Electrochemical hydride generation atomic absorption spectrometry for determination of cadmium

An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead-tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett-Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20 ng ml⁻¹of cadmium. The concentration detection limit (3σ, n = 8) of 0.2 ng ml⁻¹ and repeatability (relative standard deviation, n = 7) of 3.1% were achieved at 10.0 ng ml⁻¹. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.     

聚苯胺修饰电极-电化学氢化物发生原子荧光光谱法测定食品中锡含量

运用以聚苯胺修饰的石墨电极为阴极的电化学氢化物发生装置实现了锡元素的电化学氢化物发生.在电极表面聚合一层聚苯胺,能够有效地提高锡元素的电化学氢化物发生效率,通过与原子荧光光谱仪联用,成功地测定了食品中的锡含量.本工作对各种实验参数和干扰情况进行了详细研究.方法对锡的检出限为1.2 ng/mL(3σ)；样品分析精密度(R...     

Speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry

A simple procedure was developed for the speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry (EcHG–AAS), without pre-reduction of As(V). Glassy carbon was selected as cathode material in the flow cell. An optimum catholyte concentration for simultaneous generation of arsine from As(III) and As(V) was 0.06 mol l⁻¹ H₂SO₄. Under the optimized conditions, adequate sensitivity and difference in ratio of slopes of the calibration curves for As(III) and As(V) can be achieved at the electrolytic currents of 0.6 and 1 A. The speciation of inorganic arsenic can be performed by controlling the electrolytic currents, and the concentration of As(III) and As(V) in the sample can be calculated according to the equations of absorbance additivity obtained at two selected electrolytic currents. The calibration curves were linear up to 50 ng ml⁻¹ for both As(III) and As(V) at 0.6 and 1 A. The detection limits of the method were 0.2 and 0.5 ng ml⁻¹ for As(III) and As(V) at 0.6 A, respectively. The relative standard deviations were of 2.1% for 20 ng ml⁻¹ As(III) and 2.5% for 20 ng ml⁻¹ As(V). The method was validated by the analysis of human hair certified reference material and successfully applied to speciation of soluble inorganic arsenic in Chinese medicine.     

Electrochemical hydride generation of thallium

An electrochemical hydride generation (ECHG) technique was developed to improve the determination of thallium by atomic spectrometry. The technique is based on the catholyte variation system for production of thallium hydride. Using Pb-Sn alloy as cathode, a transient peak shaped signal was achieved and its height, the maximum absorbance value, was taken as an analytical parameter. Parameters that might affect the hydride generation efficiency were investigated and the analytical performance of the method under the optimized experimental conditions was assessed. The linear range was 1-250 ng mL⁻¹ for thallium and the relative standard deviation of the method was 4.2% (RSD, n = 7). The LOD for thallium was found to be 0.8 ng mL⁻¹, showing a significant improvement relative to conventional chemical hydride generation techniques. The proposed method was applied to the determination of thallium in unalloyed zinc standard reference material. This method offers high sensitivity, simplicity, rapidness, freeness from reagent and low acid consumption.     

Study of interferences by transition metal ions in hydride generation atomic absorption spectrometry of antimony

The mechanism of the interference of metal ions in the hydride generation atomic absorption spectrometry (AAS) of antimony was studied. Experiments on the decomposition rate of sodium tetrahydroborate in acidic media were done in the presence of interfering metals, with and without the addition of masking agents. The results were compared with experiments on the sensitivity of AAS in the presence of the same interfering metals with and without the addition of the same masking agents. AAS experiments are described in which the product of the reaction between sodium tetrahydroborate and one of the interfering metals was present during hydride formation. This reaction product was certainly one of the causes of interference, but the contribution of the catalytic decomposition of sodium tetrahydroborate to interference is not clear.     

Determination of antimony by using a quartz atom trap and electrochemical hydride generation atomic absorption spectrometry

The analytical performance of a miniature quartz trap coupled with electrochemical hydride generator for antimony determination is described. A portion of the inlet arm of the conventional quartz tube atomizer was used as an integrated trap medium for on-line preconcentration of electrochemically generated hydrides. This configuration minimizes transfer lines and connections. A thin-layer of electrochemical flow through cell was constructed. Lead and platinum foils were employed as cathode and anode materials, respectively. Experimental operation conditions for hydride generation as well as the collection and revolatilization conditions for the generated hydrides in the inlet arm of the quartz tube atomizer were optimized. Interferences of copper, nickel, iron, cobalt, arsenic, selenium, lead and tin were examined both with and without the trap. 3σ limit of detection was estimated as 0.053 μg l^− 1 for a sample size of 6.0 ml collected in 120 s. The trap has provided 18 fold sensitivity improvement as compared to electrochemical hydride generation alone. The accuracy of the proposed technique was evaluated with two standard reference materials; Trace Metals in Drinking Water, Cat # CRM-TMDW and Metals on Soil/Sediment #4, IRM-008.     

Determination of Te in soldering tin using continuous flowing electrochemical hydride generation atomic fluorescence spectrometry

An electrochemical hydride generation system was developed for the detection of Te by coupling an electrochemical hydride generator with atomic fluorescence spectrometry. Since TeH₂ is unstable and easily decomposes in solution, a reticular W filament cathode was used in the present system. The TeH₂ generated on the cathode surface was effectively driven out by sweeping gas from the cathode chamber. In addition, a low temperature electrochemical cell (10 °C) was applied to reduce the decomposition of TeH₂ in solution. The limit of detection (LOD) was 2.2 ng ml^− 1 and the relative standard deviation (RSD) was 3.9% for nine consecutive measurements of standard solution. This method was successfully employed for determination of Te in soldering tin material.     

Electrochemical hydride generation for the determination of hydride forming elements by atomic fluorescence spectrometry

The determinations of As, Bi, Ge, Sb and Se were performed by atomic fluorescence spectrometry following their electrochemical hydride generation. An electrochemical hydride generator based on a screw-thread seal arrangement, working in a continuous flow mode was used. The effects of cathode material, shape and area of material, catholyte, sample flow rate, applied current, catholyte solution concentration and interference of transition metals on signal intensity were studied. Five kinds of materials including lead, graphite, copper, tungsten and platinum with different shapes were tested as cathode materials. The signal obtained from a 3-dimensional electrode was higher than that from a 2-dimensional electrode under the same conditions. The signal intensity of Ge in HNO₃ medium within a narrow concentration range of 0.05–0.10 mol L^{− 1} was stronger than that in other acidic medium, such as HCl and H₂SO₄. However, the signal intensity of Ge was rapidly decreased with HNO₃, HCl and H₂SO₄ concentration increasing, and then reached approximately zero. In general, limits of detection and a precision were improved using a graphite cathode in H₃PO₄ medium. The analysis of the reference materials showed good agreement with the certified values for As, Bi, Ge, Sb and Se. The method was successfully applied in the determination of As, Bi, Ge, Sb and Se in traditional Chinese medicine samples.     

电化学氢化物发生-原子荧光法测定环境样品中的Se(Ⅳ)和Se(Ⅵ)

设计了一种新的电化学氢化物发生装置, 用于测定不同价态的硒. 通过对传统的平板电解池的改进, 设计了全新的圆盘电解池并采用螺纹密封的方式, 极大地缩短了电解池的装配时间, 提高了电解池的使用寿命和密封性能. 结合热水浴在线还原技术, 将 Se(Ⅵ)在高浓度HCl介质中120 s内还原成Se(Ⅳ), 通过电化学氢化物发生技术生成氢化物, 成功的进行硒的在线价态分析. 对各种实验参数进行了详细的研究, Se(Ⅳ) 和Se(Ⅵ)的相对标准偏差分别为2.6% 和 3.1% (n=11);Se(Ⅳ)和总硒的检出限分别为0.32和0.27 μg/L (3σ).     

Design and application of a novel integrated electrochemical hydride generation cell for the determination of arsenic in seaweeds by atomic fluorescence spectrometry

An integrated electrochemical hydride generation cell, mainly composed of three components (a gas liquid separator, a graphite tube cathode and a reticulate Pt wire anode), was laboratory constructed and employed for the detection of arsenic by coupling to atomic fluorescence spectrometry. This integrated cell was free of ion-exchange membrane and individual anolyte, with the virtues of low-cost, easy assembly and environmental-friendly. Using flow injection mode, the sample throughput could come to 120 h⁻¹ attributed to the small dimension of the cathode chamber. The operating conditions for the electrochemical hydride generation of arsenic were investigated in detail and the potential interferences from oxygen or various ions were also evaluated. Under the optimized conditions, no obvious oxygen quenching effects were observed. The limit of detection of As (III) for the sample blank solution was 0.2 ng mL⁻¹ (3σ) and the relative standard deviation was 3.1% for nine consecutive measurements of 5 ng mL⁻¹ As (III) standard solution. The calibration curve was linear up to 100 ng mL⁻¹. The accuracy of the method was verified by the determination of arsenic in the reference materials GBW08517 (Laminaria Japonica Aresch) and GBW10023 (Porphyra crispata) and the developed method was successfully applied to determine trace amounts of arsenic in edible seaweeds.     

Modular L-design of hydride atomizers for atomic absorption spectrometry

A novel modular L-shaped design of hydride atomizer for atomic absorption spectrometry is described. It makes it possible to replace the optical tube of the atomizer and, mainly, to employ optical tubes made also from other materials than fused quartz. The design is useful mainly for further improvement of hydride atomizers based on the multiatomizer concept. Employing selenium hydride as the analyte and arsine as the interferent, a preliminary evaluation of performance of three types of L-shaped multiatomizers based on various optical tubes in terms of sensitivity, linearity of calibration graph and resistance to atomization interferences is made. The “classical” T-shaped multiatomizer was employed as a reference.The L-shaped multiatomizer with the optical tube analogous to that employed in the “classical” T-shaped multiatomizer offers virtually the same performance as the reference multiatomizer. Optical tube made of fused quartz with holes with smaller diameters does not offer significantly better performance compared to the reference T-shaped multiatomizer. However, the L-shaped multiatomizer with optical tube fabricated from porous quartz glass overpowers all the other multiatomizers substantially in terms of the resistance against interferences: even the maximum As interferent concentration of 5 µg ml^− 1 does not significantly influence the observed signal. This should be compared with multiatomizers based on plain fused quartz tubes with holes: tolerance limit around 0.5 µg ml^− 1; interferent concentration of 1 µg ml^− 1 causing 20% signal depression.     

Interferences in electrochemical hydride generation of hydrogen selenide

Interferences from Cu(II), Zn(II), Pt(IV), As(III) and nitrate on electrochemical hydride generation of hydrogen selenide were studied using a tubular flow-through generator, flow injection sample introduction and quartz tube atomic absorption spectrometry. Comparison with conventional chemical generation using tetrahydroborate was also performed. Lead and reticulated vitreous carbon (RVC), both in particulate form, were used as cathode materials. Signal supressions up to 60–75%, depending on the cathode material, were obtained in the presence of up to 200 mg l⁻¹ of nitrate due to the competitive reduction of the anion. Interference from As(III) was similar in electrochemical and chemical generation, being related to the quartz tube atomization process. Zinc did not interfere up to Se/Zn ratios 1:100, whereas copper and platinum showed suppression levels up to 50% for Se/interferent ratios 1:100. Total signal suppression was observed in presence of Se/Cu ratios 1:100 when RVC cathodes were used. No memory effects were observed in any case. Scanning electron microscopy and squared wave voltametry studies supported the interference mechanism based on the decomposition of the hydride on the dispersed particles of the reduced metal.     

Determination of major antimony species in seawater by continuous flow injection hydride generation atomic absorption spectrometry

The capabilities and limitations of the continuous flow injection hydride generation technique, coupled to atomic absorption spectrometry, for the speciation of major antimony species in seawater, were investigated. Two pre-concentration techniques were examined. After continuous flow injection hydride generation and collection onto a graphite tube coated with iridium, antimony was determined by graphite furnace atomic absorption spectrometry. The low detection limits obtained (∼5 ng l⁻¹ for Sb(III) and ∼10 ng l⁻¹ for Sb(V) for 2.5 ml seawater samples) permitted the determination of Sb(III) and total antimony in seawater with the use of selective hydride generation and on-line UV photooxidation. The number of samples that can be analyzed is about 15 per hour for Sb(III) determinations and 10 per hour for total antimony determinations. The analysis of seawater samples showed that Sb(V) was the predominant species, even in the presence of important biological activity.     

Inter-element interferences in the determination of arsenic and antimony by hydride generation atomic absorption spectrometry with a quartz tube atomizer

The interferences between arsenic and antimony on each other during the hydride generation atomic absorption spectrometry (HGAAS) determination of arsenic and antimony using a quartz tube atomizer (QTA) were examined. In order to eliminate or reduce such interferences by selective heat decomposition of arsine and stibine, a Pyrex adsorption U-tube trap containing glass wool was placed between the drying tube and the quartz tube atomizer. Although at 250 °C stibine decomposes and is held almost completely by the trap, arsine is also decomposed to an extent of 24% and, therefore, thermal decomposition is not useful to eliminate antimony interference on arsenic determination. The effect of coating the glass wool in the U-tube with antimony on the arsenic suppression of the antimony signal was studied. The results showed that the antimony coating in the U-tube could not hold arsenic effectively and its interference on the antimony signal could not be eliminated by this means. In the second part of the study, oxygen was supplied to the quartz tube atomizer during atomization in order to study the effect of supplying oxygen on the antimony signal and on the interference of arsenic in the antimony determination. Sensitivity was increased in the presence of oxygen and interferences of arsenic on antimony determination was decreased by about 10% when oxygen was supplied. It was also observed that the extent of interferences depended mainly on the interferent concentration rather than the analyte concentration.     

Determination of selenium in vegetables by hydride generation atomic fluorescence spectrometry

A digestion mixture of H₂SO₄/HNO₃/H₂O₂/HF/V₂O₅ was investigated for decomposition of plant samples and sensitive detection of selenium was achieved by hydride generation atomic fluorescence spectrometry (HG-AFS). The method was found to be accurate and reproducible, with a low detection limit (DL) (0.14 ng g⁻¹ solution). The repeatability of the determination was mostly around 10%, the reproducibility over a period of 8 months for determination of selenium in the standard reference material Trace Elements in Spinach Leaves, NIST 1570a, was 9% and the relative measurement uncertainty was 7% using a coverage factor of 2.3 at 95% probability. The average recovery of the whole procedure was 90%. The characteristics of this method are simple and inexpensive equipment, low consumption of chemicals and the ability to analyse many samples in a short time. The whole procedure was carried out in the same PTFE tube, and in addition only a simple cleaning procedure is needed. As a consequence of all these advantages, the described method is suitable for environmental and nutritional studies. The selenium content was determined in 44 vegetable samples from different regions of Slovenia and the contents found were in the range 0.3-77 ng g⁻¹ wet weight.     

Development of a new electrochemical hydride generator with tungsten wire cathode for the determination of As and Sb by atomic fluorescence spectrometry

A novel electrochemical hydride generator has been developed for the determination of As and Sb. This newly devised hydride generator is constructed from a flowing electrolytic cell, in which the tungsten wire is selected as cathode. Compared with some cathode material usually used in electrochemical hydride generator, the tungsten cathode is of better interference tolerance, corrosion-resistant and longer working time. The characteristics of the cathode material, hydride generating efficiency and interferences of concomitant have been studied in detail. The detection limits (3σ) of As and Sb in sample solution were 0.10 μg L⁻¹ and 0.15 μg L⁻¹, the precisions for 11 replicate measurements of 20 μg L⁻¹ As and Sb were 1.3% and 1.7%. The electrochemical hydride generator coupled with atomic fluorescence spectrometry has been applied to the determination of total As and Sb in tobacco samples.     

Determination of the different oxidation states of As and Sb by a new electrochemical hydride generator coupled with atomic fluorescence spectrometry

A novel disk electrochemical hydride generator has been developed for the determination of As and Sb. Compared with the traditional thin-layer cell, the disk cell combined the advantages of quick assembly and easy operation. This electrochemical system for hydride generation in neutral buffer solutions has been studied for analytical usefulness in coupling with atomic fluorescence spectrometry. It was found that the use of neutral phosphate buffer solution could markedly increase the fluorescence intensity of As(III) and Sb(III) and reduce the impact of cathode erosion on the stability of signal intensity. At the same time, the fluorescence intensity of As(V) and Sb(V) were almost suppressed totally. The detection limits (3σ) of 0.031 μg L⁻¹ As(III) and 0.026 μg L⁻¹ Sb(III) in aqueous solutions were obtained, respectively. The precisions (n = 11) for 20 μg L⁻¹ As(III) and Sb(III) were 2.0% and 2.7%, respectively. The method was successfully applied for determination of different oxidation states of As and Sb in environmental samples.     

氢化物-原子吸收光谱法测定冶金企业废水中的砷

采用HNO3/HClO4(体积比10∶1)消解冶金废水样品,经6mol.L-1 HCl溶液酸化后,加入碘化钾(3%)、抗坏血酸(1%)及硫脲(1%)混合溶液进行还原,用氢化物-原子吸收光谱法(HG-AAS)测定了样品中的As含量.结果表明,该方法的检出限为0.297μg/L,相对标准偏差RSD为5.463%,样品加标回收率为93%～108%;其操作方便、选择性好、灵敏度高、干扰少,适合于复杂废水中微量和痕量As的测定.     

A novel analytical system involving hydride generation and gold-coated W-coil trapping atomic absorption spectrometry for selenium determination at ng l level

A novel analytical technique was developed where gaseous hydrogen selenide formed by sodium tetrahydroborate reduction is transported to and trapped on a resistively heated gold-coated W-coil atom trap for in situ preconcentration. Gold coating on W-coil was prepared by using an organic solution of Au. The atom trap is held at 165 °C during the collection stage and is heated up to 675 °C for revolatilization; analyte species formed are transported to an externally heated quartz T-tube where the atomization takes place and the transient signal is obtained. The carrier gas consisted of 112.5 ml min^− 1 Ar with 75 ml min^− 1 H₂ during the collection step and 112.5 ml min^− 1 Ar with 450 ml min^− 1 H₂ in the revolatilization step. The half width of the transient signal obtained is less than 0.5 s. The RSD for the measurements was found to be 3.9% (n = 11) for 0.10 µg l^− 1 Se using peak height measurements.     

磷酸盐缓冲介质电化学氢化物发生原子荧光法测定环境样品中的锑

本文通过对传统的电化学氢化物发生技术进行改进,使用中性磷酸盐缓冲体系作为电解质,研究锑化氢的电解生成情况。实验发现在磷酸盐缓冲体系中, Sb(III)的响应信号比酸性介质中提高了一倍,同时Sb(V)几乎没有响应信号,因此可以在缓冲体系中进行价态分析;同时使用中性缓冲体系消除了酸性介质对电极的腐蚀,延长了电解池及电极的使用寿命,提高了信号的稳定性;对传统的平板式电解池进行了改进,利用螺纹密封的方式代替螺丝密封,电解池安装时间从原来的20分钟缩短为1分钟,并且提高了密封性能,同时有效地解决了电解池渗漏问题。对各种实验参数进行了详细的研究,检出限为0.038μg/L (3σ),相对标准偏差为3.9%(,n=11)。利用该体系分析了多种环境样品中的锑,结果满意。