Development of a new hybrid technique for rapid speciation analysis by directly interfacing a microfluidic chip-based capillary electrophoresis system to atomic fluorescence spectrometry

This paper represents the first study on direct interfacing of microfluidic chip-based capillary electrophoresis (chip-CE) to a sensitive and selective detector, atomic fluorescence spectrometry (AFS) for rapid speciation analysis. A volatile species generation technique was employed to convert the analytes from the chip-CE effluent into their respective volatile species. To facilitate the chip-CE effluent delivery and to provide the necessary medium for subsequent volatile species generation, diluted HCl solution was introduced on the chip as the makeup solution. The chip-CE-AFS interface was constructed on the basis of a concentric "tube-in-tube" design for introducing a KBH4 solution around the chip effluent as sheath flow and reductant for volatile species generation as well. The generated volatile species resulting from the reaction of the chip-CE effluent and the sheath flow were separated from the reaction mixture in a gas-liquid separator and swept into the AFS atomizer by an argon flow for AFS determination. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were chosen as the targets to demonstrate the performance of the present technique. Both mercury species were separated as their cysteine complexes within 64 s. The precision (relative standard deviation, RSD, n = 5) of migration time, peak area, and peak height for 2 mg.L(-1) Hg(II) and 4 mg.L(-1) MeHg(I) (as Hg) ranged from 0.7 to 0.9%, 2.1 to 2.9%, and 1.5 to 1.8%, respectively. The detection limit was 53 and 161 microg.L(-1) (as Hg) for Hg(II) and MeHg(I), respectively. The recoveries of the spikes of mercury species in four locally collected water samples ranged from 92 to 108%.     

Analysis of inorganic mercury species associated with airborne particulate matter/aerosols: method development

This paper describes a method for speciation of Hg associated with airborne particulate matter. This method uses a mini-sampler for sample collection and analysis, thermal desorption for separating Hg species, and inductively coupled plasma mass spectrometry (ICP–MS) for identification and quantification of Hg. Coal fly ash spiked with different Hg compounds (e.g. Hg⁰, HgCl₂, HgO, and HgS) was used for qualitative calibration. A standard reference material with a certified value for Hg concentration was used to evaluate the method. When the temperature of the furnace was programmed at a linear rate of increase of 50° min^–1, different Hg compounds could clearly be separated. Three airborne particulate matter samples were collected in parallel in Toronto, ON, Canada and analyzed using this method. Reproducible results were obtained and Hg⁰, HgCl₂, HgO, and HgS species from these samples were detected.     

Some aspects of speciation and reactivity of mercury in various matrices

Speciation of mercury compounds in environmental and biological samples requires different techniques and different approaches. This speciation is mandatory to explain the toxicity, the reactivity and the bioavailability of mercury. It is dominated by inorganic mercury species Hg(II) and Hg(0), and the organic mercury species CH₃Hg and (CH₃)₂Hg. In this paper, some aspects of mercury speciation are presented in terms of:- mercury reactivity (Hg(II) complexation and reduction),- mercury species distribution in the main compartments of the environment     

Artifact formation of methyl- and ethyl-mercury compounds from inorganic mercury during derivatization using sodium tetra(n-propyl)borate

Sodium tetra(n-propyl)borate (NaBPr₄) was introduced as derivatization reagent to extend the possibility for determining ethyl-mercury compounds. This study investigated the artifact formation of methyl- and ethyl-mercury compounds during NaBPr₄ derivatization, together with the influence of this artifact on organomercury analysis in environmental samples. The artifact methyl- and ethyl-mercury compounds during NaBPr₄ derivatization were evident and depended strongly on the amount of Hg(II) present in the solution for derivatization. Some unidentified organomercury compounds were found when the amount of Hg(II) in the derivatization solution was over 1 μg. The amounts of NaBPr₄ and acetate buffer and the presence of organometallic compounds other than organomercury showed little influence on the artifact effect. The artifact monoethylmercury encompasses 0.99-2.9% of the amount of Hg(II) present and interferes strongly with the monoethylmercury analysis. The formation rate of artifact monomethylmercury is much lower and ca. 0.03-0.28% of the Hg(II) present. The artifact affects remarkably the monomethylmercury analysis for solid samples when these have a low ratio of monomethylmercury-to-total Hg concentrations (≤0.003) and the recovery of Hg from the samples is high. Mathematical correction seems to be difficult due to the low reproducibility of this artifact effect. Formation of artifact organomercury compounds caused during NaBPr₄ derivatization may lead to false Hg speciation and overestimate concentrations of organomercury compounds.     

Determination of mercury species using thermal desorption analysis in AAS

Analytical aspects of the determination of inorganic mercury (Hg) species by thermal desorption followed by atomic absorption spectrometry (AAS) detection were investigated in this work. Characteristic Hg release curves of the following species were observed: Hg⁰, HgCl₂, HgO, HgSO₄, HgS, and the Hg bound to humic acids. Particular attention was dedicated to the thermal stability and change of bond of Hg⁰ in the following matrices: sand, kaolinite, granite, peat, power plant ash, and soil. The bond of elemental Hg in environmental materials was described on basis of this experiment. Contaminated soil samples from two locations in the Czech Republic were investigated by thermal desorption analysis. Afterwards, the contents of volatile and plant-available Hg in the studied samples were determined. The determination of Hg⁰ using the thermal method was related to the results of liquid sequential extraction. The development of Hg speciation and the stability of Hg were assessed on basis of the data obtained. Thus, the analytical procedure used is a suitable tool for the study of inorganic Hg species in contaminated soils.     

Living organisms as an alternative to hyphenated techniques for metal speciation. Evaluation of baker's yeast immobilized on silica gel for Hg speciation

The use of living organisms for metal preconcentration and speciation is discussed. Among substrates, Saccharomyces cerevisiae baker's yeast has been successfully used for the speciation of mercury [Hg(II) and CH₃Hg⁺], selenium [Se(IV) and Se(VI)] and antimony [Sb(III) and Sb(V)]. To illustrate the capabilities of these organisms, the analytical performance of baker's yeast immobilized on silica gel for on-line preconcentration and speciation of Hg(II) and methylmercury is reported. The immobilized cells were packed in a PTFE microcolumn, through which mixtures of organic and inorganic mercury solutions were passed. Retention of inorganic and organic mercury solutions took place simultaneously, with the former retained in the silica and the latter on the yeast. The efficiency uptake for both species was higher than 95% over a wide pH range. The speciation was carried out by selective and sequential elution with 0.02 mol L⁻¹ HCl for methylmercury and 0.8 mol L⁻¹ CN⁻ for Hg(II). This method allows both preconcentration and speciation of mercury. The preconcentration factors were around 15 and 100 for methylmercury and mercury(II), respectively. The method has been successfully applied to spiked sea water samples.     

An improved speciation method for mercury by GC/CVAFS after aqueous phase ethylation and room temperature precollection

An improvement has been made in previous mercury speciation methods, which omits the use of liquid nitrogen by modifying the GC conditions. In addition, the sometimes observed thermal decomposition of ethylation derivatives in the process of desorbing the compounds to the GC column has been investigated and overcome. The resulting improvements have allowed simultaneous determination of methylmercury (MMHg) and inorganic mercury (Hg(II)). They have also increased the precision of the ethylation reaction and refined the MMHg determination. Optimal conditions for MMHg were confirmed and supplemented, while the parameters for dimethyl mercury (DMHg) and Hg(II) were thoroughly investigated for the first time. The absolute detection limits (DL) for 2sigma of the reagent blanks as Hg and about 0.6, 0.6 and 1.3 pg for DMHg, MMHg and Hg(II), respectively. The improved method is five-fold faster than the original method, allowing up to 80 samples to be analyzed within 8 hr.     

Miniaturized membrane-assisted solvent extraction combined with gas chromatography/electron-capture detection applied to the analysis of volatile organic compounds

A new module of membrane-assisted solvent extraction (MASE) with miniaturized membrane bags was applied to the determination of seven volatile organic compounds (VOCs): chloroform, 1,1,1-trichloroethane, trichloroethylene, 1,1,2-trichloroethane, tetrachloroethene, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane with boiling points between 61 and 147 degrees C in aqueous samples. Different from the known procedure the new, shortened membrane bags were filled with 100 microl of an organic solvent. The membrane bags were placed in a 20 ml headspace vial and filled with 15 ml of the aqueous sample. The vial was transferred into an autosampler where it was stirred for a definite time at elevated temperature. After the extraction, 1 microl of the organic extract was transferred into the spilt/splitless injector of a GC system equipped with an electron-capture detector. This work included optimization of the membrane device, the determination of the optimized extraction conditions such as stirring rate, extraction time and the impact of salt addition. The validation of the method involved repeatability, recovery and detection limit studies, followed of its application towards real water samples. The repeatability, expressed as the relative standard deviation of the peak areas of six extractions was below 10%. The detection limits (LODs) were between 5 ng/l (tetrachloroethene) and 50 ng/l (chloroform). Calibration was performed in a range from 5 ng/l to 150 microg/l, since the concentration in the aqueous samples was expected quite various in this concentration range. Five river water samples of Bitterfeld, Saxony-Anhalt, Germany were analyzed with miniaturized-MASE and the results were compared with those obtained with Headspace-Analysis. The method can be fully automated and moreover, it allows the simultaneous determination of volatile and semi volatile compounds.     

Analytical Methods for Speciation of Organotins in the Environment

The growing awareness over the environmental fate of organotin compounds is reflected in the large number of analytical methods developed for their separation. Organotin compounds have varying degrees of toxicological properties, depending on the nature and number of alkyl groups bonded to the tin atom. Most of the analytical speciation methods applied to actual environmental media have involved prior derivatization to transform organotin compounds into volatile hydrophobic analytes amenable to separation and identification by gas chromatography coupled to a sensitive and selective tin-detector. Evidence exists that members of the same homologous series are related by environmental degradation pathways. Chemical treatment prior to analysis, or high temperatures associated with gas chromatography separation, may alter the relative amounts of organotins in samples and blur the true environment picture. To avoid species redistribution that may occur during derivatization or gas speciation analysis, methods based on liquid chromatography and supercritical fluid chromatography have been investigated. This review documents analytical methods for determination of tin and speciation of organotin compounds, in the hope that it will be of value to those interested in initiating a programme for assessing the impact of such species on the environment.     

Monitoring volatile compounds during dry-cured ham ripening by solid-phase microextraction coupled to a new direct-extraction device

Key flavour volatile compounds were monitored during ripening of dry-cured ham by solid-phase microextraction (SPME) coupled to a new direct-extraction device (DED). DED allows the insertion of the SPME fibre into the core of solid materials with no damage to the fibre. This enables extraction of volatiles from solid foodstuffs while avoiding sample handling. Major groups of volatile compounds extracted with SPME-DED agreed with available scientific literature about dry-cured ham volatiles. Moreover, volatile compounds previously highlighted as quality markers in dry-cured ham, such as 3-methylbutanal or hexanal, were satisfactorily extracted using SPME-DED. Changes in the profile of volatile compounds throughout the processing followed a typical pattern of volatile compounds formation. Therefore, SPME-DED appears as a new and promising method for monitoring ripening of dry-cured hams with no depreciation of the product, which might substitute traditional subjective methods currently used in the ham processing industry. However, the use of the internal standard method is not possible with this technique. Therefore, results using SPME-DED only point out a trend in the volatile profile. Further attempts relating data obtained using SPME-DED in dry-cured hams with sensory and chemical data from the same samples would be necessary for optimising this method as a quality control method in dry-cured ham industries.     

Stability study on a Westöö-based methodology to determine organomercury compounds in polluted soil samples

This paper concerns with the evaluation of a speciation methodology for organomercury compounds in soil samples. The methodology used is based on the Westöö method, which includes an acid leaching of the soil followed by an organic solvent extraction and a re-extraction with a selective aqueous reagent (cysteine). The separation and quantification of organomercury compounds is achieved by capillary electrophoresis technique, using an ultraviolet-visible detection system (HPCE-UV). The main steps in the speciation process are discussed, from the point of view of possible degradation processes. Frozen, de-frozen and non-frozen soil samples have been analyzed, characterizing the influence of light and temperature. Equally, the effect of light and temperature, as well as the chemical form of cysteine, have been analyzed on aqueous extracts. Organomercury degradation has been observed in the aqueous phase and related results are discussed.     

Focused ultrasound and molecularly imprinted polymers: a new approach to organotin analysis in environmental samples

There is a high interest in speciation of organotin compounds (OTCs) in biota and marine sediment samples, due to their influence in the transmission of the contamination in the trophic chain. Sample treatment is still the most "compromising" step of speciation analysis. Extraction methods are in general time-consuming due to long extraction times and several analytical steps involved. In addition, in most cases there are problems of low recovery, especially for MBT. These drawbacks, added to the high matrix effects generally present in biota samples, make the sample treatment for organotin analysis a serious challenge for environmental issues. Here we present a novel, fast and efficient two steps method for organotin speciation in mussel and oyster tissue as well as in marine sediments. The first step based on the use of ultrasonic probe extraction for species leaching allowed us to quantitatively extract these compounds in a few minutes. Matrix interferences drastically decreased by applying a clean-up step based on the use of an imprinted polymer especially designed for tributyltin (TBT). This procedure increased accuracy and precision of the GC-FPD analysis and improving the limit of detection, Besides, this new method prevents the use of standard addition calibration method, which is mandatory without the clean-up step. The optimization and validation has been performed by using three reference materials: mussel tissue CRM-477, oyster candidate T-38 and sediment PACS-2.     

High-performance liquid chromatography-UV diode array,inductively coupled plasma mass spectrometry (ICMPS) and orthogonal acceleration time-of-flight mass spectrometry (oa-TOFMS) applied to the simultaneous detection and identification of metabolites of 4-bromoaniline in rat urine

Summary The paper describes the role and tasks of environmental analysis and monitoring. It emphasises the leading role played by gas chromatography, especially when coupled with suitable sample preparation. This is demonstrated by some literature evidence and mainly by the author's original work on the design of sample preparation apparatus and development of GC-based methods of determination of a wide variety of organic pollutants in environmental samples. A typical example is the physical speciation of PAHs and PCBs in river environment with the use of a home-made filtration vessel coupled with SPE cartridges to prepare samples for GC-MS analysis; thin layer head space with self-generation of aqueous concentrate to prepare humane urine samples for DAI (direct aqueous injection)-GC-ECD analysis for the content of volatile chloro-organic compounds; studies on capillary denuders in sampling organic air pollutants; passive dosimeters in indoor air quality measurements; design and application of thermal desorbers for the introduction of analytes into GC columns and modification of a speciation analyser for organometalic environmental pollutants. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

On-line hyphenation of flow injection, miniaturized capillary electrophoresis and atomic fluorescence spectrometry for high-throughput speciation analysis

A hyphenated technique was developed for high-throughput speciation analysis by on-line coupling of flow injection (FI), miniaturized capillary electrophoresis (CE) and atomic fluorescence spectrometry (AFS). Two interfaces were used to couple all three systems: the first to couple FI and CE and the second to couple miniaturized CE and AFS. The first interface was a modified flow through chamber, connected to the FI valve with a piece of PTFE tube (0.1mm i.d.x 20 cm long). The capillary outlet was coupled to the AFS by using the second concentric "tube-in-tube" interface. Split sampling was achieved in the electrokinetic mode. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were taken as model analytes to demonstrate the performance of the developed hyphenated technique. A volatile species generation (VSG) technique was employed to convert the analytes from the CE effluent into their respective volatile species. Baseline separation of Hg(II) and MeHg(I) was achieved by CE in a 50 microm i.d.x 8 cm long capillary at 3.0 kV within 60s. The precisions (RSD, n=12) were in the range of 0.7-0.9% for migration time, 3.8-4.2% for peak area, and 2.1-3.5% for peak height. The detection limits were 0.1 and 0.2 microgmL(-1) (as Hg) for Hg(II) and MeHg(I) with a sample throughput of 60 samples h(-1). The recoveries of both mercury species in the water samples studied were in the range of 93-106%.     

Preconcentration speciation method for mercury compounds in water samples using solid phase extraction followed by reversed phase high performance liquid chromatography

A simple and rapid method for in situ preconcentration of inorganic and organic mercury compounds in water samples, based on solid phase extraction using dithizone immobilised on a reversed-phase C18 cartridge, has been developed. The adsorbed complexes were stable on the cartridge for at least 2 weeks. The speciation analysis of methylmercury (MeHg), phenylmercury (PhHg) and inorganic mercury (Hg (II)) were done by reversed-phase high performance liquid chromatography. The calibration graphs of MeHg, PhHg and Hg (II) were linear (r>0.999) from the detection limits (0.58, 0.66 and 0.54 ng) to 38, 25 and 26 ng of Hg, respectively. The average recoveries of MeHg, PhHg and Hg (II) from spiked samples (0.3-48.0 mug l(-1) Hg) were 98+/-3, 99+/-1 and 100+/-7%, respectively. By applying SPE procedure a 200-fold concentration of the sample was obtained.     

Study of alkyl phosphates in industrial petroleum mixtures by comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

Dialkyl phosphate esters used as gellants in some oil well fracturing processes for conventional oil production can result in contamination of the collected crude. Though the exact mechanism is unclear, such compounds form volatile phosphorus that compromises refinery processes. Our initial research involved producing a comprehensive two-dimensional gas chromatographic method (GC × GC) for the detection and quantification of alkyl phosphate esters in petroleum samples, which surpassed the current method employed in sensitivity and speciation capabilities. However, selective detection is required for such analytes in petroleum matrices. This article describes the application of GC × GC with time-of-flight mass spectrometry for selective detection to the analysis of di- and tri-alkyl phosphates in petroleum samples. Features in the electron impact mass spectra of alkyl phosphates are discussed along with the GC × GC retention characteristics of the compounds. Based on these discussions, a preliminary classification and quantification of alkyl phosphate contamination in a suite of industrial samples is then presented.     

A purge and trap technique to capture volatile compounds combined with comprehensive two‐dimensional gas chromatography/time‐of‐flight mass spectrometry to investigate the effect of sulfur‐fumigation on Radix Angelicae Dahuricae

Sulfur‐fumigation is known to reduce volatile compounds that are the main active components in herbs used in herbal medicine. We investigated changes in chemical composition between sun‐dried and sulfur‐fumigated Radix Angelicae Dahuricae using a purge and trap technique to capture volatile compounds, and two‐dimensional gas chromatography/time‐of‐flight mass spectrometry for identification. Using sun‐dried Radix Angelicae Dahuricae samples as a reference, the results showed that 73 volatile compounds, including 12 sulfide compounds, were found to be present only in sulfur‐fumigated samples. Furthermore, 32 volatile compounds that were found in sun‐dried Radix Angelicae Dahuricae samples disappeared after sulfur‐fumigation. The proposed method can be applied to accurately discriminate sulfur‐fumigated Radix Angelicae Dahuricae from different commercial sources. Copyright © 2014 John Wiley & Sons, Ltd.     

The discovery of hidden arsenic species in coastal waters

The analysis of ultraviolet (UV)-irradiated and untreated seawater samples has shown that the dissolved arsenic content of marine waters cannot be completely determined by hydride generation–atomic absorption spectrophotometry without sample pretreatment. Irradiation of water samples obtained during a survey of arsenic species in coastal waters during the summer of 1988 gave large increases in the measured speciation. Average increases in the measured speciation. Average increases in total arsenic, monomethylarsenic and dimethylarsenic were 0.29 μg As dm^?3 (25%), 0.03 μg As dm^?3 (47%) and 0.12 μg As dm^?3 (79%), respectively. Overall, an average 25% increase in the concentration of dissolved arsenic was observed following irradiation. This additional arsenic may be derived from compounds related to algal arsenosugars or to their breakdown products. These do not readily yield volatile hydrides when treated with borohydride and are not therefore detected by the normal hydride generation technique. This has important repercussions as for many years this procedure, and other analytical procedures which are equally unlikely to respond to such compounds, have been accepted as giving a true representation of the dissolved arsenic speciation in estuarine and coastal waters. A gross underestimate may therefore have been made of biological involvement in arsenic cycling in the aquatic environment.     

A membrane introduction flame ionization/electron capture detection (MIFID/ECD) system for the rapid, real-time screening of volatile disinfection byproducts and hydrocarbon contaminants in water

Described is a system that employs an online membrane introduction (MI) interface coupled with parallel flame ionization and electron capture detectors (FID/ECD). We report the use of a MIFID/ECD system as an online method to detect total volatile organic halides (ΣVOXs) and volatile organic compounds (ΣVOCs) as aggregate parameters in environmental water samples at sub parts-per-billion levels without the need for sample handling or analyte pre-concentration. The instrument provides rapid screening and real-time monitoring capabilities of important classes of water contaminants in a simple system without the vacuum requirements of MS detectors. Furthermore, the MIFID/ECD instrument was successfully employed as a real-time reaction monitor for the photodegradation of toluene by an advanced oxidation process and the formation of volatile disinfection byproducts in the chlorination of natural waters. The results of these experiments compare favorably to those obtained using membrane introduction mass spectrometry (MIMS).     

Extraction techniques in speciation analysis of environmental samples

One of the main problems in speciation analysis is that the different species of metals are present in complex matrices at very low concentration levels. Thus it is almost always necessary to separate the analytes of concern from the matrix and to concentrate them up to detectable concentration levels. Special care should be paid during extraction in order to avoid any contamination of samples, losses and changes in speciation of analytes of concern. The most common extraction techniques for speciation analysis of Pb, Sn, Hg, Cr, As, Se and Sb in liquid and solid samples are presented and briefly discussed. Due to the large quantity of material to be covered, speciation of alkyl, aryl, and macromolecular compounds (porphyrines, thioneines, etc.) has not been taken into account.