Speciation of arsenic compounds by using ion-pair chromatography with atomic spectrometry and mass spectrometry detection

Rapid detection of ultratrace urinary arsenic by direct sampling microplasma vaporization based on silicon nitride

At present, immediate monitoring urinary arsenic is still a challenge for treating arsenic poisoning patients. Thus, a fast, reliable and accurate analytical approach is indispensable to monitor ultratrace arsenic in urine sample for health warning. In this work, a silicon nitride (SN) rod was first integrally utilized as a sample carrier for ≤50 μL urinary aliquot, an electric heater for removing water and ashing sample as well as a high voltage electrode for dielectric barrier discharge vaporization (DBDV). The direct analytical method of arsenic in urine without sample digestion was thus developed using atomic fluorescence spectrometer (AFS) as a model detector. After 4 V electrically heating the SN rod for 60 s, urine sample was dehydrated and ashed outside; then, DBD was exerted under 0.8 A with 0.8 L/min H₂ + Ar (1:9, v:v) for 20 s to vaporize arsenic analyte from the SN rod. After optimization, 0.014 μg/L arsenic detection limit (LOD) was reached with favorable analytical precision (RSD <5%) and accuracy (91-110% recoveries) for real sample analysis. As a result, the whole analysis process only consumes <3 min to exclude complicated sample preparation; furthermore, the designed DBDV system only occupies 25 W and <2 kg, which renders a miniature sampling component to hyphenate with a miniature detector to detect arsenic. Thus, this direct sampling DBDV method extremely fulfills the fast, sensitive and precise detection of ultratrace arsenic in urine sample.

Arsenobetaine: the ongoing mystery

Arsenobetaine (AsB) is a non-toxic organoarsenical identified as a major arsenic species in marine animals and a number of terrestrial mushrooms. Since its first identification nearly 40 years ago, numerous studies investigating the biosynthesis and function of AsB have been carried out, although molecular mechanisms have not been fully elucidated. Where and how is AsB formed? Why do marine animals acquire high concentrations of AsB? This review briefly summarizes the current progress of AsB research toward understanding its origin, function and the putative pathways for its biosynthesis. This paper also suggests potential future studies in the attempt to solve the AsB mystery.

Different arsenate and phosphate incorporation effects on the nucleation and growth of iron(III) (Hydr)oxides on quartz

Iron(III) (hydr)oxides play an important role in the geochemical cycling of contaminants in natural and engineered aquatic systems. The ability of iron(III) (hydr)oxides to immobilize contaminants can be related to whether the precipitates form heterogeneously (e.g., at mineral surfaces) or homogeneously in solution. Utilizing grazing incidence small-angle X-ray scattering (GISAXS), we studied heterogeneous iron(III) (hydr)oxide nucleation and growth on quartz substrates for systems containing arsenate and phosphate anions. For the iron(III) only system, the radius of gyration (Rg) of heterogeneously formed precipitates grew from 1.5 to 2.5 (± 1.0) nm within 1 h. For the system containing 10(-5) M arsenate, Rg grew from 3.6 to 6.1 (± 0.5) nm, and for the system containing 10(-5) M phosphate, Rg grew from 2.0 to 4.0 (± 0.2) nm. While the systems containing these oxyanions had more growth, the system containing only iron(III) had the most nucleation events on substrates. Ex situ analyses of homogeneously and heterogeneously formed precipitates indicated that precipitates in the arsenate system had the highest water content and that oxyanions may bridge iron(III) hydroxide polymeric embryos to form a structure similar to ferric arsenate or ferric phosphate. These new findings are important because differences in nucleation and growth rates and particle sizes will impact the number of available reactive sites and the reactivity of newly formed particles toward aqueous contaminants.

Organic solvent-free reversed-phase ion-pairing liquid chromatography coupled to atomic fluorescence spectrometry for organoarsenic species determination in several matrices

A novel method has been developed to determine As-containing animal feed additives including roxarsone (ROX), p-arsanilic acid (p-ASA) and nitarsone (NIT), as well as other organic As species (dimethylarsonic acid (DMAA) and monomethylarsonic acid (MMAA)) by ion-pairing high-performance liquid chromatography coupled to hydride generation atomic fluorescence spectrometry (IP-HPLC-HG-AFS). A simple isocratic reversed-phase (RP) HPLC method with a mobile phase containing citric acid and sodium hexanesulfonate (pH 2.0) was developed using a C(18) column. The use of an organic solvent free mobile phase turns this methodology into an environmentally friendly alternative. Several ion pair forming agents, such as sodium hexanesulfonate, tetrabutylammonium bisulfate and perfluoroheptanoic acid, were studied. The limits of detection for As species were calculated in standard solution and resulted to be 0.2, 0.5, 0.6, 1.6, and 1.6 μg As L(-1) for MMAA, DMAA, p-ASA, ROX and NIT, respectively. This method exhibited convenient operation, high sensitivity and good repeatability. It was applied to As speciation in different samples including arugula, dog food, dog urine and chicken liver.

Methylated Metal(loid) Species in Humans

While the metal(loid)s arsenic, bismuth, and selenium (probably also tellurium) have been shown to be enzymatically methylated in the human body, this has not yet been demonstrated for antimony, cadmium, germanium, indium, lead, mercury, thallium, and tin, although the latter elements can be biomethylated in the environment. Methylated metal(loid)s exhibit increased mobility, thus leading to a more efficient metal(loid) transport within the body and, in particular, opening chances for passing membrane barriers (blood-brain barrier, placental barrier). As a consequence human health may be affected. In this review, relevant data from the literature are compiled, and are discussed with respect to the evaluation of assumed and proven health effects caused by alkylated metal(loid) species.

Speciation of five arsenic species (arsenite, arsenate, MMAAV, DMAAV and AsBet) in different kind of water by HPLC-ICP-MS

A method using Ion Chromatography hyphenated to an Inductively Coupled Plasma-Mass Spectrometer has been developed to accurately determine arsenite (As(III)), arsenate (As(V)), mono-methylarsonic acid (MMAA(V)), dimethylarsinic acid (DMAA(V)) and arsenobetaine (AsBet) in different water matrices. The developed method showed a high sensitivity with detection limits for each arsenic species close to 0.4pg injected. Arsenite and arsenate were the major species found in surface and well waters, but AsBet and DMAA(V) were found in some surface waters, which has never been reported before, while in some natural mineral waters located in volcanic region, the arsenic content exceeded the maximal admissible arsenic content by European legislation standards and the predominant form was As(V).

The application of inductively coupled plasma mass spectrometry in pharmaceutical and biomedical analysis

With the development of life science, pharmaceutical and biomedical analysis becomes more and more important in medical science. Further studies will be hopefully established if it is possible to use inorganic elemental standards or small organic compounds in the quantitative determination of all kinds of drugs, nucleotides and sulfur or phosphorus containing peptides and proteins at appropriate concentration with an acceptable accuracy. Since 1980, inductively coupled plasma mass spectrometry (ICP-MS) has emerged as a new and powerful analytical technique which is suitable for element and isotope analysis. It offers extremely wide detection range of element and co-analysis of most elements in the periodic table. Also, it can be applied to perform qualitative, semiquantitative, and quantitative analysis and isotopic ratios through mass-to-electric charge ratio. With the help of ICP-MS, the struggle of searching for an excellent quantification technique in, e.g. drugs and proteomics has come appreciably close to an end. This review mainly focuses on the introduction of application of ICP-MS in pharmaceutical and biomedical analysis. Some problems in application and the handling strategies are simply presented at the end.

Comparative study of atomic fluorescence spectroscopy and inductively coupled plasma mass spectrometry for mercury and arsenic multispeciation

Mercury and arsenic are two elements of undoubted importance owing to their toxic character. Although speciation of these elements has been developed separately, in this work for the first time the speciation of As and Hg using two atomic fluorescence detectors in a sequential ensemble is presented. A coupling based on the combination of high-performance liquid chromatography (where mercury and arsenic species are separated) and two atomic fluorescence detectors in series, with several online treatments, including photooxidation (UV) and hydride generation, has allowed the determination of mercury and arsenic compounds simultaneously. The detection limits for this device were 16, 3, 17, 12 and 8 ng mL(-1) for As(III), monomethylarsinic acid, As(V), Hg2+ and methylmercury, respectively. This coupling was compared with an analogous one based on inductively coupled plasma-mass spectrometry (ICP-MS) detection, with detection limits of 0.7, 0.5, 0.8, 0.9 and 1.1 ng mL(-1), respectively. Multispeciation based on ICP-MS exhibits better sensitivity than the coupling based on tandem atomic fluorescence, but this second device is a very robust system and exhibits obvious advantages related to the low cost of acquisition and maintenance, as well as easy handling, which makes it a suitable system for routine laboratories.

Arsenic and its speciation analysis using high-performance liquid chromatography and inductively coupled plasma mass spectrometry

It is known that arsenic has different toxicological properties dependent upon both its oxidation state for inorganic compounds, as well as the different toxicity levels exhibited for organic arsenic compounds. The field of arsenic speciation analysis has grown rapidly in recent years, especially with the utilization of high-performance liquid chromatography (HPLC) coupled to inductively coupled plasma mass spectrometry (ICP-MS), a highly sensitive and robust detector system. Complete characterization of arsenic compounds is necessary to understand intake, accumulation, transport, storage, detoxification and activation of this element in the natural environment and living systems. This review describes the essential background and toxicity of arsenic in the environment, and more importantly, some currently used chromatographic applications and sample handling procedures necessary to accurately detect and quantify arsenic in its various chemical forms. Applications and work using only HPLC-ICP-MS for arsenic speciation of environmental and biological samples are presented in this review.

Simultaneous determination of mercury and arsenic species in natural freshwater by liquid chromatography with on-line UV irradiation, generation of hydrides and cold vapor and tandem atomic fluorescence detection

An approach based on the coupling HPLC-UV-CV/HG-mAFS-AFS has been developed for the simultaneous determination of mercury and arsenic species. A home modified AFS detector has been used for the analysis of mercury coupled in series with another similar detector for arsenic determination. The determined species were Hg2+, methylmercury (MeHg+), As(III), As(V) and monomethylarsinate (MMA). A critical aspect is the chromatographic separation, which was carefully optimized for the separation of all the species. The detection limits for these species are 11, 8, 17, 17 and 3 ng ml(-1), respectively. Linear curves for MMA were obtained between 10 and 200 ng ml(-1). The linear dynamic range for all the other species was comprised between the detection limit and 500 ng ml(-1). The influence of cations and anions at the concentration usually present in natural freshwater was studied. The procedure was validated by application to spiked natural freshwater samples from the south-west Spain, and it can be considered for routine analysis of polluted sites.

Determination of trivalent methylated arsenicals in rat urine by liquid chromatography–inductively coupled plasma mass spectrometry after solvent extraction

A method for the determination of trivalent arsenicals in urine was examined. Trivalent arsenicals, extracted as complexes with diethylammonium diethyldithiocarbamate (DDDC) into carbon tetrachloride, were determined by liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS). The trivalent methylated arsenicals monomethylarsonous acid (MMA(III)), dimethylarsinous acid (DMA(III)), and trimethylarsine (TMA) were detected in urine of rats that had received dimethylarsinic acid (DMA(V)) or monomethylarsonic acid (MMA(V)) at concentration of 200 microg ml(-1) in drinking water for 24 weeks. This method is the first to permit quantification of trivalent methylated arsenicals in urine without significant changes in concentration during storage or pretreatment.

Elemental speciation studies--new directions for trace metal analysis

Elemental speciation is reviewed as a new approach to trace metals analysis. The importance of metal speciation relative to total metal analysis is considered. Various types of chromatographic separation methods using inductively coupled plasma-mass spectrometry (ICP-MS) detection are discussed. A brief introduction to the instrumental techniques is given, as well a discussion of coupling the instrumentation. Various chromatographies are included with an emphasis on liquid chromatography (LC). Gas chromatography (GC) and capillary electrophoresis (CE) are also discussed. Application examples contrast and compare the advantages and disadvantages of ICP- MS with other detection methods. Summary tables are included for two of the LC methods.

Liquid chromatography-inductively coupled plasma mass spectrometry

It is known that while many elements are considered essential to human health, many others can be toxic. However, because the intake, accumulation, transport, storage and interaction of these different metals and metalloids in nature is strongly influenced by their specific elemental form, complete characterization of the element is essential when assessing its benefits and/or risk. Consequently, interest has grown rapidly in determining oxidation state, chemical ligand association, and complex forms of a many different elements. Elemental speciation, or the analyses that lead to determining the distribution of an element's particular chemical species in a sample, typically involves the coupling of a separation technique and an element specific detector. A large number of methods have been developed which utilize a multitude of different separation mechanisms and detection instruments. Yet, because of its versatility, robustness, sensitivity and multi-elemental capabilities, the coupling of liquid chromatography to inductively coupled plasma mass spectrometry (LC-ICP-MS) has become one of the most popular techniques for elemental speciation studies. This review focuses on the basic principles of LC-ICP-MS, its historical development and the many ways in which this technique can be applied. Different liquid chromatography separations are discussed as well as the factors that must be considered when coupling each to ICP-MS. Recent applications of LC-ICP-MS to the speciation of environmental, biological and clinical samples are also presented.

Urinary arsenic speciation in subjects with or without restriction from seafood dietary intake

In order to understand whether ingestion of seafood affects the urinary arsenic metabolites. About 42 women and 36 men were recruited from the students, parents and teachers in Taipei Medical University and National Taiwan University. The study subjects were interviewed about dietary habits, cigarette smoking habits, drug and vitamin intake, and consumption of seafood. Urine samples were collected from study subjects before and after refraining from eating seafood for 3 days, respectively. The urine samples were frozen at -20 degrees C separated by high-performance liquid chromatography (HPLC), and on line linked to hydride generator atomic absorption spectrometry (HGAAS) to quantify the levels of various species of inorganic arsenic and its metabolites. The levels of arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), total inorganic arsenic metabolites, inorganic arsenic percent, MMA percent and DMA percent were similar before and after refraining from eating seafood for 3 days. The frequencies of fish, shellfish and seaweed dietary intake were not significantly correlated with urinary arsenic species.

Determination of trivalent methylated arsenicals in biological matrices

The enzymatically catalyzed oxidative methylation of As yields methylated arsenicals that contain pentavalent As (As(V)). Because trivalent As (As(III)) is the favored substrate for this methyltransferase, methylated arsenicals containing As(V) are reduced to trivalency in cells. Methylated arsenicals that contain As(III) are extremely potent inhibitors of NADPH-dependent flavoprotein oxidoreductases and potent cytotoxins in many cell types. Therefore, the formation of methylated arsenicals that contain As(III) may be properly regarded as an activation step, rather than a means of detoxification. Recognition of the role of methylated arsenicals that contain As(III) in the toxicity and metabolism of As emphasizes the need for analytical methods to detect and quantify these species in biological samples. Hence, a method was developed to exploit pH-dependent differences in the generation of arsines from inorganic and methylated arsenicals that contain either As(V) or As(III). Reduction with borohydride at pH 6 generated arsines from inorganic As(III), methyl As(III), and dimethyl As(III), but not from inorganic As(V), methyl As(V), and dimethyl As(V). Reduction with borohydride at pH 2 or lower generated arsines from arsenicals that contained either As(V) or As(III). Arsines are trapped in a liquid nitrogen-cooled gas chromatographic trap, which is subsequently warmed to allow separation of the hydrides by their boiling points. Atomic absorption spectrophotometry is used to detect and quantify the arsines. The detection limits (ng As ml(-1)) for inorganic As(III), methyl As(III), and dimethyl As(III) are 1.1, 1.2, and 6.5, respectively. This method has been applied to the analysis of arsenicals in water, human urine, and cultured cells. Both methyl As(III) and dimethyl As(III) are detected in urine samples from individuals who chronically consumed inorganic As-contaminated water and in human cells exposed in vitro to inorganic As(III). The reliable quantitation of inorganic and methylated arsenicals that contain As(III) in biological samples will aid the study of the toxicity of these species and may provide a new biomarker of the effects of chronic exposure to As.

A combined treatment approach using Fenton's reagent and zero valent iron for the removal of arsenic from drinking water

Studies on the development of an arsenic remediation approach using Fenton's reagent (H2O2 and Fe(II)) followed by passage through zero valent iron is reported. The efficiency of the process was investigated under various operating conditions. Potable municipal water and ground water samples spiked with arsenic(III) and (V) were used in the investigations. The arsenic content was determined by ICP-QMS. A HPLC-ICPMS procedure was used for the speciation and determination of both As(III) and (V) in the processed samples, to study the effectiveness of the oxidation step and the subsequent removal of the arsenic. The optimisation studies indicate that addition of 100 microl of H2O2 and 100 mg of Fe(II) (as ferrous ammonium sulphate) per litre of water for initial treatment followed by passing through zero valent iron, after a reaction time of 10 min, is capable of removing arsenic to lower than the US Environmental Protection Agency (EPA) guideline value of 10 microg/l, from a starting concentration of 2 mg/l of As(III). Using these suggested amounts, several experiments were carried out at different concentrations of As(III). Residual hydrogen peroxide in the processed samples can be eliminated by subsequent chlorination, making the water, thus, processed, suitable for drinking purposes. This approach is simple and cost effective for use at community levels.

Speciation of arsenic and selenium compounds by ion-pair reversed-phase chromatography with electrothermic atomic absorption spectrometry. Application of experimental design for chromatographic optimisation

An off-line system is proposed consisting of ion-pair reversed-phase liquid chromatography, collections of fractions at the outflow of the column and furnace atomic absorption spectrometry. The so-called system allowed determination of both arsenic and selenium species mainly found in the environment and in mammals (arsenite, arsenate, monomethylarsonate, dimethylarsinate, selenite, selenate, selenocystamine, selenocystine, selenomethionine and selenoethionine). In order to study the retention behaviour of these compounds and to estimate the optimal conditions for the chromatographic separation, central composite designs were used to evaluate the influence of the eluent parameters such as pH, tetrabutylammonium phosphate (TBA) concentration and sodium hydrogenphosphate amounts. The retention factors of each species and the selectivity were established as response criteria. Response surfaces and isoresponse curves were drawn from the mathematical models and enabled one to determine the optimal conditions and to visualise the method robustness. The predicted optimal zone was situated at pH 5.5-6.5, 4.0 mM Na2HPO4 and 3.0-4.0 mM TBA. Regression models suggested linearity for the studied compounds in the range 25-200 microg selenium and arsenic per litre investigated.

On-line reversed-phase liquid chromatography hydride generation emission spectrometry: speciation of arsenic in urine of patients intravenously treated with As2O3

Hydride generation inductively coupled plasma-atomic emission spectrometry (HG ICP-AES) was used as a continuous detection system for the determination of arsenic in the eluate from a high-performance liquid chromatographic (HPLC) system. Four arsenic species [arsenite As(III), arsenate As(V), monomethylarsonate (MMA), and dimethylarsinate (DMA)] present in the urine samples of patients treated intravenously with arsenite, were analyzed separately by HPLC-HG-ICP-AES using a non-polar C18 column. This analytical method allowed the sensitive determination of the arsenic species in the submicrogram per liter range. Urine samples collected on different days after arsenite administration were found to contain arsenite predominantly--monomethylarsonate and dimethylarsinate were also detected.

Arsenic speciation in human urine reference materials using high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

Six arsenic compounds including arsenocholine, arsenobetaine, dimethylarsinic acid, methylarsonic acid, arsenous acid and arsenic acid were separated by high-performance liquid chromatography (HPLC) on a Hamilton PRP-X100 anion-exchange column using isocratic elution and detected by inductively coupled plasma mass spectrometry (ICP-MS). This analytical procedure was applied to the speciation of arsenic compounds in human urine. The influence of urine matrix on the separation of arsenic compounds was evaluated and the determination of arsenic compounds was not hampered by the ArCl interference which has often been encountered in ICP-MS. Three human urine reference materials, SRM 2670 normal level, SRM 2670 elevated level and Lyphocheck urine metal control 1, were analyzed with respect to arsenic compounds by HPLC-ICP-MS. The results were found to be in good agreement with the certified total arsenic concentration in the reference materials. Six arsenic compounds were detected. Arsenobetaine was found to be present in all of the investigated human urine reference materials.

Liquid chromatography-inductively coupled plasma mass spectrometry

The technique of coupling liquid chromatography to inductively plasma mass spectrometry (ICP-MS) is reviewed. A brief introduction to the ICP-MS instrument is given as well as methods to couple the two analytical instruments together. The various types of LC that have been used with ICP-MS detection are discussed and advantages over traditional methods of detection are highlighted, such as the improvements in sensitivity and selectivity. Several applications that have been described in the literature are reviewed. An outlook for the future of LC-ICP-MS, particularly with regard to elemental speciation is given.

Effect of arsenosugar ingestion on urinary arsenic speciation

We developed and evaluated a method for the determination of μg/L concentrations of individual arsenic species in urine samples. We have mainly studied arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMAA), and dimethylarsinic acid (DMAA) because these are the most commonly used biomarkers of exposure by the general population to inorganic arsenic and because of concerns over these arsenic species on their toxicity and carcinogenicity. We have also detected five unidentified urinary arsenic species resulting from the metabolism of arsenosugars. We combined ion pair liquid chromatography with on-line hydride generation and subsequent atomic fluorescence detection (HPLC/HGAFS). Detection limits, determined as three times the standard deviation of the baseline noise, are 0.8, 1.2, 0.7, and 1.0 μ/L arsenic for arsenite, arsenate, MMAA, and DMAA, respectively. These correspond to 16, 24, 14, and 20 pg of arsenic, respectively, for a 20-μL sample injected for analysis. The excellent detection limit enabled us to determine trace concentrations of arsenic species in urine samples from healthy subjects who did not have excess exposure to arsenic. There was no need for any sample pretreatment step. We used Standard Reference Materials, containing both normal and increased concentrations of arsenic, to validate the method. Interlaboratory studies with independent techniques also confirmed the results obtained with the HPLC/HGAFS method. We demonstrated an application of the method to the determination of arsenic species in urine samples after the ingestion of seaweed by four volunteers. We observed substantial increases of DMAA concentrations in the samples collected from the volunteers after the consumption of seaweed. The increase of urinary DMAA concentration is due to the metabolism of arsenosugars that are present in the seaweed. Our results suggest that the commonly used biomarkers of exposure to inorganic arsenic, based on the measurement of arsenite, arsenate, MMAA, and DMAA, are not reliable when arsenosugars are ingested from the diet.