Determination of Arsenic in Honey,Propolis, Pollen,and Honey Bees by Microwave Digestion and Hydride Generation Flame Atomic Absorption

The toxic properties of arsenic are well known. Honey has been widely used for monitoring this element. The present work reports a novel method for the determination of arsenic in honey, bees, pollen, and propolis, based on the coupling of microwave digestion and hydride generation. Method development included the quantitative reduction of arsenic(V) to arsenic(III), the acid used for dilution, and the complete removal of the gases following digestion. The method performance was satisfactory with recoveries between 83% and 111% and corresponding relative standard deviations between 3.1% and 24%. Among the 32 samples of honey, propolis, pollen, and honey bees analyzed, arsenic was detected in four out of six propolis samples at the method limit of detection (0.4?µg?g^?1). The results indicate that propolis may be an efficient indicator for arsenic.     

Determination of Immunoglobulin G by a Hemin–Manganese(IV) Oxide-Labeled Enzyme-linked Immunosorbent Assay

An enzyme-linked immunosorbent assay (ELISA) is reported for human immunoglobulin G based on synthesized hemin–MnO₂ nanocomposite as the label. Enhanced sensitivity was obtained due to the increased catalytic activity of the hemin–MnO₂ nanocomposite toward 3,3′,5,5′-tetramethylbenzidine compared to hemin and MnO₂ alone. The synthesized hemin–MnO₂ nanocomposite was characterized by transmission electron microscopy and its catalytic activity to 3,3′,5,5′-tetramethylbenzidine was investigated by ultraviolet–visible absorption spectroscopy. After assembly of the sandwich-type immunoassay in the 96 wells of the plate the hemin–MnO₂-based label catalyzed 3,3′,5,5′-tetramethylbenzidine into blue compounds that were monitored by a plate reader. The absorbance increased with the concentration of human immunoglobulin G. The immunoassay displayed high sensitivity, a long linear dynamic range, and good selectivity for human immunoglobulin G. The immunoassay was also used for the determination of human immunoglobulin G in serum with favorable results. The developed assay combines the high throughput and low cost of ELISA with the simplicity of nanocomposite labeling and is suitable for application in clinical diagnosis.     

Determination of Chromium (VI) in Airborne Particulate Matter by Electrothermal Atomic Absorption Spectrometry

Hexavalent chromium Cr(VI) is a well-established carcinogen associated with lung, nasal, and sinus cancer. Cr(VI) threshold limit values in workroom air have been recently lowered. Consequently, the currently available analytical methods are insufficiently sensitive or high cost. In this paper, a simple, cost-effective, sensitive, and reproducible method using solid-phase extraction with electrothermal atomic absorption spectrometry for determination of hexavalent chromium in airborne samples is reported. The method validation included selectivity, linearity, accuracy, and precision. Interferences from other ions likely to be present in airborne samples, including trivalent chromium, were tested and selectivity was demonstrated. The detection and quantification limits were, respectively, as low as 0.1 and 0.4?µg?L^?1. The linearity ranged from 0.5 to 50.0?µg?L^?1, with a regression coefficients exceeding 0.998. The extraction recovery exceeded 98%. The developed method was successfully compared with a reference spectrophotometric method. The performances achieved were similar to ion chromatography and high-performance liquid chromatography approaches. The novel method was tested on airborne samples collected from the workplace. The method’s performance suggests that it may be an alternative to high-cost techniques for monitoring occupational exposure to hexavalent chromium.     

In situ PM‐IRRAS studies of organothiols and organosilane monolayers–ZnO interfaces at high water activities

In situ photoelastic‐modulated Fourier transform infrared reflection absorption spectroscopy has been applied for the investigation of interfacial stability of organothiol and organosilane monolayer films on nanocrystalline zinc oxide thin films. It has been shown that for octadecyltriethoxysilane films, exposure to high water activities results in physisorption of water in the cross‐linked film. This high water activity at the interface leads to a reversible wet de‐adhesion of the interfacial silanol groups from the ZnO surface. However, the organothiol seems to form a denser monolayer and a stable by S–Zn bond that is resistant to the competition with adsorbed water. The reversible attachment for cross‐linked organosilanol films has been demonstrated for the first time by means of an in situ spectroscopic method on model ZnO surfaces. Copyright © 2016 John Wiley & Sons, Ltd.     

五乙烯六胺改性金属有机骨架材料MIL-101(Cr)对CO_2的吸附性能

采用溶剂热法合成金属有机骨架材料MIL-101(Cr),用回流法将五乙烯六胺(PEHA)负载到MIL-101(Cr)孔道中的不饱和金属位点上,使用扫描电镜、粉末X射线衍射、氮气物理吸附、元素分析和傅里叶变换红外光谱等表征手段考察材料的结构和形貌,测试氨基改性前后的MIL-101(Cr)在25℃、不同压力下对CO_2的吸附效果。结果表明,负载0.24 m L五乙烯六胺后的MIL-101(Cr)对CO_2的吸附效果最好,在25℃、常压下对CO_2的饱和吸附量可达58.944 mg/g,相比未负载五乙烯六胺的MIL-101(Cr)吸附量(CO_2饱和吸附量为44.208 mg/g)增加了33%。随着吸附压力的增加,MIL-101(Cr)和0.24PEHAM IL-101(Cr)对CO_2的饱和吸附量逐渐增加,当吸附压力为1.1 MPa时,两者的吸附量分别为1 147.59和1 256.74 mg/g,表明该类材料在高压下对CO_2有着良好的吸附效果。     

Cu分隔开的Pd单原子用于乙炔选择加氢:Cu担载量的影响

大量乙烯中少量乙炔的去除是化工生产中的重要过程之一,理想途径是将其选择加氢生成乙烯.负载型Pd催化剂因具有很高的乙炔转化率而被广泛用于该过程,但乙烯选择性很低,同时会使原料气中的乙烯被加氢,造成原料气的浪费.采用其它元素对Pd纳米粒子表面修饰,覆盖部分活性位,可以在一定程度上提高乙烯选择性,但是会大大降低Pd的利用率.因此,制备兼具高活性和高选择性且经济实用的催化剂,仍是这一过程亟待解决的主要问题之一.我们的前期工作中,将Pd与IB族金属(Au,Ag,Cu)分别结合制备得到了一系列含Pd的合金单原子催化剂(SAC),发现它们在大量乙烯存在条件下的乙炔选择加氢反应中表现出优异的催化性能.其中,Pd的用量仅为ppm级别,大大提高了Pd的利用率.作为IB族最为廉价的金属,Pd与Cu形成的合金SAC在提高Pd原子利用率的同时,能够进一步降低催化剂的经济成本.然而,当形成合金SAC时,Cu/Pd原子比例的极限值仍然不确定.本文通过固定Pd的担载量,采用简单的等体积共浸渍的方法,制备了一系列不同Cu/Pd原子比例的氧化硅负载的双金属催化剂.首先,我们采用程序升温还原(TPR)和X射线衍射(XRD)对催化剂的还原能力和双金属纳米粒子的尺寸进行了考察.进一步,采用X射线吸收光谱(XAS,包括EXAFS和XANES)对双金属催化剂中Pd的配位环境进行了分析.最后,结合它们在大量乙烯存在条件下的乙炔选择加氢反应中的催化性能,对形成合金SAC时Cu/Pd原子比例进行了讨论.TPR结果显示,Cu与Pd结合时会促进双金属纳米粒子的还原.XRD结果表明,随着Cu含量的降低,双金属纳米粒子的尺寸明显减小.XANES结果证实,当Pd与Cu结合时,Pd会带有部分负电荷,这也与Pd的电负性大于Cu相一致.通过对EXAFS拟合结果进行分析,我们发现当Cu/Pd的原子比例≥40/1时,Pd原子可以被Cu原子完全分隔开,形成含Pd的合金SAC,使其在大量乙烯存在条件下的乙炔选择加氢反应中表现出优异的催化性能.通过对还原温度的考察,我们发现还原温度由250 oC升高到400 oC时,对同一催化剂的催化性能影响不大;EXAFS拟合结果显示,对比分别经过250和400 oC还原后的催化剂,Pd的配位环境变化不明显,这可能是导致催化性能相似的主要原因.     

Absorption,transportation and distribution of imidacloprid in maize

The neonicotinoid imidacloprid is a very important insecticide in maize cultivation in China. A laboratory experiment was conducted to investigate its absorption, transportation and distribution in maize plants. Plants were exposed to an aqueous solution of imidacloprid at five concentrations (10, 20, 50, 100 and 200 μg/mL). The residues of imidacloprid in different plant parts were determined by using a quick and effective method of high-performance liquid chromatography. Results showed that the average recoveries ranged from 85.16% to 102.23%, with relative standard deviations of 1.82–4.40% at three different spiking levels in each different matrix. The half-lives of imidacloprid in hydroponic maize water were from 5.33 to 11.55 days. The concentrations in roots, stems and leaves were from 5.61 to 7.48, 1.03 to 4.03 and 0 to 30.57 μg/mL after 6 h–7 days exposed in 10 μg/mL imidacloprid aqueous solutions, respectively. Our study showed that imidacloprid was strongly absorbed by roots and mainly accumulated in leaves. Quantity ratio and bioconcentration factors (BCFs) were also used to estimate the distribution and accumulation in maize. The values of quantity ratios were the highest in the leaves while lowest in the root after 7 days treatments, with the ranking of leaves > stem > root. The BCFs were 0.63–1.66, 0.52–0.92 and 3.20–6.78 in root, stem and leaves, respectively. These results demonstrated that the exposed time and imidacloprid application concentrations were also the main factors influencing the absorption. This study enhances our understandings of the uptake and distribution of imidacloprid in maize plants.     

Determination of selected trace elements in marine biota samples with the application of fast temperature programs and solid sampling continuous source high resolution atomic absorption spectroscopy: method validation

Analytical procedure for the determination of As, Cd, Cu, Ni, Co and Cr in marine biota samples using solid sampling high-resolution continuum source atomic absorption spectrometry (HR CS AAS) and accelerated fast temperature programmes has been developed. Calibration technique based on the use of solid certified reference materials similar to the nature of the analysed sample and statistics of regression analysis were applied. A validation approach in line with the requirements of ISO 17025 standard and Eurachem guidelines was followed. Accordingly, blanks, selectivity, calibration, linearity, working range, trueness, repeatability and reproducibility, limits of detection and quantification and expanded uncertainty for all investigated elements were assessed. The major contributors to the combined uncertainty of the analyte mass fractions were found to be the homogeneity of the samples and the microbalance precision. Traceability to the SI system of units of the obtained with the proposed analytical procedure results was also demonstrated. The potential of the proposed analytical procedure based on solid sampling HR CS AAS technique was demonstrated by direct analysis of marine reference biota samples. Overall, the use of solid sampling HR CS AAS permits obtaining significant advantages for the determination of selected trace elements in marine biota samples, such as straightforward calibration, a high sample throughput, sufficient precision, a suitable limit of detection and reduced risk of analyte loss and contamination.     

Switchable solvent based liquid phase microextraction of palladium coupled with determination by flame atomic absorption spectrometry

A switchable solvent-based micro-extraction method for pre-concentration and separation of ultratrace palladium was developed prior to its flame atomic absorption spectrometric detection. Reverse change of hydrophilicity of N,N-dimethylcyclohexylamine (DMA) was achieved by reaction with carbonated water. The hydrophilic bicarbonate salt of the protonated DMA was used as extractant for palladium complexed with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). Formation of the hydrophobic form of switchable solvent from hydrophilic form of switchable solvent phase was achieved by addition of sodium hydroxide into the extractant-sample solution. The effect of key parameters affected extraction recovery was studied and optimised by using Plackett–Burman design, central composite design and three dimension (3D) surfaces response. The calibration plot was linear in the range 0.015–1.6 mg L^?1 of palladium with a correlation coefficient of 0.999. The limit of detections values of palladium for liquid and solid samples were 4.28 μg L^?1 and 0.54 µg g^?1, respectively. The pre-concentration factor was 37.5. The accuracy was confirmed by determination of palladium in certified reference material. The procedure was also applied for determination of palladium content of real samples as automotive catalytic converter, roadside dust, sea water and river water.