Coupling nanoliter high‐performance liquid chromatography to inductively coupled plasma mass spectrometry for arsenic speciation

Nanoliter high‐performance liquid chromatography shows low consumption of solvents and samples, offering one of the best choices for arsenic speciation in precious samples in combination with inuctively coupled plasma mass spectrometry. A systematic investigation on coupling nanoliter high‐performance liquid chromatography to inductively coupled plasma mass spectrometry from instrument design to injected sample volume and mobile phase was performed in this study. Nanoflow mobile phase was delivered by flow splitting using a conventional high‐pressure pump with reuse of mobile phase waste. Dead volume was minimized to 60 nL for the sheathless interface based on the previously developed nanonebulizer. Capillary columns for nanoliter high‐performance liquid chromatography were found to be sensitive to sample loading volume. An apparent difference was also found between the mobile phases for nanoliter and conventional high‐performance liquid chromatography. Baseline separation of arsenite, arsenate, monomethylarsenic, and dimethylarsenic was achieved within 11 min on a 15 cm C₁₈ capillary column and within 12 min on a 25 cm strong anion exchange column. Detection limits of 0.9–1.8 μg/L were obtained with precisions variable in the range of 1.6–4.2%. A good agreement between determined and certified values of a certified reference material of human urine (GBW 09115) validated its accuracy along with good recoveries (87–102%).     

Solvent bar microextraction combined with electrothermal vaporization inductively coupled plasma mass spectrometry for the speciation of inorganic arsenic in water samples

A new method of solvent bar microextraction (SBME) combined with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the speciation of As(III) and As(V) in water samples was developed. The method is based on the chelation of As(III) and ammonium pyrrolidine dithiocarbamate (APDC) under the selected conditions, and the As(III)-PDC complex could be extracted into the organic phase, while As(V) remained in aqueous solution. The post-extraction organic phase was directly injected into ETV-ICP-MS for determination of As(III) with the use of iridium as permanent chemical modifier. As(V) was reduced to As(III) by L-cysteine and was then subjected to SBME prior to total As determination. The assay of As(V) was based on subtracting As(III) from total As. The factors affecting on the SBME, such as organic solvent, sample pH, chelating reagent concentration, stirring rate and extraction time, and chemical modification of iridium in ETV-ICP-MS have been studied. Under the optimized conditions, the enrichment factor of 220-fold could be achieved in 15 min extraction, the limit of detection (LOD) for As(III) was 0.32 pg mL^− 1, and the relative standard deviation (RSD) was 8.8% (0.1 ng mL^− 1, n = 9). Compared with hollow fiber liquid phase microextraction (HF-LPME), SBME has a higher enrichment factor and faster extraction kinetics. In order to validate the accuracy of the method, a Certified Reference Material of GSBZ50004-88 (No. 200420) water sample was analyzed and the results obtained were in good agreement with the certified values. The developed method was also applied to the speciation of inorganic As in environmental waters with satisfactory results.     

毛细管电泳-电感耦合等离子体质谱法测定藻类中6种不同形态的砷化合物

建立了一种利用毛细管电泳与电感耦合等离子体质谱联用技术(CE-ICP-MS)分析检测6种不同形态砷化合物的方法。详细研究了缓冲溶液的种类、pH值和浓度,分离电压以及进样时间等因素对6种砷化合物的分离度、灵敏度和重现性等的影响。结果表明,在最佳条件下,三价砷(As3+)、一甲基砷(MMA)、二甲基砷(DMA)、五价砷(As5+)、砷胆碱(AsC)和砷甜菜碱(AsB)6种化合物在25 min内得到完全分离。6次平行测定中,6种砷化合物峰面积的相对标准偏差(RSD)为3%～5%,检出限(以As计)(3倍信噪比)为0.08～0.12 μg/L。应用该方法成功地对海带中6种砷化合物进行了分析,回收率为90%～103%。该方法具有耗时短、灵敏度高、样品消耗量少、稳定性好等优点,可用于藻类样品中不同形态砷化合物的分析。     

Determination of different arsenic species in food‐grade spirulina powder by ion chromatography combined with inductively coupled plasma mass spectrometry

A “two‐step” pressurized microwave‐assisted extraction method coupled with ion chromatography with inductively coupled plasma mass spectrometry for the determination of different arsenic species in spirulina samples was developed. The extraction method used H₂O₂/H₂O (1:5, v/v) as solvent to extract all arsenic species except arsenite, which was extracted by using water as solvent. The extraction method had a satisfactory recovery (>96%) and took a short time (20.0 min). With our method, all arsenic species in spirulina samples were completely separated and determined with recoveries of 84–105% and relative standard deviations of 2–4%. Food‐grade spirulina powder samples from seven provinces (Inner Mongolia, Zhejiang, Fujian, Hainan, Yunnan, Jiangsu, and Guangxi) in China were analyzed using the optimized protocol. Arsenate was detected at the concentration range of 170–394 ng/g in all the spirulina samples. Dimethylarsinic acid was detected at the concentration range of 32–839 ng/g in spirulina from above‐six provinces except Guangxi. Monomethylarsonic acid (67 ± 3 ng/g) was detected only in spirulina from Yunnan province. Arsenite was detected at the concentration range of 28–147 ng/g in spirulina from above five provinces except Hainan and Guangxi. Five unknown organic arsenic species were found in spirulina from above six provinces except Guangxi.     

Determination of arsenic, lead, selenium and tin in sediments by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry using Ru as permanent modifier and NaCl as a carrier

A procedure for the determination of As, Pb, Se and Sn in sediment slurries by electrothermal vaporization inductively coupled plasma mass spectrometry is proposed. The slurry, 1 mg ml⁻¹, is prepared by mixing the sample ground to a particle size 50 μm with 5% v/v nitric and 1% v/v hydrofluoric acids in an ultrasonic bath. The slurry was homogenized with a constant flow of argon in the autosampler cup, just before transferring an aliquot to the graphite furnace. The tube was treated with Ru as a permanent modifier, and an optimized mass of 1 μg of NaCl was added as a physical carrier. The pyrolysis temperature was optimized through pyrolysis curves, and a compromised temperature of 800 °C was used; the vaporization temperature was 2300 °C. The effect of different acid concentrations in the slurry on the analyte signal intensities was also evaluated. The accuracy of the method was assured by the analysis of certified reference sediments MESS-2, PACS-2 and HISS-1 from the National Research Council Canada, SRM 2704 and SRM 1646a from the National Institute of Standards and Technology and RS-4 from a round robin test, using external calibration with aqueous standards prepared in the same medium as the slurries. The obtained concentrations were in agreement with the certified values according to the Student's t-test for a confidence level of 95%. The detection limits in the samples were: 0.17 μg g⁻¹ for As; 0.3 μg g⁻¹ for Pb; 0.05 μg g⁻¹ for Se and 0.28 μg g⁻¹ for Sn. The precision found for the different sediment samples, expressed as R.S.D. was 1–8% for As, 2–9% for Pb, 6–12% for Se and 3–8% for Sn (n=5).     

以DDTP为化学改进剂,低温电热蒸发ICP-OES 测定环境样品中的钴和镍

提出了以二乙基二硫代磷酸（DDTP）为化学改进剂,低温电热蒸发ICP-OES法检测环境样品中的钴和镍,对影响金属螯合物形成及其蒸发条件进行了考察与优化。试验结果表明,在pH〉4．5,DDTP质量浓度为8．0g／L的条件下,试剂DDTP可与钴（Ⅱ）,镍（Ⅱ）形成稳定的螯合物。并以螯合物的气态形式从石墨炉中。定量蒸发和传输至等离子体中,用于ETV-ICP-OES检测。钴（Ⅱ）和镍（Ⅱ）的检出限分别为19．6和17．3μg／L,与常规的ETV-ICP-OES法相比待测元素的蒸发温度降低了1200℃左右。方法已用于土壤和水系沉积物标准样品中钴和镍的检测。     

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.     

Polymer monolithic capillary microextraction combined on‐line with inductively coupled plasma MS for the determination of trace rare earth elements in biological samples

A rapid and sensitive method based on polymer monolithic capillary microextraction combined on‐line with microconcentric nebulization inductively coupled plasma MS has been developed for the determination of trace/ultratrace rare earth elements in biological samples. For this purpose, the iminodiacetic acid modified poly(glycidyl methacrylate‐trimethylolpropane trimethacrylate) monolithic capillary was prepared and characterized by SEM and FTIR spectroscopy. Factors affecting the extraction efficiency, such as sample pH, sample flow rate, sample/eluent volume, and coexisting ions were investigated in detail. Under the optimal conditions, the LODs for rare earth elements were in the range of 0.08 (Er) to 0.97 ng/L (Nd) with a sampling frequency of 8.5 h^?1, and the RSDs were between 1.5% (Sm) and 7.4% (Nd) (c = 20 ng/L, n = 7). The proposed method was successfully applied to the analysis of trace/ultratrace rare earth elements in human urine and serum samples, and the recoveries for the spiked samples were in the range of 82–105%. The developed method was simple, rapid, sensitive, and favorable for the analysis of trace/ultratrace rare earth elements in biological samples with limited sample volume.     

Thermo-responsive polymer coated fiber-in-tube capillary microextraction and its application to on-line determination of Co, Ni and Cd by inductively coupled plasma mass spectrometry (ICP-MS)

The poly(N-isopropylacrylamide) (PNIPA) gel is a widely studied thermo-responsive material that exhibits discontinuous change in volume when the external temperature is increased. In this paper, PNIPA gel was prepared and applied as a novel polymer coating for fiber-in-tube capillary microextraction of trace Co, Ni and Cd followed by on-line ICP-MS detection. The PNIPA coating was synthesized by using ethylene triethoxysilane (ETEOS) as the cross-linking agent under acidic conditions. This siloxane incorporated PNIPA gel achieves a dramatically rapid response rate when the external temperature is changed. The micro-structure of PNIPA coating was examined by scanning electron micrograph (SEM). Various experimental parameters including pH, temperature, sample flow rate and volume, elution solution and interfering ions affecting the extraction of the target analytes have been carefully investigated and optimized. Under the optimized conditions, the limits of detection were 0.45, 4.6 and 6.9 ng L⁻¹ for Co, Ni and Cd, respectively. With a sampling frequency of 13 h⁻¹, the relative standard deviations (RSDs) for Co, Ni and Cd were 4.8, 5.1 and 6.4% (C = 1 μg L⁻¹, n = 7), respectively. The proposed method had been successfully applied to the determination of Co, Ni and Cd in human urine. To validate the proposed method, certified reference materials of NIES No. 10-b rice flour and GBW07601 (GSH-1) human hair were analyzed and the determined values were in a good agreement with the certified values. The PNIPA coated fiber-in-tube capillary can be reused for more than 150 times without decreasing the extraction efficiency.     

Simultaneous separation and determination of thallium in water samples by high‐performance liquid chromatography with inductively coupled plasma mass spectrometry

An analytical method for separation and determination of thallium species in water using high‐performance liquid chromatography with inductively coupled plasma mass spectrometry was developed. The composition and concentration of mobile phase, injection volume, and pH value were optimized respectively with an anion or cation exchange column. The results showed that Tl(I) and Tl(III) were effectively separated using anion exchange column Hamilton PRP‐X100, with the mobile phase consisting of 200 mmol/L ammonium acetate and 10 mmol/L diethylenetriaminepentaacetic acid (pH = 4.2). When using a Dionex cation exchange guard column, CS12A, 15 mmol/L HNO₃, and 3 mmol/L diethylenetriaminepentaacetic acid as the mobile phase, Tl(I) and Tl(III) could be effectively separated. The detection limits of the methods were 3–6 and 9–12 ng/L, respectively. In a solution containing Fe ions and oxalic acid, a significant quantity of Tl(I) was oxidized. Fe ions and oxalic acid in the water samples did not interfere with high‐performance liquid chromatography‐inductively coupled plasma mass spectrometry measurement results.     

Hollow fiber liquid phase microextraction combined with electrothermal atomic absorption spectrometry for the speciation of arsenic (III) and arsenic (V) in fresh waters and human hair extracts

A new method of hollow fiber liquid phase microextraction (HF-LPME) using ammonium pyrrolidine dithiocarbamate (APDC) as extractant combined with electrothermal atomic absorption spectrometry (ETAAS) using Pd as permanent modifier has been described for the speciation of As(III) and As(V). In a pH range of 3.0-4.0, the complex of As(III)-APDC complex can be extracted using toluene as the extraction solvent leaving As(V) in the aqueous layer. The post extraction organic phase was directly injected into ETAAS for the determination of As(III). To determine total arsenic in the samples, first As(V) was reduced to As(III) by l-cysteine, and then a microextraction method was performed prior to the determination of total arsenic. As(V) assay was based on subtracting As(III) form the total arsenic. All parameters, such as pH of solution, type of organic solvent, the amount of APDC, stirring rate and extraction time, affecting the separation of As(III) from As(V) and the extraction efficiency of As(III) were investigated, and the optimized extraction conditions were established. Under optimized conditions, a detection limit of 0.12 ng mL⁻¹ with enrichment factor of 78 was achieved. The relative standard deviation (R.S.D.) of the method for five replicate determinations of 5 ng mL⁻¹ As(III) was 8%. The developed method was applied to the speciation of As(III) and As(V) in fresh water and human hair extracts, and the recoveries for the spiked samples are 86-109%. In order to validate the developed method, three certified reference materials such as GBW07601 human hair, BW3209 and BW3210 environmental water were analyzed, and the results obtained were in good agreement with the certified values provided.     

Solid phase extraction for analysis of biogenic carbonates by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS): an investigation of rare earth element signatures in otolith microchemistry

Uptake of trace elements into fish otoliths is governed by several factors such as life histories and environment in addition to stock and species differences. In an attempt to elucidate the elemental signatures of rare earth elements (REEs) in otoliths, a solid phase extraction (SPE) protocol was used in combination with electrothermal vaporization (ETV) as a sample introduction procedure for the determinations by inductively coupled plasma quadrupole mass spectrometry (ICP-MS). Effects of various parameters, such as carrier gas flow rate, atomization temperature and chemical modification, were examined for optimization of the conditions by ETV-ICP-MS. Atomization was achieved at 2800 °C. Lower temperatures (i.e. 2600 °C) resulted in severe memory problems due to incomplete atomization. Palladium was used as a chemical modifier. It was found that an increase in Pd concentration up to 0.5 μg in the injection volume (70 μl) led up to four-fold enhancement in the integrated signals. This phenomenon is attributed to the carrier effect of Pd rather than the stabilization since no significant losses were observed for high temperature drying around 700 °C even in the absence of Pd. Preconcentration was performed on-line at pH 5 by using a mini-column of Toyopearl AF-Chelate 650M chelating resin, which also eliminated the calcium matrix of otolith solutions. After preconcentration of 6.4 ml of solution, the concentrate was collected in 0.65 ml of 0.5% (v/v) HNO₃ in autosampler cups, and then analyzed by ETV-ICP-MS. The method was validated with the analysis of a fish otolith certified reference material (CRM) of emperor snapper, and then applied to samples. Results obtained from otoliths of fish captured in the same habitat indicated that otolith rare earth element concentrations are more dependent on environmental conditions of the habitat than on species differences.     

Imaging of metals in biological tissue by laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS): state of the art and future developments

Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) is well established as a sensitive trace and ultratrace analytical technique with multielement capability for bioimaging of metals and studying metallomics in biological and medical tissue. Metals and metalloproteins play a key role in the metabolism and formation of metal‐containing deposits in the brain but also in the liver. In various diseases, analysis of metals and metalloproteins is essential for understanding the underlying cellular processes. LA–ICP–MS imaging (LA–ICP–MSI) combined with other complementary imaging techniques is a sophisticated tool for investigating the regional and cellular distribution of metals and related metal‐containing biomolecules. On the basis of successful routine techniques for the elemental bioimaging of cryosections by LA–ICP–MSI with a spatial resolution between 200 and ~10 µm, the further development used online laser microdissection ICP–MSI to study the metal distribution in small biological sample sections (at the cellular level from 10 µm to the submicrometer range). The use of mass spectrometric imaging of metals and also nonmetals is demonstrated on a series of biological specimens. This article discusses the state of the art of bioimaging of metals in thin biological tissue sections by LA–ICP–MSI with spatial resolution at the micrometer scale, future developments and prospects for quantitative imaging techniques of metals in the nanometer range. In addition, combining quantitative elemental imaging by LA/laser microdissection–ICP–MSI with biomolecular imaging by matrix‐assisted laser desorption/ionization–MSI will be challenging for future life science research. Copyright © 2013 John Wiley & Sons, Ltd.     

Separation of selenium species and their sensitive determination in rice samples by ion‐pairing reversed‐phase liquid chromatography with inductively coupled plasma tandem mass spectrometry

A highly sensitive method was developed for the simultaneous separation and determination of organic and inorganic selenium species in rice by ion‐pairing reversed‐phase chromatography combined with inductively coupled plasma tandem mass spectrometry. To achieve a good separation of these species, a comparison between anion‐exchange chromatography and ion‐pairing reversed‐phase chromatography was performed. The results indicated that ion‐pairing reversed‐phase chromatography was more suitable due to better separation and higher sensitivity for all analytes. In this case, a StableBond C18 column proved to be more robust or to have a better resolution than other C18 columns, when 0.5 mM tetrabutylammonium hydroxide and 10 mM ammonium acetate at pH 5.5 were used as the mobile phase. Moreover, an excellent sensitivity was obtained in terms of interferences by means of tandem mass spectrometry in the hydrogen mode. The detection limits were 0.02–0.12 μg/L, and recoveries of five selenium species were 75–114%, with relative standard deviations ≤ 9.4%. This method was successfully applied to the analysis of rice samples. Compared with previous studies, the proposed method not only gave comparable results when used for measuring selenium‐enriched rice, but it can provide greater sensitivity for the detection of low concentrations of selenium species in rice.     

Gel electrophoresis in combination with laser ablation–inductively coupled plasma mass spectrometry to quantify the interaction of cisplatin with human serum albumin

Cisplatin and its second and third generation analogues are widely used in the treatment of cancer. To study their reactions with proteins, we present a method based on SDS‐PAGE separation and laser ablation–inductively coupled plasma‐mass spectrometry (LA–ICP‐MS) for platinum detection in the reaction between human serum albumin (HSA) and cisplatin. We developed matrix‐matched standards of HSA/cisplatin mixtures and used them to quantify the amount of adducts formed at different HSA:cisplatin ratios. We noted that cisplatin incubation with HSA resulted in the formation of higher order HSA n‐mers, depending on the amount of cisplatin added. This caused a depletion of the HSA dimer bands, while the majority of HSA was present as the monomer. Inducing the formation of such higher molecular weight species may have an impact on the mode of action of metallodrugs.     

On-line preconcentration and separation of Co, Ni and Cd via capillary microextraction on ordered mesoporous alumina coating and determination by inductively plasma mass spectrometry (ICP-MS)

In this paper, an ordered mesoporous alumina coating was prepared and applied to capillary microextraction (CME) of trace Co, Ni and Cd for the first time. The coated capillary was used for on-line coupling CME with inductively plasma mass spectrometry (ICP-MS) for the determination of trace metals of Co, Ni and Cd. The porous structure of Al₂O₃ coating was examined by SEM and TEM. The effects of the extraction parameters including pH, sample flow rate and volume, elution solution and interfering ions on the recovery of analytes have been investigated and optimized. Under the optimized conditions, the limits of detection were 0.33, 1.5 and 1.4 ng L⁻¹ for Co, Ni and Cd, respectively, with a preconcentration factor of 10 times. The precisions for all investigated elements were 2.7, 4.1 and 2.5% (c = 0.05 ng L⁻¹, n = 7), for Co, Ni and Cd, respectively, and the sample frequency was 8 h⁻¹.The proposed method was successfully applied for the analysis of trace metals in water, rice and urine samples with the recovery of 94-105%. In order to validate the proposed method, two certified reference materials of GBW 0913 human urine and NIES No.10-b rice flour were analyzed, and the determination values are in good agreement with the certified values. The ordered mesoporous Al₂O₃ coated capillary can be used more than 20 times without decreasing the extraction efficiency.     

Cadmium (II) imprinted 3-mercaptopropyltrimethoxysilane coated stir bar for selective extraction of trace cadmium from environmental water samples followed by inductively coupled plasma mass spectrometry detection

Cd(II) imprinted 3-mercaptopropyltrimethoxysilane (MPTS)-silica coated stir bar was prepared by sol–gel technique combining with a double-imprinting concept for the first time and was employed for stir bar sorptive extraction (SBSE) of trace Cd(II) from water samples followed by inductively coupled plasma mass spectrometry (ICP-MS) detection. A tetramethoxysilane (TMOS) coating was first in situ created on the glass bar surface. Afterward, a sol solution containing MPTS as the functional precursor, ethanol as the solvent and both Cd(II) and surfactant micelles (cetyltrimethylammonium bromide, CTAB) as the template was again coated on the TMOS bar. The structures of the stir bar coating were characterized by FT-IR spectroscopy. Round-bottom vial was used for the extraction of Cd(II) by SBSE to avoid abrasion of stir bar coatings. The factors affecting the extraction of Cd(II) by SBSE such as pH, stirring rate and time, sample/elution volume and interfering ions have been investigated in detail, and the optimized experimental parameters were obtained. Under the optimized conditions, the adsorption capacities of non-imprinted and imprinted coating stir bars were found to be 0.5 μg and 0.8 μg bar⁻¹. The detection limit (3σ) based on three times standard deviations of the method blanks by 7 replicates was 4.40 ng L⁻¹ and the relative standard deviation (RSD) was 3.38% (c = 1 μg L⁻¹, n = 7). The proposed method was successfully applied for the analysis of trace Cd(II) in rain water, East Lake and Yangtze River water. To validate the proposed method, certified reference material of GSBZ 50009-88 environmental water was analyzed and the determined value is in a good agreement with the certified value. The developed method is rapid, selective, sensitive and applicable for the analysis of trace Cd(II) in environmental water samples.