Determination of arsenic in gold by flow injection inductively coupled plasma mass spectrometry with matrix removal by reductive precipitation

Arsenic was determined in gold by flow injection hydride generation inductively coupled plasma-mass spectrometry following a batch mode reductive precipitation removal of the interfering gold matrix. A solution of potassium iodide, L-ascorbic acid, and hydrochloric acid was used as the reluctant. The recovery of gold by precipitation and filtration was 99 ± 3%. The detection limit for arsenic in gold was 55 ng g⁻¹ in the solid. The concentration of arsenic that was determined in the Royal Canadian Mint gold sample FAU-10 was 29.7 μg g⁻¹ in the solid; this value was indistinguishable, with 95% confidence, from values determined at the Royal Canadian Mint by graphite furnace atomic absorption spectrometry and by inductively coupled plasma-mass spectrometry. The standard deviation for four replicate determinations of the arsenic in FAU-10 was 0.972 μg g⁻¹ in the solid.     

Mass spectroscopy and SEC of SRM 1487, a low molecular weight poly(methyl methacrylate) standard

Matrix Assisted Laser Desorption Ionization (MALDI) Time of Flight (TOF) Mass Spectrometry (MS) was used to study the molecular weight distribution (MWD) and the number of α-methyl styrene (α-MeSty) repeat units in SRM 1487, a narrow MWD poly(methyl methacrylate) (PMMA) standard reference material of about 6300 g/mol, which was initiated with α-MeSty. It was found that each PMMA polymer chain had from zero to seven α-MeStys per chain. The MWD of the polymer chains containing a fixed number of α-MeStys was obtained. The MWD, M_w, and the average number of α-MeSty at a given molecular weight from MALDI TOF MS compare well with those obtained from more traditional methods such as ultracentrifugation and Size Exclusion Chromatography (SEC). The implications of the number of α-MeStys per chain is discussed in terms of the chemistry of anionic polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2409–2419, 1997     

基质与分析物的摩尔比和激光能量对分析物离子信号的影响

A method of aerosol introduction for matrix-assisted laser desorption/ionization (MALDI) is described. The aerosol particles containing matrix and analyte enter directly into the aerosol time-of-flight mass spectrometer (ATOFMS) at atmospheric pressure. The scattered light signals from the aerosol particles are collected by a photomultiplier tube (PMT) and are passed on to an external electronic timing circuit, which determines particle size and is used to trigger a 266 nm pulsed Nd:YAG laser. The aerosol MALDI mass spectra and aerodynamic diameter of single particles can be obtained in real-time. Compared with other methods of liquid sample introduction, this method realizes detection of single particles and, more importantly, the sample consumption is lower. The effects of matrix-to-analyte ratio and laser pulse energy on analyte ion yield are examined. The optimal matrix-to-analyte ratio and laser energy are 50-110:1 and 200-400 μJ respectively.     

蓄冷器丝网填料的空隙率的估算方法探讨

首先简要介绍一下目前蓄冷器采用的丝网材料的性能、现状、要求。由于其空隙率对制冷机的性能有很大的影响,以及在进行制冷机设计计算与性能模拟中,丝网材料的空隙率也是一个很重要的参数,文中针对目前存在的多种丝网空隙率的估算方法进行统计分析,并根据较精确的实测结果来对比,得出结论:在蓄冷器进行设计计算以及性能模拟时,可以选择文中的公式(4)对空隙率进行较好的估算。     

Impact of Eutectic Solvents Utilization in the Microwave Assisted Extraction of Proanthocyanidins from Grape Pomace

The extraction of proanthocyanidins (PACs), despite being an important and limiting aspect of their industrial application, is still largely unexplored. Herein, the possibility of combining eutectic solvents (ESs) with microwave assisted extraction (MAE) in the extraction of PACs from grape pomace (GP) is explored, aiming to improve not only the extraction yield but also the mean degree of polymerization (mDP). The combination of choline chloride with lactic acid was shown to be the most effective combination for PACs extraction yield (135 mg_PAC/g_GP) and, despite the occurrence of some depolymerization, also enabled us to achieve the highest mDP (7.13). Additionally, the combination with MAE enabled the process to be completed in 3.56 min, resulting in a considerably reduced extraction time.     

HPTLC and ATR/FTIR Characterization of Antioxidants in Different Rosemary Extracts

The effect of spontaneous fermentation by lactic acid bacteria on the extraction yield of bioactive compounds and antioxidant activity from rosemary leaf extracts was investigated using high-performance thin-layer chromatography (HPTLC). Brining and spontaneous fermentation with lactic acid bacteria more than doubled extraction of polyphenolics and antioxidants from the rosemary leaves. The results show that lactic acid fermentation enhances antioxidant activity in extracts by increasing the total phenolic content but does not increase extraction of phytosterols. Increased extraction of phenolic oxidants during fermentation assisted extraction, results from the in situ generated natural eutectic solvent from the plant sample. ATR-FTIR spectra from the bioactive bands suggests that this increased antioxidant activity is associated with increased extraction of rosmarinic acid, depolymerised lignin, abietane diterpenoids and 15-hydroxy-7-oxodehydroabietic acid.     

Isolation and Characterization of a Bioactive Polysaccharide from Panax Quinquefolium L.

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离散时间代数Riccati方程的解矩阵的下界与上界

本文讨论离散时间代数Ｒｉｃｃａｔｉ方程ＡＴＸＡ－Ｘ－（ＡＴＸＢ＋Ｌ）（Ｒ＋ＢＴＸＢ）＾－１（ＬＴ＋ＢＴＸＡ）＋Ｑ＝０的唯一对称正定解的上界和下界。     

激光探针等离子质谱法分析岩石样品时相对元素响应及基体效应

研究了ＬＡＭ－ＩＣＰ－ＭＳ法分析岩石样品时以＾４３Ｃａ和＾５５Ｍｎ为内标的相对元素响应因子特征并进行了对比。以＾４３Ｃａ为内标不能消除ＬＡＭ－ＩＣＰ－ＭＳ分析中的基体效应,而以＾５５Ｍｎ为内标可明显地减弱基体效应的影响。测定了６个日本火成岩岩石标样中的３２个微量元素,除个别样品（如ＪＧ－３）和少数轻质量元素Ｐ、Ｓｃ、Ｃｒ以及重稀土元素Ｄｙ、Ｅｒ、Ｙｂ等外,绝大多数微量元素的分析值与标准植的相对偏差     

石墨炉原子吸收光谱法测定生物样品中微量锗

采用钼酸铵浸渍处理石墨管 ,研究了苯基荧光酮为螯合剂 ,四氯化碳为萃取剂 ,N ,N 二甲基甲酰胺 (DMF)为反萃取剂的萃取富集锗的新方法 ,用硝酸镍作为基体改进剂 ,石墨炉原子吸收光谱法直接测定各种生物样品中微量锗。方法绝对灵敏度 (1%吸收 )为 1.67× 10 - 11g ,相对标准偏差 3.5 4 %～ 6.15 % ,回收率为 96%～ 10 2 %