Preconcentration of Trace Cu(II) in Water Samples with Nano-Sized ZnO and Determination by GFAASSCIEI北大核心CSCD

The content of copper in natural water is very low, and direct determination is difficult. Therefore, it is very meaningful for the combination of efficient separation-enrichment technology and highly sensitive detection. Based on the high adsorption capacity of Cu(II) onto nano-sized ZnO, a novel method by using nano-sized ZnO as adsorbent and graphite furnace atomic absorption spectrometry as determination means was in this work. The adsorption behaviors of Cu(II) on nano-sized ZnO was studied. Effects of acidity, adsorption equilibrium time, adsorbent dosage and coexisting ions on adsorption rates were investigated. The results showed that the adsorption efficiency was above 95% in a pH range from 3.0 to 7.0. Compared with other adsorbents for trace element enrichment such as activated carbon, nano-sized TiO2 powder, the most prominent advantage is nanosized ZnO precipitate with the concentrated element can directly dissolved in HCl solution without any filtration and desorption process can directly analyzed by graphite furnace atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry. Compared with colloid nano materials, nano-sized ZnO is the true solution after dissolving have small matrix effect and viscosity more suitable for graphite furnace atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry detection. The proposed method possesses low detection limit (0.13 mu g.L-1) and good precision (RSD=2.2%). The recoveries for the analysis of environmental samples were in a rang of 91.6%-92.6% and the analysis results of certified materials were compellent by using the proposed method.     

Determination of Trace Elements in Vegetable Oils and Biodiesel by Atomic Spectrometric Techniques—A Review

Abstract

The determination of trace elements in edible oils and biodiesel using atomic spectrometric methods is reviewed. Problems related to sample pretreatment for appropriate sample introduction and calibration are addressed as well as the strategies to overcome them. Recent trends aimed at simplifying sample manipulation are presented. The applications and scope of atomic absorption spectrometry (AAS), flame optical emission spectrometry (F-OES), inductively coupled plasma–optical emission spectrometry (ICP-OES), and inductively coupled plasma–mass spectrometry (ICP-MS) techniques for the determination of trace metals in edible oils and biodiesel are discussed, as well as some current instrumental new developments.     

Simultaneous Determination of Sn and S in Methyltin Mercaptide by Microwave-Assisted Acid Digestion and ICP-OESSCIEI北大核心CSCD

Methyltin mercaptide is widely used as one of the best heat stabilizer in the polyvinylchloride (PVC) thermal processing due to its excellent stability, good transparency, high compatibility and weather resistance. The content of sulfur and tin significantly affects its quality and performance, so it is of great significance to develop an analytical method for the simultaneous determination of sulfur and tin. Inductively coupled plasma atomic emission spectrometry (ICP-OES) has been a powerful analytical tool for a myriad of complex samples owing to its advantages of the low detection limits, rapid and precise determinations over wide dynamic ranges, freedom from chemical inter-element interferences, the high sample throughput and above all, simultaneous multi-elements analysis. Microwave technique as a well-developed method for sample preparation can dramatically reduce the digestion time and the loss of volatile elements compared with the traditional open digestion. Hereby, a microwave-assisted acid digestion (MW-AAD) procedure followed by inductively coupled plasma optical emission spectroscopy (ICP-OES) analysis was developed for the simultaneous determination of Sn and S in methyltin mercaptide. This method has the advantages of simplicity, rapidness, good accuracy, green and less use of samples. Parameters affecting the MW-AAD such as the digestion solution and digestion time were optimized by using a chemical analyzed reference sample (DX-181) to attain tin and sulfur quantitative recoveries. HNO3-HCl-HClO4(v/v/v=9 : 3 : 1) and 10 min were the optimum digestion solution and digestion time, respectively. Under optimum conditions, the standard addition method and the standard calibration curve method were both been used to detect Sn and S in DX-181. There was no significant difference between two methods and the relative deviations to the chemical analysis values were both less than 2%. Additionally, the accuracy of the MW-AAD method was examined by analyzing three methyltin mercaptide samples (DX-181, DX-990, DX-960). The results were satisfactory with the relative deviations (<3%) and the recoveries of standard addition (99%-102%).     

Determination of Trace Elements in High‐Purity Palladium by Inductively Coupled Plasma Mass Spectrometry Using an Internal Standard Method

Method validation of inductively coupled plasma mass spectrometry analyses for trace impurities in high‐purity materials is often limited not only by the lack of suitable reference materials with the same matrix composition but also by the lack of a significant number of certified trace element concentrations in the available reference materials. This paper demonstrates a new and simple method for the direct determination of 44 trace elements in high‐purity palladium using inductively coupled plasma mass spectrometry and an internal standard method. Sc and In were employed as internal standards to effectively eliminate nonspectral interferences from the Pd matrix. The detection limits of the 44 trace impurities were from 0.00078 to 0.46 µg/mL and the relative standard deviations (n=6) were below 3.5%. The method was further validated using a palladium standard material (Aldrich palladium standard material, CAS no. 7440053). The analytical results are in good agreement with the certified values.     

Quantitatively Determination of Available Phosphorus and Available Potassium in Soil by Near Infrared Spectroscopy Combining with Recursive Partial Least SquaresSCIEI北大核心CSCD

Soil available phosphorus (P) and available potassium (K) don't possess direct spectral response in the near infrared (NIR) region. They are predictable because of their correlation with spectrally active constituents (organic matter, carbonates, clays, water, etc.). Such correlation may of course differ between the soil sample sets. Therefore, the NIR calibration models with fixed structure are difficult to achieve good prediction performances for soil P and K. In this work, the method of recursive partial least squares (RPLS), which is able to update the model coefficients recursively during the prediction process, has been applied to improve the predictive abilities of calibration models. This work compared the performance of partial least squares regression (PLS), locally weighted PLS (LW-PLS), moving window LW-PLS (LW-PLS2) and RPLS for the measurement of soil P and K. The entire data set of 194 soil samples was split into calibration set and prediction set based on soil types. The calibration set was composed of 120 Anthrosols samples, while the prediction set included 29 Ferralsols samples, 23 Anthrosols samples and 22 Primarosols samples. The best prediction results were obtained by the RPLS model. The coefficient of determination (122) and residual prediction deviation (RPD) were respectively 0.61, 0.76 and 1.60, 2.05 for soil P and K. The results indicate that RPLS is able to learn the information from the latest modeling sample by recursively updating the model coefficients. The proposed method RPLS has the advantages of wider applicability and better performance for MR prediction of soil P and K compared with other methods in this work.     

Simultaneous Determination of Se and Te in Ores by HG-AFS After Online Preconcentration with Nano-TiO2 Immobilized on Silica GelSCIEI北大核心CSCD

A simple, sensitive and interference-free method was established for simultaneous determination of trace selenium and tellurium in ore samples by HG-AFS, by using nano-TiO2-immobilized on a silica gel packed microcolumn for online preconcentration. Selenium and tellurium were selectively adsorbed to the microcolumn in acidic condition and then completely eluted with 2% (m/v) NaOH solution. The experimental conditions for hydride generation, adsorption, elution and potential interference were investigated in detail. Under the optimum conditions, the detection limits of selenium and tellurium by the proposed method with 180 s sampling time were 4.0 and 3.6 ng.L-1, with sensitivity enhancement of 20- and 13-fold compared to conventional hydride generation method, respectively. The relative standard deviation (RSD, n=5) of this method for 1 mu g.L-1 Se(IV) and Te(IV) were 0.7% and 2.3, respectively. This method was applied to determination of selenium and tellurium in several ore samples.     

Transport and Pinning Properties of FeSe北大核心CSCD

利用固相反应法合成了FeSe超导体,根据名义组分和热处理工艺的不同共得到四组FeSe样品,利用X射线衍射仪(XRD)和物性测试系统(PPMS)分别对样品的晶体结构和电输运性能进行表征,并分析了磁通钉扎特性.XRD测试结果表明所有的样品主相均为β-FeSe四方相,同时在样品中也存在少量杂相,包括α-FeSe和Fe,不同名义组分和不同热处理工艺对晶体结构的影响较小.电阻率测试结果表明所有的样品均发生了超导转变,Tc大约为9K,在零场下的转变宽度约为3K,但是四个样品的正常态电阻率明显不同,通过测试四个样品在不同磁场下的电阻率随温度的变化曲线,随着磁场的增加,电阻率曲线出现展宽效应,分析表明FeSe的磁通钉扎行为是由于在不同磁场下热激活磁通蠕动引起的,其上临界磁场可达23T.     

Research on Quantitative Analytical Model for Determination of Phosmet by Using Surface Enhanced Raman SpectroscopySCIEI北大核心CSCD

Raman spectroscopy combined with surface enhanced technology was adopted for analysis of phosmet pesticide. Continuous wavelet transforms (CWT) and successive projections algorithm (SPA) were used for Raman spectral preprocess and characteristic Raman shifts selection, respectively. Multi-linear regression (MLR) was used for spectral modeling. It is shown that enhanced chips can achieve enhanced Raman spectral signal for low concentration of pesticides. CWT can improve spectral resolution and smoothness, and remove translation error. Characteristic Raman shifts selection method of SPA can improve analytical precision, and simplify modeling variables of MLR CWT-SPA-MLR model can improve correlation coefficient (r) of prediction from 0. 823 to 0. 903, and reduce root mean square error of prediction (RMSEP) from 1. 640 to 1. 122. CWT-SPA-MLR method can be used for constructing analytical models for Raman spectra and has good interpretability and repeatability.     

Determination of Trace Amounts of Zinc in Welding Fumes by Flow‐Injection Flame Atomic Absorption Spectrometry

A flow‐injection flame atomic absorption spectrometric method for the determination of zinc in welding fumes has been developed. The method is based on the continuous ultrasound‐assisted dissolution of the zinc oxide collected on the air filter. Variables such as sonication time, nature and concentration of the acid solution used as dissolving solution, dissolution temperature, flow rate of the continuous manifold, and dissolving solution volume were simultaneously studied by applying a Plackett–Burman design. Results showed that only the concentration of nitric acid solution used as dissolving solution was a statistically significant variable (confidence interval of 95%). Factors such as dissolution temperature and sonication time were finally optimized by using a central composite design. The detection limit was 1.1 µg/m³ and the repeatability of the overall method is 1.6% (n=11) for a zinc concentration of 75.4 µg/m³. The proposed method was applied to the determination of zinc in welders' workplace environments.     

Energy and life of electrons and holes in the columnar nanometer system北大核心CSCD

利用S-矩阵理论,在有效质量近似下,求出柱状纳米系统电子和空穴的能量和寿命,并与球状纳米系统相比较.以HgS/CdS/HgS柱状纳米系统为例,探讨了线度和势垒宽度对电子和空穴的能量和寿命的影响.结果表明:柱状纳米系统中,电子和空穴的能量和寿命随线度的变化规律相似,即势垒宽度一定时,能量随内半径增大而减小,寿命随内半径增大而增大;内半径一定时,能量随势垒宽度增大而减小,但变化甚微,而寿命随势垒宽度增大而迅速增大;势垒宽度Δ<4aCdS时,电子和空穴的寿命均为零,但电子和空穴寿命不为零的势垒宽度范围不同,空穴的寿命要比电子的寿命小.柱状和球状纳米系统电子和空穴寿命的变化规律相似,形状的影响很小.     

Absorption and Fluorescence Properties of Chromophoric Dissolved Organic Matter Produced by AlgaeSCIEI北大核心CSCD

Four kinds of diatom (Chaetoceros curvisetus, Phaeodactylumtricornutum, Nitzschia closterium f. minutissima and Navicula halophile) and two kinds of dinoflagellates (Prorocentrum donghaiense and Gymnodinium) were cultured under laboratory conditions. Variations of optical properties of chromophoric dissolved organic matter (CDOM) were studied with absorption and fluorescence excitation-emission matrix spectroscopy(EEM) during growth of marine microalgae in incubation experiment. Absorption spectrum revealed absorption coefficient a(355) (CDOM absorption coefficients at 355 nm) of 6 kinds of marine microalgae above increased by 64.8%, 242.3%, 535.1%, 903.2%, 836% and 196.4%, respectively. Simultaneously, the absorption spectral slope(Sg), determined between 270 and 350 rim, representing the size of molecular weight of CDOM and humic-like composition, decreased by 8.7%, 34.6%, 39.4%, 53.1%, 46.7%, and 35.7%, respectively. Applying parallel factor analysis (PARAFAC) together with EEM got four components of CDOM: C1(Ex/Em=350(260) nm/450 nm), C2 (Ex/Em=260 (430) nm/525 nm) 03 (Ex/Em=325 nm/400 nm) and C4(Ex/Em=275 nm/325 nm), which.were relative to three humic-like and one protein-like fluorescent components of Nitzschia closterium f. minutissima and Navicula halophile. In incubation experiment, fluorescence intensity of these four components during growth of Nitzschia closterium f. minutissima increased by, respectively, 8.68, 24.9, 7.19 and 39.8 times, and those of Navicula halophile increased by 2.64, 0.07, 4.39 and 12.4 times, respectively. Significant relationships were found between the fluorescence intensity of four components of CDOM, a(355) and Sg. All results demonstrated that both content and molecular weight of CDOM produced by diatom and dinoflagellate studied in incubation experiment increased, but these two parameters changed more obviously of the diatom than those of dinoflagellate; the proportion of humic-like components in the composition of CDOM also increased clearly with the growth of marine microalgae, but protein-like fluorescent component had only a slow growth. Furthermore, the absorption spectrum of CDOM produced by different species of algae changed obviously and the relative composition fluorescence intensity of CDOM produced by different microalgae were found to vary among different composition from EEM, which suggested CDOM produced by different microalgae make quite different contributions to CDOM in natural seawater.     

Femtosecond Laser-Induced Breakdown Spectroscopy for Detection of Trace Elements in Sophora Leaves

Sophora leaves from several areas in Beijing are analysed by femtosecond laser-induced breakdown spectroscopy （femto-LIBS）. Although the used spectral detection system is not time-resolved, the spectral lines of trace mineral elements are detected and analysed. It is proven that the femto-LIBS can be an efficient method to detect mineral trace elements contained in tree leaves which is a biomonitor for atmospheric pollution assessment or botanic studies. An interesting case of correlation between trace elements detected in tree leaves and the pollution of the concerned area is presented, for the first time to our knowledge.     

Feature Selection and Interpretation in Infrared Quantitative Models of Liquiritin and Glycyrrhizin in Radix GlycyrrhizaeSCIEI北大核心CSCD

Feature selection can improve the interpretation of the modeling variables to a certain extent by selecting variables from the complex spectra backgrounds. However, the improvement of models interpretation does not mean that the modeling variables have the exact physical or chemical significance. In this paper, We explore the relation between the chemical characteristics of target components and the spectrum variables selected with 3 kinds of variables selection methods which are moving window partial least squares regression (mwPLS), synergy interval partial least squares regression (siPLS) and competitive adaptive reweighted sampling(CARS), and compare the interpretation difference of the variables selected with the above variables selection methods. The results show that the variables selected with mwPLS accord with nu(phi)C=C of liquiritin and delta(CH3) or delta(CH2) of glycyrrhizin, which are the obvious spectra differences between the flavonoids and saponins in Radix Glycyrrhizae, and the variables selected with siPLS are the characteristic intervals combinations of the flavonoids or saponins in Radix Glycyrrhizae, which is the combination of nu(phi) nu(o) o nu(o)(C-H) of flavonoids or the combination of nu c-o nu c H, O-H of saponins while the variables selected with CARS can better accord with most of the characteristic peaks from 1 000 to 4 000 cm(-1) of liquiritin or glycyrrhizin in Radix Glycyrrhizae, and the predict performance of the infrared quantitative model established on the spectroscopic variables selected with CARS can be improved. Therefore, most of the variables selected with CARS can be interpreted by the characteristic peaks in the infrared characteristic region of the target components, which is beneficial to improve the interpretation of the quantitative model.     

Detection and jamming experiment of optical surveillance device in night equipment transportation北大核心CSCD

针对装备运输过程中可能遭遇侦拍的风险,结合运输安全需求,分析市面上常见的4类消费级侦拍装置(手机、卡片数码相机、单反相机和数码摄像机)的光电可探测性,并实现对各装置的有效干扰。通过搭建“猫眼”激光探测、激光干扰及回波信号接收系统,重点突破典型小口径侦拍装置的探测与识别,以及“猫眼”探测端与目标端的双向成像等理论和关键技术。在此基础上分析不同距离、干扰波长和孔径情况下可见光波段激光对“猫眼”目标的探测及成像干扰效果,并提出一种图像干扰效果评价标准及不同光学侦拍装置的有效干扰阈值。实验结果表明:典型光学侦拍装置在实验距离内具有良好的光电可探测性,并且可被有效干扰;在激光束完全覆盖镜头通光孔径时,目标与装置距离越近,激光束散角越小,波段越接近人眼敏感程度最大波段(555 nm),激光光束产生的非伤害性成像干扰效果越好。     

Comparison and Analysis of IR Spectra of Four Dendrobium SpeciesEI北大核心CSCD

In this paper, Fourier transform infrared spectroscopy (FTIR) was used to compare the five dendrobium species' infrared absorption spectra of stem powder. The stem of Dendrobium is rich in saccharides. The saccharides of Dendrobium Officinale, Dendrobium Paxt and Dendrobium wardianum Warner are complex in composition. And the sugar units are mainly galactopyranose, grape pyranose, mannopyranose, arabinopyranose and xypyranose. The sugar components in the stem of Dendrobium strongylanthum Rchb. f. were simple. The sugar units were galactopyranose, grape pyranose and mannopyranose. Dendrobium wardianum Warner had the same chemical structure as Dendrobium strongylanthum Rchb. Dendrobium Officinale had the same chemical structure as Dendrobium devonianum Paxt. The species of Dendrobium could be identified by the characteristic absorption peak of the polysaccharide fingerprint absorption region.     

Biosorption and Biomineralization of Uranium(VI) from Aqueous Solutions by Landoltia PunctataSCIEI北大核心CSCD

The biosorption and biomineralization characteristics of uranium by the duckweed Landoltia punctata was investigated in aqueous solutions enriched with 1 to 250 mg . L-1 of U(VI) supplied as uranyl nitrate [UO2(NO3)(2) center dot 6H(2)O]. The maximum uranium removal for the plant cultivar occurred at pH 4 similar to 5 of solution and their uranium removal efficiencies exceeded 90% after 24 h. In kinetics studies, the dried powder of duckweed can finished nearly 80% adsorption within 5 min, the batch adsorption equilibrium can be reached within 24 h for the living and dried powder of duckweed, Both for the living and dried powder of duckweed, the experimental data were well fitted by the pseudo-second-order rate model with the degree of fitting (r) higher than 0.99. The adsorption isotherms could be better described by the Freundlich model than the Langmuir model. In addition, Fourier transform infrared spectroscopy (FTIR) revealed that the surface of Landoltia punctata possess many active groups such as hydroxyl, carboxyl, phosphate and amide groups, the hydroxyl, amino groups involved in adsorption of U(VI) by living and dried powder of Landoltia punctata, and the phosphate groups also participated in the adsorption behavior of U(VI) by the living Landoltia punctata. The living Landoltia punctata reduction part of U(VI) to U(IV) was observed by XPS analysis. SEM and energy dispersive X-ray spectroscopy (EDS) of duckweed from 10 similar to 200 mg . L-1 uranium treatments indeed showed root surface of living Landoltia punctata formed a significant portion of U precipitates with nanometer sized schistose structures that consisted primarily U and P, not containing C. Inorganic phosphate was released by the root cells of Landoltia punctata during the experiments providing ligands for formation of insoluble U(VI) and U(IV) phosphates. The distinct uranium peaks in the EDS spectra of the cluster on the root surface can be observed after biosorption and the uranium and phosphorus mass ratio of the cluster spot was measured to be 82.5% and 8.76% of the total component weight, respectively, and the atomic percentage of 30.89% and 25.19%, respectively. It is worth noting that the phosphorus mass ratio and the atomic rate of the control group is only 0.24% and 0.11%, respectively. But there was no similar crystals observed on the surface of dried powder of Landoltia punctata after biosorption. The present work suggests that living and dried powder of Landoltia punctata can remove more than 90% U(VI) from solution simultaneously precipitated together with phosphate by the living Landoltia punctata, and the dried powder of Landoltia punctata adsorption U(VI) is mainly through the effect of electrostatic attraction, ion exchange and complexation coordination, etc. Here, for the first time, the presence of U immobilization mechanisms within one aquatic plant is reported using Landoltia punctata.     

Development of ship-borne electro-optical tracking and fire control system北大核心CSCD

舰载光电跟踪与火控系统是一种远距离监视、跟踪与火力打击装置,按照体系结构可以分为分立式和综合式两类。对比分析了德国MSP500、意大利“梅杜莎MK4”、英国2500型、以色列Toplite、美国SeaFLIR 280-HD和380-HD、瑞典EOS 500、法国EOMS NG和PASEO等典型光电指向器的结构形式、传感器配置、作用距离及与火控系统的关系。指出光电指向器的结构由“T型”逐渐发展为“U型”,光电传感器的波段由单一波段发展为多个波段,光电跟踪系统的功能由单一功能向综合多功能转变。随着现代海战对抗加剧,舰载光电跟踪与火控系统将朝着多传感器协同探测、信息融合、多目标识别、智能跟踪、使命任务多样化方向发展。     

Laser-Induced Growth Device and Optical Properties of ZnO MicrocrystalsEI北大核心CSCD

ZnO is third-generation semiconductors which can be used as the carrier of ultraviolet photoluminescence and multiresonance mode laser. In recent years, ZnO microcrystals prepared by optical vapor supersaturation precipitation (OVSP) have shown important advantages in photocatalysis, efficient multi-color light source and efficient electroluminescence. However, the high preparation cost and low production efficiency hinder the development of the large-scale device. In this work, we designed and built a set of growth devices with a working wavelength of 1 080 nm and a power of 18% (@2 500 W) laser heating. The height of the raw material rod was 6. 5 mm, and the diameter was 8 mm. The results show that the morphology, structure, and luminescence properties of the products prepared by this device are very close to those prepared by the OVSP method, and the production efficiency is greatly improved (similar to 500 %). The growth device successfully prepared acceptor-rich ZnO single crystal micro rods with complete hexagonal cross-section morphology. The diameter and length of ZnO micro rods are about 3. 8 and 10 similar to 20 mu m, respectively. Raman spectra show that the Raman peaks of ZnO micro rods are sharp, and the Raman mode at 437 cm(-1) indicates that the ZnO micro rods are hexagonal wurtzite structures with good crystallinity. By analysing the PL spectra of ZnO micro rods, it was found that the ZnO microtubes prepared by the OVSP method had a similar ultraviolet bimodal structure, indicating that there exists an abundant zinc-vacancies acceptor. In the 80 similar to 280 K range, with the increase of temperature, the fluorescence intensity of ZnO microrods appears "thermal quenching-negative thermal quenching-thermal quenching" behavior. The negative thermal quenching behavior in the range of 166 similar to 200 K is related to the intermediate state energy level (trap center) at 477 meV below the conduction band bottom, and the thermal quenching phenomenon in the range of 200 similar to 280 K is related to the non-radiative recombination center at 600 meV below the conduction band bottom. The appearance of both is related to the prepared ZnO microrod oxygen vacancy (V-o) defect. The laser growth device developed in this paper has high feasibility and practicability. This preparation method lays a technical foundation for the rapid batch growth of ZnO single crystal micro rods with rich acceptors and is also of great significance for its application in optoelectronic devices.     

Selection and optimization of mirror structure of off-axis two-mirror afocal system北大核心CSCD

According to the structural characteristics of aspheric off-axis two-mirror optical system, the imaging characteristics of the system were analyzed by using primary aberration theory. Based on the characteristics of different aspheric surfaces, the vector expression of system aberrations was derived. Using the Seidel coefficients, the primary wave aberration of systems were expanded and values of system aberration for different aspheric surface shapes were specifically calculated. After the evaluation index of the off-axis structure was determined, the imaging qualities of different surface shape combinations were compared. Then the optimal surface shape selection method was analyzed by quantitative comparison results. The results show that compared with other reflector combination methods, the spherical aberration, coma and astigmatism of the off-axis double paraboloid system are all 0, the wavefront RMS is much better than λ/14 (λ=0.587 6 μm), and the Strehl ratio is greater than 0.8. According to the calculation results, it not only has a stronger ability to suppress multiple primary aberrations, but also can effectively compress the volume of the system. Copyright ©2022 Journal of Applied Optics. All rights reserved.