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Determination of five arsenic species in aqueous samples by HPLC coupled with a hexapole collision cell ICP-MS
Abstract
A new method has been developed for the simultaneous determination of AsV, monomethylarsenic (MMA), dimethylarsenic (DMA), AsIII, and arsenobetaine (AsB) in aqueous samples. The method utilizes a multi-mode ion exchange column coupled with a hexapole collision cell inductively coupled plasma mass spectrometer (ICP-MS). A mixture of 10 mM NH4NO3 and 0.05% HNO3 was used as the mobile phase, pumped by a high-performance liquid chromatography (HPLC) pump running in an isocratic mode at a flow rate of 0.4 mL min−1. Under these conditions, the five As species were separated within 14 min. The column outlet was connected directly to the ICP-MS via a low flow Meinhard concentric nebulizer. A river water certified reference material (SLRS-4), spiked with five As species at 20 µg L−1
(As cation) each, was used
to validate the chromatographic separation and quantification in a real sample matrix. Based on replicate analyses of SLRS-4, the precision varied from 2% for AsV to 10% for MMA. The detection limits (3s) ranged from 0.02 µg L−1 for AsB to 0.4 µg L−1 for MMA. The new method was applied to water samples collected during As toxicity test experiments. The results indicated that transformation of inorganic As species (AsV and AsIII) occurred during the toxicity test experiments, but no methylation of inorganic As species was detected.
... A Dionex AG-7, AS-7 anion exchange column was used, which functions as a multi-mode ion exchanger. The four As compounds (As (III), As (V), MMA and DMA) contain acidic groups and their acidic dissociation constants (pK a ) are listed in table 6.1 [169]. The degree of deprotonation of the compounds depends on pH and ionic strength of the mobile phase. ...
... Dissociation constants of arsenic compounds[169] 6.1.1 Selection of the mobile phaseA non-volatile mobile phase of phosphate buffer (such as sodium and potassium phosphates) is very often utilized in reversed-phase HPLC when using a UV detector because of its UV transparent property. ...
... Thus, a volatile mobile phase that does not introduce additional spectroscopic interferences would be more appropriate for ICP-MS detection. For example,1% v/v nitric acid is the most commonly used matrix in ICP-MS because it does not introduce extra spectroscopic interferences.Ammonium nitrate, which has the same elemental composition as nitric acid, is considered an optimal eluent in IC-ICP-MS due to its following features[169]:1. Thermal volatility, hence no significant salt deposition on the cones.2. ...
... Zorbax 300 PRP-X100 2 20 mM NH 4 H 2 PO 4 6,0 As(III) (2,0); DMA (2,7); MA (3,5); As(V) (7,5) Zorbax 300 7 10 mM C 5 H 5 N 2,3 1,5 DMA (1,6); AB (2,0); TMAO (3,2); AC (4,9); TMA + (5,5) Sauces de poissons Rodriguez et al. (2008) PRP X100 2 30 mM (NH 4 ) 2 CO 3 9,0 1,0 AB + AC (2,5); As(III) (3,0); DMA (4,0); MA (9,0); As(V) (17,0) DORM 2 a , poissons Ackley et al. (1999) PRP X100 2 15 mM C 4 H 6 O 6 2,9 1,5 AB (6,6); MA (7,0); DMA (8,3); As(III) (11,6); As(V) (19,7) Urine, SRM 2670n b Chen et al. (2002) Pak A HR 8 10 mM NaH 2 PO 4 / Na 2 HPO 4 (4/1) 6,0 0,5 AB (1,8); As(III) (2,3); DMA (3,3); MA (3,8); As(V) (11,5) Plantes, graines Van den Broeck et al. (1998) Pak Anion HR 9 10 mM (NH 4 ) 2 CO 3 10,0 1,0 AB (0,9); As(III) (1,4); DMA (2,3); MA (3,9); As(V) (5,0) Carrottes Vela et al. (2001) Ion-Exchange 10 10 mM NH 4 NO 3 -0,4 As(V) (7,1); MA (8,0); DMA (9,1); As(III) (10,8); AB (12,9) Eaux Xie et al. (2002) PRP-X100 2 10 mM HPO 4 2-/ H 2 PO 4 -8,5 1,5 AB (1,5); As(III) (1,9); DMA (2,6); MA (4,0); As(V) (10,5) Riz; SRM 1568a c , poulet, poissons, CRM 627 d Sanz et al. (2005a) Pak Anion HR 8 10 mM (NH 4 ) 2 CO 3 pH 10,0 1,0 AB (3,0); DMA (4,8); As(III) (7,4); MA (12,0); As(V)(15,2) Riz, SRM 1568a f Heitkemper et al. ...
... ) et As(V)) et des espèces méthylées (MA et DMA) alors que la séparation par échanges cationiques (PRP-X 200, LC SCX, Zorbax 300 SCX ou IC-CS-10),avec un éluant constitué de pyridine (C 5 H 5 N) ou d'acide formique (CH 2 O 2 ), est utilisée pour les espèces organiques (AB, AC, TMAO, TMA + , etc.).(Guérin et al., 1999 ;Gong et al., 2002 ; Francesconi et Kuenelt, 2004 ;B'Hymer et Caruso, 2004) Une combinaison de ces deux méthodes est couramment utilisée pour séparer l'ensemble des espèces concernées mais engendre fatalement une augmentation significative du temps d'analyse (temps de séparation et temps de stabilisation des colonnes).L'utilisation unique d'une colonne à échange d'anions en mode isocratique apparaît délicate dans la mesure où la résolution des pics AB et As(III) est généralement faible.(Ackley et al., 1999 ;Van den Broeck et al., 1998 ;Vela et al., 2001 ;Xie et al., 2002 ;Sanz et al., 2005a) Toutefois, les travaux deZheng et al. (1999) et Chen et al. (2002) ont démontré que l'acide tartrique (C 4 H 6 O 6 ), utilisé comme éluant, forme un complexe anionique avec l'arsénite, permettant une séparation de 5 composés (As(III), As(V), MA, DMA et AB) en moins de 15 minutes. Une autre étude réalisée par Saverwyn et al. (1997) montre qu'il est possible de séparer ces 5 composés en optant pour une colonne LC SAX avec un éluant phosphaté. ...
The government agencies generally evaluate the food risks related to the presence of arsenic in seafood samples by analyzing only total arsenic, without considering the various involved forms nor their bioavailability. The main objective of this study was to develop and validate a method allowing the French Food Safety Agency (AFSSA) to propose with its supervisions a better evaluation of the risks incurred by the consumer by determining the speciation and the bioaccessibility of the various arsenic forms in the seafood samples. The first part of this work was to develop a method of separation of the principal arsenic species usually found in the seafood samples by coupling separation by ions exchange chromatography (IEC) and detection by ICP-MS. The experimental designs methodology used in this work, allowed, in a minimum of experiments, on the one hand to evaluate the influence of the various factors and their possible interactions on the separation from 7 to 9 arsenic species and on the other hand, to determine the optimal analytical conditions while minimizing the time of analysis (less than 15 minutes), preserving satisfactory resolutions and improving the sensitivities of the compounds considered. The second part of this work related to the development of the method to extract the arsenic species in seafood samples by microwaves assisted extraction (MAE). The optimisation of the conditions of extraction in various certified reference materials showed clearly that a solvent only composed of water was sufficient to obtain satisfactory total arsenic and arsenic species recoveries. The evaluation of the analytical criteria showed that the method was practically validated for arsenic speciation in seafood samples, even if internal reproducibility will have to necessarily be refined by evaluating it later on. Then, the validated method could be applied to the speciation of arsenic in aqueous samples, and also to the certification of a dogfish liver samples organized by the Canadian NRC. The last part of this work related to the development of a fast and pragmatic in vitro method of evaluation of the maximum total arsenic and arsenic species bioaccessibility in seafood samples, by combining a continuous leaching method (for measurement in real-time by ICP-MS of the arsenic portion released by artificial gastrointestinal fluids) and the validated speciation method. The results show that the bioaccessible arsenic (approximately 50% of the total arsenic in the samples) is released very quickly (in less than 5 min) by saliva with nothing else is then released by gastrointestinal juices. In addition, this work highlighted that the inorganic arsenic species bioaccessibility appears less important than that of the organic species in seafood samples.
... In this respect, some analytical techniques have been employed to minimize polyatomic interference. Mathematical correction equations, cool plasma conditions, collision cell technique (CCT), dynamic reaction cell (DRC), and collision reaction interface (CRI) were introduced to correct for polyatomic interference [15][16][17][18][19][20]. Among these techniques, Microchemical Journal 120 (2015) 77-81 the CCT facilitates the physical collision process in an octopole pressurization chamber with the aid of He or H 2 gas, and is garnering attention owing to its simplicity and versatility. ...
... Among these techniques, Microchemical Journal 120 (2015) 77-81 the CCT facilitates the physical collision process in an octopole pressurization chamber with the aid of He or H 2 gas, and is garnering attention owing to its simplicity and versatility. Many researchers have reported successful applications of CCT to the removal of 40 Ar 35 Cl + interference [11,16]. However, a strategy to improve the analytical sensitivity of As remains a necessity. ...
Feasibility of collision cell (CC) technique with the aid of a methanol modifier for the trace determination of arsenic (As) in a high-chloride-containing sample using ICP-MS was assessed to eliminate the analytical bias induced by polyatomic interference from 40Ar35Cl+ without reducing 75As+ intensity, thereby lowering the limit of detection (LOD). The signal intensity of 2% HCl measured at 75 m/z was suppressed entirely by introducing He gas into the CC at a flow rate of at least 3 mL min- 1. Results from the calibration experiments revealed that excess He gas in the CC could also decrease the 75As+ intensity. Therefore, an optimized He flow rate should be employed, which seemed to be 3 mL min- 1 in this study. To obtain greater sensitivity in the As analysis, the effect of methanol added to the sample solution in varying concentrations (0 to 5% v/v) was assessed. In accordance with previous studies, 3% methanol addition improved As sensitivity by a factor of 2.5 to 3. Also, the methanol addition seemed to decrease the formation of 40Ar35Cl+. Overall, the combined use of both strategies with optimized conditions achieved a lower LOD value of 3 ng L- 1 with a high accuracy.
... [32][33][34] Despite the widespread application of Ar-sustained ICP-MS, isobaric or polyatomic spectral interferences on isotopes arising from the sample matrix or plasma gas 35 often hinder accurate determination of elements of interest. Numerous strategies have been developed to mitigate spectral interferences for accurate elemental quantification during ICP-MS analysis, 36 such as the use of collision/reaction cells 37,38 or high resolution mass spectrometers. 39,40 Non-instrumental approaches such as mathematical corrections [41][42][43] or careful selection of interference-free isotopes for quantification are also common. ...
The performance of a nitrogen (N 2 )-sustained Microwave Inductively Coupled Atmospheric-Pressure Plasma (MICAP) - Quadrupole Mass Spectrometer (QMS) was explored as an alternative to the traditional argon (Ar) equivalent for arsenic...
... Dissolved arsenic was measured using a hexapole inductively coupled plasma mass spectrometry (ICP-MS) (Platform XS, GV Instruments, Manchester, UK), calibrated over the range of 0.1-100 μg L -1 using standards prepared in 1% nitric acid (Optima Trace Metal Grade, Fisher Scientific™, USA) from a stock standard of 1000 mg L -1 (SPEX CertiPrep) obtained from Fisher Scientific (St. Louis, MO, USA). Arsenic species were separated and measured using ion chromatography (IC) with multi-mode ion exchange chromatographic column (ASK-1, Micromass, Manchester, UK) directly coupled to the ICP-MS (Xie et al., 2002). A mobile phase of 10 mM NH 4 NO 3 and 0.05% HNO 3 supplied by an isocratic HPLC pump (SSI Series I, State College, USA) provided separation of As(III) and As(V). ...
Dissolved arsenic typically results from chemical weathering of arsenic rich sediments and is most often found in oxidized forms in surface water. The mobility of arsenic is controlled by its valence state and also by its association with iron oxides minerals, the forms of which are both influenced by abiotic and biotic processes in aqueous environment. In this study, speciation methods were used to measure and confirm the presence of reduced arsenic species in the surface water of Frenchman creek, a gaining stream that crosses the Colorado-Nebraska border. Selective extraction analysis of aquifer and stream bed sediments shows that the bulk of the arsenic occurs with labile iron-rich oxy(hydroxide) minerals. Total dissolved arsenic in surface and groundwater ranged from ~3 to 18 µg L⁻¹, and reduced arsenic species comprise about 41% of the total dissolved arsenic (16.0 µg L⁻¹) in Frenchman creek. Leachable arsenic in the aquifer sediment samples ranged up to 1,553 µg kg⁻¹, while samples from Frenchman creek bed sediments contained 4,218 µg kg⁻¹. Dynamic surface and groundwater interaction sustains arsenite in iron-rich surface headwaters, and the implied toxicity of reduced arsenic in this hydrogeological setting, which can be important in surface water environments around the globe.
... A number of methods have been employed and reviewed in the scientific literature, including spectroscopy, chromatography and electrochemical methods (Jain, 2000;Franscesconi, 2000;Szpunar, 1999 and2000). ICP-MS is often a favoured method for the determination of arsenic because of its sensitivity and ability to couple to HPLC for the separation and measurement of arsenic species at low concentrations (Feldmann, 1999;Gong, 2002;Hamon, 2004;Polya, 2003;Sathrugnan, 2004;Xie, 2002). ...
... For example, Zheng et al. 11 observe an advanced reduction step of As(V) to As(III) in sediment pore waters that is marked by the high proportion of thioarsenical species. Xie et al. 12 could monitor changes in As speciation over time during toxicity testing experiments using Chironomus tentans. They suspect that a detoxication occurs due to the bacterial growth in solution via the oxidation of As(III) to As(V). ...
A new sensitive chromatographic method has been developed for As speciation determination in anoxic pore waters. Starting from aliquots of 25 µL, the different As species As(III), As(V), MMAAV and DMAAV were separated in less than 4 min by HPIC-ICP-MS using the IonPac® AG7-AS7 anion-exchange column set and dilute HNO3 as mobile phase. The detection limits were below or equal to 0.25 µg L-1 for each As species, which makes the method efficient to determine As speciation in poorly-contaminated sediments. In addition, no precipitation of iron and manganese (hydr)-oxides was observed since the anoxic samples were systematically carefully manipulated under nitrogen atmosphere. Chlorides were eliminated by the chromatographic separation, thus making possible speciation analysis in estuarine or seawater samples. The use of internal standard was not necessary due to good signal stability (< 10 %) at m/z 75 over 4 h of analysis. An environmental application has also been successfully performed in the Marque River (Northern France). Inorganic As species were detected in pore waters at low concentrations [below 1 and 10 µg L-1, for As(V) and As(III) respectively]. Others As species, identified as thioarsenic species, were also detected.
... One way to overcome the lack of CRMs is to spike the real samples with a known amount of Cr species. This method is widely applied in speciation analysis [53,[82][83][84]. The result is then compared to the unspiked sample value and presented as the recovery. ...
Chromium holds a special position among living organisms because depending on its species it can be either essential or toxic. Cr(VI) even at very low concentrations is harmful and carcinogenic, while Cr(III) is a necessary microelement for cellular metabolism. Therefore, a simple analysis of Cr concentration in collected samples will not be able to distinguish these differences effectively: for a proper chemical analysis we need to perform a reliable detection and quantification of Cr species. Separation and detection of chromium can be accomplished with high performance liquid chromatography hyphenated to inductively coupled plasma mass spectrometry (HPLC/ICP-MS) in a one-step. Our review assembles articles published since 2000 regarding chromium speciation in water samples with the use of HPLC/ICP-MS. It addresses the following issues: chromium chemistry, the possibilities of dealing with interferences, metrological aspects, analytical performance and speciated isotope dilution mass spectrometry (SIDMS) which is a definitive measurement method. The authors would like to advocate this hyphenated advanced technique as well as the metrological approach in speciation analysis of chromium.
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... The most frequent approach for estimating the trueness of the method is using particular CRMs. In this study, the trueness was evaluated by the standard addition method, because suitable reference materials for chromium speciation are not available [10, 29, 30]. This method allowed the authors to verify the efficiency of the optimized analytical procedure through determining the recovery of each assayed analyte. ...
The approach presented in this article refers to the modification of a method for the detection and quantitative determination of chromium species in water by high-performance liquid chromatography inductively coupled plasma mass spectrometry. The main aim of this work was to establish a detailed validation of the analytical procedure and an estimation of the budget of measurement uncertainty which was helpful in recognizing the critical points of the presented method. As a result of the method validation experiment, the obtained limit of quantification, repeatability and intermediate precision were satisfied for the quantification Cr(III) and Cr(VI) in water matrices. The trueness of the method was verified via an estimation of the recovery of the spiked real samples. The recovery rate of both determined analytes was found to be between 93 and 115 %. Considering that the validation of the method and the evaluation of measurement uncertainty are crucial for quantitative analysis, the above-mentioned assessment of the uncertainty budget was performed in two different ways: a modelling approach and a single-laboratory validation approach. The measurement uncertainties of the results were found to be 4.4 and 7.8 % for Cr(III), 4.2 and 7.9 % for Cr(VI) using the classical concept and method validation data, respectively. This paper is the first publication to presenting all the steps needed to evaluate the measurement uncertainty for the speciation analysis of chromium species. In summary, the obtained results demonstrate that the method can be applied effectively for its intended use.
... A two step method (20 mM and 60 mM NH 4 NO 3 , pH 8.7) demonstrated these unique properties in multi-elemental speciation [169]. This eluent was also chosen for a reliable detection in nano multimode-IC (15 mM NH 4 NO 3 , pH 3, [170]), micro-AEX (5 mM and 80 mM NH 4 NO 3 -steps, pH 8.3, [171]) and in narrow bore AEX (0.5-70 mM NH 4 NO 3 -gradient, pH 8.3, [130]). Up to now, this is the only eluent used to perform the separation around the sample pH or at any other freely selectable pH since its eluent strength does not depend on the pH. ...
Multiple acute and chronic toxicity of arsenic species and its mobilisation from geological deposits into ground and drinking water resources are one of the greatest threats to human health. Arsenic speciation analysis, mostly done by liquid chromatography, is a challenging task which requires an intense high quality work with respect to extraction, preservation, separation, detection and validation. A growing number of As-species and low regulatory limits (10 μg/L) may require more than one speciation method preferably performed by species specific procedures and detectors. Beside As-fractionation for special application there are many selective speciation methods based on high performance separation techniques like capillary elec-trophoreses, gas and liquid chromatography. Both, fractionation and speciation methods are reviewed. How-ever, the focus is on scopes and limits of ion chromatographic separations, the most frequently used methods. Based on IC-principles the methods applied are critically discussed and recommendations given which should result in more robust and reliable As-speciation.
... The use of spectrometric methods in combination with the hydride generation atomic absorption spectrometry as a detector in gas or liquid chromatography has considerably extended the possibilities of speciation determinations. The hyphenated systems HPLC-HGICP-MS [6], HPLC-HGAFS [ [6] or others [11], [12] and compete with the systems combined with direct detection HPLC-ICP-MS [14], [15]. The possibility of determination of organic species of arsenic has been achieved by applying on-line mineralisation of organic compounds realised by the thermal method [1], with microwave heating [12], UV-radiation assisted UV [8], [11] or sometimes with preliminary reduction of arsenic species to As(III) [10]. ...
The paper presents the principles and advantages of a technique combining high performance liquid chromatography and hydride
generation atomic absorption spectrometry (HPLC-HGAAS) applied to speciation analysis of inorganic species of arsenic As(III)
and As(V) in ground water samples. With separation of the arsenic species on an ion-exchange column in the chromatographic
system and their detection by the hydride generation atomic absorption spectrometry, the separation of the analytical signals
of the arsenic species was excellent at the limits of determination of 1.5 ng/ml As(III) and 2.2 ng/ml As(V) and RSD of 4.3%
and 7.8% for the concentration of 25 ng/ml. The hyphenated technique has been applied for determination of arsenic in polluted
ground water in the course of the study on migration of micropollutants. For total arsenic concentration two independent methods:
HGICP-OES and HGAAS were used for comparison of results of real samples analysis.
... In the speciation analysis, a significant role is played by hyphenated techniques, by which the forms of determined elements are separated using chromatographic methods, with spectrometric techniques as detectors. Hyphenated systems, such as HPLC–HG–ICP–MS (Le et al., 1994), HPLC–ICP–MS (Xie et al., 2002), HPLC–HG–AFS (Suner et al., 2000) or HPLC–HG–AAS (Le et al., 1994; Gomez-Ariza et al., 1998) allowed determination of the content of arsenic forms, both inorganic As(III) and As(V) and organic. In the case of using hyphenated techniques in the speciation analysis, an important stage is the previous extraction of arsenic forms from a soil or deposit sample. ...
Biotic ligand model (BLM) was extended to predict the toxicity of inorganic arsenate (iAs(V)) to the luminescent bacteria, Aliivibrio fischeri. As the pH increased from 5 to 9, the HAsO42- form predominated more than the H2AsO4- form did, and the EC50[As]T (50% effective iAs(V) concentration) decreased drastically from 3554 ± 393 to 39 ± 6 μM; thus, the HAsO42- form was more toxic to A. fischeri than H2AsO4-. As the HPO42- activity increased from 0 to 0.44 mM, the EC50{HAsO42-} values (50% effective HAsO42- activity) increased from 31 ± 6 to 859 ± 128 μM, indicating that the toxicity of iAs(V) decreased, owing to the competition caused by the structural similarity between iAs(V) and phosphate ions. However, activities of Ca2+, Mg2+, K+, SO42-, NO3-, and HCO3- did not significantly affect the EC50{HAsO42-} values. The BLM was reconstructed to take into account the effects of pH and phosphate, and the conditional binding constants for H2PO4-, HPO42-, H2AsO4-, and HAsO42- to the active binding sites of A. fischeri were obtained; 3.424 for logKXH2PO4, 4.588 for logKXHPO4, 3.067 for logKXH2AsO4, and 4.802 for logKXHAsO4. The fraction of active binding sites occupied by iAs(V) to induce 50% toxicity (fmix50%) was found to be 0.616.
Inorganic-organic nanoscale materials have recently received significant interest as tunable, next generation, sorbents for the separation of metal and metalloid contaminants, including arsenic (As) and chromium (Cr), among others. In this work, we have designed and synthesized IONCs coated with specific functionalized organic materials with the goal of variable explicit evaluation. Specifically, single domain, superparamagnetic, monodisperse IONCs were synthesized and transferred into water via surface functionalization by ligand exchange and encapsulation methods. As synthesized, hybrid materials showed high performance for both As(V) and Cr(VI) sorption when nanocrystals are coated with positively charged organic surface coatings such as, polyethyleneimine (PEI) and cetyltrimethylammonium bromide (CTAB). IONC cores coated with negatively charged organic coating materials (polyethyleneglycol (PEG), oleic acid (OA), sodium dodecyl sulfate (SDS)) and silica (SiO2) demonstrated significantly lower sorption capacities. When silica coated IONCs (Fe3O4@SiO2, core-shell materials) were surface coated with PEI, sorption capacities for As(V) and Cr(VI) of Fe3O4@SiO2@PEI are comparable to Fe3O4@PEI, underscoring the importance of surface coating functionality. To complement these studies, real-time sorption behavior of As(V) and Cr(VI) with PEI was explored by quartz crystal microbalance with dissipation (QCM-D).
In the analysis of arsenic (As) with ICP-MS, the phenomenon that methanol addition to the sample decreases the amount of ⁴⁰Ar³⁵Cl⁺ formed was observed in the previous study. To investigate the effect of methanol addition on generation of isobaric polyatomic ions and its mechanism, a diluted HCl solution and 10 μg/L As solution with varying amounts of methanol (0, 1, 2, 3, and 4 v/v%) respectively were analyzed using ICP-MS in a variety of mass spectra (m/z = 35, 47, 75, 82, 117, and 152). With addition of methanol to the sample, the signal intensity of ¹²C³⁵Cl⁺ increased 11.1-fold while that of ⁴⁰Ar³⁵Cl⁺ only increased 1.17-fold. In this regard, carbon atoms that are not ionized in the plasma (¹²C) originated from methanol seemed to convert ⁴⁰Ar³⁵Cl⁺ to ¹²C³⁵Cl⁺ through a substitution reaction. Furthermore, carbon atoms ionized in the plasma (¹²C⁺) converted ⁷⁵As into ⁷⁵As⁺ via the charge transfer reaction and thus increased signal intensity for As. At the same time, the amount of ⁴⁰Ar³⁵Cl⁺ formed in the plasma decreased additionally since the ¹²C regenerated from ¹²C⁺ during the charge transfer process can act as a reactant in the substitution reaction aforementioned.
Speciation refers to the various physical and chemical forms in which an element can exist in a real-world material. The forms of an element are its manifestations differing in isotopic composition, electronic structure or oxidation number, or the structure of the molecule or complex [1]. Speciation analysis is the procedure of identifying individual forms of a particular element and their quantification. The above definition concisely outlines the purpose of an analyst’s activities. However, the quality of identification of compounds is often dependent on the available equipment, the general state of knowledge about the biochemistry of the investigated element, and the experience of the analyst. Correct identification is a challenging task for many reasons, one of them being that it is necessary to determine the properties of a compound of an element present at the trace level, and inadequate sensitivity is the most common drawback of molecule-specific techniques. Another problem is that analyses often seek to determine the identity of compounds that have not yet been described in the literature. If this is the case, the practical analytical procedure must ultimately isolate the chemical form being searched for, and obtain it in a purity that is typical of the standard substance. The process usually involves several stages.
The importance of measuring arsenic (As) species has been appreciated for a long time mainly because of the wide spread knowledge of arsenic's toxicity and its use as a poison. Increasingly health, environmental and food regulations have been written around As species rather than total concentrations. Knowledge of As speciation is important as the chemical form of As controls its bioavailability, toxicity, mobility and therapeutic benefits. Arsenic is present as inorganic (arsenate, arsenite, thioarsenates), complexed (arsenic glutathionines and phytochelatins), low molecular weight (monomethylarsonate, dimethylarsenate, arsenobetaine, arsenocholine etc.) and high molecular weight (arsenic hydrocarbons and arsenic phospholipids) species. In this review we cover the intergrity of As species during collection, storage, sample preparation and measurement by HPLC-ICPMS and HPLC-HG-AFS. It is essential to ensure that As species, especially in waters and sediments, are not artefacts of the preservation or extraction procedure. Most samples can be stored frozen (-20 °C), but the stability of water and sediment samples is matrix dependent and depends on preservation technique applied. Arsenic cannot be extracted from samples using a single set of conditions but must be optimised for each sample type. Methanol-water mixtures with microwave heating are commonly used to extract polar As species from tissues while As-lipids required a non-polar solvent. Dilute acid can be used to increase the efficiencies of extraction of hard to extract tissue As species. Freeze drying is suitable for the drying of biotic material while sediments should not be dried before analysis. Extraction efficiencies are critically dependent on particle size. Polar As species have a wide variety of ionic characteristics thus complimentary chromatographic approaches utilising ion-exchange or reverse phase columns with modifiers are needed to separate all the As species. Arsenic-lipids require the use of a reverse phase column and gradient elution with high concentrations of organic solvents and require compensation for carbon enhancement effects in the ICPMS. Care must be taken that chromatographic peaks are not misidentified and matrix interferences accounted for that may influence quantification. Finally, to ensure accurate results, mass balances and extraction and column recoveries need to be determined at all steps. Methods need to be evaluated using As spikes and certified reference materials to provide a means of assessing the quality of results.
The determination of inorganic arsenic species in water, beverages and foods become crucial in recent years, because arsenic species are considered carcinogenic and found at high concentrations in the samples. This communication describes a new cloud-point extraction (CPE) method for the determination of low quantity of arsenic species in the samples, purchased from the local market by UV-Visible Spectrophotometer (UV-Vis). The method is based on selective ternary complex of As(V) with acridine orange (AOH(+)) being a versatile fluorescence cationic dye in presence of tartaric acid and polyethylene glycol tert-octylphenyl ether (Triton X-114) at pH 5.0. Under the optimized conditions, a preconcentration factor of 65 and detection limit (3Sblank/m) of 1.14μgL(-1) was obtained from the calibration curve constructed in the range of 4-450μgL(-1) with a correlation coefficient of 0.9932 for As(V). The method is validated by the analysis of certified reference materials (CRMs).
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This paper describes a user-friendly method for bromate determination that can be implemented easily on any inductively coupled plasma-mass spectrometer present in drinking water laboratories. The method uses low pressure liquid chromatography coupled to an ICP-quadrupole mass spectrometry instrument (ICP-QMS) or an ICP-sector field mass spectrometry instrument (ICP-SFMS) and is compared to that relying on high performance liquid chromatography (HPLC) coupled to an ICP-QMS instrument. The low pressure LC/ICP-MS method uses a low-pressure delivery six-port valve and a 5 cm anion exchange column, which allows a fully resolved separation of bromate in 13 min and achieves a limit of quantification of 0.2 μg bromate L−1. The low pressure LC system is small and easy to install and its operation is fully integrated within the ICP-MS software. The method allows fit-for-purpose assessment of bromate, potentially present as a Br-containing disinfection by-product in drinking water, and meets all performance characteristic requirements set by the European Council for the monitoring of the quality of water intended for human consumption. A median bromate concentration of 0.5 μg L−1 was obtained for 80 tap water samples collected during regulatory monitoring campaigns from 2009 until 2012 and covering different water supply areas in the Flemish region of Belgium.
In a stream of aqueous sample, trace arsenic ions were quantitatively coprecipitated and detected in ICP-AES through hydride generation. In was used as a coprecipitating reagent. The precipitate was collected on a filter and dissolved by HCl. The eluted As was sent into the reaction coil to generate hydrides and analyzed by ICP. With optimal conditions, and with a sample of 0.3 mL, an enrichment of 70 was obtained with the sampling speed of 10/hr. When compared with coprecipitation and hydride generation technique, the sensitivity was increased by 7 and 10 times, respectively. The limit of detection limit was 0.020 and the precision was 7-10%. Separation of were possible using citric acid in hydride generation.
Arsenic species, including arsenous acid, arsenic acid, methylarsonic acid, and dimethylarsinic acid, were determined using HPLC-ICPMS. The species were separated with a Discovery HS F5 column and a simple, volatile, and isocratic mobile phase of 0.1% (v/v) formic acid and 1% (v/v) methanol. The Discovery HS F5 column with a pentafluorophenyl (PFP) stationary phase gave sharp peaks and full separation of the arsenic species in 5min, and other PFP columns showed lower performance. This separation method was applied to arsenic species analysis in rice. The extraction of arsenic from rice samples was performed using 0.15M nitric acid. The methodology was validated by use of certified reference materials, NMIJ CRM 7503-a and NIST SRM 1568a, and extremely low arsenic rice samples as blank samples.
The use of high-pressure liquid chromatography coupled directly or by a hydride generation system to an inductively coupled plasma mass spectrometer for the unambiguous measurement of 13 arsenic species in marine biological extracts is described. The use of two chromatography systems; a Supelcosil LC-SCX cation-exchange column eluted with a 20 mM pyridine mobile phase adjusted to pH 2.2 and 2.6 with formic acid, with a flow rate of 1.5 mL min(-1) at 40degreesC, and a Hamilton PRP-X100 anion-exchange column eluted with 20 mM NH4H2PO4 buffer at pH 5.6, with a flow rate of 1.5 mL min(-1) at 40degreesC, was required to separate and quantify cation and anion arsenic species. Under these conditions, arsenous acid could not be separated from other arsenic species and required the use of an additional hydride generation step. Arsenic species concentrations in a locally available Tasmania kelp (Durvillea potatorum), a certified reference material (DORM-2), and a range of commercially available macroalgae supplements and sushi seaweeds have been measured and are provided for use as in-house quality control samples to assess the effectiveness of sample preparation, extraction, and measurement techniques.
This review considers the basics, principles of operation and practical application of spectral interference suppression systems based on multipole gas-filled cells.
Trace levels of arsenic (As) in soil samples can be determined by conventional ICP-QMS with closed vessel digestion, but always suffer from interference of ions originating from the complicated matrix, mainly including 40Ca35Cl+, 40Ar35Cl+, 39K36Ar+, 150Nd2+, 150Eu2+ and 150Sm2+etc. In this study, 75As+, the mass for general detection, was effectively changed to 75As16O+ which could be detected at m/z 91 by reaction with oxygen in a Dynamic Reaction Cell (DRC). For the new interference of 91Zr+ on 75As16O+, boiling aqua regia extraction was used to remove most of the zirconium in the sample preparation procedure, and the residual 91Zr+ was oxidized to 91Zr16O+ by oxygen in the DRC. In addition, the signal intensity of 75As16O was improved 4-fold by addition of 4% methanol into the sample solution. The signal to background ratio (SBR) of As was obviously improved from 0.18 to 205 (the certified arsenic concentration is 1 μg L−1), and a limit of quantification (LOQ, 10σ) of 0.1 ng g−1 was obtained. The proposed method was successfully applied to analyze 20 soil samples collected from pig farms in livestock farming processes, and shows its great potential for trace As determination in environmental and geological samples.
This chapter discusses the biomedical applications of inductively coupled plasma mass spectrometry (ICP-MS) as an element specific detector for chromatographic separations. Typically, in an ICP, the gas flows into three concentric tubes. These tubes are assembled together in what is commonly referred to as the plasma torch. ICP-MS is a powerful analytic technique that is finding popularity as an element specific detector for chromatographic separations. The technique has rapidly matured into the technique of choice for routine ultra trace-element analysis. This is mainly due to its advantages in terms of detection limits, relative freedom from interference, and speed of analysis. This has opened the door for novel research in the biomedical field investigating the metabolic fate of drugs, phosphorylation reactions, the role of essential trace elements in human health, and the mechanisms in which toxic elements affect the human body. The technique offers selectivity, sensitivity, and quantitative determinations and, as such, it is rapidly gaining acceptance as a routine tool for biomedical and pharmaceutical research.
Elemental speciation involves the separation and quantification of different oxidation states or chemical forms of a particular trace element. Trace metals exhibit widely different toxicities depending on their elemental species in the environment. On the other hand, inductively coupled plasma mass spectrometry (ICP-MS) is considered to be the method of choice for elemental analysis for several reasons. In this review, the speciation analysis of arsenic and antimony in environmental samples using ICP-MS detection is described. In this sense, the use of ICP-MS coupled with various separation techniques (e.g., HPLC, CE, GC, etc.) for the purpose of elemental speciation has recently gained a lot of attention.
Among the various methods applied to reduce spectral interference in ICP-MS, collision technology, which utilizes gaseous molecules to eliminate interfering ions, has been demonstrated to be one of the most effective techniques. Helium, hydrogen, ammonia, methane and oxygen are mainly used as collision gases. Although by-product ions are sometimes found as a result of the ion-molecule reactions involved in this technology, these undesirable ions are successfully suppressed by energy discrimination, or a band-pass tuning technique. The principle of the technology, the optimization method of the instrumental parameters and the major applications to various samples are described along with comments on the possibilities and limitations of the technology.
A nano-high performance liquid chromatography-inductively coupled plasma mass spectrometry (nano-HPLC-ICPMS) method is developed, using a demountable direct injection high efficiency nebulizer (d-DIHEN), to reduce sample and mobile phase consumption, minimize organic waste generation, decrease analysis time, and enhance separation efficiency. A HPLC column (50 mm × 0.3 mm id), packed with 3.5 μm C18 material, is explored for chromatographic separation of five arsenic species naturally present in the environment or introduced as a pollutant: sodium (meta)arsenite [As(III)], arsenic acid [As(V)], dimethylarsenic acid (DMA), disodium methylarsenate (MA), and p-arsanilic acid (p-ASA). A fast chromatographic separation of five arsenic species is achieved in less than 12 min at a solution flow rate of 0.9 μL min−1 using a 50 nL sample injection. The HPLC-ICPMS interface provides well defined flow injection profiles at various concentrations, giving a correlation coefficient of 0.999 for each individual arsenic species calibration curve. Precision values for peak height and area of five arsenic species range from 0.5 to 6.5% RSD and absolute detection limits are within 0.4 to 5.4 pg arsenic, which are comparable to previously reported data at higher solution uptake rates (20 μL min−1 to 1 mL min−1) and larger sample injection volumes (20–100 μL).
A mixture of organic and inorganic arsenic compounds has been separated using ion exchange liquid chromatography and detected using a particle beam glow discharge mass spectrometer (PB-GDMS). The particle beam interface makes use of nebulization and momentum separation to deliver a stream of dry analyte particles to the glow discharge source from the LC output. In the glow discharge, the analyte particles are vaporized and ionized at or near the cathode surface. The ions are analyzed by a quadrupole mass spectrometer collecting data in either single ion monitoring (SIM) or total ion counting (TIC) modes. The separation of arsenobetaine (2-(trimethylarsonio)acetate), arsenic(III) chloride and dimethylarsenic acid was performed on a universal cation-exchange column using an isocratic mobile phase, with a total elution time of less than four minutes. The mass spectrum for each of these compounds contains a strong elemental arsenic signal as well as the molecular fragments that allow for the identification of the specific species responsible for the chromatographic peak. The limits of detection (LOD) for organic arsenic (dimethylarsenic acid) were found to be 2 ppm (90 ng DMA molecular ion) in the TIC mode and 15 ppb (0.8 ng As from DMA) in the SIM mode. Inorganic arsenic(III) chloride has an LOD of 11 ppb or 0.55 ng As absolute. This work suggests that the PB-GDMS has high potential as a comprehensive (inorganic/ organic) detector for both biological and environmental speciation work.
We describe a hyphenation technique between HPLC and ICP-SFMS for ultra-trace arsenic speciation analysis. Exceptional analytical performance was achieved using a MicroMist nebulizer preceded by a high-pressure splitter. Despite a 1 : 7.5 flow splitting, the detection limits in the range of 1.2 to 2.4 pg mL 21 were about two times lower than those obtained with a concentric nebulizer without any flow splitting, demonstrating the applicability of coupling conventional HPLC system (1.5 mL min 21 eluent flow) with microflow nebulizer for ultra-trace arsenic speciation analysis. This set-up offers an advantage for on-line fraction collection for either multidimensional chromatographic separation of co-eluting As compounds or for structural identification of unknown compounds without sacrificing analytical sensitivity. In addition, this system showed good accuracy and repeatability. The method was applied to the determination of arsenic compounds in freshwater fish samples from an arsenic-rich lake, Moira Lake, Canada. Using cation-exchange chromatography, tetramethylarsonium ion (Tetra) was detected in freshwater fish samples for the first time. Moreover, in pumpkinseed, Tetra was found to be the major arsenic species, indicating that the biomethylation pathway in freshwater ecosystems may include the tetramethyl stage.
Hydride generation (HG) coupled with AAS, ICP–AES, and AFS techniques for the speciation analysis of As, Sb, Se, and Te in environmental water samples is reviewed. Careful control of experimental conditions, offline/online sample pretreatment methods employing batch, continuous and flow-injection techniques, and cryogenic trapping of hydrides enable the determination of various species of hydride-forming elements without the use of chromatographic separation. Other non-chromatographic approaches include solvent extraction, ion exchange, and selective retention by microorganisms. Sample pretreatment, pH dependency of HG, and control of NaBH4/HCl concentration facilitate the determination of As(III), As(V), monomethylarsonate (MMA), and dimethylarsinate (DMA) species. Inorganic species of arsenic are dominant in terrestrial waters, whereas inorganic and methylated species are reported in seawater. Selenium and tellurium speciation analysis is based on the hydrides generation only from the tetravalent state. Se(IV) and Se(VI) are the inorganic selenium species mostly reported in environmental samples, whereas speciation of tellurium is rarely reported. Antimony speciation analysis is based on the slow kinetics of hydride formation from the pentavalent state and is mainly reported in seawater samples.
The analytical conditions for the simultaneous determination of arsenic (As) compounds in human urine were examined using high-performance liquid chromatography (HPLC) with an ion-exchange column combined with a hexapole collision cell inductively coupled plasma mass spectrometer. The addition of 0.1 mM EDTA to the mobile phase of HPLC (a mixture of 10 mM NH4NO 3 and 0.05% HNO3, pH 3.1) was necessary for good reproducibility of the peaks. The five As species {As(V), monomethylarsonic (MMA), dimethylarsinic (DMA), As(III), and arsenobetain (AB)} were separated within 14 min, however, arsenocholine(AC), trimethylarsine oxide (TMAO) and tetramethylarsonium (TeMA) were not individually separated but eluted together at about 40 min of retention time. This method was applied to urine samples from 8 male Japanese. Although As(V), MMA, DMA, and AB were detected in all urine samples, the relative amounts of these compounds were different depending on the person. The order of concentrations of arsenic compounds in urine from 4 person were AB > DMA > MMA > As(V), but those in the other samples were AB ≒ DMA or AB < DMA, suggesting the individual difference in the eating habits of sea foods.
In this review we present an overview of hyphenated techniques using an ICPMS detector with an emphasis on extraction techniques for the measurement of metalloids by high pressure liquid chromatography–inductively plasma mass spectrometry (HPLC–ICPMS). Five modes of using hyphenated ICPMS systems; HPLC–ICPMS, HPLC–hydride generation-ICPMS, Cryogenic trapping ICPMS, in-situ Cryogenic trapping ICPMS and Gas Chromatography–ICPMS are described together with their application for the measurement of arsenic, selenium, mercury and antimony species. Two classes of metalloid species are described; “Easy to extract species,” stable species existing as discrete molecules or relatively weakly bound to cellular constituents, and Hard to extract species,” unstable species that dissociate on extraction and species incorporated within cellular constituents such as proteins. Measurements described include, arsenic species: arsenobetaine, arsenoribosides, arsenic bound to lipids and phytochelatins and other minor arsenic species including thioarsenic species. Selenium species: selenocysteine and selenomethionine, Se-methyl selenomethionine, Se-methyl selenocysteine, y-glutamyl-Se-methylselenocysteine, dimethylselenide and dimethyldiselenide. Mercury species: inorganic Hg and methyl Hg. Antimony species: antimonite and antimonate. Germanium species: inorganic. Extraction methods are discussed in terms of their extraction efficiencies, stability of species and artifact formation.
IntroductionSampling and storage for speciation analysisSpeciation with CE-ICP-MSSpeciation with HPLC-ICP-MSGC-ICP-MSSpeciation using ICP-MS with reaction/collision cell technologySpeciation using high resolution and MC-ICP-MSReferences
Different collision gases (H2, He and premixed 7% H2 in He) used in the hexapole collision cell of an inductively coupled plasma–mass spectrometer (ICP–MS) were compared, and the gas-flow rates were optimized for the determination of arsenic (), iron () and selenium (). The study showed that the argon-based interferences at mass-to-charge ratios (m/z) of 56, 75 and 80 can be overcome by the optimized gas flows (7.5 ml min−1 premixed 7% H2 in He and 2 ml min−1 H2) in the hexapole collision cell. Detection limits of 15.5 ng l−1 for iron () and 29 ng l−1 for selenium () in 2% (v/v) HNO3 were obtained under optimized collision cell conditions. The detection limit for arsenic () obtained in difficult hydrochloride acid matrix (5% HCl (v/v)) was 153 ng l−1. The accuracy of the optimized method was confirmed by analyzing two moss reference materials. The results obtained by ICP–MS for arsenic, selenium and iron from both moss reference samples were, in most cases, in good agreement with the certified values.
The development and utilization of collision and reaction cells in atomic mass spectrometry is reviewed. These devices have been used for decades in fundamental studies of ion–molecule chemistry and have only recently been applied in the GD-MS and ICP-MS fields. Such cells are used to promote reactive and non-reactive collisions, with resultant benefits in interference reduction, isobar separation, and thermalization/focusing of ions in ICP-MS. Novel ion–molecule chemistry schemes, using a variety of reaction gas reagents selected on the basis of thermodynamic and kinetic principles and data, are now designed and empirically evaluated with relative ease. These chemical resolution techniques can avert interferences requiring mass spectral resolutions of w600 000 (m/Dm). Purely physical ion beam processes, including collisional dampening and collisional dissociation, are also employed to provide improved sensitivity, resolution and spectral simplicity. Collision and reaction cell techniques are now firmly entrenched in current-day ICP-MS technology, enabling unprecedented flexibility and freedom from many spectral interferences. A significant body of applications has now been reported in the literature. Collision/reaction cell techniques are found to be most useful for specialized or difficult analytical needs and situations, and are employed in both single-and multi-element determination modes.
Principles to inductively coupled plasma generationEquilibrium in a plasmaLine intensitiesLine profilesTemperature definitionsTemperature measurementsElectron number density measurementIonic to atomic line intensity ratioActive methodsSpatial profilesTemperature and electron number densities observed in analytical ICPsPlasma perturbationMultiline diagnostics
IntroductionIonization effectsThermal conductivityUse of alternative gases (mixed gas plasmas) in ICP-OESMixed gas plasmas for use with ICPMSLow-pressure plasmasLow-power plasmasConclusions
IntroductionFundamentalsDifferent sources of uncertainty affecting isotope ratios when measured using ICPMSID: general conceptsSelected applicationsGeneral conclusions
IntroductionSample introduction characteristics of the ICP sourceLiquid aerosol generationVapour generationElectrothermal vaporizationSolid sampling via LAConclusion
IntroductionAnalysis of airAnalysis of waterAnalysis of clinical samplesConclusions
IntroductionMechanistic aspects of electrospray ionizationMass analysers used with ESElement speciation using ES-MSConclusions
The ICP as an ion sourceIon samplingMass analysersIon detectionInstrumentation for interference removal
IntroductionAnalytical challengesSample collection and storageSample preparationSample pretreatmentQuantificationQuality controlSpeciation studiesFuture trends
Detection limits and sensitivityAccuracy and precisionMultielement capability and selectivityInstrumental overviewRadiofrequency generatorsTorchesSpectrometersDetectorsNebulisers and spray chambersRead-out devices, instrument control and data processingRadial and axial plasmasInstrumentation for high-resolution spectrometryMicroplasmas and plasma on a chip
The atomization of hydride-forming elements, Se, Sb and Sn, has been studied with an atmospheric pressure dielectric barrier discharge atomizer. The elements were first converted to hydride through the reaction with NaBH4. Then the hydride were atomized in the atomizer and detected by atomic absorption spectrometry. The effects of operational parameters such as power, gas flow rate and concentrations of HCl and NaBH4 were investigated. Compared with other hydride atomization methods, the proposed atomizer shows the following features: (1) small size, which is preferable for the miniaturization of the total analytical system; (2) low temperature, which would be helpful for further improvement in the compactness of the total analytical system; (3) low power consumption, which is also necessary for the development of analytical instrumentation for in situ detection of environmentally important elements. The analytical performance of the atomizer has also been investigated. The detection limits of Sb, Se and Sn obtained with the present method were 13.0, 0.6 and 10.6 μg l− 1. This detector is a very promising technique for hydride detection.
The application of an ion-guiding buffer gas-filled hexapole collision and reaction cell in ICP-MS has been studied in order
to give a preliminary performance characterization of a new instrument providing this feature for increasing the ion yield
and decreasing contributions from Ar induced interfering molecular ions. As buffer gas He was used while H2 served as reaction gas. Addition of the latter can be an effective means for reduction of typical argon induced polyatomic
ions (Ar+, ArO+, Ar2
+) by orders of magnitude owing to gas phase reactions. Molecular interferences generated in the cell can be suppressed by
a retarding electric field established by a dc hexapole bias potential of –2 V.
Extracts of 11 samples of shrimp, crab, fish, fish liver, shellfish and lobster digestive gland (hepatopancreas), including five certified reference materials, were investigated for their contents of arsenic compounds (arsenic speciation). The cation-exchange high-performance liquid chromatography procedure was optimized to separate six cationic arsenicals present in the samples with internal chromatographic standardization by the trimethylselenonium ion, which was detected at m/z 82 (82Se), in addition to arsenic at m/z 75, by inductively coupled plasma mass spectrometry. The content of each species (as arsenic atom) relative to the total arsenic extracted from the samples were: arsenobetaine 19–98%, arsenocholine and trimethylarsine oxide 0–0.6% and the tetramethylarsonium ion 0–2.2%. Additionally, an unknown arsenic species (U1) was present at 3.1–18% in the shellfish and in the lobster digestive gland, and another unknown (U2) was present at 0.2–6.4% in all samples. The contents of arsenite and arsenate were 0–1.4%, dimethylarsinate 8.2–29% while monomethylarsonate was detected only in oyster at 0.3% of the total extracted arsenic. Finding tetramethylarsonium ion and arsenocholine in a variety of samples indicates steps of a biosynthetic pathway of arsenic leading to arsenobetaine in the marine environment. The intake of inorganic arsenic via ingestion of the seafood samples that were analysed did not represent a toxicological problem to humans. The limits of detection (LOD) were in the range 10–50 ng g–1(dry mass) with the exception of arsenobetaine for which the LOD was 360 ng g–1.
Using directly coupled ion-pair, reversed-phase, high-performance liquid chromatography and inductively coupled plasma mass spectrometry, arsenic acid (AsV) was identified as a major arsenic species in spring-waters and bottled mineral waters. Spring-waters were collected from a volcanic area in the centre of France and bottled waters were purchased from local supermarkets. Two bottled waters also contained traces of arsenious acid (AsIII); no monomethylarsonic acid (MMA) or dimethylarsinic acid (DMA) were characterized in the samples. Using this developed method, six arsenic species were determined with limits of detection sufficiently low to study the chemical species at their naturally occurring concentration levels. Detection limits were in the range of 1.0–3.0 µg l–1 and a good mass balance was obtained with total As content in samples determined by a hydride generation system.
Arsenocholine (I), arsenite [As(III)], dimethylarsinic acid (II), arsenobetaine (III), arsenate [As(V)] and methylarsonic acid (IV) were separated in <10 min on a Supelcosil LC SAX column (25 cm × 4.6 mm) with 0.02M-NH4H2PO4 (pH 3.9) containing 1% of methanol as mobile phase (1 ml/min). Diagrams of the thermospray nebulizer (Vanhoe et al., Ibid., 1994, 9, 815; 1995, 10, 575) and desolvation system used are presented. Clogging of the injector tube and the formation of a deposit on the sampling cone was counteracted by using an additional HPLC pump to rinse the nebulizer with 0.14M-HNO3 between measurements. Peak heights at m/z 75 were evaluated by the method of standard additions. The detection limits for I, As(III), II, III, As(V) and IV were 120, 120, 60, 60, 40 and 80 ng/l of As and the RSD (n = 6) at 1 µg/l of As were 19.5, 15.8, 11.1, 6.9, 11.3 and 11.3%, respectively. High chloride concentrations interfered with the determination of As(V). Only As(V) was found in mineral waters, whereas all the species except I were found in tenfold-diluted deproteinized urine.
The inductively coupled plasma–mass spectrometer (ICP–MS) is one of the most widely used detectors for elemental speciation studies. ICP–MS is used for the routine determination and quantification of trace elements in aqueous solution, although with slight modifications, these instruments may analyze gaseous samples. Solid samples may also be analyzed by ICP–MS when used in conjunction with solid sampling techniques such as laser ablation (LA) or electrothermal vaporization (ETV). Speciation analyses are most typically performed with liquid sample introduction or gaseous sample introduction. ICP–MS is capable of analyzing samples containing metallic elements as well as metalloids such as arsenic. However, non-metals including the halogens are difficult to analyze because they possess higher ionization potentials than metallic elements, and the argon ICP cannot ionize these elements as efficiently. The ICP–MS possesses several characteristics that make it a very attractive detector for elemental speciation studies. For most elements, the detection limits obtained with ICP–MS are significantly lower than those achieved with inductively coupled plasma-atomic emission spectroscopy (ICP–AES), another frequently used detector for speciation studies.
Four anionic and four cationic arsenic compounds in urine were separated by anion- and cation-exchange high-performance liquid chromatography and detected by inductively coupled plasma mass spectrometry (ICP-MS) at m/z 75. The species were the anions arsenite, arsenate, monomethylarsonate and dimethylarsinate and the cations arsenobetaine, trimethylarsine oxide, arsenocholine and the tetramethylarsonium ion. Hexahydroxyantimonate(III) was co-chromatographed with the arsenic anions but detected at m/z 121 and used as an internal standard for their qualitative analysis. Arsenite was prone to oxidation to arsenate in urine but was stable after at least 4-fold dilution of the urine with water. Arsenite was unstable in both urine samples and standard mixtures when diluted with the basic (pH 10.3) mobile phase used for anion chromatography. This could not be prevented by adding ascorbic acid as antioxidant. The argon chloride interference at m/z 75 was eliminated by chromatographic separation of the chloride present in the sample from the arsenic analytes. The ClO+ ion detected at m/z 51 and 53 was used to monitor the retention time of chloride in the anion-exchange system. The chloride eluted about 100 s after the last analyte peak and the intensity of ArCl+ was negligible even after injection of a 1% NaCl solution (less than 200 ions s–1). The recovery of all arsenic species in urine was close to 100%. The chromatographic peaks were evaluated by their peak heights and calibration was carried out by the method of standard additions. The calibration graphs were linear for all species (r > 0.999). The limits of detection were 3–6 ng cm–3 for the cations and 7–10 ng cm–3 for the anions in urine.
An isocratic high performance liquid chromatographic (HPLC) system is well suited for introduction into the inductively coupled plasma mass spectrometer (ICP-MS) because of the stability of the detector response and high degree of analyte sensitivity attained. Anion and cation exchange HPLC systems were optimized and were used for As speciation in contaminated groundwater and in an in house shrimp reference sample. Coupled with tandem mass spectrometry with electrospray ionization, the HPLC retention time provides almost conclusive evidence of the identity of the analyte species.
This review deals with liquid phase separation of major arsenic and selenium species followed by element specific detection. It concerns papers published since 1980 and describing only currently used methods that were or could be applied to As and Se speciation in environmental matrices. Methods performances are compared on the basis of efficiency, rapidity, absolute and concentration detection limits and applicability to real world environmental samples.
A method has been developed for determination of (ultra)trace amounts of As(III) and As(V) in water by flow injection on-line sorption preconcentration and separation coupled with inductively coupled plasma mass spectrometry (ICPMS) using a knotted reactor (KR). The determination of As(III) was achieved by selective formation of the As(III)-pyrrolidine dithiocarbamate complex over a sample acidity range of 0.01-0.7 mol L-1 HNO3, its adsorption onto the inner walls of the KR made from 150-cm-long, 0.5-mm-i.d. PTFE tubing, elution with 1 mol L-1 HNO3, and detection by ICPMS. Total inorganic arsenic was determined after prereduction of As(V) to As(III) in a 1% (m/v) L-cysteine-0.03 mol L-1 HNO3 media. The concentration of As(V) was calculated by difference (the total inorganic arsenic and As(III)). Owing to the group-specific character of the chelating agent, and the use of an efficient rinsing step before elution, the interferences encountered in conventional ICPMS from common major matrix, alkali and alkaline earth metals, and chlorides were eliminated. The presence of organoarsenic species such as monomethylarsonate and dimethylarsinate in water samples had no effect on the results of As(III) and As(V). Thus, the method can be applied to the speciation analysis of inorganic arsenic at submicrogram per liter levels in aqueous solutions with high total content of dissolved solid and/or high content of chlorides. Using a preconcentration time of 60 s and a sample flow rate of 5 mL min-1, an enhancement factor of 22 was achieved in comparison with conventional ICPMS. The time required for a single determination was 200 s. The detection limits (3s) was evaluated to be 0.021 microgram L-1 for As(III) and 0.029 microgram L-1 for total inorganic arsenic. The precision for 14 replicate determinations of 1 microgram L-1 As(III) was 2.8% (RSD) with drift correction and 3.9% (RSD) without drift correction. The concentrations of As(III) and As(V) in synthetic mixtures obtained by the present method were in good agreement with expected values. Results obtained by the proposed method for total arsenic in a river water reference material agreed well with certified and recently reevaluated values. The method was also applied to the speciation analysis of inorganic arsenic in porewaters.
365, 415. 15 Ph. Quevauviller, in Elemental Speciation: New Approaches for Trace Element Analysis
- N Feldmann
- D Jakubowski
- Stuewer
Feldmann, N. Jakubowski and D. Stuewer, Fresenius' J. Anal. Chem., 1999, 365, 415. 15 Ph. Quevauviller, in Elemental Speciation: New Approaches for Trace Element Analysis, ed. J. A. Caruso, K. L. Sutton and K. L. Ackley, Elsevier, Amsterdam, 2000, pp. 531–569.
The Effects of As Speciation and Dissolved Oxygen Conditions on Benthic Invertebrates, 22nd Annual Meeting of the Society of Environmental Toxicology and Chemistry Biotic Oxidation of As(III) to As(V) in the Aquatic Environment: Implications for Toxicity
- K Irving
- J Liber
- R Culp
- C Lowell
- Q Casey
- R Xie
- Q Kerrich
- E Xie
- R Irving
- K Kerrich
- J Liber
- Culp
Irving, K. Liber, J. Culp, R. Lowell, C. Casey, Q. Xie and R. Kerrich, The Effects of As Speciation and Dissolved Oxygen Conditions on Benthic Invertebrates, 22nd Annual Meeting of the Society of Environmental Toxicology and Chemistry, North America, Baltimore, MD, November 11–15, 2001. 17 Q. Xie, E. Irving, R. Kerrich, K. Liber and J. Culp, Biotic Oxidation of As(III) to As(V) in the Aquatic Environment: Implications for Toxicity, Toxic Substances Research Initiative (TSRI) National Conference, Ottawa, Canada, March 5–8, 2002. J. Anal. At. Spectrom., 2002, 17, 1037–1041