DETERMINATION OF ANTIMONY IN WATER SAMPLES BY FLOW-INJECTION HYDRIDE GENERATION ATOMIC ABSORPTION SPECTROMETRY WITH ON-LINE ION-EXCHANGE COLUMN PRECONCENTRATION

On-line ion-exchange separation and preconcentration were combined with flow-injection hydride generation atomic absorption spectrometry (HGAAS) to determine ultra-trace amounts of antimony in water samples. Antimony(Ⅲ) was preconcentrated on a micro-column packed with CPG-8Q chelating ion-exchanger using time-based sample loading and eluted by 4 mol l^(-1) HCl directly into the hydride generation AAS system. A detection limit (3σ) of 0.0015μg l^(-1) Sb(Ⅲ) was obtained on the basis of a 20 fold enrichment and with a sampling frequency of 60h^(-1). The precision was 1.0% r.s.d.(n=11) at the 0.5μg l^(-1) Sb(Ⅲ) level. Recoveries for the analysis of antimony in tap water, snow water and sea water samples were in the range 97-102%.

Determination of total arsenic by photo-decomposition of organoarsenic compounds and hydride generation electrothermal atomic absorption spectrometry

A method was developed for the determination of total arsenic concentration in less than ng/ml level by decomposition of organoarsenicals using photo -oxidation combined with in situ trapping of arsenic hydride on a palladium coated graphite tube with subsequent atomization and detection by AAS. The organoarsenicals include monomethylarsenic, dimethylarsenic, arsenobetaine, arsenocholine, o -aminobenzenarsenate and p -aminobenzenarsenate. The method is simple and sensitive. Detection limit was obtained from different arsenic compounds over the range from 0. 058 to 0.063 ng/ml as As (based on three times of the standard deviation of 10 blank measurements) and the relative standard deviations for ten replicate measurements were from 2.0 to 3.8%. The calibration curves of arsenic compounds including inorganic and organic arsenicals were linear over the range from 0.1 to 3.0 ng/ml as As. The recommended method has been applied to the determination of total arsenic in tap and lake water samples at ng/ml levels.

Determination of Mecruy at Trace Level in Natural Water Samples by Hydride Generation Atomic Absorption Spectrophotometry after Cloud Point Extraction Preconcentration

A method for the determination of trace mercury in water samples by hydride generation atomic absorption spectrophotometry after cloud point extraction was proposed in the present work. The effects of pH, concentration of surfactant, and equilibration time on cloud point extraction were discussed. The enhancement factor of 20 and the detection limit of 0.039 μg/L were obtained for mercury with relative standard deviation of 4.8% （n = 11）.

Computational Modelling of the Hydride Generation Reaction in a Tubular Reactor and Atomization in a Quartz Cell Atomizer

In this study, we present a model whereby the centre of the atomization channel is shown to be the optimal location for the spectrometric data acquisition in a quartz cell atomizer. The study aims to explore the hydride generation technique which is normally coupled with efficient thermal source to apply determination of heavy metals in water samples via spectrometric analysis. The arsenic hydride generation process and the atomization of the generated hydride in a quartz cell atomizer were studied analytically as model case studies. The hydride generation (HG) process was analyzed by adopting two hypotheses, the nascent hydrogen and formation of intermediate hydroboron species, where the results based on the second hypothesis are found to be more realistic for design purposes. Moreover, the release of the generated hydride from the liquid phase and their transport to the gas phase is simulated in a helical tubular section, in which the actual tubular section length required for separation is deduced. The analytical results have been verified experimentally by measuring the signal intensity for the free arsenic atoms against several reaction tube lengths, in which increasing the tubular section length from 12 cm to 100 cm results in signal amelioration by no more than 6.6%. Furthermore, the atomization of the hydride and the distribution of the generated free atoms are deduced in two configurations of tubular quartz atomizers. The results obtained from both studied cases illustrate that a high concentration of the free analyte atoms is generated in the first part of the atomization channel, saturates to a maximum in a position at the atomizer centre, and dissipates at the inside wall of the tubular atomizer before reaching the atomizer outlet edge, which is found to be in total agreement with the current understanding of atomization mechanism in tubular atomizer and emphasizes the fact that the centre of the quartz cell atomizer is the best location for the spectrometric data acquisition.

Determination of Phosphorus by Inductively Coupled Plasma Atomic Emission Spectroscopy after Hydride Generation

A continuous phosphine (PH3) generation was developed and applied to the sensitive detection of phosphorus by ICP-AES. Phosphate ion in aqueous solution was converted to phosphine by passing the sample solution through an incandescent copper silica-tube. Detection limit is 2 ng/mL. The relative standard deviation is 4.2% for 20 ng/mL. The method is rapid and simple with low contamination and high sensitivity.

Iodine Determination by Microwave Plasma Torch Atomic Emission Spectrometer Coupled with Online Preconcentration Vapor Generation Technique

This article focuses on iodine determination by microwave plasma torch atomic emission spectrometry （MPT-AES） coupled with online preconcentration vapor generation method. A new desolvation device, multistrand Nafion dryer, was used as the substitute for condenser desolvation system. Some experimental conditions, such as preconcentration time, acidity of sample solution, rinsing solution acidity and dynamic linear range were investigated and optimized. The new desolvation system eliminates the problem of decreasing emission intensity of I（I） 206.238 nm line with the increase of working time on a conventional condenser desolvation system, thus greatly improving the reproducibility.

Comparison of masking agents for antimony speciation analysis using hydride generation atomic fluorescence spectrometry

A sensitive atomic spectrometric method for the redox speciation analysis of Sb in water is described. The proposed method is based on the selective generation of stibine from Sb（III） in a continuous flow system using non-dispersive atomic fluorescence spectrometry for detection. The effects of the HCI concentration on the fluorescence intensities of Sb（III） and Sb（V） were investigated. The results indicated that atomic fluorescence emission due to Sb（V） can constructively interfere with the determination of Sb（III）. For the determination of Sb（III）, four compounds were tested as masking agents to inhibit the generation of stibine from Sb（V）. The effects of the concentrations of the masking agents and of HC1 on the fluorescence signals from Sb（III） and Sb（V） were studied. The results indicated that citric acid and NaF can successfully suppress hydride generation from Sb（V）. To evaluate the developed methodology and the influence of the matrix, the recovery of Sb（III） from natural water that was spiked with different Sb（III） and Sb（V） concentrations was tested.

Determination of Inorganic Arsenic Species by Electrochemical Hydride Generation Atomic Absorption Spectrometry with Selective Electrochemical Reduction

A new direct procedure for the determination of inorganic arsenic species was developed by electrochemical hydride generation atomic absorption spectrometry （EcHG-AAS） with selective electrochemical reduction. The determination of inorganic arsenic species is based on the fact that As（Ⅲ） shows significantly higher absorbance at low electrolytic currents than As（Ⅴ） in 0.3 mol·L^-1 H2SO4. The electrolytic current used for the determination of As（Ⅲ） without considerable interferences of As（Ⅴ） was 0.4 A, whereas the current for the determination of As（Ⅲ） and As（Ⅴ） was 1.2 A. For equal concentrations of As（Ⅲ） and As（Ⅴ） in a sample, the interferences of As（Ⅴ） during the As（Ⅲ） determination were smaller than 5%. The absorbance for As（Ⅴ） could be calculated by subtracting that for As（Ⅲ） measured at 0.4 A from the total absorbance for As（Ⅲ） and As（Ⅴ） measured at 1.2 A, and then the concentration of As（Ⅴ） can be obtained by its calibration curve at 1.2 A. The methodology developed provided the detection limits of 0.3 and 0.6 ng·mL^-1 for As（Ⅲ） and As（Ⅴ）, respectively. The relative standard deviations were of 3.5% for 20 ng·mL^-1 As（Ⅲ） and 3.2% for 20 ng·mL^-1 As（Ⅴ）. The method was successfully applied to determination of soluble inorganic arsenic species in Chinese medicine.

Ultrasensitive determination of mercury by solution anode glow discharge atomic emission spectrometry coupled with hydride generation

An innovative method for the ultrasensitive detection of mercury by solution anode glow discharge atomic emission spectroscopy(SAGD-AES) coupled with hydride generation(HG) was first investigated.In this method,the mercury vapor generated by the HG was transmitted to the SAGD through the miniature hollow tungsten tube for excitation and detected by a miniaturized spectrograph.A thorough parametric evaluation of the HG and SAGD system was performed,including the type and concentration of ca rrier acid,He flow rate,concentrations of NaBH4,discha rge current and discharge gap.Under optimal operating conditions,the detection limit for Hg^(2+) achieved 0.03 μg/L,with a relative standard deviation of 1.1% at the Hg^(2+) concentration of 5 μg/L.Moreover,the correlation coefficient of the calibration curve was 0.9996 in the range between 0.1 and 10 μg/L.The accuracy and practicability of HG-SAGD-AES were verified by measuring GBW09101 b(human hair),GBW10029(fish),soil and rice samples.The results showed good agreement with the certified values and values from direct mercury analyzer(DMA).

黄皮叶中5种重金属元素的含量测定

黄皮叶药材经硝酸－高氯酸（10＋2）湿法消解后，采用原子吸收分光光度法测定铜元素含量，采用原子荧光法测定砷、汞、铅、镉元素的含量，建立了黄皮叶药材中5种重金属元素的含量测定方法，并测定了不同产地及批次黄皮叶药材中这5种元素的含量。5种元素回收率在94．25％～104．1％之间，8批黄皮叶中铜、砷和铅元素含量均低于国家限量标准，部分产地和批次药材中的重金属汞、镉元素含量高于国家限量标准。

Selenium speciation in flue desulfurization residues

Flue gas from coal combustion contains significant amounts of volatile selenium （Se）. The capture of Se in the flue gas desulfurization （FGD） scrubber unit has resulted in a generation of metal-laden residues. It is important to determine Se speciation to understand the environmental impact of its disposal. A simple method has been developed for selective inorganic Se（IV）, Se（VI） and organic Se determination in the liquid-phase FGD residues by hydride generation atomic fluorescence spectrometry （AFS）. It has been determined that Se（IV）, Se（VI） and organic Se can be accurately determined with detection limits （DL） of 0.05, 0.06 and 0.06 μg/L, respectively. The accuracy of the proposed method was evaluated by analyzing the certified reference material, NIST CRM 1632c, and also by analyzing spiked tap-water samples. Analysis indicates that the concentration of Se is high in FGD liquid residues and primarily exists in a reduced state as selenite （Se（IV））. The toxicity of Se（IV） is the strongest of all Se species. Flue gas desulfurization residues pose a serious environmental risk.

Real-time AGC dispatch units considering wind power and ramping capacity of thermal units

The high penetration of wind energy sources in power systems has substantially increased the demand for faster-ramping thermal units participating in the frequency regulation service.To fulfill the automatic generation control(AGC)and compensate the influence of wind power fluctuations simultaneously,ramping capacity should be considered in the dispatch model of thermals.Meanwhile,conventional methods in this area do not take the impact of transmission loss into the dispatch model,or rely on offline network model and parameters,failing to reflect the real relationships between the wind farms and thermal generators.This paper proposes an online approach for AGC dispatch units considering the above issues.Firstly,the power loss sensitivity is online identified using recursive least square method based on the real-time data of phasor measurement units.It sets up power balance constraint and results in a more accurate dispatch model.Then,an improved multi-objective optimization model of dispatch is proposed and a connection is established between the thermal units with fast ramping capacity and the wind farms with rapid fluctuations.Genetic algorithm is used to solve the dispatch model.The proposed method is compared with conventional methods in simulation case in the IEEE 30-bus system.Finally,simulation results verify the validity and the feasibility of identification method and optimization model.

Uptake and Speciation of Inorganic Arsenic with Cellulose Fibre Coated with Yttrium Hydroxide Layer as a Novel Green Sorbent

A novel adsorbent was developed by coating yttrium hydroxide precipitate layer on cellulose fibre. This material takes up ca. 98% of 5 μg·L 1 As（Ⅲ） and As（V） at low pH （pH〈7）, while a favorable selectivity for As（V） was achieved within pH 11--12. In practice, a mini-column packed with Y（OH）3 precipitate layer coated cellulose fibre particles was incorporated into a sequential injection system for selective uptake of arsenate at pH 11.5. The retained arsenate was afterwards recovered with 50μL of 0.8 mol.L l NaOH solution as eluent, followed by hydride generation in a reaction medium of 2.0 mol·L-1 HCl and 1.0% NaBH4 solution （W/V, in 0.5% NaOH） after pre-reduction of arsenate to arsenite by KI-ascorbic acid （5%, W/V）, with detection by atomic fluorescence spec- trometry. Total inorganic arsenic was quantitatively taken up at pH 6.0 by following the same procedure and arsenic speciation was performed by difference. With a sample volume of 1.0 mL, an enrichment factor of 16.4 was derived with a detection limit of 17 ng.L-1 within a linear range of 0.05--2.0μg.L ]. A relative standard deviation （RSD） of 2.6% （0.5 μg·L-1, n= 11） was achieved. The procedure was validated by analyzing arsenic in a certified refer- ence material GBW 09101 （human hair）, and speciation process requires no organic solvents, thus Y（OH）3 coated of inorganic arsenic in natural water samples. The entire cellulose fibre provides a green adsorbent.