRC Tort-2 (lobster Hepatopancreas), respectively. These are in good agreement with the certified values of 233 ± 10, 13.2 ± 0.7 and 152 ± 13 μg Hg kg −1 (as 95% confidence interval), respectively. The method detection limits (3 σ) for MeHg and EtHg are 0.3 μg Hg kg −1. The method detection limit was estimated by using a 0.5 g of subsample, sufficiently low for the risk assessment of MeHg and EtHg in foods. The spiked recoveries of MeHg and EtHg in different food matrices were between 87 and 117% and the RSDs were less than 15%. When isotopic dilution mass spectrometry (IDMS) analysis was performed with a commercial available 201Hg-enriched monomethylmercury (Me 201Hg) solution as internal standard, concentrations of 244 ± 13.4, 13.9 ± 0.25 and 161 ± 1.3 μg Hg kg −1 were obtained for MeHg in NIST SRM 1947, SRM 1566b and NRC Tort-2, respectively. It shown clearly that IDMS analysis got improvement in precision and accuracy, however, EtHg cannot be analyze simultaneously and the cost of analysis is higher.

Mercury speciation in whole blood by gas chromatography coupled to ICP-MS with a fast microwave-assisted sample preparation procedure

A simple and fast method is described for simultaneous determination of methylmercury (MeHg), ethylmercury (Et-Hg) and inorganic mercury (Ino-Hg) in blood samples by using capillary gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS) after derivatization and alkaline digestion. Closed-vessel microwave assisted digestion conditions with tetramethylammonium hydroxide (TMAH) have been optimized. Derivatization by using ethylation and propylation procedures have also been evaluated and compared. The absolute detection limits (using a 1 μL injection) obtained by GC-ICP-MS with ethylation were 40 fg for MeHg and Ino-Hg, respectively, and with propylation were 50, 20 and 50 fg for MeHg, Et-Hg and Ino-Hg, respectively. Method accuracy is traceable to Standard Reference Material (SRM) 966 Toxic Metals in Bovine Blood from the National Institute of Standards and Technology (NIST). Additional validation is provided based on the comparison of results obtained for mercury speciation in blood samples with the proposed procedure and with a previously reported LC-ICP-MS method. With the new proposed procedure no tedious clean-up steps are required and a considerable improvement of the time of analysis was achieved compared to other methods using GC separation.

A Fast and Effective Routine Method Based on SPME and GC/ICP-MS for the Monitoring of Organotin Compounds in Surface and Sea Water

The quality assessment of water in term of organometallic compounds is one of the key tasks of modern environmental analytical chemistry. For this purpose a rapid and very sensitive method based on solid-phase microextraction (SPME) followed by gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS) was developed and validated aimed at the determination of dimethyl-, dibutyl- and tributyltin in water samples. A divinylbenzene/ carboxen/polidimethylsiloxane fiber was used for the SPME sample treatment. Coupling of the ICP-MS with GC was accomplished developing an easy-to-fit in-house interface. In general optimal conditions were found by using the enhanced “hot plasma/protective ion extraction” introduction system. Validation was carried out in terms of limit of detection, limit of quantitation, linearity, precision and trueness. GC-ICPMS made possible the detection of the organotin compounds at ultratrace levels, quantitation limits ranging from 0.04 to 5 ng l-1. Linearity was established over two orders of magnitude for all the investigated compounds. Good precision was obtained both in terms of intra-day repeatability and between-day precision on two concentration levels (RSD lower than 15%). Recovery values ranging from 75±2% to 99±1.2% (n = 3) were calculated. The method was proved rapid, GC-ICPMS allowing for the separation of organotin species in less than 7 minutes. The method was used in routine analysis of environmental samples (fresh and marine water samples). Keywords: Dimethyltin, Dibutyltin, Tributyltin, Solid-phase microextraction, Gas chromatography-inductively coupled plasma mass spectrometry, Home-made interface

Headspace stir bar sorptive extraction combined with GC-ICP-MS for the speciation of dimethylselenide and dimethyldiselenide in biological samples

A new method for the determination of volatile organo seleno compounds (dimethylselenide (DMSe) and dimethyldiselenide (DMDSe)) has been developed using a headspace sorptive extraction combined with capillary gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS). The DMSe and DMDSe retained on the sorptive bar were desorbed by methanol and introduced into GC-ICP-MS for separation and determination. The extraction performance of various sorptive bar coatings, including poly(dimethylsiloxane) (PDMS), PDMS-poly(vinyl alcohol) (PVA), carbowax (CW)-PDMS-PVA, PDMS-β-cyclodextrin (β-CD) has been studied, and the best extraction efficiencies for DMSe and DMDSe were obtained by PDMS-PVA sorptive bar coating. The factors affecting extraction and desorption of DMSe and DMDSe were studied and the optimized operation conditions were established. The limits of detection were 33 and 7.1 ng L−1 for DMSe and DMDSe, respectively, and the correlation coefficients of 0.9986 for DMSe and 0.9998 for DMDSe were obtained in the concentration range 0.5–500 ng mL−1 and 0.025–50 ng mL−1, respectively. Repeatability, based on seven replicate determinations, expressed as relative standard deviations (RSDs), were 8.0% (CDMSe = 5 ng mL−1) and 6.1% (CDMDSe = 0.5 ng mL−1) for DMSe and DMDSe, respectively. The proposed method was applied for the analysis of DMSe and DMDSe in biological samples (garlic, onion and their juice) and a good agreement was obtained between the analytical results obtained by standard addition and external calibration methods.

Separation and determination of seleno amino acids using gas chromatography hyphenated with inductively coupled plasma mass spectrometry after hollow fiber liquid phase microextraction

A new derivatization-extraction method for preconcentration of seleno amino acids using hollow fiber liquid phase microextraction (HF-LPME) was developed for the separation and determination of seleno amino acids in biological samples by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS). Derivatization was performed with ethyl chloroformate (ECF) to improve the volatility of seleno amino acids. Parameters influencing microextraction, including extraction solvent, pH of sample solution, extraction time, stirring speed, and inorganic salt concentration have been investigated. Under the optimal conditions, the limits of detection (LODs) obtained for Se-methyl-selenocysteine (SeMeCys), selenomethionine (SeMet), and selenoethionine (SeEth) were 23, 15, and 11 ng Se l(-1), respectively. The relative standard deviations (RSDs) were 14.6%, 16.4%, and 19.4% for SeMeCys, SeMet, and SeEth (c = 1.0 ng ml(-1), n = 7), respectively, and the RSDs for SeMeCys, SeMet could be improved obviously if SeEth was utilized as the internal standard. The proposed method was applied for the determination of seleno amino acids in extracts of garlic, cabbage, and mushroom samples, and the recoveries for the spiked samples were in the range of 96.8-108% and 93.4-115% with and without the use of SeEth as internal standard. The developed method was also applied to the analysis of SeMet in a certified reference material of SELM-1 yeast and the determined value is in good agreement with the certified value.

Plasma Gas-Switching Method for Gas Chromatography/ Inductively Coupled Plasma Mass Spectrometry and Determination of Polybrominated Diphenylethers with High Precision and Sensitivity

The drift in sensitivity due to carbon deposition on the sampling cone, skimmer cone and ion lenses has been a serious problem in gas chromatography/inductively coupled plasma mass spectrometry (GC/ICP-MS). To overcome this problem, a high-speed switching method between a mixed-gas plasma and a pure-argon plasma (named plasma gas-switching method) using an oxygen permeation tube and a switching valve was developed. This enabled both the cleaning of deposited carbon and an enhancement of the sensitivity; as a consequence, both the repeatability and the sensitivity of polybrominated diphenylether (PBDE) were improved by more than 3 and 4 times, respectively. The drifts of sensitivity over a period of 8 h were less than 5% in most cases. Concerning the analytical performance of thermally labile congeners from octa- to deca-BDE, the detection limits, dynamic ranges of the calibration graphs and unequivalent sensitivities were remarkably improved by using a metal capillary separation column coated with a very thin (0.05 micromm) film of immobilized-polydimethylsiloxane. The detection limits ranged from 0.014 pg (BDE-154) to 0.093 pg (BDE-209), which were equal or superior to the lowest values reported hitherto by GC/MS (high resolution). A remarkable loss of sensitivity for highly-brominated congeners, such as nona- and deca-BDE, was observed in an analysis of PBDE technical mixtures when the solvent was methanol. The loss of sensitivity turned out to be due to an activation of the retention gap used for on-column injection; this problem was solved by changing methanol to isooctane in the sample-preparation step before analysis.