Determination Of Arsenic Species Research Articles

Ultra-trace determination of arsenic species in environmental waters, food and biological samples using a modified aluminum oxide nanoparticle sorbent and AAS detection after multivariate optimization

We describe a simple and efficient method for solid phase extraction and speciation of trace quantities of arsenic. It is based on the use of functionalized aluminum oxide nanoparticles and does not require any oxidation or reduction steps. The experimental parameters affecting extraction and quantitation were optimized using fractional factorial design methods. Adsorbed arsenic was eluted from the sorbent with 1 M hydrochloric acid and determined by graphite furnace atomic absorption spectrometry. Preconcentration factors up to 750 were achieved depending on the sample volume. Studies on potential interferences by various anions and cations showed the method to be highly selective. Under optimum conditions, the calibration plots are linear in the 5.0 to 280 ng L−1 and 8.0 to 260 ng L−1 concentration ranges for As(III) and total arsenic, respectively. The detection limits (calculated for S/N ratios of 3) are 1.81 and 1.97 ng L−1 for As(III) and total arsenic, respectively. The method was successfully applied to the determination and speciation of arsenic in (spiked) environmental, food and biological samples and gave good recoveries. The method was validated using a certified geological reference material.

Enzyme-assisted extraction and liquid chromatography mass spectrometry for the determination of arsenic species in chicken meat

Chicken is the most consumed meat in North America. Concentrations of arsenic in chicken range from μgkg−1 to mgkg−1. However, little is known about the speciation of arsenic in chicken meat. The objective of this research was to develop a method enabling determination of arsenic species in chicken breast muscle. We report here enzyme-enhanced extraction of arsenic species from chicken meat, separation using anion exchange chromatography (HPLC), and simultaneous detection with both inductively coupled plasma mass spectrometry (ICPMS) and electrospray ionization tandem mass spectrometry (ESIMS). We compared the extraction of arsenic species using several proteolytic enzymes: bromelain, papain, pepsin, proteinase K, and trypsin. With the use of papain-assisted extraction, 10 arsenic species were extracted and detected, as compared to 8 detectable arsenic species in the water/methanol extract. The overall extraction efficiency was also improved using a combination of ultrasonication and papain digestion, as compared to the conventional water/methanol extraction. Detection limits were in the range of 1.0–1.8μg arsenic per kg chicken breast meat (dry weight) for seven arsenic species: arsenobetaine (AsB), inorganic arsenite (AsIII), dimethylarsinic acid (DMA), monomethylarsonic acid (MMA), inorganic arsenate (AsV), 3-nitro-4-hydroxyphenylarsonic acid (Roxarsone), and N-acetyl-4-hydroxy-m-arsanilic acid (NAHAA). Analysis of breast meat samples from six chickens receiving feed containing Roxarsone showed the presence of (mean±standard deviation μgkg−1) AsB (107±4), AsIII (113±7), AsV (7±2), MMA (51±5), DMA (64±6), Roxarsone (18±1), and four unidentified arsenic species (approximate concentration 1–10μgkg−1).

Determination of Inorganic Arsenic Speciation in Municipal Solid Waste Incineration Fly Ash by High Performance Liquid Chromatography-Hydride Generation-Atomic Fluorescence Spectroscopy with Phosphoric Acid as Extracting Agent

A method for the determination of arsenic speciation in municipal solid waste incineration fly ash was developed by high performance liquid chromatography (HPLC) coupled with hydride generation atomic fluorescence spectroscopy (HG-AFS). Before determination, various forms of arsenic were extracted with phosphoric acid through microwave digestion. The effect of phosphoric acid in the extracted solution on the speciation analysis of inorganic arsenic (As(III)/As(V)) was studied in detail. The results showed that when using diammonium phosphate as the mobile phase, the determination of As(V) was adversely affected. The increasing flow rate of mobile phase hardly reduced the adverse influence caused by phosphoric acid. The adverse influence was effectively suppressed when a mixed solution of disodium hydrogen phosphate/potassium dihydrogen phosphate (pH = 6.864) was used as the mobile phase. By using the improved method, As(III) and As(V) could be separated in 5 min, and the detection limits of As(III) and As(V) were 0.063 μg L−1 and 0.110 μg L−1, respectively. The recovery rate of As(III) and As(V) in spiked standard sample was satisfactory (86.9%–102.6%). The determination of arsenic species in fly ashes sampled from four different municipal solid waste incineration plants were successfully accomplished by using the method. The results showed that the arsenic was predominantly in the form of As(V).

An approach for identification and determination of arsenic species in the extract of kelp.

The National Institute of Standards and Technology is developing a kelp powder standard reference material (SRM) in support of dietary supplement measurements. Edible seaweeds such as kelp and laver consumed as diet or dietary supplement contain tens of mg/kg arsenic. The speciation information of arsenic in the seaweed should be provided because the total arsenic alone does not fully address the safety issue of the dietary supplement as the value assignment is originally intended. The inability to avail all arsenic species for value assignment measurements prevented the certification of arsenic species in the candidate SRM; however, approximately 70% of total arsenic extracted with a 1:1 volume fraction of methanol:water mixture allowed arsenic speciation values to be assigned to a procedure-defined extract, which may be used for method validation in research to improve upon current extraction and measurement practices. Arsenic species in kelp and laver were identified using electrospray ionization ion trap time of flight mass spectrometry (ESI-IT-TOF). Arsenosugars As(328), As(482), and As(392) were found in the kelp candidate SRM while As(328) and As(482) were found in GBW 08521, a certified reference material (CRM) of laver produced by the National Institute of Metrology of China (NIM). A discovery that the digests of kelp and laver contained only dimethylarsinic acid led to the conclusion that the seaweeds did not contain detectible levels of arsenobetaine, arsenocholine or trimethylarsine oxide that could overlap with the peaks of arsenosugars in the separation. The mean ± s of (5.68 ± 0.28) mg/kg and (13.43 ± 0.31) mg/kg found for As(482) and As(392) in kelp, respectively, using instrumental neutron activation analysis (INAA) demonstrated that value assignment measurement of arsenosugars was possible without arsenosugar calibration standards.

Determination of arsenic species in rice samples using CPE and ETAAS

A highly sensitive and selective procedure for the determination of arsenate and total arsenic in food by electrothermal atomic absorption spectrometry after cloud point extraction (ETAAS/CPE) was developed. The procedure is based on the formation of a complex of As(V) ions with molybdate in the presence of 50.0mmolL−1 sulfuric acid. The complex was extracted into the surfactant-rich phase of 0.06% (w/v) Triton X-114. The variables affecting the complex formation, extraction and phase separation were optimized using factorial designs. Under the optimal conditions, the calibration graph was linear in the range of 0.05–10.0μgL−1. The detection and quantification limits were 10 and 33ngL−1, respectively and the corresponding value for the relative standard deviation for 10 replicates was below 5%. Recovery values of between 90.8% and 113.1% were obtained for spiked samples. The accuracy of the method was evaluated by comparison with the results obtained for the analysis of a rice flour sample (certified material IRMM-804) and no significant difference at the 95% confidence level was observed. The method was successfully applied to the determination of As(V) and total arsenic in rice samples.

Report of the key comparison CCQM-K108 determination of arsenic species, total arsenic and cadmium in brown rice flour

The CCQM-K108 key comparison was organised by the Inorganic Analysis Working Group(IAWG) of CCQM to test the abilities of national metrology institutes (NMIs) or designated institutes (DIs) to measure the mass fractions of arsenic species, total arsenic and cadmium in brown rice flour. The National Metrology Institute of Japan (NMIJ) acted as the coordinating laboratory. The participants used different measurement methods, though most of them used inductively coupled plasma mass spectrometry (ICP-MS) or isotope-dilution inductively coupled plasma mass spectrometry (ID-ICP-MS) for Cd and ICP-MS for total arsenic. Regarding arsenic speciation, all participants used ICP-MS coupled with liquid chromatography (LC). Accounting for relative expanded uncertainty, comparability of measurement results for each of total arsenic and cadmium was successfully demonstrated by the participating NMIs or DIs for the measurement of the measurand at the level of less than 0.5 mg/kg. Regarding arsenic species (inorganic arsenic and dimethylarsinic acid (DMAA)), there was, however, a measurement problem still to be solved and that part of CCQM-K108 will be repeated.It is expected that arsenic, cadmium and other metals at mass fractions greater than approximately 0.1 mg/kg in rice flour can be determined by each participant using the same technique(s) employed for this key comparison to achieve similar uncertainties mentioned in the present report. Furthermore, the results of this key comparison can be utilised along with the IAWG core capability approach.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Capabilities of several phosphonium ionic liquids for arsenic species determination in water by liquid–liquid microextraction and electrothermal atomic absorption spectrometry

Different phosphonium ionic liquids have been assayed for liquid–liquid microextraction of As species.

Activated carbon-modified knotted reactor coupled to electrothermal atomic absorption spectrometry for sensitive determination of arsenic species in medicinal herbs and tea infusions

A flow injection system based on a modified polytetrafluoroethylene (PTFE) knotted reactor (KR) was developed for arsenite [As(III)] and arsenate [As(V)] species preconcentration and determination by electrothermal atomic absorption spectrometry (ETAAS). Activated carbon (AC) was immobilized on the inner walls of a PTFE KR by a thermal treatment. A significant increase in analyte retention was obtained with the AC-modified KR (100%) as compared to the regular PTFE KR (25%). The preconcentration method involved the on-line formation of As(III)-ammonium pyrrolidinedithiocarbamate (As-APDC) complex, followed by its adsorption onto the inner walls of the AC-modified KR. After analyte retention, the complex was eluted with acetone directly into the graphite furnace of ETAAS. The parameters affecting the flow injection system were evaluated with a full central composite face centered design with three center points. Under optimum conditions, a preconcentration factor of 200 was obtained with 10ml of sample. The detection limit was 4ngL−1 and the relative standard deviation (RSD) for six replicate measurements at 0.2μgL−1 of As were 4.3% and 4.7% for As(III) and As(V), respectively. The developed methodology was highly selective towards As(III), while As(V), monomethylarsonic acid [MMA(V)] and dimethylarsinic [DMA(V)] were not retained in the AC-modified KR. The proposed method was successfully applied for As speciation analysis in infusions originated from medicinal herbs and tea.

Establishment of a method for determination of arsenic species in seafood by LC-ICP-MS

An analytical method for determination of arsenic species (inorganic arsenic (iAs), methylarsonic acid (MA), dimethylarsinic acid (DMA), arsenobetaine (AB), trimethylarsine oxide (TMAO) and arsenocholine (AC)) in Brazilian and Spanish seafood samples is reported. This study was focused on extraction and quantification of inorganic arsenic (iAs), the most toxic form. Arsenic speciation was carried out via LC with both anionic and cationic exchange with ICP-MS detection (LC-ICP-MS). The detection limits (LODs), quantification limits (LOQs), precision and accuracy for arsenic species were established. The proposed method was evaluated using eight reference materials (RMs). Arsenobetaine was the main species found in all samples. The total and iAs concentration in 22 seafood samples and RMs ranged between 0.27–35.2 and 0.02–0.71mgAskg−1, respectively. Recoveries ranging from 100% to 106% for iAs, based on spikes, were achieved. The proposed method provides reliable iAs data for future risk assessment analysis.

Arsenic speciation in natural sulfidic geothermal waters

The speciation of arsenic in natural sulfidic geothermal waters was studied using chemical analyses and thermodynamic aqueous speciation calculations. Samples were collected in three geothermal systems in Iceland, having contrasting H2S concentrations in the reservoir (high vs. low). The sampled waters contained 7–116ppb As and <0.01–77.6ppm H2S with pH of 8.56–9.60. The analytical setup used for the determination of arsenic species (Ion Chromatography-Hydride Generation Atomic Fluorescence Spectrometry, IC-HG-AFS) was field-deployed and the samples analyzed within ∼5min of sampling in order to prevent changes upon storage, which were shown to be considerable regardless of the sample storage method used. Nine aqueous arsenic species were detected, among others arsenite (HnAsIIIO3n-3), thioarsenite (HnAsIIIS3n-3), arsenate (HnAsVO4n-3), monothioarsenate (HnAsVSO3n-3), dithioarsenate (HnAsVS2O2n-3), trithioarsenate (HnAsVS3On-3) and tetrathioarsenate (HnAsVS4n-3). The results of the measured aqueous arsenic speciation in the natural geothermal waters and comparison with thermodynamic calculations reveal that the predominant factors determining the species distribution are sulfide concentration and pH. In alkaline waters with low sulfide concentrations the predominant species are AsIII oxyanions. This can be seen in samples from a liquid-only well, tapping water that is H2S-poor and free of oxygen. At intermediate sulfide concentration AsIII and AsV thio species become important and predominate at high sulfide concentration, as seen in two-phase well waters, which have high H2S concentrations in the reservoir. Upon oxidation, for instance due to mixing of the reservoir fluid with oxygenated water upon ascent to the surface, AsV oxyanions form, as well as AsV thio complexes if the sulfide concentration is intermediate to high. This oxidation process can be seen in samples from hot springs in the Geysir geothermal area. While the thermodynamic modeling allows for a first-order estimation of the dominant species, discrepancies between the model results and the field data highlight the fact that for such dynamic chemical systems the exact speciation cannot be calculated, thus on-site and preferentially in-situ analysis is of crucial importance.

Determination of arsenic speciation in Scomberomorus niphonius by capillary electrophoresis-inductively coupled plasma mass spectrometry

A method for the detection of arsenocholine (AsC), arsenobetaine (AsB), As(III), dimethylarsinic (DMA), monomethylarsonic (MMA) and As (V) by capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS) was established. The results showed that the six species of arsenic were separated within 20 min under the optimized conditions. Good linearities of 6 arsenic species were observed in the range from 2 to 50 μg x L(-1) with the linear correlation greater than 0.996, the detection limits were 0.10-1.08 μg x L(-1) and the RSDs (n = 5) of the peak areas were smaller than 7%. The method was successfully adopted to the determination of the species in Scomberomorus niphonius. The recoveries were between 93% and 98%, and we found the arsenobetaine (AsB) was the main species in the sample. The method was suitable for the analysis of other biological samples with the advantages of good stability, less sample consumption, short analysis time and convenience.

Determination of Arsenic Species in Fruit Juice and Fruit Drink Products Using Ion Pair Chromatography Coupled to Inductively Coupled Plasma Mass Spectrometry

Ion-pair chromatography coupled to inductively coupled plasma mass spectrometry (ICP-MS) was evaluated and validated for the determination of arsenic species in fruit juice and fruit drink products. A Phenomenex analytical column (Prodigy 3 μ ODS (3) 4 μm × 2.0 mm × 150 mm) and a mobile phase consisting of 5 mmol l−1 malonic acid, 3 mmol l−1 of tetrabutylammonium hydroxide solution and 5 % methanol were used to achieve arsenic speciation separation. The arsenic species were detected at m/z 75 with an Agilent 7500cx ICP-MS. After demonstrating the method was sensitive, accurate and fit for purpose, and it was applied to analyze 96 fruit juice and fruit drink samples. Speciation analysis of the 96 fruit juice and fruit drink products revealed that inorganic arsenic was the major species found in the majority of juice products tested in the study. The concentration of inorganic arsenic (sum of As3+ and As5+) ranged from<limit of quantification (LOQ) to 23.9 μg l−1, with a mean value of 3.57 ± 4.42 μg l−1. Dimethylarsenate (DMA) was found in 32 of the samples, and the mean value is 0.30 ± 0.55 μg l−1. Monomethylarsenate (MMA) was found in 26 of the samples, and the mean value is 0.30 ± 0.71 μg l−1.

Determination of arsenic speciation in sulfidic waters by Ion Chromatography Hydride-Generation Atomic Fluorescence Spectrometry (IC-HG-AFS)

A method for the analysis of arsenic species in aqueous sulfide samples is presented. The method uses an ion chromatography system connected with a Hydride-Generation Atomic Fluorescence Spectrometer (IC-HG-AFS). With this method inorganic AsIII and AsV species in water samples can be analyzed, including arsenite (HnAsIIIO3n−3), thioarsenite (HnAsIIIS3n−3), arsenate (HnAsVO4n−3), monothioarsenate (HnAsVSO3n−3), dithioarsenate (HnAsVS2O2n−3), trithioarsenate (HnAsVS3On−3) and tetrathioarsenate (HnAsVS4n−3). The peak identification and retention times were determined based on standard analysis of the various arsenic compounds. The analytical detection limit was ~1–3µgL−1 (LOD), depending on the quality of the baseline. This low detection limit makes this method also applicable to discriminate between waters meeting the drinking water standard of max. 10µgL−1 As, and waters that do not meet this standard. The new method was successfully applied for on-site determination of arsenic species in natural sulfidic waters, in which seven species were unambiguously identified.

Speciation analysis of arsenic in prenatal and children's dietary supplements using microwave-enhanced extraction and ion chromatography–inductively coupled plasma mass spectrometry

A study was conducted to develop a microwave-enhanced extraction method for the determination of arsenic species in prenatal and children's dietary supplements prepared from plant materials. The method was optimized by evaluating the efficiency of various solutions previously used to extract arsenic from the types of plant materials used in the dietary supplement formulations. A multivitamin standard reference material (NIST SRM 3280) and a prenatal supplement sample were analyzed in the method optimization. The identified optimum conditions were 0.25g of sample, 5mL of 0.3molL−1 orthophosphoric acid (H3PO4) and microwave heating at 90°C for 30min. The extracted arsenic was speciated by cation exchange ion chromatography–inductively coupled plasma mass spectrometry (IC–ICP-MS). The method detection limit (MDL) for the arsenic species was in the range 2–8ngg−1. Ten widely consumed prenatal and children's dietary supplements were analyzed using the optimized protocol. The supplements were found to have total arsenic in the concentration range 59–531ngg−1. The extraction procedure recovered 61–92% of the arsenic from the supplements. All the supplementary products were found to contain arsenite (As3+) and dimethylarsinic acid (DMA). Arsenate (As5+) was found in two of the supplements, and an unknown specie of arsenic was detected in one product. The results of the analysis were validated using mass balance by comparing the sum of the extracted and non-extracted arsenic with the total concentration of the element in the corresponding samples.

Determination of Arsenic Species in Underground Water by Capillary Electrophoresis-Inductively Coupled Plasma Mass Spectrometry

Determination of Arsenic Species in Underground Water by Capillary Electrophoresis-Inductively Coupled Plasma Mass Spectrometry

Determination of five arsenic species in rice by liquid chromatography-inductively coupled plasma-mass spectrometry

A method was developed for the simultaneous determination of arsenic acid [As (V)], arsenious acid [As (III)], arsenobetaine (AsB), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in rice by liquid chromatography-inductively coupled plasma-mass spectrometry (LC-ICP-MS). The extraction reagent was 0.3 mol/L nitric acid with heat-assistant condition for 1.5 h at 95 degrees C. Then, the five arsenic species were separated by an anion exchange column (Dionex IonPac AS19, 250 mm x 4 mm) and detected by ICP-MS. Four kinds of extracted solutions were compared through the extraction efficiency. The concentration of nitric acid, the temperature and the extraction time were optimized. The recoveries of the five arsenic species spiked in rice at two levels ranged from 89.6% to 99.5% with the relative standard deviations (RSDs, n = 5) of 0.6% - 3.6%. The measured values of the arsenic species in standard rice materials were consistent with their standard values. The linear ranges were 0.05 - 200 microg/L for AsB and DMA, 0.10-400 microg/L for As (III) and MMA, 0.15-600 microg/L for As (V). The limits of detection for the five arsenic species were 0.15-0.45 microg/kg. The results showed that the method is much more precise for the risk assessment of the rice. This method is simple, accurate and durable for the determination of arsenic species in rice.

Arsenic speciation in water by high-performance liquid chromatography/inductively coupled plasma mass spectrometry-method validation and uncertainty estimation

In order to obtain reliable analytical results for the separation and determination of arsenic species by high-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICP-MS), the analytical procedure must be fully validated and the measurement uncertainty of the analytical result should be estimated. The total arsenic concentration of the samples was determined by ICP-MS. Separation of the arsenic species, AsB, As(III), DMA, MMA and As(V), was accomplished by liquid chromatography, which was hyphenated to inductively coupled plasma mass spectrometry, used for detection purposes. Automated handling of these systems was achieved with Chromera software. The separation capability between the analytical signals of arsenic species, AsB-As(III), As(III)-DMA, DMA-MMA and MMA-As(V), was 1.3, 1.1, 5.1 and 4.6, respectively. The limit of detection (LOD) values ranged from 0.070 µg L(-1) for DMA to 0.13 µg L(-1) for MMA. The expanded uncertainty U [%] values for coverage factor k = 2 estimated for AsB, As(III), DMA, MMA and As(V) were 12 %, 13 %, 5.6 %, 9.6 % and 8.6 %, respectively. This study reports, for the first time, building the uncertainty budgets for five arsenic species and estimation of the expanded uncertainty (for k = 2). The qualitative and quantitative parameters determined in the validation process indicate that the presented analytical procedure can be applied for the determination of AsB, As(III), DMA, MMA and As(V) in water.

An Investigation on Inorganic Arsenic in Seaweed by Ion Chromatography Combined with Inductively Coupled Plasma-Atomic Emission Spectrometry

This study focused on the matrix interference for the qualitative and quantitative analysis of inorganic arsenic species in seaweed by ion chromatography (IC) combined with inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The matrix of seaweed has a significant effect on the determination of inorganic arsenic species. In particular, the retention times of inorganic arsenic species in the in the standard solution were different from those in seaweed because of the matrix interference. Thus, it was not suitable to use the chromatographic method for the determination of the arsenic species in seaweed. We investigated an alternative method for the determination of inorganic arsenic species in seaweed. The method was applied for the seaweed samples such as laver, green laver, sea tangle and sea mustard. The sample extraction methods of the arsenic species were also investigated in this study.

Determination of arsenic species in rice grains using HPLC-ICP-MS

Determination of As species in rice is necessary because inorganic As species (arsenate (AsV) and arsenite (AsIII)) are more toxic than organic As (monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA)). This study evaluated the As species in Korean and USA rice grains. Levels were determined using microwave extraction and high performance liquid chromatography coupled with inductively coupled plasma-mass spectrometry (HPLC-ICPMS). Arsenite and DMA were the major species detected in Korean and USA rice. The percentage of inorganic As was 76.94% (54.50–87.86%) for Korean rice and 69.28% (52.94–72.92%) for USA samples. The order and percentage of As species observed in Korean and USA rice were AsIII (70%)>DMA (24%)>AsV (5%)>MMA (1%), and AsIII (64%)>DMA (28%)>AsV(5%)>MMA (3%), respectively. The AsIII concentrations were not significantly different in Korean rice grains, compared to USA grains. The high AsIII predominance indicates an elevated toxic effect of As in rice grains and needs further attention.

A need for determination of arsenic species at low levels in cereal-based food and infant cereals. Validation of a method by IC–ICPMS

The present study arose from the need to determine inorganic arsenic (iAs) at low levels in cereal-based food. Validated methods with a low limit of detection (LOD) are required to analyse these kinds of food. An analytical method for the determination of iAs, methylarsonic acid (MA) and dimethylarsinic acid (DMA) in cereal-based food and infant cereals is reported. The method was optimised and validated to achieve low LODs. Ion chromatography-inductively coupled plasma mass spectrometry (IC–ICPMS) was used for arsenic speciation. The main quality parameters were established. To expand the applicability of the method, different cereal products were analysed: bread, biscuits, breakfast cereals, wheat flour, corn snacks, pasta and infant cereals. The total and inorganic arsenic content of 29 cereal-based food samples ranged between 3.7–35.6 and 3.1–26.0μgAskg−1, respectively. The present method could be considered a valuable tool for assessing inorganic arsenic contents in cereal-based foods.