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Fast ion chromatography-ICP-QQQ for Arsenic Speciation
Abstract
Two methods for the fast separation of arsenic species are presented. The general approach is to modify existing methodology utilizing carbonate eluents for a small particle size, short column length Hamilton PRPX100 column which is interfaced with the Agilent 8800 ICP-QQQ using oxygen as reaction gas and detection of AsO at m/z 91. Using H2O2 in the extractant to oxidize As(III) to As(V) it is possible to separate arsenobetaine from DMA, MMA and As(V) in 1.5 minutes. Such a method may be useful where a measure of total inorganic As is sufficient, for example for regulatory compliance in food or beverage testing. It is possible to separate six As species. i.e the four above and arsenocholine and As(III) in 4.5 minutes using a gradient separation. Such a method could be useful analysis of urinary arsenic species. Coupling with high sensitivity of ICP-QQQ yields equivalent or better detection limits than conventional methods with run times up to 5 times faster, which is a significant benefit for sample throughput and method development.
... By focusing only on iAs, the costs of materials, instruments, time, and labor can be reduced in comparison to methods that entail full speciation of As. Speciation is ordinarily conducted using high-performance liquid chromatography (HPLC) followed by As measurement with inductively coupled plasma (ICP)-mass spectrometry (MS) [2][3][4][5][6][7][9][10][11]. Such instrumentation is very expensive to purchase, operate, and maintain, including the need for highly qualified analysts. ...
... Such instrumentation is very expensive to purchase, operate, and maintain, including the need for highly qualified analysts. Elegant ICP-MS methods have been reported [3][4][5][6][7]10], including recent improvements in speed [9][10][11], but for current needs, we considered use of older well-developed methods to determine iAs [12] as well as others recently proposed [13][14][15][16]. Although methods using solid-phase extraction to separate the As from the sample extracts have been reported [14][15][16], we did not find these as useful in higher sample throughput applications. ...
Arsenic exposure through rice consumption is a growing concern. Compared to Continuous Flooding (CF), irrigation practices that dry the soil at least once during the growing season [referred to here as Alternate Wetting and Drying (AWD)] can decrease As accumulation in grain; however, this can simultaneously increase grain Cd to potentially unsafe levels. We modelled grain As and Cd from field studies comparing AWD and CF to identify optimal AWD practices to minimize the accumulation of As and Cd in grain. The severity of soil drying during AWD drying event(s), quantified as soil water potential (SWP), was the main factor leading to a reduction in grain total As and inorganic As, compared to CF. However, lower SWP levels were necessary to decrease grain inorganic As, compared to total As. Therefore, if the goal is to decrease grain inorganic As, the soil needs to be dried further than it would for decreasing total As alone. The main factor driving grain Cd accumulation was when AWD was practiced during the season. Higher grain Cd levels were observed when AWD occurred during the early reproductive stage. Further, higher Cd levels were observed when AWD spanned multiple rice growth stages, compared to one stage. If Cd levels are concerning, the minimum trade-off between total As and Cd accumulation in rice grain occurred when AWD was implemented at a SWP of −47 kPa during one stage other than the early reproductive. While these results are not meant to be comprehensive of all the interactions affecting the As and Cd dynamics in rice systems, they can be used as a first guide for implementing AWD practices with the goal of minimizing the accumulation of As and Cd in rice grain.
... By focusing only on iAs, the costs of materials, instruments, time, and labor can be reduced in comparison to methods that entail full speciation of As. Speciation is ordinarily conducted using high-performance liquid chromatography (HPLC) followed by As measurement with inductively coupled plasma (ICP)-mass spectrometry (MS) [2][3][4][5][6][7][9][10][11]. Such instrumentation is very expensive to purchase, operate, and maintain, including the need for highly qualified analysts. ...
... Such instrumentation is very expensive to purchase, operate, and maintain, including the need for highly qualified analysts. Elegant ICP-MS methods have been reported [3][4][5][6][7]10], including recent improvements in speed [9][10][11], but for current needs, we considered use of older well-developed methods to determine iAs [12] as well as others recently proposed [13][14][15][16]. Although methods using solid-phase extraction to separate the As from the sample extracts have been reported [14][15][16], we did not find these as useful in higher sample throughput applications. ...
With the establishment by CODEX of a 200 ng/g limit of inorganic arsenic (iAs) in polished rice grain, more analyses of iAs will be necessary to ensure compliance in regulatory and trade applications, to assess quality control in commercial rice production, and to conduct research involving iAs in rice crops. Although analytical methods using high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) have been demonstrated for full speciation of As, this expensive and time-consuming approach is excessive when regulations are based only on iAs. We report a streamlined sample preparation and analysis of iAs in powdered rice based on heated extraction with 0.28 M HNO3 followed by hydride generation (HG) under control of acidity and other simple conditions. Analysis of iAs is then conducted using flow-injection HG and inexpensive ICP-atomic emission spectroscopy (AES) or other detection means. A key innovation compared with previous methods was to increase the acidity of the reagent solution with 4 M HCl (prior to reduction of As5+ to As3+), which minimized interferences from dimethylarsinic acid. An inter-laboratory method validation was conducted among 12 laboratories worldwide in the analysis of six shared blind duplicates and a NIST Standard Reference Material involving different types of rice and iAs levels. Also, four laboratories used the standard HPLC-ICP-MS method to analyze the samples. The results between the methods were not significantly different, and the Horwitz ratio averaged 0.52 for the new method, which meets official method validation criteria. Thus, the simpler, more versatile, and less expensive method may be used by laboratories for several purposes to accurately determine iAs in rice grain. Open image in new window Graphical abstract Comparison of iAs results from new and FDA methods
... As speciation was quantified in ripe grain (polished) and bran, using established protocols with dilute acid extraction and HPLC-ICP-MS analysis (Jackson, 2015). Briefly,~200 mg of ground material was extracted in 2% TMG HNO 3 at 95°C for 10 min (Kirby et al., 2004). ...
... Chromatography was performed with a PRP-X100 anion exchange column (2.1 × 50 mm, Phenomenex) while an Agilent 7500 ICP-MS was used to monitor m/z 75 for As operating in He collision mode. The mobile phase consisted of 3% methanol in deionized water (eluent A) and 50 mM ammonium carbonate in 3% methanol (eluent B, pH~9) (Jackson, 2015). Initially, the mobile phase consists of 20% eluent B (flow 1 mL/min), increasing to 100% eluent B at 1.5 min (flow 2 mL/min), and finally reverting to the initial mixture after 3.5 min. ...
We studied plot-scale biogeochemical impacts of Si-rich amendments to paddy soil. • Si-rich amendments increased Si and decreased Mn and As in rice plants. • Si-rich amendments increased organic As in grain and ferrihydrite in root plaque. • Only Husk treatment increased CH4 emissions, but 3× lower than predicted for straw. An emerging approach to limit rice uptake and grain As targets the shared root-uptake pathway between As(III) and Si. We amended rice paddy mesocosms with Si-rich rice residues (husk and husk char) or silicate fertilizer to evaluate the impact of different Si sources on rice uptake of Si and As including As speciation in grain under background soil As. For a systems-approach, we also measured plant biomass, rice yield, porewater chemistry, mesocosm-scale CH 4 and CO 2 fluxes, plant concentrations of nutrients and metals, and root Fe plaque mineralogy. Relative to the control, Si-rich amendments increased plant Si and proportion of ferrihydrite on root plaque, decreased root-to-shoot Mn transfer and As uptake, and shifted grain As from inorganic to organic As. The charred husk treatment, which resulted in the most Si accumulation in rice shoots, most decreased plant As and grain As. Husk treatment led to the highest CH 4 emissions, but all treatments had lower CH 4 emissions than has been reported for straw treatments. Collectively, Si-rich amendments performed similarly across several biogeochemical benchmarks, with charred husk best restricting plant As, suggesting these amendments can be used to reduce toxicity of As from rice grain while maintaining yield.
... Oxygen is usually used as the reaction gas for measuring Si, Se, P, S, As, and rare earth elements at so-called mass-shift mode. [1][2][3][4][5][6][7] In these measurements, an ion of interest m M + was permitted to pass through the first quadruple and to enter the reaction cell. After reaction with oxygen, a monoxide ion m M 16 O + was obtained and permitted to pass through the second quadruple and counted by the detector. ...
Online generated ozone was introduced as the cell gas of tandem quadrupole inductively coupled plasma mass spectrometry. Product ions of ozone reaction showed that the formation of singly charged monoxide ions and dioxide ions were apparently improved for most elements, resulting improvement of signal intensity by over 1000 times.
... (Ali & Jain, 2004). The most commonly used anion exchange columns for arsenic (As) speciation studies include Hamilton PRP-X100 (Jackson, 2015;Raber et al., 2010), Hamilton PRP-X100S (Peng et al., 2014), Shodex RSpak NN-614 (Suzuki et al., 2009), and IonPac AS7. Similarly, the most commonly used cation exchange columns are Hamilton PRP-X200 (García-Salgado et al., 2012), Spheris S5SCX (Özcan et al., 2016), IonoSpher 5C (Hansen et al., 2011), and Zorbax 300-SCX (Ruiz-Chancho et al., 2008). ...
The accurate determination of arsenic species is of crucial importance, as more than 100 arsenic (As) compounds with different mobility, toxicity, and chemical forms are present in the soil, plant, and water samples. Due to the toxicology, health, and safety properties, it is crucial to quantitatively measure the As species. The toxic properties and bioavailability of the elements depend on their concentration and speciation. This chapter serves as an overview of the As species and their toxicity, as well as available pretreatment, separation, and determination techniques of As species in soil, plants, and water samples. The evaluation of the available literature shows that HPLC-ICP-MS is the most widely used technique for As speciation and followed by hydride generation atomic spectroscopy. Finally, some suggestions are made to indicate the gaps that need to be addressed for the further development of As speciation tools.
... Arsenic speciation was performed with a modified fast method based on Jackson (2015) with a Hamilton PRPX100 column. 50 mM ammonium carbonate [(NH 4 ) 2 CO 3 ] (pH 9) in 3 % methanol eluent was used as the sole eluent to measure inorganic As(III) and As(V) (Jackson, 2015). The total As sorption was determined by the difference between the initial added As concentration and the total aqueous As concentration at the subsequent time points. ...
Manganese-oxides are some of the strongest oxidants and sorbents in the environment, which impact many geochemical processes. However, nearly all our understanding of manganese-oxides' reaction kinetics is based on laboratory-synthesized minerals. This study quantifies the oxidative kinetics and adsorptive capacity of five soils rich in pedogenic manganese-and iron-oxides through arsenite oxidation batch reactions over a range of pHs and temperatures to mimic diverse environmental conditions. The two A horizons were less reactive and enriched in manganese(IV), compared to the B horizons, particularly the subsoil containing the manganese-rich wad material. The reaction kinetics fit a pseudo-first-order reaction with distinct fast and slow phases. The baseline reactions were pH 7.2 at 23 • C. Adjusting pH to 4.5 or 9.0 increased the reaction rates. Decreasing the temperature to 4.0 • C reduced the reaction kinetics, while raising the temperature to 40 • C increased the arsenite oxidation rate. pH and temperature changes alter the reaction kinetics due to shifts related to the point of zero charge, the total system energy, and surface passivation from adsorbing arsenic and manganese species. Synchrotron X-ray fluorescence mapping indicates arsenic only penetrates the surficial layers of most manganese-oxide-containing nodules found in the soil. After the arsenite oxidation reaction in the pedogenically weathered subsoil, X-ray absorption spectroscopy demonstrates significant differences in the average manganese oxidation number between the nodules' outer layers compared to the soil matrix and nodule centers. The kinetic and sorption parameters give critical insight into determining the mobility and species of arsenic and other redox-sensitive contaminants in manganese-containing environmental systems over appropriate timescales.
... An example chromatogram for soil water is given in Fig. S4. The operating parameters for HPLC are listed in Table S2 and adapted from the literature (Jackson 2015). ...
Arsenic (As) in soils harms soil organisms and plants, and it can enter the human food chain via the dietary consumption of crops. The mobility, bioavailability and toxicity of As are determined by its concentration and speciation. A greenhouse pot experiment was conducted to study the effects of soil microbial disturbance and maize plants on arsenic concentration and speciation in soil (pore) water and soils. Three soil treatments with varying microbial disturbance were designed for this experiment: native soil, sterilized soil and sterilized soil reconditioned with soil indigenous microbes. The three soil treatments were intersected with three levels of As in soils (0, 100 and 200 mg kg⁻¹ spiked As). Ten pots of each treatment were planted with maize, while three pots were filled with soil without maize. The difference between native and reconditioned soil indicated the abiotic sterilization effect (artifact of the sterilization process), while the difference between sterilized and reconditioned soil showed the microbial disturbance effect. Both effects increased As release into soil water. The microbial disturbance effect was more pronounced for organic As species, showing the influence of soil microbes involved in As methylation. The abiotic sterilization effect was more evident in unplanted pots than planted pots and the microbial disturbance effect was observed only in unplanted pots, suggesting that both effects were mitigated by the presence of maize.
... This porewater was acidified to 2 % HNO 3 to prevent oxidation of Fe(II) prior to ICP-MS analysis (Agilent 7500cx), dissolved organic carbon (DOC) analysis (vario TOC cube), and As speciation by IC-ICP-MS (Thermo iCAP). Arsenic species were separated using a PRP-X100 column and the ammonium carbonate gradient elution described by Jackson (2015). For ICP and DOC measurements, acidified blank samples were run every 20-40 samples. ...
Rice production results in residues of straw and husk, and the management of these residues has implications for the sustainability of the rice agroecosystem. Rice straw is typically incorporated into soil either as fresh residue or is burned prior to incorporation. Rice husk is not typically returned to rice fields. However, rice husk contains high levels of silicon, which has been shown to decrease rice accumulation of arsenic. In this work, we studied the resulting biogeochemical changes in rice paddy soils when paddies were amended with either straw or burned straw and either no husk, husk, or burned husk over two years. Using a full-factorial design, we observed that the higher lability of rice straw carbon controlled redox-sensitive processes despite the application of husk and straw at similar carbon rates. Amending paddies with straw, rather than burned straw, increased porewater Fe and As, plant As, and methane emissions regardless of husk amendment. Husk addition provided insignificant Si to the plant despite its high concentration of Si, suggesting limited short-term mobility of Si and that long-term additions of husk or higher rates may need to be studied.
... Briefly, samples were oxidized with 10% H 2 O 2 , this converts all inorganic arsenic to arsenate, which simplifies and enhances the chromatography but does not otherwise affect the organic arsenic species (Scheer et al., 2012). The urine samples were analyzed by anion chromatography, Hamilton PRPX100 column with carbonate eluant, coupled to ICP-MS using an Aglient 1260 HPLC and 8900 ICP-MS (Agilent, Wilmington DE) (Jackson, 2015). Quality control included duplicate and spiked species samples and continuing analysis of reference urines NIST 2669 level 1 and 2 every ten samples. ...
Background:
Differences in arsenic metabolism capacity may influence risk for type 2 diabetes, but the mechanistic drivers are unclear. We evaluated the associations between arsenic metabolism with overall diabetes prevalence and with static and dynamic measures of insulin resistance among Mexican Americans living in Starr County, Texas.
Methods:
We utilized data from cross-sectional studies conducted in Starr County, Texas, from 2010-2014. A Mendelian randomization approach was utilized to evaluate the associations between arsenic metabolism and type 2 diabetes prevalence using the intronic variant in the arsenic methylating gene, rs9527, as the instrumental variable for arsenic metabolism. To further assess mechanisms for diabetes pathogenesis, proportions of the urinary arsenic metabolites were employed to assess the association between arsenic metabolism and insulin resistance among participants without diabetes. Urinary biomarkers of arsenic metabolites were modeled as individual proportions of the total. Arsenic metabolism was evaluated both with a static outcome of insulin resistance, homeostatic measure of assessment (HOMA-IR), and a dynamic measure of insulin sensitivity, Matsuda Index.
Results:
Among 475 Mexican American participants from Starr County, higher metabolism capacity for arsenic is associated with higher diabetes prevalence driven by worse insulin resistance. Presence of the minor T allele of rs9527 is independently associated with an increase in the proportion of monomethylated arsenic (MMA%) and is associated with an odds ratio of 0.50 (95% CI: 0.24, 0.90) for type 2 diabetes. This association was conserved after potential covariate adjustment. Furthermore, among participants without type 2 diabetes, the highest quartile of MMA% was associated with 22% (95% CI: -33.5%, -9.07%) lower HOMA-IR and 56% (95% CI: 28.3%, 91.3%) higher Matsuda Index for insulin sensitivity.
Conclusions:
Arsenic metabolism capacity, indicated by a lower proportion of monomethylated arsenic, is associated with increased diabetes prevalence driven by an insulin resistant phenotype among Mexican Americans living in Starr County, Texas.
... An example chromatogram for soil water is given in Fig. S4. The operating parameters for HPLC are listed in Table S2 and adapted from the literature (Jackson 2015). ...
Zinc (Zn) is an important micronutrient but can be toxic at elevated concentrations. We conducted an experiment to test the effect of plant growth and soil microbial disturbance on Zn in soil and plants. Pots were prepared with and without maize and in an undisturbed soil, a soil that was disturbed by X-ray sterilization and a soil that was sterilized but reconditioned with the original microbiome. The Zn concentration and isotope fractionation between the soil and the soil pore water increased with time, which is probably due to physical disturbance and fertilization. The presence of maize increased the Zn concentration and isotope fractionation in pore water. This was likely related to the uptake of light isotopes by plants and root exudates that solubilized heavy Zn from the soil. The sterilization disturbance increased the concentration of Zn in the pore water, because of abiotic and biotic changes. Despite a threefold increase in Zn concentration and changes in the Zn isotope composition in the pore water, the Zn content and isotope fractionation in the plant did not change. These results have implications for Zn mobility and uptake in crop plants and are relevant in terms of Zn nutrition.
... Among the 310 participants with arsenic data, 298 and 12 had their urinary arsenic speciation measured in samples collected at 26and 16-week gestation, respectively. The Trace Element Analysis Core (TEA) at Dartmouth College determined urinary arsenic speciation (Jackson, 2015;Signes-Pastor et al., 2020). TEA analyzed the urine samples with an Agilent LC 1260 equipped with a Thermo AS7, 2 × 250 mm column and a Thermo AG7, 2 × 50 mm guard column interfaced with an Agilent 8900 inductively coupled plasma mass spectrometry in oxygen reaction cell mode. ...
Arsenic exposure during pregnancy may increase the risk for intellectual deficits in children, but limited data exist from prospective epidemiologic studies, particularly at low arsenic exposure levels. We investigated the association between prenatal maternal urinary arsenic concentrations and childhood cognitive abilities in the Health Outcomes and Measures of the Environment (HOME) Study. We used anion exchange chromatography coupled with inductively coupled plasma mass spectrometry detection to measure arsenic species content in pregnant women's urine. The summation of inorganic arsenic (iAs), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) refers to ∑As. We assessed children's cognitive function (n = 260) longitudinally at 1-, 2-, and 3-years using Bayley Scales of Infant and Toddler Development, at 5 years using Wechsler Preschool and Primary Scale of Intelligence, and at 8 years using Wechsler Intelligence Scale for Children. We observed a modest decrease in mental development index and full-scale intelligence quotient at ages 3 and 5 years with each doubling of ∑As with estimated score (ß) differences and 95% confidence interval (CI) of −1.8 from −4.1 to 0.5 and −2.5 from −5.1 to 0.0, respectively. This trend was stronger and reached statistical significance among children whose mothers had lower iAs methylation capacity and low urinary arsenobetaine concentrations. Our findings suggest that arsenic exposure levels relevant to the general US population may affect children's cognitive abilities.
... Samples were analyzed using ICP-MS (Agilent 7500cx). For As speciation, grain was extracted using 2% HNO 3 following Maher et al. 54 and was analyzed using HPLC-ICP-MS (Agilent 7500cx) following Jackson 69 . NIST 1568B was used to ensure appropriate recovery of total and speciated As. ...
Previous work has shown that inorganic As localizes in rice bran whereas DMA localizes in the endosperm, but less is known about co-localization of As and S species and how they are affected by growing conditions. We used high-resolution synchrotron X-ray fluorescence imaging to image As and S species in rice grain from plants grown to maturity in soil (field and pot) and hydroponically (DMA or arsenite dosed) at field-relevant As concentrations. In hydroponics, arsenite was localized in the ovular vascular trace (OVT) and the bran while DMA permeated the endosperm and was absent from the OVT in all grains analyzed, and As species had no affect on S species. In pot studies, soil amended with Si-rich rice husk with higher DMA shifted grain As into the endosperm for both japonica and indica ecotypes. In field-grown rice from low-As soil, As localized in the OVT as arsenite glutathione, arsenite, and DMA. Results support a circumferential model of grain filling for arsenite and DMA and show Si-rich soil amendments alter grain As localization, potentially lessening risk to rice consumers.
... Grain As speciation in brown rice grain was also determined via extraction with dilute HNO3, and analysis via HPLC-ICP-MS with a PRP-X100 anion exchange column (2.1 x 50 mm, Phenomenex) and Thermo Scientific™ iCAP™ TQ ICP-MS. Detailed descriptions of these procedures can be found (Kirby et al. 2004;Maher et al. 2013;Jackson 2015;Limmer et al. 2018a). Recoveries of porewater As, Cd, and Si from check standards were 102.0 ±12.4%, 99.1 ±2.5%, and 96.8 ±7.5%, respectively; recoveries of As and Cd from standard reference material digests were 143 ±57% and 114 ±49% (NIST 1568b), 98 ±18% and 94 ±4% (NIST 1570a), and 95 ±29% and 95 ±4% (NIST 1573a), respectively. ...
Purpose
Rice is a staple crop worldwide and a silicon (Si) hyperaccumulator with Si levels reaching 5–10% of its mass; this can result in desilication and Si-deficiency if plant residues are not managed correctly. Rice is also uniquely subject to arsenic (As) and cadmium (Cd) contamination depending on soil conditions. Our goal is to quantify the effects of rice husk (a Si-rich milling byproduct) amendments and different water management strategies on rice uptake of Si, As, and Cd.
Methods
We employed 4 husk amendment treatments: Control (no husk), Husk (untreated husk), Biochar (husk pyrolyzed at 450 °C), and CharSil (husk combusted at > 1000 °C). Each of these amendments was studied under nonflooded, alternate wetting and drying (AWD), and flooded water management in a pot study. Porewater chemistry and mature plant elemental composition were measured.
Results
Husk and Biochar treatments, along with flooding, increased porewater and plant Si. Vegetative tissue As decreased with increasing porewater Si, but grain As and plant Cd were primarily controlled by water management. Grain As and Cd were inversely correlated and are simultaneously minimized in a redox potential (Eh) range of 225–275 mV in the studied soil. Ferrihydrite in root iron plaque decreased As translocation from porewater to grain, but amendments were not able to increase plaque ferrihydrite content.
Conclusion
We conclude moderate husk amendment rates (i.e., 4 years’ worth) with minimal pretreatment strongly increases rice Si content but may not be sufficient to decrease grain As in low Si and As soil.
... Considering the human risk assessment of different arsenic species via the consumption of seafood, the accurate identification and quantification of arsenic species in this type of food are crucial (Taylor et al., 2017;Zhang, Guo, Song, Du, & Zhang, 2018). Speciation was carried out using different separation, detection and quantification techniques (Jackson, 2015;Jin et al., 2016;Liu et al., 2018;Zhang et al., 2018;Zhang, Chen, Zhou, Wu, & Zhang, 2016). Among the analytical methods used were various hyphenated separation and detection techniques, an example of which was a robust and sensitive high-performance liquid chromatography (HPLC) technique coupled with online detection using inductively coupled plasma-mass spectrometry (ICP-MS) which played an essential role in analysing arsenic species in environmental and complex biological matrices (Reid et al., 2020;Yu, Li, Tian, & Jiang, 2020). ...
Quantitative, rapid, selective and sensitive methods for the determination of total arsenic (tAs) and six arsenic compounds (arsenite (As(III)), arsenate (As(V)), arsenobetaine (AsB), arsenocholine (AsC), monomethylarsonic acid (MMA), dimethylarsonic acid (DMA)) in seafood were developed. The measurement of the tAs concentration was performed using quadrupole inductively-coupled plasma mass spectrometry (ICP-MS). Microwave-assisted extraction was used for the isolation of arsenic species. The separation and quantification of analysed compounds were performed by ion-exchange chromatography coupled with ICP-MS in one chromatographic run using ammonium carbonate-based buffers, which has little effect on ICP-MS sensitivity compared to commonly used phosphate buffers. The results of validation and proficiency tests confirmed the reliability, robustness, and applicability of the developed procedures to various types of matrices. The proposed methods are relatively simple, time- and cost-efficient, therefore could be used to routinely analyse tAs content and arsenic species in different types of seafood at trace and ultra-trace levels.
... The establishment of the new arsenic speciation analysis program not only improves our understanding of arsenic biogeochemistry, toxicity and metabolism but also provides a lot of information about exposure biomarkers and arsenic cycling in the natural environment. However, it is still a challenge to completely isolate the target arsenic compound from background interference [25]. Therefore, a quick and simple method is needed to analyze the arsenic species in different matrices. ...
There are more than 100 different arsenic with different characteristics in the soil-water-plant ecosystem. The identification and quantification of individual arsenic species is essential for understanding the distribution, environmental fate and behavior, metabolism and toxicity of arsenic. Due to the hazardous nature of arsenic, people have a high interest in the measurement of arsenic species. The reaction of the formation of arsenic speciation in the soil-water-plant environment is briefly studied. There is little information on methods used to quantify arsenic forms and species in contaminated soil, water and plant. The purpose of this article is to understand the available sample pretreatment, extraction, separation, detection and method validation techniques for arsenic speciation analysis of arsenic species in soil, water and plant. The performances of various sample preparation and extraction processes, as well as effective separation techniques, that contribute greatly to excellent sensitivity and selectivity in arsenic speciation when coupling with suitable detection mode, and method validity are discussed. The outlines of arsenic speciation techniques are discussed in view of the importance to the completeness and accuracy of analytical data in the soil-water-plant samples. To develop cheap, fast, sensitive, and reproducible techniques with low detection limits, still needed to confine research on arsenic speciation present in environmental matrices.
... DCB extractions of root plaque and plant tissue acid digestions were subject to elemental analysis using ICP-OES (As, Al, B, Ca, Cu, Fe, K, Mg, Mn, P, Si, and Zn) or ICP-MS (As in grain, husk, straw, and root, Agilent 7500). In addition, grain As speciation was analyzed via HPLC-ICP-MS (Agilent 7500) after extraction in 2% trace metal grade HNO 3 at 100 °C for 10 min (Maher et al. 2013) using a Hamilton PRP-100X column (4.1 × 50 mm, 5 µm) with 50 mM ammonium carbonate mobile phase in 3% optima grade methanol (Jackson 2015). For acid digests, certified reference materials (NIST 1568a rice flour, WEPAL IPE 883 dianthus straw, and ERM CD281 rye grass) and method blanks were included in each digestion set. ...
Purpose
Arsenic (As) cycling in flooded rice paddies is driven by soil microbes which among other transformations can cause conversion between inorganic and organic As species. Silicon (Si)-rich soil amendments cause increased methylated As species, particularly DMA, in grain likely because they influence the microbial community responsible for As methylation, but the mechanism remains unclear.
Methods
To investigate how Si-rich amendments influenced the microbial community, we sequenced the 16S rRNA and arsM genes from rhizosphere soil collected at grain ripening from unamended rice paddy mesocosms or those amended with Si-rich rice husk, charred husk, or calcium silicate, and paired these data with geochemistry and As speciation in grain.
Results
We found that Si amendments influenced the 16S rRNA and arsM community composition. Increased C storage from calcium silicate amendment drove differences in the 16S rRNA community, whereas low soil redox potential drove differences in the arsM community. Differences in grain As were observed independent of Si-rich amendments, and did not correspond to differences in either the 16S rRNA or arsM community. Instead, methane flux and soil redox potential correlated with differences in grain DMA.
Conclusions
Si-rich amendments drove changes in the microbial community composition and the subset of arsM-bearing organisms, but higher grain DMA levels were not directly caused by Si-rich amendments. Our findings imply that microbes active at lower soil redox potentials where As is mobilized are likely involved in DMA production, and future work should focus on linking the active community with DMA production.
... DCB extractions of root plaque and plant tissue acid digestions were subject to elemental analysis using ICP-OES (As, Al, B, Ca, Cu, Fe, K, Mg, Mn, P, Si, and Zn) or ICP-MS (As in grain, husk, straw, and root, Agilent 7500). In addition, grain As speciation was analyzed via HPLC-ICP-MS (Agilent 7500) after extraction in 2% HNO 3 (Maher et al. 2013) using a Hamilton PRP-100X column with 50 mM ammonium carbonate mobile phase in 3% methanol (Jackson 2015). For acid digests, certi ed reference materials (NIST 1568a rice our, WEPAL IPE 883 dianthus straw, and ERM CD281 rye grass) and method blanks were included in each digestion set. ...
Purpose: Arsenic (As) cycling in flooded rice paddies is driven by soil microbes which among other transformations can cause conversion between inorganic and organic As species. Silicon (Si)-rich soil amendments cause increased methylated As species, particularly DMA, in grain likely because they influence the microbial community responsible for As methylation, but the mechanism remains unclear.
Methods: To investigate how Si-rich amendments influenced the microbial community, we sequenced the 16S rRNA and arsM genes from rhizosphere soil collected at grain ripening from unamended rice paddy mesocosms or those amended with Si-rich rice husk, charred husk, or calcium silicate, and paired these data with geochemistry and As speciation in grain.
Results: We found that Si-amendments influenced the 16S and arsM community composition. Increased C storage from calcium silicate amendment drove differences in the 16S community, whereas low redox from husk amendments drove differences in the arsM community. High grain DMA was not associated with treatment or microbial community, but with low redox.
Conclusions: Differences in grain As were observed independent of amendments, and did not correspond to differences in either the 16S or arsM community. Instead, methane flux and redox correlated with differences in grain DMA, implying that methanogen activity and redox are more important factors than community composition in determining grain As speciation. Silicon amendments did not impact grain As, but impacted the microbial community composition, and the subset of arsM-bearing organisms. These findings imply that redox, porewater As, and methanogen activity are likely more important factors than arsM or overall microbial community composition in determining grain DMA levels.
... Unpolished grain samples were extracted in 2% (v/v) HNO 3 at 100°C, diluted to 1% HNO 3 and filtered (0.22 μm) for As speciation analysis (Maher, Foster, Krikowa, Donner, & Lombi, 2013). Separation was achieved using a Hamilton PRPx100 column with gradient elution using 50 mM ammonium carbonate and 3% (v/v) methanol (Jackson, 2015), and quantification with ICP-MS (Thermo, iCap-TQ). Blanks and a duplicate certified rice NIST1568b analyses were included for quality control. ...
Arsenic (As) and cadmium (Cd) are two toxic elements found in rice (Oryza sativa L.) grain that pose threats to human health. While attention has focused on major rice‐growing regions, rice has been grown on small‐scale farms in the northeastern United States since approximately 2005, but the grain As and Cd levels were not previously reported. Unpolished grain from these farms have mean As of 0.12 mg kg⁻¹ and mean Cd of 0.007 mg kg⁻¹, more than 40% lower than previously reported in U.S. rice. Therefore, rice from these farms poses low risk for consumers.
... When measuring As(III), As(V), DMA, and MMA, anion exchange separation is sufficient for retention and separation because all four species are anionic. Methods that use anion exchange columns, including the Hamilton PRP-X100 column, are widespread [6][7][8] , and when paired with a nitrate/phosphate mobile phase are promising for achieving good separation of As(III) and DMA, which can be particularly challenging. These methods have been applied to the analysis of As species in rice and reagent water [ 6 , 9 , 10 ] but method performance in surface water and groundwater matrices has not been previously described. ...
Robust and sensitive methods for monitoring inorganic and organic As species As(III), As(V), dimethylarsinate (DMA), and monomethylarsonate (MMA) in environmental water are necessary to understand the toxicity and redox processes of As in a specific environment. The method is sufficiently sensitive and selective to ensure accurate and precise quantitation of As(III), As(V), DMA, and MMA in surface water and groundwater samples with As species concentrations from tens of nanograms per liter to 50 µg/L without dilution of the sample. Mean recoveries of the four species spiked into reagent water, surface water and groundwater and measured periodically over three months ranged from 87.2 % to 108.7 % and relative standard deviation of replicates of all analytes ranged from 1.1 % to 9.0 %.
•A PRP-X100 column and nitrate/phosphate mobile phase was used to separate As(III), As(V), DMA, and MMA in 0.45 µm filtered surface water and groundwater matrices.
•Oxygen was used in the collision cell of the inductively coupled plasma-mass spectrometer with MS/MS mode to shift the measured As mass from 75 to 91.
•The analytical performance of the method and figures of merit including detection limits, precision, accuracy, and interferences when applied to surface water and groundwater matrices were investigated.
... After extraction, the samples were centrifuged, filtered (0.22 μm nylon), and diluted to 1% nitric acid. Arsenic speciation was analyzed by HPLC-ICP-MS (Agilent 7500cx) using a Hamilton PRP-X100 column and a gradient elution of water and 50 mM ammonium carbonate (both with 3% methanol) (Jackson, 2015). For each grain extraction, a blank and NIST 1568b rice flour was analyzed. ...
Rice (Oryza sativa L.) readily accumulates the nutrient silicon (Si) and the toxin arsenic (As), elements that can interact antagonistically both in the plant and in the soil. Thus, many studies have been performed where Si‐rich materials are incorporated into soils to increase plant‐available Si and thereby decrease plant As. However, studies have not examined the dissolution kinetics of Si from Si‐rich materials over multiple seasons and the resulting effects on rice systems. Here, we analyzed the porewater chemistry, CH4 emissions, and rice elemental concentrations from rice paddies in Year 2 that had been amended with Si‐rich materials (silicate fertilizer, rice husk, and charred rice husk) in Year 1. After two crop cycles, plant‐available Si and plant Si concentrations remained elevated in Si‐amended paddies. Silicon‐rich amendments also decreased plant As concentrations, although this effect was only observed in the vegetative tissues. Husk treatment resulted in the lowest porewater redox, highest CH4 emissions, and highest porewater inorganic As. Porewater concentrations and dynamics of inorganic As, dimethylarsinic acid (DMA), and trimethylarsine oxide (TMAO) differed for each amendment, but Si‐rich amendments exhibited elevated inorganic and organic As early in the growing season. These Si‐rich amendments can continue to provide Si and impact rice systems two growing seasons after application.
... For arsenic speciation, extraction followed the U.S. FDA dilute nitric acid extraction (Kubachka et al. 2012) followed by LC-ICP-MS using a PRP-X100 column and ammonium carbonate gradient method described by Jackson (2015). For each extraction run a blank and NIST 1568b reference material was run (Table S4). ...
Aims
Dimethylarsinic acid (DMA), an organic arsenic compound found in rice grain, is a causal agent of straighthead disorder, which can decimate yields. To minimize rice accumulation of DMA, we tested 9 molecules for antagonistic effects with DMA. We also tested whether the source of nitrogen is able to affect DMA uptake, as DMA is a weak acid and different nitrogen sources have differing effects on rhizospheric pH.
Methods
We grew rice (Oryza sativa L. cv. Lemont) hydroponically to maturity in two different experiments. First, 9 potential competitors (boric acid, calcium, glycerol, glycine, lactic acid, phosphoric acid, serine, silicic acid, and urea) were included in the hydroponic solution at a molar ratio ≥ 100:1 competitor:DMA. Second, rice receiving 5 μM DMA was grown under ammonium, nitrate, or a 1:1 mix of ammonium and nitrate. Yield metrics and plant elemental concentrations were measured after harvest.
Results
Of the potential competitors, only silicic acid was able to alleviate straighthead disorder and no competitors were able to reduce grain As by ≥30%. Under differing nitrogen sources, nitrate decreased plant concentrations of As relative to ammonium, but not in the grain.
Conclusions
While Si can alleviate DMA uptake, there remains uncertainty in how most DMA enters the plant.
... In the premise of efficient separation, the arsenic speciation methods tend to be developed with the expansion of analytes and the reduction of separation time. Jackson et al. reported a quick separation of AsB, DMA, MMA and As V in 1.5 min by using a small and short anion exchange column (5 μm stationary phase, 4.1 × 50 mm length column) when coupling with the highly sensitive ICP-QQQ [106]. It was 2.5-5 times faster than conventional chromatographic method, which was a significant benefit for sample throughput and method development. ...
Arsenic (As) species is ubiquitous in environmental and biological samples, and their toxicity is much different based on individual species. Therefore, the determination of arsenic and analysis of arsenic species have always received great attention. Atomic spectrometry is a preferred method for arsenic analysis mainly owning to its high selectivity and sensitivity. In recent years, a great deal of research has involved the determination and speciation of arsenic in various environmental and biological samples by atomic spectrometry. This review covers the sample preparation and arsenic separation/pre-concentration process in arsenic determination and speciation analysis by atomic spectrometry, and emphasizes on their development and prospects.
... After diluting the sample, the acid fraction was analyzed for total As using ICP-MS. Grain As speciation utilized a 2% HNO 3 extraction [49] followed by separation by HPLC-ICP-MS using a carbonate eluent and a Hamilton PRP-X100 column [50]. ...
Arsenic availability to rice is tied to biogeochemical cycling of Fe and Mn in rice soils. Two strategies to minimize As uptake by rice—increasing Si and decreasing water—affect soil Fe and Mn pools. We synthesized data from several soil-based experiments with four rice cultivars across pot and field trials with manipulations of Si, water, or both. Increasing Si alters the mineral composition of Fe plaque more than decreasing water, with the former promoting relatively more ferrihydrite and less lepidocrocite. Nonflooded conditions decrease lepidocrocite but slightly increase goethite compared to flooded rice. Plaque As, which was a mixture of arsenite (15–40%) and arsenate (60–85%), was correlated positively with ferrihydrite and negatively with lepidocrocite and goethite. Plaque As was also positively correlated with F1 and F2 soil As, and F2 was correlated positively with porewater As, total grain As, and grain organic As (oAs). Grain inorganic As (iAs) was negatively correlated with oxalate-extractable Fe and Mn. Our data and multiple linear regression models suggest that under flooded conditions iAs is released by poorly crystalline Fe oxides to porewater mainly as iAs(III), which can either be taken up by the plant, adsorbed to Fe plaque, oxidized to iAs(V) or methylated to oAs. Increasing Si can promote more desorption of iAs(III) and promote more poorly-ordered phases in plaque and in bulk soil. The ultimate effectiveness of a Si amendment to decrease As uptake by rice depends upon it being able to increase exogenous Si relative to As in porewater after competitive adsorption/desorption processes. Our data further suggest that poorly crystalline Fe and Mn soil pools can retain inorganic As and decrease plant uptake, but these pools in bulk soil and plaque control grain organic As.
... Significant effort has been devoted to reducing the analysis time and improving chromatographic separation for the simultaneous analysis of major arsenicals in aquatic organisms (Sun et al. 2015;Choi et al. 2011). However, completely isolating target arsenicals from background interference remains a challenge (Pell et al. 2013;Jackson 2015). Therefore, a rapid and simple method for analyzing arsenic speciation in different matrices is required. ...
Arsenic contamination in marine environments is a serious issue because some arsenicals are very toxic, increasing the health risks associated with the consumption of marine products. This study describes the development of an improved rapid method for the quantification of arsenic species, including arsenite (AsIII), arsenate (AsV), arsenocholine (AsC), arsenobetaine (AsB), dimethylarsinic acid (DMA), and monomethyl arsonic acid (MMA), in seaweed, sediment, and seawater samples using high-performance liquid chromatography/inductively coupled plasma-mass spectrometry (HPLC/ICP-MS). ICP-MS based on dynamic reaction cells was used to eliminate spectral interference. Ammonium nitrate- and phosphate-based eluents were used as the mobile phases for HPLC analysis, leading to shorter overall retention time (6 min) and improved peak separation. Arsenicals were extracted with a 1% HNO3 solution that required no clean-up process and exhibited reasonable sensitivity and peak resolution. The optimized method was verified by applying it to hijiki seaweed certified reference material (CRM, NMIJ 7405-a) and to spiked blank samples of sediment and seawater. The proposed method measured the concentration of AsV in the CRM as 9.6 ± 0.6 μg/kg dry weight (dw), which is close to the certified concentration (10.1 ± 0.5 μg/kg dw). The recovery of the six arsenicals was 87-113% for the sediment and 99-101% for the seawater. In the analysis of real samples, AsV was the most abundant arsenical in hijiki and gulfweed, whereas AsB was dominant in other seaweed species. The two inorganic arsenicals (AsIII and AsV) and AsV were the most dominant in the sediment and seawater samples, respectively.
... In epidemiological studies, collection and storage protocols, long term archival storage, repeated freeze-thaw cycles for sub-sample aliquoting and other variables make the recovery of As III uncertain. When analyzing the effects of inorganic As exposure, epidemiological studies often combine As III and As V and may also include the inorganic As metabolites MMA and DMA[31,46,47]. The instability of As III could explain the reported recovery of As III that was 3–7 times lower than the certified value in the Clinchek 1 material[40]. ...
The speciation analysis of As in urine samples can provide important information for epidemiological studies. Considering that these studies involve hundreds or thousands of samples, a fast and reliable method using a simple LC system with short-length mixed bed ion exchange chromatographic column coupled to ICP-MS for As speciation in human urine samples was developed in this work. Separation of AB+TMAO, DMA, AC, MMA and AsIII + AsV was accomplished within 5 min with good resolution when ammonium carbonate solutions were used as mobile phases and H2O2 was added to samples to quantitatively convert AsIII to AsV. Repeatability studies yielded RSD values from 2.0 – 4.8% for all species evaluated. Limits of detection (LOD) for As species ranged from 0.003 – 0.051 ng g⁻¹. Application of the method to human urine samples from a non-contaminated area showed that the sum of species measured corresponded to 62–125% of the total As in the sample. The recovery values for these species in urine SRM 2669 were in the range of 89–112% and demonstrated the suitability of the proposed method for epidemiological studies.
... The analyte reacts with the reactive gas pressurized in the cell, e.g., O 2 , to form an ion with different m/z of the interfering polyatomic species; thus, it is detected by monitoring the formed oxide in Q 2 (Q 1 = m/z and Q 2 = m/z + 16). Critical spectral interferences for the determination of As have been solved by using a MS/MS mass-shift mode strategy with O 2 as the reaction gas Amaral et al. 2015a, b;Balcaen et al. 2013;Balcaen et al. 2015;Jackson 2015;Jackson et al. 2015;Pétursdóttir et al. 2014;Virgilio et al. 2015) and gas mixture, e.g., CH 3 F mixed with He Flórez et al. 2016). ...
Reports from the US media have raised the attention towards a possible contamination of apple juices by As. The study here described presents the development of an analytical procedure using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) for determination of As in apple and orange juices commercialized in the Tetra Pack® package. The microwave-assisted acid digestion of juice was carried out using closed vessels and 2 mol/L HNO3 plus H2O2. These conditions are favorable for a better analytical blank control. Suitable recoveries were reached when promoting reaction with O2 inside the octopole reaction system (ORS³), and the monitoring of ⁷⁵As¹⁶O⁺ significantly improved the accuracy of the analysis reaching a limit of detection of 0.013 μg/L. Recoveries varied from 88 to 109 % in the MS/MS mass-shift mode. The As concentrations determined in fruit juices ranged from 0.126 to 1.45 μg/L, and they were significantly lower than the maximum tolerable limits imposed by the US and Brazilian legislations. Thus, ICP-MS/MS operated in the reaction mode was an effective instrumental strategy for overcoming spectral interferences, such as ⁴⁰Ar³⁵Cl⁺, in As determination as ⁷⁵As¹⁶O⁺ and allowed the accurate determination of As at trace levels.
Arsenic found in environmental segments like lithosphere, hydrosphere and in atmosphere in various inorganic and organic forms like Arsenate (AsV), Arsenite (AsIII), Monomethylarsine (MMA), Dimethylarsine (DMA), Trimetylarsine (TMA, Gossiogas), Trimethylarsineoxide (TMAO), AB (Arsenobetaine), AC (Arsenocholine) etc. Some forms are toxic while others are less toxic. In this review, we studied about biotransformation of various organic and inorganic arsenic species in aqueous environment, soil and atmosphere. Marine organisms like fishes, lobsters, fungi, bacteria, cytoplasm of microorganisms, yeast, some enzymes like, ArsC, algae, genes like aos, aio, aox, photosynthetic microorganisms etc., do biotransformation of arsenic as oxidation and reduction in inorganic arsenic species and do methylation in organic arsenic. Many researchers proposed different pathways of arsenic biotransformations. Arsenic speciation generally completes in three steps i.e. extraction, separation, and detection. There are several techniques for arsenic extraction, separation and detection. Voltametric methods i.e. DPP (Differential pulse polarography), CSV (Cathodic stripping Voltametry), ASV (Anodic stripping Voltametry) and Hydride generation (HG) are the main techniques for extraction. Similarly for separation and detection chromatography are used with spectroscopic detection systems.KeywordsArsenic biotransformationArsenic speciationMethylation of arsenicSpeciation techniques
A highly selective and ultra-sensitive electrochemical sensing probe was proposed by combining sulfated-carboxymethyl cellulose (CMC-S) and a functionalized-multiwalled carbon nanotube (f-MWNT) nano-composite with high conductivity and durability. The CMC-S/MWNT nanocomposite was impregnated on a glassy carbon electrode (GCE) to construct the non-enzymatic and mediator-free electrochemical sensing probe for trace detection of As(iii) ions. The fabricated CMC-S/MWNT nanocomposite was characterized by FTIR, SEM, TEM, and XPS. Under the optimized experimental conditions, the sensor exhibited the lowest detection limit of 0.024 nM, a high sensitivity (69.93 μA nM-1 cm-2) with a good linear relationship in the range of 0.2-90 nM As(iii) concentration. The sensor demonstrated strong repeatability, with the current response continuing at 84.52% after 28 days of use, in addition to good selectivity for the determination of As(iii). Additionally, with recovery ranging from 97.2% to 107.2%, the sensor demonstrated comparable sensing capability in tap water, sewage water, and mixed fruit juice. The electrochemical sensor for detecting trace levels of As(iii) in actual samples is anticipated to be produced by this effort and is expected to possess great selectivity, good stability, and sensitivity.
Rice is planted as a rotation crop in the sugarcane-dominant Everglades Agricultural Area (EAA) in southern Florida. The Histosols in this area are unlike other mineral soils used to grow rice due to the high organic content and land subsidence caused by rapid oxidation of organic matter upon drainage. It remains unknown if such soils pose a risk of arsenic (As) or cadmium (Cd) mobilization and uptake into rice grain. Both As and Cd are carcinogenic trace elements of concern in rice, and it is important to understand their soil-plant transfer into rice, a staple food of global importance. Here, a mesocosm pot study was conducted using two thicknesses of local soil, deep (D, 50 cm) and shallow (S, 25 cm), under three water managements, conventional flooding (FL), low water table (LWT), and alternating wetting and drying (AWD). Rice was grown to maturity and plant levels of As and Cd were determined. Regardless of treatments, rice grown in these Florida Histolsols has very low Cd concentrations in polished grain (1.5-5.6 μg kg-1) and relatively low total As (35-150 μg kg-1) and inorganic As (35-87 μg kg-1) concentrations in polished grain, which are below regulatory limits. This may be due to the low soil As and Cd levels, high soil cation exchange capacity due to high soil organic matter content, and slightly alkaline soil pH. Grain As was significantly affected by water management (AWD < FL = LWT) and its interaction effect with soil thickness (AWD-D ≤ AWD-S ≤ FL-D = LWT-S = LWT-D ≤ FL-S), resulting in as much as 62 % difference among treatments. Grain Cd was significantly affected by water management (AWD > FL > LWT) without any soil thickness impact. In conclusion, even though water management has more of an impact on rice As and Cd than soil thickness, the low concentrations of As and Cd in rice pose little health risk for consumers.
This study aimed to create a miniaturized electrochemical platform for detecting As(III) contamination in herbal medicines. To reduce the operational steps of modification and determination, only a single drop of mixed standard Au(III) and sample solution is proposed to perform the electrochemical measurements using a screen-printed graphene electrode (SPGE). Square wave anodic stripping voltammetry was employed to integrate the simultaneous modification and determination processes. To perform the measurement, As(III) and Au(III) migrate to the SPGE surface while the reduction potential is held at -0.5 V, forming an Au-As intermetallic alloy. Then, As is stripped off for the electrochemical determination of As(III). The total assay time is less than 3 min. Under suitable conditions, the electrochemical sensing system can detect As(III) at concentrations ranging from 0.1 to 3.0 ppm, with a limit of quantification and limit of detection of 0.1 and 0.03 ppm, respectively. The applicability and accuracy of the proposed sensor were verified by determining As(III) in herbal medicinal samples, and they were found to be in line with the standard method (ICP-OES). The benefits of simple operation, rapid detection, portability, and low cost (<1 USD) make this a more powerful tool for routine monitoring and on-site analysis applications.
Reductive dissolution is one of the main causes for arsenic (As) mobilisation in flooded soils while biomethylation and biovolatilisation are two microbial mechanisms that greatly influence the mobility and toxicity of As. Climate change results in more extreme weather events such as flooding and higher temperatures, potentially leading to an increase in As release and biotransformations. Here, we investigated the effects of flooding and temperature on As release, biomethylation and biovolatilisation from As-rich soils with different pH and source of As (one acidic and anthropogenic (Salanfe) and one neutral and geogenic (Liesberg)). Flooded soils incubated at 23 °C for two weeks showed a ~ 3-fold (Liesberg site) and ~ 7-fold (Salanfe site) increase in the total As concentration of soil solution compared to those incubated at 18 °C. Methyl- and thio-As species were found in the acidic soil and soil solution. High temperatures enhanced thiolation and methylation although inorganic As was predominant. We also show that volatile As fluxes increased more than 4-fold between treatments, from 18 ± 5 ng/kg/d at 18 °C to 75 ± 6 ng/kg/d at 23 °C from Salanfe soil. Our results suggest that high As soils with acidic pH can become an important source of As to the surrounding environment according to realistic climatic scenarios, and that biovolatilisation is very sensitive to increases in temperature. This study provides new data and further justifies further investigations into climate-induced changes on As release and speciation and its links to important factors such as microbial ecology and sulfate or iron biogeochemistry.
Synopsis
In the studied Swiss soils elevated temperature increases arsenic mobility through volatilisation and methylation.
The developers of medical devices evaluate the biocompatibility of their device prior to FDA's review and subsequent introduction to the market. Chemical characterization, described in ISO 10993-18:2020, can generate information for toxicological risk assessment and is an alternative approach for addressing some biocompatibility end points (e.g., systemic toxicity, genotoxicity, carcinogenicity, reproductive/developmental toxicity) that can reduce the time and cost of testing and the need for animal testing. Additionally, chemical characterization can be used to determine whether modifications to the materials and manufacturing processes alter the chemistry of a patient-contacting device to an extent that could impact device safety. Extractables testing is one approach to chemical characterization that employs combinations of non-targeted analysis, non-targeted screening, and/or targeted analysis to establish the identities and quantities of the various chemical constituents that can be released from a device. Due to the difficulty in obtaining a priori information on all the constituents in finished devices, information generation strategies in the form of analytical chemistry testing are often used. Identified and quantified extractables are then assessed using toxicological risk assessment approaches to determine if reported quantities are sufficiently low to overcome the need for further chemical analysis, biological evaluation of select end points, or risk control. For extractables studies to be useful as a screening tool, comprehensive and reliable non-targeted methods are needed. Although non-targeted methods have been adopted by many laboratories, they are laboratory-specific and require expensive analytical instruments and advanced technical expertise to perform. In this Perspective, we describe the elements of extractables studies and provide an overview of the current practices, identified gaps, and emerging practices that may be adopted on a wider scale in the future. This Perspective is outlined according to the steps of an extractables study: information gathering, extraction, extract sample processing, system selection, qualification, quantification, and identification.
Climate change is expected to increase growing temperatures in rice cultivating regions worldwide. Recent research demonstrates that elevated temperature can increase arsenic concentrations in rice tissue, exacerbating an existing threat to rice quality and human health. However, the specific temperature-induced changes in the plant-soil system responsible for increased arsenic concentrations remain unclear and such knowledge is necessary to manage human dietary arsenic exposure in a warmer future. To elucidate these changes, we established four temperature treatments in climate-controlled growth chambers and grew rice plants (Oryza sativa cv. M206) in pots filled with Californian paddy soil with arsenic concentrations of 7.7 mg kg⁻¹. The four chosen temperatures mimicked IPCC forecasting for Northern California, with a roughly 2.5 °C increase between treatments (nighttime temperatures ~2 °C cooler). We observed that arsenic concentrations in porewater, root iron plaque, and plant tissue increased in response to elevated temperature. There was a positive linear relationship between temperature and rice grain arsenic, almost all of which was present as inorganic As (III). Above-ground allocation patterns were consistent across treatments. We found no upregulation in the gene encoding the OsABCC1 transporter, believed to be important for arsenic sequestration in vacuoles and thereby preventing arsenic transfer to grain. Rice plants grown at higher temperatures had more adsorbed arsenic per unit of iron plaque (measured as [As]/[Fe]), indicating temperature may impact arsenic sorption to root plaque. We present evidence that increased soil mobilization of arsenic was the driving factor responsible for increased arsenic uptake into rice grain. Transpiration, which can increase arsenic transport to roots, was also heightened with elevated temperature but appeared to play a secondary role. Our system had low soil arsenic concentrations typical for California. Our findings highlight that elevated growing temperatures may increase the risk of dietary arsenic exposure in rice systems that were previously considered low risk.
Since the development of atomic spectrometry, trace element and isotopic analysis has been mainly based on the monitoring of atomic spectra and monoionic species. However, according to the literature and considering the current instrumental developments, it seems that some of the remaining challenges in this field can be mitigated via the measurement of molecular spectra or of polyatomic ions. This review discusses recent advances in three of the most important atomic techniques (laser-induced breakdown spectrometry, high-resolution continuum source atomic absorption spectrometry and inductively coupled plasma mass spectrometry) and how the monitoring of such molecules or polyatomic ions containing the target analyte enables attaining better selectivity and opens new ways to determine non-metals and to obtain isotopic information.
Silicon (Si) addition to flooded rice paddy soil tends to decrease grain inorganic arsenic (iAs) and increase grain dimethylarsinic acid (DMA) concentrations, but the mechanism for the increase in plant-available DMA is unresolved. It has been suggested that Si displaces DMA from soil solids, rendering it plant-available; however, we hypothesize that Si desorbs primarily iAs from soil solids, which stimulates methylation to DMA. We added silicic acid to a contaminated paddy soil and a flooded upland soil that had been historically contaminated with lead arsenate in a batch incubation experiment, and measured changes in solid-phase As speciation, porewater As speciation, and As-methylating microbial (AsMM) abundance over time. We found that DMA was not detectable in soils prior to the start of the experiment nor throughout the experiment, so it comprised a trace amount of total soil As. Upon Si addition to paddy soil, total As increased in porewater following Si spike and this increase was mainly due to iAs desorption, and an order of magnitude less MMA and DMA was desorbed. The upland soil transitioned to reducing conditions throughout the experiment, but when they were achieved, iAs was desorbed first and this was followed by an increase of MMA and then DMA compared to control soils. Total microbial community abundance increased over the course of the experiments and arsM gene abundance increased from initial conditions, but did not differ between treatments. In the paddy soil, the ratio of arsM:16S gene abundance decreased from the initial conditions, but it increased in the upland soil with historic As contamination. These results suggest that Si-induced desorption of DMA is small and likely does not explain the increases of plant-available DMA upon Si fertilization in prior work. Likely, Si-induced iAs desorption drives microorganisms to methylate iAs, but degree of methylation will differ between soils.
A frontal chromatography – ICP-MS method (FC-ICP-MS) is proposed as an innovative approach for fast elemental speciation analysis: inorganic arsenic speciation was selected as the first case-study to prove the feasibility of the technique and to explore its potentialities and limits. The principal benefits of the FC-ICP-MS approach are the short analysis time and the very simple instrumental setup. As(III) and As(V) front separation is performed over a strong anion exchanger at pH 7.5. After the optimization of the instrumental setup and the frontal chromatographic parameters, As(III) and As(V) concentrations up to 240 µg/kg can be determined within 120-140 seconds using different univariate and multivariate calibration approaches. Best results in terms of accuracy in prediction were obtained using the Partial Least Squares (PLS) calibration achieving LODs of 0.18 and 0.21 µg/kg for As(III) and As(V), respectively. This approach was also used to establish the figures of merit of the method. The proved feasibility and good performances (in terms of analysis time and accuracy) of this technique lays the groundwork for future applications of FC-ICP-MS for the speciation of other elements.
The composition of inorganic elements is a key factor in determining the quality of fruit wines. However, the use of direct sample injection is challenging for multi-elemental analysis of fruit wine samples. In this paper, an analytical method using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) was established for determining multiple elements (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Cd, Hg, and Pb) in fruit wine. The fruit wine was diluted using ultrapure water and acidified with nitric acid before injecting into the ICP-MS/MS. Spectral interferences in the complex matrix composition of different fruit wine samples, in the MS/MS mode, were eliminated using mixed reaction gases of O2/H2 and NH3/He/H2 through the mass shift and on-mass methods. The limits of detection ranged from 0.41 to 58.1 ng L-1. This study demonstrates a new approach for multi-elemental analysis in fruit wine with great convenience and high accuracy.
For individuals following a gluten-free (GF) diet, rice is commonly the major grain. People following a GF diet have a higher arsenic burden than the general population. We conducted a multielemental market basket study of GF and gluten containing ingredients and prepared foods (Mn, Fe, Ni, Cu, Zn, Cr, Co, Se, Cd, Sb, Pb, total As, As species, total Hg and methylmercury). Foods containing rice were significantly higher in As, Hg and Pb and lower in Se, Fe, Cu and Zn. Wheat-based foods were higher in Cd. Mercury concentrations were low (<3.5 ng/g); speciation was predominantly methylmercury. Arsenic and mercury in rice were correlated. GF foods contained significantly more As and Hg. Eating a wide variety of GF grains may reduce contaminant exposure and increase micronutrient status compared to a rice-based GF diet.
Background:
Rice is an important dietary source for methylmercury (MeHg), a potent neurotoxin, and inorganic arsenic (As), a human carcinogen. Rice baby cereals are a dietary source of inorganic As; however, less is known concerning MeHg concentrations in rice baby cereals and rice teething biscuits.
Methods:
MeHg concentrations were measured in 36 rice baby cereals, eight rice teething biscuits, and four baby cereals manufactured with oats/wheat (n = 48 total). Arsenic (As) species, including inorganic As, were determined in rice baby cereals and rice teething biscuits (n = 44/48), while total As was determined in all products (n = 48).
Results:
Rice baby cereals and rice teething biscuits were on average 61 and 92 times higher in MeHg, respectively, and 9.4 and 4.7 times higher in total As, respectively, compared to wheat/oat baby cereals. For a 15-g serving of rice baby cereal, average MeHg intake was 0.0092μgday(-1) (range: 0.0013-0.034μgday(-1)), while average inorganic As intake was 1.3μgday(-1) (range: 0.37-2.3μgday(-1)). Inorganic As concentrations in two brands of rice baby cereal (n = 12/36 boxes of rice cereal) exceeded 100ng/g, the proposed action level from the U.S. Food and Drug Administration. Log10 MeHg and inorganic As concentrations in rice baby cereals were strongly, positively correlated (Pearson's rho = 0.60, p < 0.001, n = 36).
Conclusions:
Rice-containing baby cereals and teething biscuits were a dietary source of both MeHg and inorganic As. Studies concerning the cumulative impacts of MeHg and inorganic As on offspring development are warranted.
This work presents an alternative method for arsenic speciation using the nano-TiO2 hydride generation photocatalytic hydride generation (PCHG) system, which is easily separated from the medium. Nano-TiO2 was studied as photocatalyst to reduction of arsenic species by UV-induced with formic acid and atomic absorption detection of different forms of arsenic [As (III), As (V), dimethylarsinic acid (DMA)] in environmental samples (water, sediment and plant). The effect of the average pH, the organic acid concentration, the ultraviolet irradiation time and their amount were investigated. With the presence of formic acid, the process was more effective in the reduction of arsenic when compared to other organic acids, mainly acetic acid. In addition, the photocatalytic hydride generation and flame atomic absorption spectrometry (nano-TiO2/PCHG-FAAS) increased the identification and quantification of different arsenic species. The ultrasound extraction procedure was used as a method to prepare samples with solutions of 1.0 mol L(-1) phosphoric acid. The accuracy of the measurements (n = 12), calculated as relative standard deviation, was less than 8.6%. The detection limits for As (III) and As (total) in samples were 0.418 and 0.574 μg g(-1), respectively.
Arsenic speciation in seafood after several culinary treatments was performed and AsB, As(iii), DMA, MMA and As(v) species were determined by liquid chromatography hyphenated to triple-quadrupole inductively coupled plasma mass spectrometry (LC-ICP-MS/MS) using O2 as the reaction gas for the conversion of ⁷⁵As to ⁷⁵As¹⁶O. The influence of culinary treatments (boiling, frying and sautéing) with or without the addition of spices (salt, lemon juice and garlic) on the As species in blacktip shark and Asian tiger shrimp was investigated. Arsenic species were extracted by using a 30 mmol L⁻¹ HNO3 solution. Ammonium phosphate (10 mmol L⁻¹) was used as the mobile phase. The influence of pH and the addition of 1% (v/v) methanol were investigated. Oil, water, butter and the spices used during cooking were analysed to perform a close mass balance of the total As. The speciation method was also employed for a certified reference material (CRM, DORM-3), and the accuracy was evaluated by statistical comparison between the certified value and the total As concentration determined by ICP-MS after acid digestion and also by a comparison of the sum of As species with the total As. It was demonstrated that the culinary treatments practically did not influence the stability of As species in uncooked seafood. On the other hand, significant analyte losses (from 15 up to 45%) were observed for boiled seafood. The speciation analysis method presented accuracy and robustness for both raw seafood and seafood after the culinary treatments. The limits of quantification were 4, 21, 4, 9 and 18 ng g⁻¹ for AsB, As(iii), DMA, MMA and As(v), respectively. This study allowed the determination of As species in seafood after culinary treatments, thus offering additional information about the behaviour of species during cooking.
Inorganic arsenic (iAs) in 13 store-bought edible seaweed samples and 34 dried kelp (Laminaria digitata) samples was determined by a newly developed, field-deployable method (FDM) with the aid of a field test kit for arsenic in water. Results from the FDM were compared to results from speciation analysis achieved by using high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The FDM consisted of a simple extraction method using diluted HNO3 to quantitatively extract iAs without decomposing the organoarsenicals to iAs followed by the selective volatilisation of iAs as arsine (AsH3) and subsequent chemo-trapping on a filter paper soaked in mercury bromide (HgBr2) solution. Method optimization with a sub-set of samples showed 80–94% iAs recovery with the FDM with no matrix effect from organo-arsenic species in the form of dimethylarsinic acid (DMA) on the iAs concentration. The method displayed good reproducibility with an average error of ±19% and validation by HPLC-ICP-MS showed that the results from the FDM were comparable (slope = 1.03, R² = 0.70) to those from speciation analysis with no bias. The FDM can be conducted within an hour and the observed limit of quantification was around 0.05 mg kg⁻¹ (dry weight). This method is well suited for on-site monitoring of iAs in seaweed before it is harvested and can thus be recommended for use as a screening method for iAs in seaweed.
Graphical abstractScreening seaweed for their inorganic arsenic concentration within one hour without bias has been made possible in the field by using a field deployable arsenic kit. Its accuracy and precision was compared to HPLC-ICPMS.
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This fit-for-purpose method was designed in response to recent and proposed food standards, both international and national, that limit inorganic arsenic rather than total, organic, or individual arsenic species such as arsenite (AsIII) and arsenate (AsV). In this method, AsIII is intentionally oxidized to AsV with H2O2 during sample preparation, converting all inorganic arsenic (the sum of AsIII and AsV) to the AsV form. Arsenic species were separated in less than 2 minutes using a short, narrow bore, 5 μm chromatography column. This analysis time is 10× faster than the current FDA regulatory method. The use of O2 reaction gas with inductively coupled plasma triple quadrupole mass spectrometry (ICP-QQQ with MS/MS capability) avoided spectral interferences and dramatically increased sensitivity, allowing for low volume injections. The small injection volume and modified mobile phase composition mitigate non-spectral interferences such as carbon enhanced ionization. Furthermore, the shortened analysis time significantly increases sample throughput. Validation data from two laboratories demonstrate the method's accuracy and reproducibility of both wine and rice matrices in a single analytical batch.
This work reviews the operating principles of ICP-tandem mass spectrometry (ICP-MS/MS) and the key applications reported on since the introduction of the technique in 2012. The main differences between single quadrupole ICP-MS and ICP-MS/MS are elucidated and the tools available for method development are addressed. Examples of real-life applications are given to demonstrate the capabilities of this novel setup in the context of elemental, speciation and isotopic analysis. Attention has been paid to the different approaches (on-mass and mass-shift) allowing interference-free conditions to be obtained.
Here we review recent developments in analytical proposals for the assessment of inorganic arsenic (iAs) content in food products. Interest in the determination of iAs in products for human consumption such as food commodities, wine, and seaweed among others is fueled by the wide recognition of its toxic effects on humans, even at low concentrations. Currently, the need for robust and reliable analytical methods is recognized by various international safety and health agencies, and by organizations in charge of establishing acceptable tolerance levels of iAs in food. This review summarizes the state of the art of analytical methods while highlighting tools for the assessment of quality assessment of the results, such as the production and evaluation of certified reference materials (CRMs) and the availability of specific proficiency testing (PT) programmes. Because the number of studies dedicated to the subject of this review has increased considerably over recent years, the sources consulted and cited here are limited to those from 2010 to the end of 2015.
A new rapid monitoring method by means of high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) following the heat-assisted extraction was developed for measurement of total inorganic arsenic species in rice flour. As(III) and As(V) eluted at the same retention time and completely separated from organoarsenic species by an isocratic elution program on a reversed phase column. Therefore, neither ambiguous oxidation of arsenite to arsenate nor the integration of two peaks were necessary to determine directly the target analyte inorganic arsenic. Rapid injection allowed measuring 3 replicates within 6 min and this combined with a quantitative extraction of all arsenic species from rice flour by a 15 minute HNO3-H2O2 extraction makes this the fastest laboratory based method for inorganic arsenic in rice flour.
This is the eighth Atomic Spectrometry Update (ASU) to focus on advances in elemental speciation and covers a period of approximately 12 months from December 2014. This ASU review deals with all aspects of the analytical atomic spectrometry speciation methods developed for: the determination of oxidation states; organometallic compounds; coordination compounds; metal and heteroatom-containing biomolecules, including metalloproteins, proteins, peptides and amino acids; and the use of metal-tagging to facilitate detection via atomic spectrometry. The review does not cover fractionation, which is sometimes termed operationally defined speciation. As with all ASU reviews the focus of the research reviewed includes those methods that incorporate atomic spectrometry as the measurement technique. However, because speciation analysis is inherently focused on the relationship between the metal(loid) atom and the organic moiety it is bound to, or incorporated within, atomic spectrometry alone cannot be the sole analytical approach of interest. For this reason molecular detection techniques are also included where they have provided a complementary approach to speciation analysis. As in previous years, As and Se speciation continues to dominate the current literature and there has also been an increase in the number of publications concerning solid state speciation. This is presumably due to the increase in the number of synchrotron facilities available and a greater awareness of their potential for speciation studies.
Addition of carbon as methanol or ammonium carbonate to the aqueous analyte solutions in combination with increased plasma power input enhanced the inductively coupled plasma mass spectrometry (ICP-MS) signal intensities of arsenic and selenium. In the presence of the optimum 3% v/v methanol concentration the signal intensities achieved were about 4500-5000 counts s-1 per ng ml-1 of arsenic and about 700-1100 counts s-1 per ng ml-1 of selenium (82Se), corresponding to enhancement factors of 3.5-4.5 compared with aqueous solution for the two elements. Differences in sensitivity (calculated on the basis of analyte atom) were observed between the individual arsenic species and between the selenium species in aqueous as well as in carbon-added solutions. The presence of 3% v/v methanol in the analyte solutions doubled the level of the background signal for arsenic and selenium, but its fluctuation (noise) was not increased. Therefore, the observed increase in analyte sensitivity led to a similar increase in signal-to-noise ratio. The addition of carbon as ammonium carbonate enhanced the arsenic signal by a similar factor but caused severe contamination of the ICP-MS instrument by carbon. In the 3% v/v methanol solutions of arsenic and selenium the signal intensity from antimony (internal standard) was enhanced by a factor of 1.5, which indicates that the enhancement effect of the arsenic and selenium signals by methanol is only to a limited extent caused by improved sample transport/nebulization efficiency. It is proposed that an increased population of carbon ions or carbon-containing ions in the plasma facilitates a more complete ionization of analytes lower in ionization energy than carbon itself. The enhanced detection power for arsenic was applied to arsenic speciation by high-performance liquid chromatography (HPLC)-ICP-MS, and made possible the detection of the arsenocholine ion (AsC) in extracts of shrimp at the 5-10 ng g-1 concentration level. The limit of detection was improved by a factor of 3.4 after addition of methanol and was 4.7 ng g-1 as the AsC ion.
Two of the core tasks of the European Union Reference Laboratory for Heavy Metals in Feed and Food (EU-RL-HM) are to provide advice to the Directorate General for Health and Consumers (DG SANCO) on scientific matters and to organise proficiency tests among appointed National Reference Laboratories. This article presents the results of the 12th proficiency test organised by the EU-RL-HM (IMEP-112) that focused on the determination of total and inorganic arsenic in wheat, vegetable food and algae. The test items used in this exercise were: wheat sampled in a field with a high concentration of arsenic in the soil, spinach (SRM 1570a from NIST) and an algae candidate reference material. Participation in this exercise was open to laboratories from all around the world to be able to judge the state of the art of the determination of total and, more in particular, inorganic arsenic in several food commodities. Seventy-four laboratories from 31 countries registered to the exercise; 30 of them were European National Reference Laboratories. The assigned values for IMEP-112 were provided by a group of seven laboratories expert in the field of arsenic speciation analysis in food. Laboratory results were rated with z and ζ scores (zeta scores) in accordance with ISO 13528. Around 85 % of the participants performed satisfactorily for inorganic arsenic in vegetable food and 60 % did for inorganic arsenic in wheat, but only 20 % of the laboratories taking part in the exercise were able to report satisfactory results in the algae test material.
A robust analytical method has been developed and validated by use of high-performance liquid chromatography inductively coupled plasma mass spectrometry with Dynamic Reaction Cell (DRC) technology that separates seven arsenic (As) species in human urine: arsenobetaine (AB), arsenocholine, trimethylarsine oxide (TMAO), arsenate (As(V)), arsenite (As(III)), monomethylarsonate, and dimethylarsinate. A polymeric anion-exchange (Hamilton PRP X-100) column was used for separation of the species that were detected at m/z 75 by ICP-DRC-MS (PerkinElmer SCIEX ELAN DRCII) using 10% hydrogen-90% argon as the DRC gas. The internal standard (As) is added postcolumn via an external injector with a sample loop. All analyte peaks were baseline-separated except AB and TMAO. Analytical method limits of detection for the various species ranged from 0.4 to 1.7 microg L(-1) as elemental As. As(III) conversion to As(V) was avoided by adjusting the urine sample to <pH 6. Analyses of the National Institute of Standards and Technology standard reference material (SRM) 2670 and 2670a elevated and National Institute for Environmental Studies certified reference material (CRM) no. 18 for arsenic species yielded results within the certified SRM-CRM limits for As species; likewise, the sum of all species compared favorably to SRM 2670 and 2670a target values for total As. This As speciation method is now being used in a production mode for the analysis of a US population survey, the National Health and Nutrition Examination Survey, as well as for other biomonitoring studies of As exposure. This method meets our requirement for sample throughput of 2,000-3,000 sample analyses per year.
We review recent research in the field of arsenic speciation analysis with the emphasis on significant advances, novel applications and current uncertainties.
Recent reports of As concentrations in certain food and drinks has garnered public concern and led to a lowering of the US guideline maximum concentration for inorganic As in apple juice and proposed limits for As in rice products. In contrast Se is an essential micro-nutrient that can be limiting when Se-poor soils yield Se-poor food crops. Rare earth element (REE) doubly charged interferences on As and Se can be significant even when initial ICP-MS tuning minimizes doubly charged formation. We analyzed NIST 1547 (peach leaves) and 1515 (apple leaves), which contain high levels of REEs, by quadrupole ICP-MS with (He) collision mode, H2 reaction mode or triple quadrupole ICP-MS (ICP-QQQ) in mass-shift mode (O2 and O2/H2). Analysis by collision cell ICP-MS significantly over-estimated As and Se concentration due to REE doubly charged formation; mathematical correction increased the accuracy of analysis but is prone to error when analyte concentration and sensitivity is low and interferent is high. For Se, H2 reaction mode was effective in suppressing Gd2+ leading to accurate determination of Se in both SRMs without the need for mathematical correction. ICP-QQQ using mass-shift mode for As+ from m/z 75 to AsO+ at m/z 91 and Se+ from m/z 78 to SeO+ at m/z 94 alleviated doubly charged effects and resulted in accurate determination of As and Se in both SRMs without the need for correction equations. Zr and Mo isobars at 91 and 94 were shown to be effectively rejected by the MS/MS capability of the ICP-QQQ.
Because arsenic occurs in food both as toxic inorganic forms and as (presumed) non-toxic organic forms, there is a pressing need for robust analytical methods to selectively and quantitatively determine inorganic arsenic in food products. We report an HPLC–ICPMS method based on sample extraction with trifluoroacetic acid/H2O2, and measurement of arsenate by anion-exchange HPLC–ICPMS using aqueous malonic acid as mobile phase. The method showed good extraction efficiencies (generally >90%) and column recoveries (>95%) for samples of rice, tuna fish and wheat. Moreover, the use of 5 or 10 mM malonic acid at pH 5.6 gave sharp well-resolved HPLC peaks and a conveniently short retention time of 5 min for arsenate, which together contributed to a low limit of detection based on signal to noise ratio of three of 0.05 μg As L−1 (for 20 μL injection) corresponding to an LOD of 1 μg As·kg−1 dry mass in the samples. The inorganic arsenic and total arsenic content (dry mass basis) of 10 rice samples was 25–171 μg As·kg−1 and 36–218 μg As·kg−1, respectively, whereas the 24 tuna fish samples contained much lower levels of inorganic arsenic (<2–18 μg As·kg−1), although the total arsenic content was much higher (730–5030 μg As·kg−1). The single wheat sample contained 166 μg As·kg−1, which was present mainly as inorganic arsenic (152 μg As·kg−1). The combination of low acid concentration for extraction, high buffering capacity of malonic acid at pH 5.6, and good peak shape results in a highly reproducible and sensitive method for the determination of inorganic arsenic in food.
In answering a request from the Directorate General for Health and Consumers of the European Commission, the European Union Reference Laboratory for Heavy Metals in Feed and Food, with the support of the International Measurement Evaluation Program, organized a proficiency test (PT), IMEP-107, on the determination of total and inorganic arsenic (As) in rice. The main aim of this PT was to judge the state of the art of analytical capability for the determination of total and inorganic As in rice. For this reason, participation in this exercise was open to laboratories from all over the world. Some 98 laboratories reported results for total As and 32 for inorganic As.The main conclusions of IMEP-107 were that the concentration of inorganic As determined in rice does not depend on the analytical method applied and that introduction of a maximum level for inorganic As in rice should not be postponed because of analytical concerns.
A systematic study on the influence of carbon on the signal of a large number of hard-to-ionize elements (i.e. B, Be, P, S, Zn, As, Se, Pd, Cd, Sb, I, Te, Os, Ir, Pt, Au, and Hg) in inductively coupled plasma–mass spectrometry has been carried out. To this end, carbon matrix effects have been evaluated considering different plasma parameters (i.e. nebulizer gas flow rate, r.f. power and sample uptake rate), sample introduction systems, concentration and type of carbon matrix (i.e. glycerol, citric acid, potassium citrate and ammonium carbonate) and type of mass spectrometer (i.e. quadrupole filter vs. double-focusing sector field mass spectrometer). Experimental results show that P, As, Se, Sb, Te, I, Au and Hg sensitivities are always higher for carbon-containing solutions than those obtained without carbon. The other hard-to-ionize elements (Be, B, S, Zn, Pd, Cd, Os, Ir and Pt) show no matrix effect, signal enhancement or signal suppression depending on the experimental conditions selected. The matrix effects caused by the presence of carbon are explained by changes in the plasma characteristics and the corresponding changes in ion distribution in the plasma (as reflected in the signal behavior plot, i.e. the signal intensity as a function of the nebulizer gas flow rate). However, the matrix effects for P, As, Se, Sb, Te, I, Au and Hg are also related to an increase in analyte ion population caused as a result of charge transfer reactions involving carbon-containing charged species in the plasma. The predominant specie is C+, but other species such as CO+, CO2+, C2+ and ArC+ could also play a role. Theoretical data suggest that B, Be, S, Pd, Cd, Os, Ir and Pt could also be involved in carbon based charge transfer reactions, but no experimental evidence substantiating this view has been found.
Current knowledge indicates that total urinary arsenic is not a suitable biomarker of exposure to toxic, i.e., inorganic, arsenic (iAs), whereas measurement of iAs and its methylated metabolites in urine using speciation analysis provides much more reliable estimates of exposure. The relative proportions of urinary iAs, monomethylarsonate (MA), and dimethylarsinate (DMA) can be used as a measure of methylation capacity, provided that there are no confounding factors such as consumption of food rich in DMA or containing As compounds metabolized to DMA. We analyzed by gradient elution anion-exchange HPLC-ICP-MS (high-performance liquid chromatography-inductively coupled plasma-mass spectrometry) urine samples from 153 residents in Latium (central Italy) chronically exposed to iAs via water and food. Excluding 26 subjects that excreted high concentrations of arsenobetaine (AB) (>= 50 mu g As/L) due to seafood consumption, iAs and related metabolites summed up about 75 % of total urinary As as measured by ICP-MS. AB and other organoarsenic compounds were detected at low concentrations in all urine samples. Considering all subjects, the sum of iAs and metabolites ranged 2-72 mu g/L and relative proportions were iAs 14 %, MA 13 %, and DMA 72 % (median values), with a wide individual variability. In addition to the above arsenocompounds, the analytical method used in this study enabled the detection of dimethylthioarsinic acid (DMTA), which was found to be present in 33 % of the samples at concentrations ranging mostly from trace amounts to similar to 6 mu g As/L. We found that part of the certified DMA content of human urine reference material SRM 2669 was present as DMTA. Four unknown arsenicals were also detected as minor species in a small proportion of samples.
Wheat appears to be the major contributor to the intake of inorganic arsenic in countries where the diet is not rice-based. Ultrasound- and microwave-assisted extraction of arsenic in wheat and wheat based food using different solvents or enzymes was investigated in terms of extraction yield and species stability. Four extraction procedures were selected for the study of arsenic speciation in wheat and wheat products by anion exchange HPLC-ICP-MS using a PRP-X100 column with 10 mM NH4H2PO4, 10 mM NH4NO3, and 2% CH3OH at pH 5.5 as the mobile phase. Total arsenic in the samples ranged from 8.6 to 29.8 ng g−1 dry weight. About 95% of the arsenic was found to be present in inorganic form with AsIII as the most abundant species, whereas the remainder was mainly DMA. Microwave-assisted extraction with HNO3 was the most effective in liberating the arsenic species, which were then satisfactorily recovered from the chromatographic column. The LODs achieved, i.e., 0.35–0.46 ng g−1 dry weight, were suitable for the determination of arsenic species at the low levels found in sample extracts.