Analytical Potential of EDS at low Voltages

 This paper addresses some of the principles underpinning chemical microanalysis of bulk specimens in the scanning electron microscope using low beam voltages ( ≤5 kV) and energy dispersive x-ray spectrometry. The advantages of this relatively new method lie primarily in the strong dependence of the sample penetration range on the electron beam energy (∼10x from 5 kV to 20 kV). This directly yields superior spatial resolution and sensitivity for the analysis of sub-micron particles, surface films and at interfaces. The correspondingly shorter x-ray escape range reduces the importance of the complex matrix absorption and fluorescence terms; the parameters for which may not always be known accurately. A useful x-ray signal can only be generated with a beam energy which is at least 1.3x the excitation energy for the relevant characteristic x-rays. Low voltage fluorescent yields are relatively low and depend strongly on overvoltage (U < 3) and low voltage x-ray signals are relatively weak. These considerations lead to the development of a radical new instrument which produces 9000 counts per second from an Aluminium target with a < 2 nm probe containing 0.2 nA of current at 5 kV, fast submicron resolution x-ray maps ( < 0.1 μm is possible), and close to 1 nm electron image resolution at 1 kV. The greatly improved (15x) EDS sensitivity and superior electron and x-ray imaging are being used to extend, to explore and to exploit more fully the superior performance envelope of the SEM with EDS at low voltages.     

波长色散X射线荧光光谱无标分析法检测树脂中的铅

建立波长色散X射线荧光光谱检测树脂中重金属元素的无标样分析方法。热塑性塑料在200℃热压成样片;热固性塑料取平面直接测量;涂料研磨成粉末后用硼酸镶边、衬底,经过压样机20 t压力30 s压制成样片。所有样品在真空模式下,以激发电流为50 mA,激发电压为60 kV,分光晶体为LiF(200),准直器为0.23°,测量谱线为Pb Lβ1,峰位(2θ)为28.258的仪器工作条件下测定树脂中铅的含量,通过康普顿比率判断结果的可信度。测定值与标准方法检测值相比,偏差小于10%,测定结果的相对标准偏差小于1%(n=6)。结果表明,波长色散荧光光谱无标分析方法可以快速准确地分析树脂样品中的铅含量。     

A Check Total for Validating Standardless and Normalised EDX Analysis at Low kV

Overlay of fitted peaks on spectra or goodness of fit indices do not always reveal element misidentifications and cannot confirm accuracy of composition, particularly at low kV where there are often strong peak interferences. The conventional Analysis Total requires beam current stability and measurement of at least one standard and is not available if results have to be normalised. If an accurate method is available to predict theoretical spectra, consistency of the peak and background content in spectra can be used to validate analyses even when results are normalised. A new Check Total is proposed that has properties similar to the conventional Analysis Total and can be used to validate a normalised set of concentrations. Check Total is calculated from the ratio of (total area of peaks/total background area) in observed and theoretically simulated spectra. If peak to total background can be predicted with an accuracy of 10% standard deviation, Check Total is useful for alerting the analyst to missing peaks, deconvolution errors at low kV and specimen charging. More accurate spectrum synthesis would make Check Total also sensitive to small errors in microscope kV calibration.     

Low Voltage EDXS and Elements of the First Transition Series

 Use of the L-lines in connection with the elements of the first transition series entails a lot of problems. The corresponding X-ray peaks are composed of contributions of a group of several lines. Because of the incompletely filled 3d-shells, the intensity ratios of the lines and thus the overall peak shapes of the X-ray peaks vary with the type of bonding of the respective element. A special problem posed is that of high energy satellites, which could be strongly absorbed even by use of low electron energies. Crucial for reliable quantitative results is a careful choice of reference spectra for peak deconvolution and peak fit. Nevertheless, with appropriate care results with an accuracy of around 10–15 wt% relative may be obtained. This has been tested by performing quantitative analysis on a haematite and magnetite specimen by use of the Fe-L lines.     

Composition Modulation in Low Temperature Growth of InGaAs/GaAs System: Influence on Plastic Relaxation

This work focuses on the characteristics of composition modulation in InGaAs/GaAs layers grown by ALMBE at 200°C, and its influence on the degree of plastic relaxation that these layers achieve. The asymmetry in the composition modulation for both directions lying in the (001) growth plane observed by Transmission Electron Microscopy is proposed to explain the asymmetry enhancement in misfit dislocations density, as has been found in these structures. Internal stresses in the material associated with this phase separation could be responsible for the hardening of these low temperature grown InGaAs layers.     

基于颜色主波长与补色波长的比色法定量检测

利用sRGB(Standard RGB)颜色空间与国际照明委员会(CIE)色度系统的转化关系以及CIE 1931色品图的性质,编写MATLAB程序实现了颜色的RGB信息到颜色主波长或补色波长的转化,并将此程序用于分析面光源下采集到的显色产物的图片。利用颜色的主波长实现了对pH值的定量检测,利用颜色的补色波长完成了对亚硝酸根离子的定量检测。当pH值分别在4.0~7.0和7.5~10.0范围内,pH值均与其显色产物颜色的主波长呈线性变化;亚硝酸根离子浓度在10~40 mg/L范围内与其显色产物颜色的补色波长有良好的线性关系,通过结合图片的G值分析,扩大了传统吸收光谱法的检测范围。     

Direct Measurement of Electron Beam Scattering in the Low Vacuum SEM

The beam-gas interactions in the low-vacuum SEM is investigated through experimental and simulation approaches. An original experimental way to characterise the skirting is proposed. We obtained directly image distribution of the primary electron beam and the scattered electrons in the low-vacuum SEM. The experimental results are compared to the electron beam profile obtained with Monte-Carlo simulation.     

近红外光谱分辨率对定量分析的影响

利用近红外光谱建立了多组分混合物中对乙酰氨基苯酚和乙水杨胺的定量分析模型。定量模型可以快速准确地测定混合物中对乙酰氨基苯酚和乙水杨胺的含量。研究发现,光谱分辨率对定量分析模型有重要影响。以光谱分辨率4cm-1获得的光谱数据建立的对乙酰氨基苯酚定量模型,其校正集回归系数达到0·9992;其标准偏差为0.2120;同时模型的验证集回归系数为0.9996,而标准偏差达到0.1848。以分辨率1cm-1和8cm-1收集的光谱为基础获得的定量模型,其预测能力呈现不同程度下降趋势。研究结果表明,针对具体样品的特定组分,需要选择合适的光谱分辨率,进而获得最佳的定量分析结果。     

Preparation of Polystyrenylphosphonous Acid of Low Polymerization Degree and Influence of Initiators upon the Free Radical Reaction Mechanism

Organophosphorus chemistry plays an important role in chemical engineering, pesticide, medicine and catalysis1,2. In recent years, after extensive research and widespread application, synthesis and preparation of new organophosphorus compounds have attracted increasing research interest. Polystyrene is a very important and versatile matrix or precursor of various kinds of functional polymer. Usually, introducing of phosphonic PO3H2 or phosphinic PO2H2 group into polystyrene matrix through…     

聚乙烯-g-聚苯乙烯对线性低密度聚乙烯/聚苯乙烯共混物机械性能和发泡行为的影响

以通过开环易位聚合、加氢反应和原子转移自由基聚合技术结合制备的聚乙烯-g-聚苯乙烯(PE-g-PS)作为增容剂,研究了加入不同PS支链长度的PE-g-PS对于线性低密度聚乙烯/聚苯乙烯(LLDPE/PS)共混物的机械性能和发泡行为的影响。 以典型组成m(LLDPE):m(PS)=70:30共混物为例,考察了PE-g-PS对共混物拉伸性能的影响。 相对于二元共混物,增容剂的加入使得断裂伸长率、拉伸强度和屈服强度皆提高,且含长PS支链的增容体系提高更明显。 采用超临界CO₂釜式发泡工艺,考察了PE-g-PS中PS支链长度对共混物发泡行为的影响。 结果表明,相对于短PS支链体系,加入PE-g-PS_1.59k(PS相对分子质量为1590)后的泡孔结构更加均一,完全没有“缝隙”形貌的出现。 当发泡温度降至80 ℃时,即使存在LLDPE发泡空间限制作用(LLDPE无法发泡),加入支链长度更长的PE-g-PS_1.59k后泡孔分布也更加均一。     

电感耦合等离子体原子发射光谱分析中自适应卡尔曼滤波法研究

将自适应卡尔曼滤波（ＡＫＦ）用于ＩＣＰ－ＡＥＳ信号处理，并对影响滤波的因素进行了探讨，对于一些典型光谱干扰，测定的回收率为８５－１０５％。在选择了合适的初始参数条件下，ＡＫＦ法分析结果优于常规卡尔曼滤波（ＮＫＦ）法。     

Studies on the Determination of Mercury by On-line Solvent Extraction and Non-Aqueous Media Hydride Generation Non-Dispersive Atomic Fluorescence Spectrometry

A new method for on-line solvent extraction covalent hydride generation in a non-aqueous extraction phase is proposed. Both liquid–liquid extraction and gas–liquid separation steps are accomplished in an online mode and with AFS as detector. Hydride generation is carried out in an aliquot of metal-complex extraction solution by sodium tetrahydroborate in N,N-dimethylformamide solution and anhydrous acetic acid. An improved U-type gas–liquid separator was used. The working conditions and manifolds scheme of flow injection were optimized. The detection limit attained for mercury was 20ngL^–1. The precision of the determination at a concentration level of around 20 times the detection limit was 5.6%. The proposed method gives improved sensitivity and eliminates interference. The method has been applied to the determination of mercury in certified reference materials with good accuracy and precision.     

低价锆化合物的研究进展

综述了低价锆（包括二价锆和三价锆）化合物的合成，反应和应用，参考文献４５篇。     

Influence of Residual Polyesterification Catalysts on the Curing of Polyesters

 Unsaturated polyesters are synthesized by means of polyesterification, often with catalysts like strong acids, metal oxides and metal-organic salts. Most often, the catalysts used cannot be separated from the bulk of the polyester. Also, some organic or inorganic additives – called fillers – which are used with the polyester in order to decrease cost, affect the curing of the polyester. In this work the effect of residual catalyst on the curing of unsaturated polyester is studied. Unsaturated polyesters were prepared using propylene glycol with a 10% molar excess over stoichiometry and a mixture of dicarboxylic acids, namely maleic acid (unsaturated) adipic acid (saturated) and phthalic anhydride (saturated) at a molar ratio 1:2:2. Lead dioxide, p-toluenesulfonic acid and zinc acetate were used as catalysts, at 0.1% w/w. After the polyesterification, the polymers were diluted with styrene at a proportion of 100:30 w/w. The resins were cured by using MEKP (methylethylketone peroxide) as initiator and CoNp (cobalt naphthenate) as accelerator. Catalysts affect the final color of the polyester. The kinetics of curing of the resins was studied by DSC analysis based on the exothermic peak due to the double bonds breaking to give crosslinked macromolecules. The heat released ΔH is decreased by the presence of catalyst, while activation energy, the frequency factor and the order of reaction are increased.     

Influence of colloidal charge on response of pH and reference electrodes: the suspension effect

The pH measured in a charged sediment is often very different from that of the supernatant solution. This effect has been studied to determine whether it is caused by an anomalous junction potential at the reference electrode, as commonly thought, or by Donnan partitioning of hydrogen ions. Electrical conductivities in sediments of a strong cation-exchange resin were much higher than predicted by the junction artifact theory; electrode measurements of pH in sediments corresponded to titratable H(+)-content, and pH-changes induced by titration and salt addition were in accord with partitioning theory. These findings suggest that most pH differences observed between colloidal sediments and supernatants are real, not junction artifacts. Guidelines for interpretation of pH measurements on colloids are suggested.     

Influence of Modifier-Free Hydroxide Eluents on the Separation of Carbohydrates by Anion Exchange Chromatography

Eluents based on low hydroxide concentrations are favourable in terms of selectivity for the separation of selected carbohydrates with anion exchange chromatography (AEC) and pulsed amperometric detection. The order of retention of many carbohydrates such as sucrose can be changed simply by selecting the appropriate hydroxide concentration.Instable retention times and weak detection efficiency were observed for hydroxide concentrations below 30mM without modifier. The time dependence of this retention loss was studied by step-changes of the eluent concentration. Linear behaviour with time is observed for all carbohydrates investigated. The slope of the relative decrease of retention is dependent on column capacity and presumably on its carbonate contents.The decrease in retention can be effectively suppressed by using a scavenger column filled with a high-capacity, strong anion exchanger. The variation of retention times were lowered from up to 100% to typically less than 1% during 72h of operation for a 10mM NaOH eluent without any modifier.     

Studies on the Efficiency of Hydrogen Selenide Generation with Different Acid Media by Continuous Flow Hydride Generation Atomic Absorption Spectrometry

The efficiency of hydrogen selenide generation by HCl, HBr, H₂SO₄, HClO₄ and HNO₃ was studied with varying NaBH₄ concentrations by continuous flow hydride generation AAS. HBr showed higher efficiency (≈20%) than the conventionally used HCl. The optimum concentration of reagents were 5 M HBr, with 0.5% NaBH₄ and 6 M HCl with 1% NaBH₄. The efficiency followed the order HBr>HCl>HClO₄>H₂SO₄>HNO₃. The sensitivity and detection limits were 0.16 μg L⁻¹ and 0.15 μg L⁻¹ with HBr, and, 0.19 μg L⁻¹ and 0.17 μg L⁻¹ with HCl. The calibration graphs were linear in the range of 2–25 μg L⁻¹ for both the acids. Se⁶⁺ was reduced to Se⁴⁺ in 1 M HCl with the addition of solid KBr (4% final solution) with 60 minutes heating at 70 °C and compared to the commonly used 6 M HCl with 15 minutes boiling. Pre-reduction with KBr showed signal enhancement by 5 to 10% in the range 2–25 μg L⁻¹ of Se⁴⁺. The application of the method to SRM 1640 demonstrated that results were in good agreement with the certified values. Groundwater samples from a suburban area were analyzed and reported.     

Interactions of norfloxacin with DNA and determination of DNA at nanogram levels based on the measurement of enhanced resonance light scattering

A novel assay of DNA at nanogram levels is presented that is based on the measurement of resonance light scattering (RLS) signals in the presence of norfloxacin. The characteristics of RLS spectra, the effective factors and the optimum conditions of the reaction have been investigated. In Britton-Robinson buffer (pH 5.87), norfloxacin has a maximum peak at 405.5 nm and the RLS intensity is greatly enhanced by trace amounts of DNA due to the interaction between norfloxacin and DNA. Mechanistic studies show that the binding of norfloxacin to DNA forms large particles, which result in the significant enhancement of RLS intensity. The enhanced intensity of RLS is proportional to the concentration of DNA in the range from 0.01–2.0 μg mL⁻¹ for yeast DNA, and from 0.02 to 2.3 μg mL⁻¹ for calf thymus DNA. The determination limit (3σ) is 0.7 ng mL⁻¹ for yeast DNA and 1.2 ng mL⁻¹ for calf thymus DNA, respectively. Synthetic samples were determined satisfactorily.     

NH4F对NH3低温选择性催化还原NO的影响研究

制备了一种新的氟掺杂氧化钒/氧化钛催化剂,探讨了掺杂模式、制备方法对低温SCR活性的影响.结果显示,在120~240℃反应温度下,由溶胶法制得的氟掺杂于钒(F-V)模式下的催化活性最佳,通过与未掺杂催化剂(COM)对比可知,在210℃时,氟掺杂催化剂的活性提高了35%,并于240℃时NO的脱除率达到了98.6%.通过X射线衍射试验(XRD)、透射电子显微镜(TEM)、比表面积测试(BET)、光电子能谱分析(XPS)以及H_2程序升温还原(H_2-TPR)等表征技术显示氟掺杂引起催化剂SCR活性提升主要与催化剂活性成分的良好分散性、粒子尺寸减小、比表面积及孔容增大、更强的氧化还原能力有关.另外,通过试验研究表明,氟掺杂催化剂不仅提升了SCR活性,拓宽了活性温度范围,而且还增强了抗硫与抗水性能.     

Solid Phase Extraction of Molybdenum on Modified Octadecyl Silica Sorbents in the Presence of Cationic Surfactants and on Silica-Based Anionic Exchanger and its Determination by Inductively Coupled Plasma Emission Spectrometry

Molybdenum was separated and preconcentrated as molybdate on microcolumns of octadecyl silica sorbents and silica-based strongly basic anion exchanger prior to its determination by ICP-AES. With octadecyl silica Separon SGX C18 and Separon SGX RPS, the retention of 0.01–0.4µg·mL^–1 Mo from 50–1000mL sample solutions was quantitative in the presence of the cationic surfactants carbethoxypentadecyltrimethylammonium bromide (Septonex^®), dodecylbenzyldimethylammonium bromide (Ajatin^®) or tetradecylbenzyldimethylammonium chloride (Zephyramine^®) at pH 6–8. 96% ethanol was the most suitable eluent of the molybdate/surfactant associate. For the strongly basic anion exchanger Separon SGX AX, the optimal conditions for sorption of 5–20µg Mo from 50–250mL sample solutions were at pH 2 in the presence of 0.05M ascorbic acid and ammonium citrate. 3M HNO₃ was a satisfactory eluent in this case. Organic solvents and excess of acids were removed by evaporation prior to the determination of Mo by ICP-AES in eluates. Both procedures can be used for the determination of ion-level molybdenum in waters.