Distribution of Arsenic Species in Different Leaf Fractions – An Evaluation of the Biochemical Deposition of Arsenic in Plant Cells

This paper describes an approach to the determination of arsenic species bonding with proteins or low-molecular peptides by separation of leaf proteins and protein precursors into three fractions and analysis of arsenic species associated to these fractions. Plants irrigated with arsenite contained not only arsenite but also arsenate and dimethylarsinate. In plants treated with arsenate, the major component was arsenite in the water-soluble fraction containing soluble protein and non-protein (F II) and in the acid-soluble non-protein fraction (F IV). Concentrations of 43 mg kg⁻¹ (As(V)-treatment) and 18 mg kg⁻¹ (As(III)-treatment) could be analyzed in the water-insoluble structure protein fraction F I (56 ± 15% of the total mass). Based on the concentration of arsenic species in all fractions, conclusions are drawn over the fixation of arsenic in the fraction of insoluble structure proteins, in the fraction of soluble cytosolic proteins as well as the fraction of amino acids.     

Mechanistic modeling of arsenic retention on natural red earth in simulated environmental systems

Arsenic retention on natural red earth (hereafter NRE) was examined as a function of pH, ionic strength, and initial arsenic loading using both macroscopic and spectroscopic methods. Proton binding sites on NRE were characterized by potentiometric titrations yielding an average pH(zpc) around 8.5. Both As(III)- and As(V)-NRE surface configurations were postulated by vibration spectroscopy. Spectroscopically, it is shown that arsenite forms monodentate complexes whereas arsenate forms bidendate complexes with NRE. When 4相似文献   

Arsenic speciation in Chinese brake fern by ion-pair high-performance liquid chromatography-inductively coupled plasma mass spectroscopy

Ion-pair reverse-phase HPLC-inductively coupled plasma (ICP) MS was employed to determine arsenite [As(III)], dimethyl arsenic acid (DMA), monomethyl arsenic (MMA) and arsenate [As(V)] in Chinese brake fern (Pteris vittata L.). The separation was performed on a reverse-phase C18 column (Haisil 100) by using a mobile phase containing 10 mM hexadecyltrimethyl ammonium bromide (CTAB) as ion-pairing reagent, 20 mM ammonium phosphate buffer and 2% methanol at pH 6.0. The detection limits of arsenic species with HPLC-ICP-MS were 0.5, 0.4, 0.3 and 1.8 ppb of arsenic for As(III), DMA, MMA, and As(V), respectively. MMA has been shown for the first time to experimentally convert to DMA in the Chinese brake fern, indicating that Chinese brake fern can convert MMA to DMA by methylation.     

A new hydride generation system applied in determination of arsenic species with ion chromatography-hydride generation-atomic fluorescence spectrometry (IC-HG-AFS)

A novel procedure was developed for the determination of arsenite (As(III)), arsenate (As(V)), monomethylarsonic (MMA) and dimethylarsinic acid (DMA) with ion chromatography-hydride generation-atomic fluorescence spectrometry (IC-HG-AFS) by employing a new gas-liquid separator (GLS). The effective separation of the four arsenic species was achieved in about 12 min. With a sample loading volume of 20 μl, the measurable minimum for As(III), DMA, MMA and As(V) were 0.02, 0.045, 0.043 and 0.166 ng, respectively, along with relative standard deviations of 1.1, 1.1, 1.7 and 2.2% at the 100 μg l⁻¹ level (n = 6) for As(III), DMA, MMA and As(V), respectively. The present procedure was applied for the speciation of arsenic in underground water and in urine samples, and the sum of the four arsenic species by IC-HG-AFS was in good agreement with the total value by HG-AFS.     

Extraction and speciation of arsenic in plants grown on arsenic contaminated soils

A sequential arsenic extraction method was developed that yielded extraction efficiencies (EE) that were approximately double those using current methods for terrestrial plants. The method was applied to plants from two arsenic contaminated sites and showed potential for risk assessment studies. In the method, plants were extracted first by 1:1 water-methanol followed by 0.1 M hydrochloric (HCl) acid. Total arsenic in plant and soil samples collected from contaminated sites was mineralized by acid digestion and detected by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and hydride generation-atomic absorption spectrometry (HG-AAS). Arsenic speciation was done by high performance liquid chromatography coupled with HG-AAS (HPLC-HGAAS) and by HPLC coupled with ICP-mass spectrometry (HPLC-ICP-MS). Spike recovery experiments with arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA) and dimethylarsinic acid (DMA) showed stability of the species in the extraction processes. Speciation analysis by X-ray absorption near edge spectroscopy (XANES) demonstrated that no transformation of As(III) and As(V) occurred due to sample handling. Dilute HCl was efficient in extracting arsenic from plants; however, extraction and determination of organic species were difficult in this medium. Sequential extraction with 1:1 water-methanol followed by 0.1 M-HCl was most useful in extracting and speciating both organic and inorganic arsenic from plants. Trace amounts of MA and DMA in plants could be detected by HPLC-HGAAS aided by the process of separation and preconcentration of the sequential extraction method. Both organic and inorganic arsenic compounds could be detected simultaneously in synthetic gastric fluid extracts (GFE) but EEs by this method were lower than those of the sequential method. The developed sequential method was shown to be reliable and applicable to various terrestrial plants for arsenic extraction and speciation.     

Complementary chromatography separation combined with hydride generation-inductively coupled plasma mass spectrometry for arsenic speciation in human urine

This study aimed to establish complementary high performance liquid chromatography (HPLC) methods including three modes of separation: ion pairing, cation exchange, and anion exchange chromatography, with detection by inductively coupled plasma mass spectrometry (ICPMS). The ion pairing mode enabled the separation of inorganic arsenate (As(V)), monomethylarsonic acid (MMA(V)), and dimethylarsinic acid (DMA(V)). However, the ion pair mode was unable to differentiate inorganic arsenite (As(III)) from arsenobetaine (AsB); instead, cation exchange chromatography was used to isolate and quantify AsB. Anion exchange chromatography was able to speciate all of the aforementioned arsenic species. Potential inaccurate quantification problem with urine sample containing elevated concentration of AsB, which eluted immediately after As(III) in anion exchange or ion pairing mode, was overcame by introducing a post-column hydride generation (HG) derivatization step. Incorporating HG between HPLC and ICPMS improved sensitivity and specificity by differentiating AsB from hydride-forming arsenic species. This paper emphasizes the usefulness of complementary chromatographic separations in combination with HG-ICPMS to quantitatively determine concentrations of As(III), DMA(V), MMA(V), As(V), and AsB in the sub-microgram per liter range in human urine.     

Capillary electrophoresis with inductively coupled plasma-mass spectrometric and electrospray time of flight mass spectrometric detection for the determination of arsenic species in fish samples

CE was coupled to inductively coupled plasma MS (ICP-MS) and ESI-MS to identify and quantify the arsenic species arsenobetaine (AsB), arsenite (As(III)), arsenate (As(V)), and dimethylarsinic acid (DMA). A GC-flame ionization detector (FID)-based German standard method and ICP-MS were used for validation of the data obtained for arsenobetaine and total arsenic, respectively. LODs obtained with the CE-ESI-TOF-MS method were 1.0x10(-7) M for AsB, 5.0x10(-7) M for DMA, and 1.0x10(-6) M for As(III) and As(V). For the CE-ICP-MS method, LODs were 8.5x10(-8) M for AsB, 9.5x10(-8) M for DMA, 9.3x10(-8) M for As(III), and 6.2x10(-8) M for As(V). While CE-ICP-MS provided high sensitivity and better reproducibility for quantitative measurements, CE-ESI-MS with a TOF mass analyzer proved to be valuable for species identification. With this setup, fish samples were prepared and analyzed and the obtained data were successfully validated with the independent methods.     

Speciation of Arsenic in Rice by Ion Chromatography with Online Anion Suppression and Inductively Coupled Plasma Mass Spectrometry

Arsenic speciation in rice has received attention due to its impact on food safety and human health. In this study, a sensitive method was developed for the determination of inorganic arsenic in rice using online anion suppression with ion chromatography and inductively coupled plasma mass spectrometry. HCl of 0.01?mol/L was the optimal extracting agent, and 38?mmol/L sodium carbonate and 15?mmol/L sodium acetate were used as the mobile phase to separate dimethylarsinic acid (DMA), arsenite, monomethylarsonic acid (MMA), and arsenate. The results showed that there were no significant losses or transformations with the anion suppressor and an improvement in sensitivity. The limits of quantification were 0.1?µg/L for DMA, As(III) and MMA, and 0.2?µg/L for As(V). The procedure was used to determine inorganic arsenic in rice; As(III) and DMA were the primary forms present. The reproducibility from seven measurements showed that the relative standard deviation was less than 1.68%. The recoveries were from 99.76 to 110.42%. The present work offers a new approach for the determination of inorganic arsenic in rice.     

Stability study of As(III), As(V), MMA and DMA by anion exchange chromatography and HG-AFS in wastewater samples

The stability of arsenic species (arsenate [As(V)], monomethylarsonate [MMA], dimethylarsinate [DMA] and arsenite [As(III)]) in two types of urban wastewater samples (raw and treated) was evaluated. Water samples containing a mixture of the different arsenic species were stored in the absence of light at three different temperatures: +4 degrees C, +20 degrees C and +40 degrees C. At regular time intervals, arsenic species were determined by high performance liquid chromatography (HPLC)-hydride generation (HG)-atomic fluorescence spectrometry (AFS). The experimental conditions for the separation of arsenic species by HPLC and their determination by AFS were directly optimised from wastewater samples. As(III), As(V), MMA and DMA were separated on an anion exchange column using phosphate buffer (pH 6.0) as the mobile phase. Under these conditions the four arsenic species were separated in less than 10 min. The detection limits were 0.6, 0.9, 0.9 and 1.8 micro g L(-1) for As(III), DMA, MMA and As(V), respectively. As(V), MMA and DMA were found stable in the two types of urban wastewater samples over the 4-month period at the three different temperatures tested, while the concentration of As(III) in raw wastewater sample decreased after 2 weeks of storage. A greater stability of As(III) was found in the treated urban wastewater sample. As(III) remained unaltered in this matrix at pH 7.27 over the period studied, while at lower pH (1.6) losses of As(III) were detected after 1 month of storage. The results show that the decrease in As(III) concentration with time was accompanied by an increase in As(V) concentration.     

Methods for the separation and quantification of arsenic species in SRM 2669: arsenic species in frozen human urine

Two independent liquid chromatography inductively coupled plasma-mass spectrometry (LC/ICP-MS) methods for the separation of arsenic species in urine have been developed with quantification by standard additions. Seven arsenic species have been quantified in a new NIST frozen human urine Standard Reference Material (SRM) 2669 Arsenic Species in Frozen Human Urine, Levels 1 and 2. The species measured were: arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA), dimethylarsinate (DMA), arsenobetaine (AB), arsenocholine (AC), and trimethylarsine oxide (TMAO). The purity of each arsenic standard used for quantification was measured as well as the arsenic species impurities determined in each standard. Analytical method limits of detection (L _D) for the various species in both methods ranged from 0.2 to 0.8 μg L⁻¹ as arsenic. The results demonstrate that LC/ICP-MS is a sensitive, reproducible, and accurate technique for the determination of low-level arsenic species in urine. Measurements of the arsenic species 3 years after initial production of the SRM demonstrate the stability of the arsenic species in the urine reference material.     

Biodegradation of arsenosugars in marine sediment

In the marine environment, arsenic accumulates in seaweed and occurs mostly in the form of arsenoribofuranosides (often called arsenosugars). This study investigated the degradation pathways of arsenosugars from decaying seaweed in a mesocosm experiment. Brown seaweed (Laminaria digitata) was placed on top of a marine sediment soaked with seawater. Seawater and porewater samples from different depths were collected and analysed for arsenic species in order to identify the degradation products using high‐performance liquid chomatography–inductively coupled plasma mass spectrometry. During the first 10 days most of the arsenic found in the seawater and the shallow sediment is in the form of the arsenosugars released from the seaweed. Dimethylarsenoylethanol (DMAE), dimethylarsinic acid (DMA(V)) and, later, monomethylarsonic acid (MMA(V)) and arsenite and arsenate were also formed. In the deeper anaerobic sediment, the arsenosugars disappear more quickly and DMAE is the main metabolite with 60–80% of the total arsenic for the first 60 days besides a constant DMA(V) contribution of 10–20% of total soluble arsenic. With the degradation of the soluble DMAE the solubility of arsenic decreases in the sediment. The final soluble degradation products (after 106 days) were arsenite, arsenate, MMA(V) and DMA(V). No arsenobetaine or arsenocholine were identified in the porewater. Copyright © 2005 John Wiley & Sons, Ltd.     

Simultaneous separation and determination of six arsenic species in rice by anion‐exchange chromatography with inductively coupled plasma mass spectrometry

The simultaneous separation and determination of arsenite As(III), arsenate As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), arsenobetaine (AsB), and arsenocholine (AsC) in rice samples have been carried out in one single anion‐exchange column run by high‐performance liquid chromatography with inductively coupled plasma mass spectrometry. To estimate the effect of variables on arsenic (As) speciation, the chromatographic conditions including type of competing anion, ionic strength, pH of elution buffer, and flow rate of mobile phase have been investigated by a univariate approach. Under the optimum chromatographic conditions, baseline separation of six As species has been achieved within 10 min by gradient elution program using 4 mM NH₄HCO₃ at pH 8.6 as mobile phase A and 4 mM NH₄HCO₃, 40 mM NH₄NO₃ at pH 8.6 as mobile phase B. The method detection limits for As(III), As(V), MMA, DMA, AsB, and AsC were 0.4, 0.9, 0.2, 0.4, 0.5, and 0.3 μg/kg, respectively. The proposed method has been applied to separation and quantification of As species in real rice samples collected from Hunan Province, China. The main As species detected in all samples were As(III), As(V) and DMA, with inorganic As accounting for over 80% of total As in these samples.     

Speciation of Arsenic in Rice by High-Performance Liquid Chromatography–Hydride Generation-Atomic Fluorescence Spectrometry with Microwave-Assisted Extraction

Arsenic speciation in paddy rice is of considerable interest due to its impact on the food safety and human health. In this study, a simple methodology was developed to simultaneously extract and analyze As species in rice from China. Arsenic species, including arsenite (As(III)), arsenate (As(V)), dimethylarsinic acid (DMA), and monomethylarsonic acid (MMA), were extracted by methanol-water (50:50, v/v) containing 0.02 mol L^?1 nitric acid with a microwave-assisted procedure, and then determined by high performance liquid chromatography–hydride generation-atomic fluorescence spectrometry (HPLC–HG-AFS). The results showed that the method has good efficiency (>90%) for rice, indicating that there were no significant losses or transformations of arsenic during sample treatment and analysis. The limits of quantification (LOQ) of the method were 8.0, 20, 12, and 12 ng g^?1 for As(III), As(V), DMA, and MMA, respectively. When this method was applied to the analysis of rice, As(III) had the highest concentration, followed by DMA, As(V), and MMA. The estimated weekly intake of inorganic As from rice by Chinese people accounted for 11.83% of the provisional tolerable weekly intake. The As speciation results in this study suggest that the risk associated with As in rice to human health may be negligible.     

A systematic study on extraction of total arsenic from down-scaled sample sizes of plant tissues and implications for arsenic species analysis

An easily feasible, species-conserving and inexpensive protocol for the extraction of total arsenic and arsenic species from terrestrial plants was designed and applied to the investigation of accumulation and metabolization of arsenite (As(III)), arsenate (As(V)), monomethylarsonate (MMA(V)), and dimethylarsinate (DMA(V)) by the model plant Tropaeolum majus. In contrast to existing extraction methods hazardous additives and elaborate procedures to enhance the extraction yields were omitted. The proposed protocol is suited to down-scale the sample sizes used for the extractions and to promote a compartmentally resolved analysis of the arsenic distribution within individual leaves, leaf stalks, and stems instead of the conventional extraction of pooled samples. In a two-step extraction, the high extraction efficiencies (85-92%) for arsenic achieved by phosphate buffer from larger amounts (200mg) of homogenized leaf material in a one-step extraction, could be enhanced to 94-100% in a second extraction step. A strong dependence of the arsenic extractability on the type of arsenic species accumulated in the tissue as well as on the type of the tissue (leaf, leaf stalk, stem) was found. For the extraction of 5mm long segments cut from individual leaves without previous homogenization of the plant parts yields between 75 and 93% depending on arsenic species prevailing in the cells were obtained using 1 or 10mM phosphate buffer. The total extraction and analysis protocol was validated using a standard reference material as well as by spiking experiments. The arsenic species analysis by IC/ICPMS revealed a number of nine unidentified metabolites in the plant extracts in addition to the species MMA(V), DMA(V), As(III), and As(V) that were provided to the plants during their growth phase.     

Blue light induces arsenate uptake in the protist Thraustochytrium

The effects of light on arsenic accumulation of Thraustochytrium CHN‐1 were investigated. Thraustochytrium CHN‐1, when exposed to blue light from light‐emitting diodes (LEDs), accumulated arsenate added to its growth medium to a much greater extent than Thraustochytrium cells exposed to fluorescent or red light, or when cultured in the dark. Arsenic compounds in Thraustochytrium CHN‐1 were analyzed by high‐performance liquid chromatography, with an inductively coupled plasma mass spectrometer serving as an arsenic‐specific detector. Arsenate, arsenite, monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA) and arsenosugar were identified. The order of arsenic species in Thraustochytrium CHN‐1 was arsenic(V)> arsenic(III)> MMAA > DMAA at an arsenic concentration of 10 mg dm^?3 in the medium in blue LED light. As it is known that blue light induces the synthesis of certain metabolites in plants and microorganisms, this indicates that the accumulation of arsenic is an active metabolic process. Copyright © 2005 John Wiley & Sons, Ltd.     

Determination of arsenic species by capillary zone electrophoresis with large-volume field-amplified stacking injection.

Determination of arsenic species by large-volume field amplified stacking injection-capillary zone electrophoresis (LV-FASI-CZE) is reported in this paper. Whole column injection was employed. The optimum buffer pH for the separation of weak acids was discussed. It was found that the optimum buffer to analyze the stacked arsenate (As(V)), monomethylarsonate (MMA), and dimethylarsinate (DMA) was 25 mM phosphate at pH 6.5. However, the optimum buffer to analyze the concentrated arsenite (As(III)) was 20 mM phosphate - 10 mM borate at pH 9.28. The limits of detection of the method developed were 0.026 mg/L for As(III), 0.023 mg/L for As(V), 0.043 mg/L for MMA, and 0.018 mg/L for DMA. An enrichment factor of 34-100 for several arsenic species was obtained. In the end, this method was applied to determine the arsenic concentration in the environmental reference materials to show the usefulness of the method developed.     

Evaluation of atomic fluorescence spectrometry as a sensitive detection technique for arsenic speciation

The potential of coupling anion-exchange high-performance liquid chromatography, hydride generation and atomic fluorescence spectrometry (HPLC–HG–AFS) for arsenic speciation is considered. The effects of hydrochloric acid and sodium tetrahydroborate concentrations on signal-to-background ratio, as well as argon and hydrogen flow rates, were investigated. Detection limits for arsenite, dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and arsenate were 0.17, 0.45, 0.30 and 0.38 μg l⁻¹, respectively, using a 20-μl loop. Linearity ranges were 0.1–500 ng for As(III) and MMA (as arsenic), and 0.1–800 ng for DMA and As(V) (as arsenic). Arsenobetaine (AsB) was also determined by introducing an on-line photo-oxidation step after the chromatographic separation. In this case the limits of detection and linear ranges for the different species studied were similar to the values obtained previously for As(V). The technique was tested with a human urine reference material and a volunteer's sample. © 1998 John Wiley & Sons, Ltd.     

微波辅助提取-液相色谱-氢化物发生-原子荧光光谱法分析沉积物中砷的形态

采用微波辅助提取-液相色谱-氢化物发生-原子荧光光谱法(LC-HG-AFS)联用技术分析了太湖沉积物中砷的形态[亚砷酸(As(III))、二甲基砷酸钠(DMA)、一甲基砷酸二钠(MMA)和砷酸As(V)]。测得沉积物中以无机砷为主,且以As(V)居多。选定以1mol/L的磷酸和0.1mol/L抗坏血酸为提取液,在微波辅助萃取(功率为60W,时间12min)下,萃取率达79.84%～91.57%,回收率在94.78%～107.6%之间。4种砷的形态在0～160μg/L之间时线性良好,检测限为0.6～2.3μg/L,相对标准偏差RSD为1.62%～2.20%。方法具有简便、快速、灵敏的特点。     

Determination of urinary arsenic and impact of dietary arsenic intake

An analytical method based on microwave decomposition and flow injection analysis (FIA) coupled to hydride generation atomic absorption spectrometry (HGAAS) is described. This is used to differentiate arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) from organoarsenic compounds usually present in seafood. Without microwave digestion, direct analysis of urine by HGAAS gives the total concentration of As(III), As(V), MMA and DMA because organoarsenic compounds such as arsenobetaine, usually found in most seafood, are not reducible upon treatment with borohydride and therefore cannot be determined by using the hydride generation technique. The microwave oven digestion procedure with potassium persulfate and sodium hydroxide as decomposition reagents completely decomposes all arsenicals to arsenate and this can be measured by HGASS. Microwave decomposition parameters were studied to achieve efficient decomposition and quantitative recovery of arsenobetaine spiked into urine samples. The method is applied to the determination of urinary arsenic and is useful for the assessment of occupational exposure to arsenic without intereference from excess organoarsenicals due to the consumption of seafood. Analysis of urine samples collected from an individual who ingested some seafood revealed that organoarsenicals were rapidly excreted in urine. After the ingestion of a 500-g crab, a 10-fold increase of total urinary arsenic was observed, due to the excretion of organoarsenicals. The maximum arsenic concentration was found in the urine samples collected approximately between 4 to 17 hr after eating seafood. However, the ingestion of organoarsenic-containing seafoods such as crab, shrimp and salmon showed no effect on the urinary excretion of inorganic arsenic, MMA and DMA.     

Arsenic Speciation Analysis in Solutions Treated with Zeolites

Experiments have been carried out to study the behaviour of organoarsenicals treated with zeolites by means of speciation analysis. IC-ICP-MS was applied to identify and quantify arsenite, arsenate and the following organoarsenicals: monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), trimethylarsine oxide (TMAO), tetramethylarsonium bromide (TMA⁺), arsenobetaine (AsB) and arsenocholine (AsC). Zeolites loaded with ferrous ions did not significantly increase the retention of inorganic arsenic species compared to the native zeolites, while there was a ten-fold removal of arsenate relating to arsenite. The formation of As(V) and DMA in the leachates containing clinoptilolites and mordenites was confirmed in the presence of natural and synthetic zeolites. Arsenobetaine and arsenocholine yielded higher levels of arsenate than the methylated species.