Electrical field-flow fractionation for metal nanoparticle characterization

The potential of electrical field-flow fractionation (ElFFF) for characterization of metal nanoparticles was investigated in this study. Parameters affecting separation and retention such as applied DC voltage and flow rate were examined. Nanoparticles with different types of stabilizers, including citrate and tannic acid, were investigated. Changes to the applied voltage showed a significant influence on separation in ElFFF, and varying flow rate was used to improve plate heights in the experiments. For nanoparticles of a fixed size, the separation was based primarily on electrophoretic mobility. Particles with low electrophoretic mobility elute earlier. Therefore, citrate stabilized gold nanoparticles (-2.72 × 10(-4) cm(2) V(-1) s(-1)) eluted earlier than tannic acid stabilized gold nanoparticles (-4.54 × 10(-4) cm(2) V(-1) s(-1)) of the same size. In addition, ElFFF can be used for characterization of gold nanoparticles with different particle sizes including 10, 20, and 40 nm with a fixed stabilizing agent. For a specific separation condition, the separation of 10, 20, and 40 nm gold nanoparticles was clearly based on the particle size as opposed to the electrophoretic mobility, as the elution order was in order of decreasing mobility for 10 (-4.54 × 10(-4) cm(2) V(-1) s(-1)), 20 (-3.97 × 10(-4) cm(2) V(-1) s(-1)), and 40 (-3.76 × 10(-4) cm(2) V(-1) s(-1)) nm particles, respectively.     

HPLC determination of cyanuric acid in swimming pool waters using phenyl and confirmatory porous graphitic carbon columns

The chlorinated salts of cyanuric acid have found an important role in recreational swimming pool waters across the United States. Upon application to pool water, they can (1) release disinfectant chlorine or (2) stabilize the free available chlorine by acting as chlorine reservoirs in the form of cyanuric acid, preventing the photolytic destruction of residual chlorine by sunlight. Recommended levels of the cyanuric acid stabilizer are in the 10-100 mg/L concentration range according to the National Swimming Pool Foundation (San Antonio, TX). Two isocratic HPLC methods with UV detection (213 nm) employing phenyl and porous graphitic carbon (PGC) columns and phosphate buffer eluents (pH 6.7 and pH 9.1, respectively) were developed to accurately measure cyanuric acid in swimming pools. The two methods allowed fast separation and detection of the stabilizer in 4 (phenyl) and 8 (PGC) min. Both methods offered practical sensitivities with method detection limits of 0.07 (phenyl) and 0.02 mg/L (PGC). Neither one of the two methods required the use of sample cleanup cartridges. They exhibit chromatograms with excellent baseline stability enabling low-level quantitation. Most important, the PGC column had a useful lifetime of five months and 500 sample analyses/column. Eleven pool water samples were fortified with 4.8-50.0 mg/L stabilizer, and the average recovery was 99.8%. Finally, statistical analysis on the relative precisions of the two methods indicated equivalence at the 0.05 critical level.     

On-column derivatization using redox activity of porous graphitic carbon stationary phase: an approach to enhancement of separation selectivity of liquid chromatography

A new on-column derivatization method based on the redox activity of porous graphitic carbon (PGC) packing materials was presented for enhancement of separation selectivity of HPLC. Two PGC packing materials were used as the solid redox agents as well as the stationary phase, and their redox activities were investigated using trans-1,2-diaminocyclohexanetetraacetate (DCTA) complexes of some metal ions as probe compounds. It was found that the redox property of PGC was modified by treating them with a solution containing a reducing agent, sodium sulfite or hydroxylammonium chloride. The original PGC packings oxidized Co(II)-DCTA to Co(III)-DCTA during elution, while the PGC treated with a reducing agent showed reduction activity converting Co(III)-DCTA to Co(II)-DCTA. These two cobalt complexes do not form their individual chromatographic zones but migrate as a single zone of their mixture on the PGC column contrary to the chromatographic behavior on a C18 bonded silica, on which Co(II)-DCTA and Co(III)-DCTA can be separated. Treatment of the PGC column with a reducing agent solution transforms the oxidative activity of the original PGC packing to a reductive one from the upper part of the column, so that the retention time of the cobalt complex can be controlled by changing the volume of the reducing agent solution to be used for treatment of the PGC column. The selective separation and determination of cobalt in a reference manganese nodule sample by the developed method was demonstrated.     

Separation and preconcentration of inorganic arsenic species in natural water samples with 3-(2-aminoethylamino) propyltrimethoxysilane modified ordered mesoporous silica micro-column and their determination by inductively coupled plasma optical emission spectrometry

A simple and sensitive method using micro-column packed with 3-(2-aminoethylamino) propyltrimethoxysilane (AAPTS) modified ordered mesoporous silica combined with inductively coupled plasma optical emission spectrometry (ICP-OES) for the speciation of inorganic arsenic (As(III) and As(V)) has been developed. The adsorption behaviors of As(III) and As(V) on AAPTS modified ordered mesoporous silica were investigated. It was found that As(V) can be selectively adsorbed on the micro-column within pH of 3-9, while As(III) could not be retained in the studied pH range and passed through the micro-column directly. Total inorganic arsenic was extracted after the oxidation of As(III) to As(V) with 50.0 micromol L(-1) KMnO(4). The assay of As(III) was based on subtracting As(V) from total As. The effect of various parameters on the separation/preconcentration of As(III) and As(V) have been investigated and the optimal experimental conditions were established. The adsorption capacity of AAPTS modified ordered mesoporous silica for As(V) was found to be 10.3 mg g(-1). The detection limit of the method for As(V) was 0.05 microg L(-1) with an enrichment factor of 100, and the relative standard deviation (R.S.D.) was 5.7% (n=7, C=1.0 microg L(-1)). In order to validate the developed method, a certified reference material GSBZ50004-88 environmental water sample was analyzed and the determined values were in good agreement with the certified values. The proposed method was successfully applied to the speciation analysis of inorganic arsenic in natural water samples.     

Development of a method for total inorganic arsenic analysis using anodic stripping voltammetry and a Au-coated, diamond thin-film electrode

We demonstrate that a Au-coated, boron-doped, diamond thin-film electrode provides a sensitive, reproducible, and stable response for total inorganic arsenic (As(III) and As(V)) using differential pulse anodic stripping voltammetry (DPASV). As is preconcentrated with Au on the diamond surface during the deposition step and detected oxidatively during the stripping step. Au deposition was uniform over the electrode surface with a nominal particle size of 23 +/- 5 nm and a particle density of 109 cm-2. The electrode and method were used to measure the As(III) concentration in standard and river water samples. The detection figures of merit were compared with those obtained using conventional Au-coated glassy carbon and Au foil electrodes. The method was also used to determine the As(V) concentration in standard solutions after first being chemically reduced to As(III) with Na2SO3, followed by the normal DPASV determination of As(III). Sharp and symmetric stripping peaks were generally observed for the Au-coated diamond electrode. LODs were 0.005 ppb (S/N = 3) for As(III) and 0.08 ppb (S/N = 3) for As(V) in standard solutions. An As(III) concentration of 0.6 ppb was found in local river water. The relative standard deviation of the As stripping peak current for river water was 1.5% for 10 consecutive measurements and was less than 9.1% over a 10-h period. Excellent electrode response stability was observed even in the presence of up to 5 ppm of added humic acid. In summary, the Au-coated diamond electrode exhibited better performance for total inorganic As analysis than did Au-coated glassy carbon or Au foil electrodes. Clearly, the substrate on which the Au is supported influences the detection figures of merit.     

Adsorption capacities of poorly crystalline Fe minerals for antimonate and arsenate removal from water: adsorption properties and effects of environmental and chemical conditions

Antimonate (Sb(V)) and arsenate (As(V)) pollution frequently occur in aqueous environment and can be absorbed by poorly crystalline Fe minerals (i.e., ferrihydrite). In this study, the adsorption capacity and rate of Sb(V) and As(V) from water with fresh ferrihydrite were compared by establishing adsorption isotherms and kinetics, and the effects of ferrihydrite dosage, solution pH and humic substances on Sb(V) and As(V) adsorption were also investigated. The adsorption isotherms results showed that the equilibrium and maximum adsorption capacities of Sb(V) on ferrihydrite were approximately equal to those of As(V) under different temperatures. The results of adsorption kinetics showed that the adsorption rate of Sb(V) derived from the pseudo-second-order equation was much lower than that of As(V). In addition, the adsorption capacity and rate of Sb(V) and As(V) were greatly affected by various ferrihydrite dosage and solution pHs. The presence of humic acid and fulvic acid (FA) significantly affected the adsorption process of Sb(V) due to competition adsorption, whereas the adsorption properties of As(V) were little affected by FA under this experimental conditions.     

Volatile analytes formed from arsenosugars: determination by HPLC-HG-ICPMS and implications for arsenic speciation analyses

It is generally accepted that the use of the hydride generation method to produce volatile analytes from arsenic compounds is restricted to the two inorganic forms (As(III) and As(V)) and the three simple methylated species methylarsonate (MA), dimethylarsinate (DMA), and trimethylarsine oxide. We report here that arsenosugars, major arsenic compounds in marine organisms, produce volatile analytes by the hydride generation (HG) method without a prior mineralization/oxidation step and that they can be quantitatively determined using HPLC-HG-ICPMS. The hydride generation efficiency depends on the type of hydride generation system and is influenced by the concentration of HCl and NaBH(4). For the four arsenosugars investigated, the hydride generation efficiencies were approximately 21-28% (or 4-6%, depending on the HG system) that obtained for As(III) under conditions optimized for As(III). This hydride efficiency was less than that shown by MA ( approximately 68% relative to As(III)) and DMA ( approximately 75%) but greater than that displayed by As(V) ( approximately 18%). Analysis of two species of brown algae, Fucus serratus and Hizikia fusiforme, by HPLC-HG-ICPMS produced results comparable with those obtained from other techniques used in our laboratory (HPLC-ICPMS and LC-ESMS for F. serratus) and with results from other laboratories taking part in a round robin exercise (H. fusiforme). This study shows for the first time the quantitative determination of arsenosugars using the hydride generation method without a decomposition step and has considerable implications for analytical methods for determining inorganic arsenic based on the formation of volatile hydrides.     

Biosorption of palladium(II) from aqueous solution by moss (Racomitrium lanuginosum) biomass: equilibrium, kinetic and thermodynamic studies

Arsenite (As(III)) and arsenate (As(V)) removal by direct contact membrane distillation (DCMD) were investigated with self-made polyvinylidene fluoride (PVDF) membranes in the present work. Permeability and ion rejection efficiency of the membrane were tested before the arsenic removal experiments. A maximum permeate flux 20.90 kg/m(2)h was obtained, and due to the hydrophobic property, the PVDF membrane had high rejection of inorganic anions and cations which was independent of the solution pH and the temperature. The experimental results indicated that DCMD process had higher removal efficiency of arsenic than pressure-driven membrane processes, especially for high-concentration arsenic and arsenite removal. The experimental results indicated that the permeate As(III) and As(V) were under the maximum contaminant limit (10 microg/L) until the feed As(III) and As(V) achieved 40 and 2000 mg/L, respectively. The 250 h simultaneous DCMD performance of 0.5mg/L As(III) and As(V) solution was carried out, respectively. The permeate arsenic was not detected during the process which showed the PVDF membrane had stable arsenic removal efficiency. Membrane morphology changed slightly after the experiments, however, the permeability and the ion rejection of the membrane did not change.     

Arsenic adsorption by polyvinyl pyrrolidone K25 coated cassava peel carbon from aqueous solution

Sorption of arsenic from aqueous solution was carried out using polyvinyl pyrrolidone K25 coated cassava peel carbon (PVPCC). Batch experiments were conducted to determine the effect of contact time, initial concentration, pH and desorption. Batch sorption data's were fitted to Lagergren kinetic studies. Column studies were also conducted using PVPCC as adsorbent. The optimized flow rate of 2.5 mL min(-1) and bed height 10 cm were used to determine the effect of metal ion concentration on removal of As(V). BDST model was applied to calculate the adsorption capacity (N(0)) of column. The N(0) value of 2.59 x 10(-5), 4.21 x 10(-5), 4.05 x 10(-5), 4.26 x 10(-5) and 3.2 x 10(-5) mg g(-1) were obtained for 0.5, 1.0, 1.5, 2.0 and 2.5 mg L(-1) of As(V), respectively. The batch sorption proved to be more efficient than the column sorption. The sorption of As(V) and the nature of the adsorbent was examined by Fourier transmission infrared spectroscopy (FTIR) and X-ray diffraction (XRD) studies, respectively.     

不同浓度硝酸处理的多孔钛及其体外生物活性

多种表面活化改性方法已用于致密钛表面活化改性, 本研究尝试用不同浓度的硝酸溶液处理浆料发泡法制备的多孔钛. 酸处理多孔钛内孔壁上出现了微小尺寸的酸蚀坑, 其微结构随酸浓度的变化而略有不同, 处理后表面磷灰石沉积能力随酸浓度变化差异显著, 其中以1:1和1:5两种浓度(体积比)的硝酸处理组最强, 并显著促进MG63细胞增殖, 细胞在样品表面和孔内得到良好粘附和铺展. 本研究结果表明硝酸处理活化多孔钛, 方法简单, 不引入杂质, 渗透性好, 可有效活化多孔钛内外表面, 是一种有效的制备生物活性多孔钛的方法.     

Arsenic speciation and identification of monomethylarsonous acid and monomethylthioarsonic acid in a complex matrix

Anion-exchange chromatography was utilized for speciation of arsenite (As(III)), arsenate (As(V)), dimethylarsinic acid (DMA(V)), monomethylarsonic acid (MMA(V)), monomethylarsonous acid (MMA(III)), and the new As species monomethylthioarsonic acid (MMTA), using inductively coupled plasma mass spectrometric (ICPMS) detection. MMA(III) and MMTA were identified for the first time in freeze-dried carrot samples that were collected over 25 years ago as part of a joint U.S. EPA, U.S. FDA, and USDA study on trace elements in agricultural crops. The discovery of MMA(III) and MMTA in terrestrial foods necessitated the analytical characterization of synthetic standards of both species, which were used for standard addition in carrot extracts. The negative ion mode, high-resolution electrospray mass spectrometry (HR-ESI-MS) data produced molecular ions of m/z 122.9418 and 154.9152 for MMA(III) and MMTA, respectively. However, ESI-MS was not sensitive enough to directly identify MMA(III) and MMTA in the carrot extracts. Therefore, to further substantiate the identification of MMA(III) and MMTA, two additional separations using an Ion-120 column were developed using the more sensitive ICPMS detection. The first separation used 20 mM tetramethylammonium hydroxide at pH 12.2 with MMA(III) eluting in less than 7 min. In the second separation, MMTA eluted at 11.2 min by utilizing 40 mM ammonium carbonate at pH 9.0. Oxidation of MMA(III) and MMTA to MMA(V) with hydrogen peroxide was observed for standards and carrot extracts alike. Several samples of carrots collected from local markets in 2006 were also analyzed and found to contain low levels of inorganic arsenic species.     

Atomization of hydride with a low-temperature, atmospheric pressure dielectric barrier discharge and its application to arsenic speciation with atomic absorption spectrometry

This paper describes a novel hydride atomizer based on atmospheric pressure dielectric barrier discharge (DBD) plasma. The plasma was generated with a 3700-V, 20.3-kHz, and 5-W electrical power supply and easily sustained with inert gases (He or Ar) at a flow rate of 250 mL.min(-1) after optimization. However, it cannot be sustained with N2. This atomizer offers the advantages of low operation temperature and low power consumption in comparison with the currently used electrothermal quartz atomization operated at 900 degrees C with a power supply of several hundred watts. To confirm the utility of the proposed atomizer, four arsenic species (As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA)) were determined by the present atomization technique. A hyphenation of HPLC coupled to hydride generation AAS with the optimized DBD atomizer has been successfully used for the speciation of arsenic in order to demonstrate the potential of this atomizer in the present study. The characteristics of the DBD atomizer and the effects of different parameters (discharge gas, gas flow rate, voltage, HCl concentration, KBH4 concentration) are discussed in the paper. Compared with other hydride atomization techniques, the proposed method shows the following features: (1) small size (70 mm x 15 mm x 5 mm), which is preferable for the miniaturization of the total analytical system; (2) low power consumption (< or =5 W), which indicates the possibility of the development of portable, fieldable analytical instrumentation for in situ detection using battery as power supply; (3) low atomizer temperature (approximately 70 degrees C), which is in favor of the compactness of the total instruments; (4) avoidance of residue moisture removal in comparison with the existed GD system, which leads to the facility of the system. The analytical figures of the present technique were evaluated. The detection limits of As(III), As(V), MMA, and DMA obtained with HG-DBD-AAS were 1.0, 11.8, 2.0, and 18.0 microg.L(-1), respectively. The accuracy of the system was verified by the determination of arsenic in reference material of orchard leaves SRM 1571. The concentration of As determined by the present method agreed well with the reference values. The speciation of arsenic in the freeze-dried urine SRM 2670 were carried out, and the results obtained were in agreement with the results of HPLC-ICPMS and the reported values by other laboratories.     

Microbial transformation of arsenic species in municipal landfill leachate

The microbial transformation of arsenic species in municipal landfill leachate (MLL) was investigated with the objective to highlight arsenic transformation in the landfill system. Across the 43 day incubation in MLL, more than 90% arsenate (iAs(V)) was found to reduce to arsenite (iAs(III)) within 20 days, while iAs(III) was comparably stable although a fraction of iAs(III) was temporarily oxidated to iAs(V) in the first 3 days. Transformation of monomethylarsonic acid (MMA(V)) to dimethylarsinic acid (DMA(V)) in MLL was slow with only 5% MMA(V) methylated to DMA(V) after 43 days incubation. A portion of DMA(V) and MMA(V) in MLL was demonstrated to transform into thiol-organoarsenic and monomethylarsonous acid (MMA(III)), which were identified to include dimethyldithioarsinic acid (DMDTA(V)), dimethylmonothioarsinic acid (DMMTA(V)) and monomethyldithioarsonic acid (MMDTA(V)) by HPLC-ICPMS and LC-ESI-MS/MS. The microbial formation of DMDTA(V), DMMTA(V) and MMDTA(V) is postulated to relate to hydrogen sulfide generated by bacteria in MLL. Differences in arsenic transformation in sterilised and non-sterilised MLLs demonstrate bacteria play a crucial role in arsenic transformation in the landfill body. This study reveals the complexity of arsenic speciation and highlights the potential risk of forming highly toxic thiol-organoarsenic and MMA(III) in the landfill environment.     

High-resolution computer simulations of stacking of weak bases using a transient pH boundary in capillary electrophoresis. 1. Concept and impact of sample ionic strength

The dynamics of focusing weak bases using a transient pH boundary was examined via high-resolution computer simulation software. Emphasis was placed on the mechanism and impact that the presence of salt, namely, NaCl, has on the ability to focus weak bases. A series of weak bases with mobilities ranging from 5 x 10(-9) to 30 x 10(-9) m2/V x s and pKa values between 3.0 and 7.5 were examined using a combination of 65.6 mM formic acid, pH 2.85, for the separation electrolyte, and 65.6 mM formic acid, pH 8.60, for the sample matrix. Simulation data show that it is possible to focus weak bases with a pKa value similar to that of the separation electrolyte, but it is restricted to weak bases having an electrophoretic mobility of 20 x 10(-9) m2/V x s or quicker. This mobility range can be extended by the addition of NaCl, with 50 mM NaCl allowing stacking of weak bases down to a mobility of 15 x 10(-9) m2/V x s and 100 mM extending the range to 10 x 10(-9) m2/V x s. The addition of NaCl does not adversely influence focusing of more mobile bases, but does prolong the existence of the transient pH boundary. This allows analytes to migrate extensively through the capillary as a single focused band around the transient pH boundary until the boundary is dissipated. This reduces the length of capillary that is available for separation and, in extreme cases, causes multiple analytes to be detected as a single highly efficient peak.     

Speciation of dimethylarsinous acid and trimethylarsine oxide in urine from rats fed with dimethylarsinic acid and dimercaptopropane sulfonate

Speciation of arsenic in urine from rats treated with dimethylarsinic acid (DMA(V)) alone or in combination with dimercaptopropane sulfonate (DMPS) were studied. Methods were developed for the determination of the methylarsenic metabolites, especially trace levels of dimethylarsinous acid (DMA(III)) and trimethylarsine oxide (TMAO), in the presence of a large excess of DMA(V). Success was achieved by using improved ion-exchange chromatographic separation combined with hydride generation atomic fluorescence detection. Micromolar concentrations of DMA(III) were detected in urine of rats fed with a diet supplemented with either 100 microg/g of DMA(V) or a mixture of 100 microg/g of DMA(V) and 5600 microg/g of DMPS. No significant difference in the DMA(III) concentration was observed between the two groups; however, there was a significant difference in TMAO concentrations. Urine from rats fed with the diet supplemented with DMA(V) alone contained 73 +/- 30 microM TMAO, whereas urine from rats fed with the diet supplemented with both DMA(V) and DMPS contained only 2.8 +/- 1.4 microM TMAO. Solutions containing mixtures of 100 microg/L DMA(V) or TMAO and 5600 microg/L DMPS did not show reduction of DMA(V) and TMAO. The significant decrease (p < 0.001) of the TMAO concentration in rats administered with both DMA(V) and DMPS suggests that DMPS inhibits the biomethylation of arsenic.     

Removal of As(V) and As(III) by reclaimed iron-oxide coated sands

This paper aims at the feasibility of arsenate and arsenite removal by reclaimed iron-oxide coated sands (IOCS). Batch experiments were performed to examine the adsorption isotherm and removal performance of arsenic systems by using the IOCS. The results show that the pH(zpc) of IOCS was about 7.0 +/- 0.4, favoring the adsorption of As(V) of anion form onto the IOCS surface. As the adsorbent dosage and initial arsenic concentration were fixed, both the As(V) and As(III) removals decrease with increasing initial solution pH. Under the same initial solution pH and adsorbent dosage, the removal efficiencies of total arsenic (As(V) and As(III)) were in the order as follows: As(V)>As(V)+As(III)>As(III). Moreover, adsorption isotherms of As(V) and As(III) fit the Langmuir model satisfactorily for the four different initial pH conditions as well as for the studied range of initial arsenic concentrations. It is concluded that the reclaimed IOCS can be considered as a feasible and economical adsorbent for arsenic removal.     

Improving aptamer selection efficiency through volume dilution, magnetic concentration, and continuous washing in microfluidic channels

The generation of nucleic acid aptamers with high affinity typically entails a time-consuming, iterative process of binding, separation, and amplification. It would therefore be beneficial to develop an efficient selection strategy that can generate these high-quality aptamers rapidly, economically, and reproducibly. Toward this goal, we have developed a method that efficiently generates DNA aptamers with slow off-rates. This methodology, called VDC-MSELEX, pairs the volume dilution challenge process with microfluidic separation for magnetic bead-assisted aptamer selection. This method offers improved aptamer selection efficiencies through the application of highly stringent selection conditions: it retrieves a small number (<10(6)) of magnetic beads suspended in a large volume (>50 mL) and concentrates them into a microfluidic chamber (8 μL) with minimal loss for continuous washing. We performed three rounds of the VDC-MSELEX using streptavidin (SA) as the target and obtained new DNA aptamer sequences with low nanomolar affinity that specifically bind to the SA proteins.     

Adsorption and removal of arsenic(V) from drinking water by aluminum-loaded Shirasu-zeolite

The demand for effective and inexpensive adsorbents is to increase in response to the widespread recognition of the deleterious health effects of arsenic exposure through drinking water. A novel adsorbent, aluminum-loaded Shirasu-zeolite P1 (Al-SZP1), was prepared and employed for the adsorption and removal of arsenic(V) (As(V)) ion from aqueous system. The process of adsorption follows first-order kinetics and the adsorption behavior is fitted with a Freundlich isotherm. The adsorption of As(V) is slightly dependent on the initial pH over a wide range (3-10). Al-SZP1 was found with a high As(V) adsorption ability, equivalent to that of activated alumina, and seems to be especially suitable for removal of As(V) in low concentration. The addition of arsenite, chloride, nitrate, sulfate, chromate, and acetate ions hardly affected the As(V) adsorption, whereas the coexisting phosphate greatly interfered with the adsorption. The adsorption mechanism is supposed as a ligand-exchange process between As(V) ions and the hydroxide groups present on the surface of Al-SZP1. The adsorbed As(V) ions were desorbed effectively by a 40 mM NaOH solution. Continuous operation was demonstrated in a column packed with Al-SZP1. The feasibility of this technique to practical utilization was also assessed by adsorption/desorption multiple cycles with in situ desorption/regeneration operation.     

Simultaneous separation and speciation of inorganic As(III)/As(V) and Cr(III)/Cr(VI) in natural waters utilizing capillary microextraction on ordered mesoporous Al2O3 prior to their on-line determination by ICP-MS

In this paper, a system of flow injection (FI) capillary microextraction (CME) on line coupled with inductively plasma mass spectrometry (ICP-MS) was proposed for simultaneous separation and speciation of inorganic As(III)/As(V) and Cr(III)/Cr(VI) in natural waters. Ordered mesoporous Al2O3 coating was prepared by sol-gel technology and used as CME coating material. Various experimental parameters affecting the capillary microextraction of inorganic arsenic and chromium species have been investigated and optimized. Under the optimized conditions, the limits of detection were 0.7 and 18 ng L(-1) for As(V) and Cr(VI), 3.4 and 74 ng L(-1) for As(III) and Cr(III), respectively, with an enrichment factor of 5 and a sampling frequency of 8h(-1). The relative standard deviations (R.S.D.) were 3.1, 4.0, 2.8 and 3.9% (C=1 ng mL(-1), n=7) for As(V), As(III), Cr(VI) and Cr(III), respectively. The proposed method was successfully applied for the analysis of inorganic arsenic and chromium species in mineral water, tap water and lake water with the recovery of 94-105%. In order to verify the accuracy of the method, two certified reference of GSBZ50027-94 and GSBZ50004-88 water samples were analyzed and the results obtained were in good agreement with the certified values. The ordered mesoporous Al2O3 coated capillary showed an excellent solvent and thermal stability and could be re-used for more than 30 times without decreasing extraction efficiency.     

Hydride generation interface for speciation analysis coupling capillary electrophoresis to inductively coupled plasma mass spectrometry

A novel hydride generation (HG) interface for coupling capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICPMS) is presented in this work. The CE-HG-ICPMS interface was applied to the separation and quantitation of common arsenic species. Lack of a commercially available HG interface for CE-ICPMS led to a three concentric tube design allowing alleviation of back pressure commonly observed in CE-HG-ICPMS. Due to the high sensitivity and element-specific detection of ICPMS, quantitative analysis of As(III), As(V), monomethylarsonic acid, and dimethylarsinic acid was achieved. Optimization of CE separation conditions resulted in the use of 20 mmol L(-1) sodium borate with 2% osmotic flow modifier (pH 9.0) and -20 kV applied potential for baseline resolution of each arsenic species in the shortest time. Hydride generation conditions were optimized through multiple electrophoretic separation analyses with 5% HCl and 3% NaBH(4) (in 0.2% NaOH) determined to be the optimum conditions. After completion of system optimization, detection limits obtained for the arsenic species were less than 40 ng L(-1) with electromigration time precision less than 1% within a total analysis time of 9.0 min. Finally, the interface was used for speciation analysis of arsenic in river and tap water samples.