Determination of As, Sb, Se, Te and Bi in milk by slurry sampling hydride generation atomic fluorescence spectrometry

A simple and fast analytical procedure has been developed for the determination of As, Sb, Se, Te and Bi in milk samples by hydride generation atomic fluorescence spectrometry (HG-AFS). Samples were treated with aqua regia for 10 min in an ultrasound water bath and pre-reduced with KBr for total Se and Te determination or with KI and ascorbic acid for total As and Sb, the determination of Bi being possible in all with or without pre-reduction. Slurries of samples, in the presence of antifoam A, were treated with NaBH₄ in HCl medium to obtain the corresponding hydrides, and AFS measurements were processed in front of external calibrations prepared and measured in the same way as samples. Results obtained by the developed procedure compare well with those found after microwave-assisted complete digestion of samples. The proposed method is simple and fast, and only 1 ml of milk is needed. The values obtained for detection limit are 2.5, 1.6, 3, 6 and 7 ng l⁻¹ for As, Sb, Se, Te and Bi respectively in the diluted samples, with average relative standard deviation values of 3.8, 3.1, 1.9, 6.4 and 1.2% for three independent analysis of a series of commercially available samples of different origin. Data found in Spanish market samples varied from 3.2±0.3 to 11.3±0.2 ng g⁻¹ As, from 3.1±0.2 to 11.6±0.4 ng g⁻¹ Sb, from 10.7±0.5 to 25.5±0.4 ng g⁻¹ Se, from 0.9±0.2 to 9.4±0.6 ng g⁻¹ Te and from 11.5±0.1 to 27.7±0.4 ng g⁻¹ Bi.     

Determination of arsenic(III) and total inorganic arsenic in water samples using an on-line sequential insertion system and hydride generation atomic absorption spectrometry

A simple and robust on-line sequential insertion system coupled with hydride generation atomic absorption spectrometry (HG-AAS) was developed, for selective As(III) and total inorganic arsenic determination without pre-reduction step. The proposed manifold, which is employing an integrated reaction chamber/gas-liquid separator (RC-GLS), is characterized by the ability of the successful managing of variable sample volumes (up to 25 ml), in order to achieve high sensitivity. Arsine is able to be selectively generated either from inorganic As(III) or from total arsenic, using different concentrations of HCl and NaBH₄ solutions. For 8 ml sample volume consumption, the sampling frequency is 40 h⁻¹. The detection limit is c_L = 0.1 and 0.06 μg l⁻¹ for As(III) and total arsenic, respectively. The precision (relative standard deviation) at 2.0 μg l⁻¹ (n = 10) level is s_r = 2.9 and 3.1% for As(III) and total arsenic, respectively. The performance of the proposed method was evaluated by analyzing the certified reference material NIST CRM 1643d and spiked water samples with various concentration ratios of As(III) to As(V). The method was applied for arsenic speciation in natural waters samples.     

On‐Line Determination of Arsenic Species in Sea Water by Selective Hydride Generation Coupled with Inductively Coupled Plasma — Mass Spectrometry

A method for direct de termination of total in organic arsenic (III+V), arsenic (III) and dimethylarsinate (DMA) in sea water was developed by combining continuous‐flow selective hydride generation and inductively coupled plasma mass spectrometry (ICP‐MS) is presented. The principle underlying selective hydride generation is based on proper control of the reaction conditions for achieving separation of the respective arsenic species. The effects of pH and composition of reaction media on mutual interference between the arsenic species were investigated in detail. The results indicate that the appropriate media for the selective determination of total in organic arsenic, DMA and As(III) are 6 M HNO₃, acetate buffer at pH = 4.63 and citrate buffer at pH = 6.54, respectively. The concentrations of total inorganic arsenic species, As(III+V), and As(III) were respectively deter mined and that of As(V) was obtained by the difference between them. As to the concentration of DMA, it was obtained after correction from the interference caused by As(III) and As(V). By following the established procedure, the detection lim its (as based on 3‐sigma criterion) for As(III+V), As(III) and DMA were 0.050, 0.009, and 0.002 ng/mL, respectively. There liability of the pro posed method was evaluated in terms of precision and spike addition. The results indicated that the precision of better than 3% and spike recovery of 95 to 105% for all the arsenic species tested in the natural sea water samples can be obtained.     

Evolution and characterization of fluorite-like nano-SrBi2Nb2O9 phase in the SrO-Bi2O3-Nb2O5-Li2B4O7 glass system

Transparent glasses of various compositions in the system (100−x)Li₂B₄O₇−x(SrO-Bi₂O₃-Nb₂O₅) (where x=10, 20, 30, 40, 50 and 60, in molar ratio) were fabricated via splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction (XRD) and transmission electron microscopic studies confirmed the amorphous nature of the as-quenched and crystallinity in the heat-treated samples. Fluorite phase formation prior to the perovskite SrBi₂Nb₂O₉ phase was analyzed by both the XRD and high-resolution transmission electron microscopy. Dielectric and the optical properties (transmission, optical band gap and Urbach energy) of these samples have been found to be compositional dependent. Refractive index was measured and compared with the values predicted by Wemple-Didomemenico and Gladstone-Dale relations. The glass nanocomposites comprising nanometer-sized crystallites of fluorite phase were found to be nonlinear optic active.     

基于协议栈的移动性技术对比分析

传统的协议栈没有对实现移动性的层次进行准确定位，所以几乎协议栈中的每一层都有实现移动性的方案，但对于移动互联网这种异质网络。分层的协议栈效率很低。根据协议栈和移动互联网移动性的特点，从协议栈的链路层、网络层、传输层和应用层上具体分析了各个层实现移动性的优缺点，通过这些分析可见，要给移动互联网中的移动节点提供良好的移动性支持，跨层实现动性是未来移动性发展的趋势。     

高效全固化钛宝石腔内倍频蓝光和四倍频紫外激光器的研究

用半导体抽运的Q开关YLF倍频激光器抽运钛宝石晶体，在平凹腔内加入组合的石英双折射滤光片压缩线宽，用LBO晶体腔内激发二次谐波，聚焦到BBO上产生四次谐波深紫外光。在抽运功率3．8w时，输出610mW．416nm蓝光。用长焦距的透镜聚焦二次谐波．得到64mW，208nm的紫外激光。基频光的谱线宽度是决定倍频效率的关键因素。实验观察到激光器的频谱宽度与双折射滤光片的带宽有一个数量级的差别，考虑到模式竞争和增益饱和效应，数值模拟了加入双折射滤光片后的钛宝石激光器的实际线宽，结果与实验中测量的数据基本一致。实验还分析了基频光的线宽对二次谐波效率的影响、二次谐波的线宽对四次谐波效率的影响、基频光的波长对四次谐波激发效率的影响。     

Salt effect on molecular orientation at air/liquid methanol interface

The salt effects on molecular orientation at air/liquid methanol interface were investigated by the polarization-dependent sum frequency generation vibrational spectroscopy(SFG-VS). We clarified that the average tilting angle of the methyl group to be u = 308 58 at the air/pure methanol surface assuming a d-function orientational distribution. Upon the addition of 3 mol/L Na I, the methyl group tilts further away from the surface normal with a new u = 418 38. This orientational change does not explain the enhancement of the SFG-VS intensities when adding Na I, implying the number density of the methanol molecules with a net polar ordering in the surface region also changed with the Na I concentrations. These spectroscopic findings shed new light on the salt effects on the surfaces structures of the polar organic solutions. It was also shown that the accurate determination of the bulk refractive indices and Raman depolarization ratios for different salt concentrations is crucial to quantitatively interpret the SFG-VS data.     

Conduction mechanism of metal-TiO2–Si structures

The conduction model has been proposed for the metal-TiO₂–Si (MIS) structures. Rutile films have been prepared on Si substrates by magnetron sputtering of TiO₂ target and annealing in the air at temperatures T?=?800 and 1050 K. The current-voltage (CVC) and capacitance-voltage characteristics of the structures have been measured over the range of T?=?283–363 K. At positive potentials on the gate, the conductivity of the MIS structures is determined by the space charge-limited current in the dielectric layer.     

Harmonic and attosecond pulse enhancement in the presence of noise

<正>In this paper,we theoretically investigate the effect of noise on the photoionization,the generation of the high-order harmonic and the attosecond pulse irradiated from a model He~+ ion.It shows that by properly adding noise fields,such as Gaussian white noise,random light or colored noise,both the ionization probabilities(IPs) and the harmonic yields can be enhanced by several orders of magnitude.Further,by tuning the noise intensity,a stochastic resonance-like curve is observed,showing the existence of an optimal noise in the ionization enhancement process.Finally,by superposing a properly selected harmonic,an intense attosecond pulse with a duration of 67 as is directly generated.