硼硅酸盐矿物硼的化学分离纯化与同位素测定方法

采用碱熔法分解电气石样品,研究了3种不同纯化分离方法对硼回收和同位素测定的影响。实验表明:电气石中富含的Fe³⁺和Al³⁺对甲亚胺-H酸分光光度法测定硼含量有较大干扰,并在硼特效树脂交换分离中形成氢氧化物沉淀,阻塞交换柱;同时吸附溶液中硼元素造成回收率降低。本实验依次采用阴/阳离子混合树脂,硼特效树脂和阴/阳离子混合树脂三步离子交换进行电气石样品的纯化分离方法,实现了复杂基体中硼的完全回收（回收率99%）。在TIMS（Triton TI）采用H3和H4法拉第杯,并通过优化Zoom Optics参数（Focus Quad:15;Dispersion Quad:-85）实现静态双接收硼同位素组成测定。本方法对NIST SRM 951标准样品测定结果为¹¹B/¹⁰B=4.05044±0.00012（2σ,n=8,1μg B）,测定内外精度优于传统的动态峰跳扫。NIST SRM951测定结果为-0.3‰,表明预处理过程中无硼同位素分馏效应。天然样品硼同位素组成分别采用静态多接收PTIMS-Cs₂BO₂⁺法和MC-ICP-MS测定,数据点基本分布在1:1线上,说明MC-ICP-MS测定结果与PTIMS方法结果相一致。     

电感耦合等离子体质谱法测定硼同位素丰度

以硼同位素标准物质NIST SRM 951配制标准溶液,在优化的仪器操作条件下对电感耦合等离子体质谱(ICP-MS)测定的硼同位素质量进行校正,求出校正因子,确定了样品的线性浓度范围,选定样品浓度为1.1 mg/L。在同样的仪器条件下首先测定了硼标准物质的硼同位素丰度比,测量误差为0.2%,然后测定了硼同位素浓缩过程中硼样品的硼同位素丰度比,测定结果的相对标准偏差为1.1%。此外考察了仪器的稳定性。实验结果表明本方法“记忆效应”小,结果可靠,测量精度高。     

多接收电感耦合等离子体质谱法高精密度测定汞同位素组成

采用多接收等离子体质谱(MC-ICP-MS)方法高精度测定了Hg同位素组成.本方法借助在线进样系统,最大程度上克服了同位素干扰和基体效应;采用同位素内标法和样品-标准交叉法以消除仪器自身的质量分馏;通过实验条件(如测定时间、进样量等)的优化,方法的内精度显著提高.研究表明: 为保证汞同位素组成的高精度测定,汞最低进样浓度为2 μg/L时,内精度＜0.02‰(RSD).运用本方法对汞标准NIST SRM 3133和UM-Almadén实验室内标样长达7个月的测定,结果表明,本方法外精度＜0.06‰(2SD).此外,对一系列环境样品的同位素组成进行了测定,样品的外精度＜0.10‰(2SD).测定样品δ202Hg变化范围为-3.48‰～0 63‰, 幅度达4.11‰.     

基于Cs2Br+静态多接收正热电离质谱法高精度测定溴同位素

采用Triton热电离质谱仪,在8 kV加速电压下,建立了基于Cs2Br+为检测离子的稳定溴同位素比值静态多接收测定方法,实现了溴同位素组成的高精度正热电离质谱法测定,并对溴同位素测试过程中B和C1元素的影响、点样顺序的影响等进行了研究.结果表明,静态多接收法测定Br同位素和传统的峰跳扫法相比具有精度高(外精度在0.09‰～0.18‰之间)、涂样量小(10～ 20 μg Br)和测试时间短(采集100个数据只需8 min)的优点,不同含量的C1对Br同位素比值的影响随着C1含量的升高而增强,B的存在使溴同位素测定值偏低.涂样顺序对溴同位素测定结果没有表现出明显差异.同时,测定了4个溴化物化学试剂中的溴同位素组成,其同位素组成介于0.61‰～ 1.68‰,呈现出明显的溴同位素分馏现象.     

氢化物发生-多接收杯电感耦合等离子体质谱同位素稀释法测定硒同位素

使用改进的巯基棉分离流程和74 硒-77 硒双稀释剂, 在氢化物(HG)-多接收器电感耦合等离子体质谱仪(MC-ICP-MS)实现了高精度硒同位素组成的测定.巯基棉用于分离样品基质中的硒, 随后使用HNO3 H2O2消除干扰的有机质, 74 硒-77 硒双稀释剂校正样品分离和质谱测定过程中的硒同位素质量分馏.硒标准溶液NIST SRM3149和MH495几个月的测定表明,该方法的外精度为0.1‰(2σ),样品的外精度为0.15 ‰～0.2‰(2σ).以TCF分离硒的平均回收率85%计算, 最小硒需要量为20 ng. 实验结果以相对于NIST SRM3149的δ82/76 Se表达, δ82/76MH495/SRM3149＝-3.44±0.1‰(2σ), 优于已发表的数据δ82/76MH495/SRM3149＝-3.04±0.5‰.测定样品的δ82/76SRM3149为-13.53 ‰～11.37‰,为硒同位素在环境、农业、生命和地球科学中的拓展应用与发展奠定了基础.     

电感耦合等离子体质谱法测定水泥样品中的铅同位素比值

研究和讨论了用电感耦合等离子体质谱仪(ICP—MS)测定铅的同位素比值测定时，影响测试结果的准确度和精密度的主要因素及其优化过程。在优化后的仪器分析条件下，测定5μg/L的NIST SRM981自然丰度铅同位素标准溶液的各对铅同位素比值，获得的^207Pb／^206Pb分析精度可优于0．1％。在该条件下测定了14个不同的水泥粉样品中的铅同位素比值，结果显示：铅的同位素比值分析技术可以用来示踪环境监测样品的铅污染源。     

低硼富含有机质的河/雨水正热电离硼同位素的测定

对低硼富含有机质的河/雨水样品硼的分离方法及硼同位素组成的测定进行了研究.采用硼特效树脂富集河/雨水样品,结合微升华技术去除有机质;采用正热离子质谱法进行硼同位素组成的测定.全流程回收率在97.50%～101.17%之间,测试数据和多接受电感耦合等离子体质谱比较接近,测试精度小于0.05‰.经本方法处理后的样品能满足同...     

磷酸硼中三氧化二硼的测定方法研究

研究了以KOH为熔剂,高温熔融样品,Pb(NO3)2分离磷酸根,甘露醇作H3BO3强化剂,电位差滴定测定磷酸硼中三氧化二硼的分析方法.该方法的回收率为98%～99%,RSD 0.3%～0.4%,能满足科研和生产的分析需要.     

催化动力学光度法测定大花红景天中的硒(Ⅳ)

建立了测定大花红景天中硒的一种新的催化动力学光度法.在酸性介质中,硒(Ⅳ)能催化H2O2氧化溴酚蓝-丁基罗丹明B的褪色反应,硒(Ⅳ)含量在0～5 μg/L范围内与褪色反应速率成正比.样品经HNO3-HClO4消化后直接测定硒(Ⅳ)的含量,该方法具有良好的选择性和准确度.用于大花红景天中硒的测定.     

应用多接收器电感耦合等离子体质谱法测定海洋碳酸盐中稳定铅同位素组成

研究了多接收器电感耦合等离子体质谱仪(MC-ICP MS)测定铅同位素比值时,影响测试结果准确度和精密度的主要因素及其优化过程。在优化条件下,10 h内连续30次测定4 ng/mL NIST SRM 981同位素标准溶液铅同位素比值,获得208Pb/206Pb、207Pb/206Pb和206Pb/204Pb相对标准偏差(RSDs)分别为0.005%、0.004%和0.054%。长期监测208Pb/206Pb、207Pb/206Pb和206Pb/204Pb,标准偏差(2SDs)分别为0.000 06、0.000 05和0.006 7。采用NEPTUNE MC-ICP MS法测定了低铅海洋碳酸盐样品中稳定铅的同位素比值,并对南海橙黄滨珊瑚(Porites lutea)和库氏砗磲(Tridacna gigas)进行了分析,得到全流程空白为8～10 pg,重复样误差优于0.1%。经0.50 mol/L HNO3洗脱之后,得到海南珊瑚样品中208Pb/206Pb、207Pb/206Pb的比值分别为2.086 2±0.001 5、0.849 90±0.001 47(n=16);海南砗磲样品中208Pb/206Pb、207Pb/206Pb的比值分别为2.116 9±0.004 2、0.864 81±0.001 62(n=9)。进一步考察了南海海洋碳酸盐中204Pb的同位素比值。分析结果表明,南海海洋碳酸盐中稳定铅同位素比值与中国气溶胶、珠江三角洲大气沉降、黄土及南海海底玄武岩等具有很好的相关性。方法适用于复杂基体高钙低铅的海洋碳酸盐样品中铅同位素比值的分析。     

Spectrophotometric assay of cephalosporins in pharmaceutical products,using chromotrope 2B and chromotrope 2R

A simple, rapid and sensitive Spectrophotometric method is proposed for the determination of cephadroxil (I), cephalexin (II) and cephradine (III). The method is based on ion-pair complex formation between these derivatives and Chromotrope 2B (C2B) or Chromotrope 2R (C2R), to give a highly coloured radical anion. The coloured products are quantified spectrophotometrically at 542 and 564 nm for C2B and C2R, respectively. The optimization of the experimental conditions is described. The method has been used for the determination of 0.4–15, 0.4–14 and 0.4–18 g/ml of drugs I, II and III, respectively. The accuracy of the method is indicated by the excellent recovery (100.0±1.7%) and the precision is supported by the low relative standard deviations 1.5%. The sensitivity of the method is discussed and the results are compared with the official method. The interference from common degradation products and excipients was also studied. The proposed method was applied successfully to the determination of the different cephalosporins in dosage forms, with good precision and accuracy. The results were compared with those given by the official B.P. 1993 method.     

Square-wave cathodic adsorptive stripping voltammetric determination of trace amounts of 2-mercaptobenzimidazole in water samples

A sensitive, simple and reproducible square-wave cathodic adsorptive stripping voltammetric method is developed for the determination of 2-mercaptobenzimidazole (MBIM) in different water samples using a static mercury drop electrode (SMDE) as a working electrode. The solution conditions and instrumental parameters were optimized for the determination of MBIM by square-wave cathodic adsorptive stripping voltammetry. This method is based on a sensitive adsorptive reduction peak of the MBIM at ?0.532 V vs. Ag/AgCl reference electrode in a Britton-Robinson buffer at pH 10.0. The linear concentration range was 20–600 ng ml^?1 when using 0.0 V as the accumulation potential. The detection limit of the method was calculated to be 8.41 ng ml^?1. The precision was excellent with relative standard deviations (n = 20) of 2.30%, 1.71%, 2.25% and 1.33% at MBIM concentrations of 40, 90, 200 and 500 ng ml^?1, respectively. The proposed voltammetric method is used for the determination of MBIM in different spiked water samples.     

Ab initio dynamic study of the reaction of Cl2LaR (R=H, CH3) with H2

In this paper, a comparison between "static" and "dynamic" determination of the thermodynamic (DeltarF degrees) and kinetic data (DeltarF#) for the reaction of Cl2LaR (R=H, CH3) and H2 is given. A difference is obtained in the case of the reaction between Cl2LaH and H2 and can be attributed to a failure of the "static" approach based on the harmonic approximation. The influence of the zero point energy correction is also analyzed but does not explain the 30% difference between the two calculated activation energies. The influence of the flatness of the potential energy surface around the transition state is proved as no such an effect is observed for the reaction of Cl2LaCH3 and H2.     

A system for the automated static headspace analysis of dissolved N2O in seawater

A new automated static headspace N₂O analysis technique has been developed that includes a CTC autosampler composed of agitator and headspace modules, a combined-valve switching system and ECD Gas Chromatography. This new CTC autosampling technique is more efficient for sample analysis than similar systems and takes approximately 10 mins to analyze each sample without pre-equilibration. The accuracy and precision of this method are approximately 2% each. Laboratory and field results demonstrate that this technique is suitable for seawater sample analysis.     

Simultaneous determination of vitamins D2 and D3 by LC-MS/MS in infant formula and adult nutritionals: First Action 2011.13

During the "Standards Development and International Harmonization: AOAC INTERNATIONAL Mid-Year Meeting" held on June 29, 2011, an Expert Review Panel (ERP) on behalf of AOAC INTERNATIONAL adopted the method "Simultaneous Determination of Vitamins D2 and D3 by LC-MS/MS in Infant Formula and Adult Nutritionals" as an AOAC Official First Action method. Vitamins D2 and D3 are extracted from the sample using pentane-ether; the extract is collected and dried under nitrogen. Vitamin D is separated from interfering compounds using UPLC, and quantitated using tandem mass spectrometry (MS/MS). Preliminary data showed the intermediate precision ranged from 3.34-8.05% and an accuracy range of 98.5-111% over the samples tested for vitamin D3. For vitamin D2, the intermediate precision ranged from 2.37-5.45% and accuracy ranged from 96.4-104% over the four matrixes evaluated. The analytical range for the method is bounded by the concentrations of the working standards, 21-270 ng/mL, and is equivalent to 0.168-2.16 mcg/100 g in ready-to-feed product. The practical method quantitation limit is 0.168 mcg/100 g product with method detection limit of 60 ng/100 g product. The ERP reviewed the data and determined that the performance characteristics of the method met the standard method performance requirements, and therefore the method was granted First Action status.     

Precision study on capillary electrophoresis methods for metacycline

A CE method for metacycline (MTC) determination was investigated in an inter-laboratory experiment. Many problems were encountered in this study, most of which were related to the transfer of the method to different CE equipment. The reported problems could be classified into different categories: problems related to the precision, to the parameters in the protocol, and to the MTC peak shape. As the peak shape problem was partially responsible for the poor precision, a new CE method was developed in order to obtain a good MTC peak shape on all equipment. The precision of this new method for MTC determination was examined in an intermediate precision study, where the influence of the factors "time" and "equipment" was investigated. Although the new method could be transferred to different instruments, the precision remained poor mainly due to the contributions of the between-replicate and the between-injection variances.     

Automation and optimization of liquid-phase microextraction by gas chromatography

Several fully automated liquid-phase microextraction (LPME) techniques, including static headspace LPME (HS-LPME) (a drop of solvent is suspended at the tip of a microsyringe needle and exposed to the headspace of the sample solution), exposed dynamic HS-LPME (the solvent is exposed in the headspace of sample vial for different time, and then withdrawn into the barrel of the syringe. This procedure is repeated a number of times), unexposed dynamic HS-LPME (the solvent is moved inside the needle and the barrel of a syringe, and the gaseous sample is withdrawn into the barrel and then ejected), static direct-immersed LPME (DI-LPME) (a drop of solvent is suspended at the tip of a microsyringe needle and directly immersed into the sample solution), dynamic DI-LPME (the solvent is moved inside the needle and the barrel of a syringe, and the sample solution is withdrawn and ejected), and two phase hollow fiber-protected LPME (HF-LPME) (a hollow fiber is used to stabilize and protect the solvent), auto-performed with a commercial CTC CombiPal autosampler, are described in this paper. Critical experimental factors, including temperature, choice of extraction solvent, solvent volume, plunger movement rate, and extraction time were investigated. Among the three HS-LPME techniques that were evaluated, the exposed dynamic HS-LPME technique provided the best performance, compared to the unexposed dynamic HS-LPME and static HS-LPME approaches. For DI-LPME, the dynamic process can enhance the extraction efficiency and the achieved method precision is comparable with the static DI-LPME technique. The precision of the fully automated HF-LPME is quite acceptable (RSD values below 6.8%), and the concentration enrichment factors are better than the DI-LPME approaches. The fully automated LPME techniques are more accurate and more convenient, and the reproducibility achieved eliminates the need for an internal standard to improve the method precision.     

Pressurised hot water extraction in continuous flow mode for thermolabile compounds: extraction of polyphenols in red onions

Extraction and analysis of labile compounds in complex sample matrices, such as plants, is often a big analytical challenge. In this work, the use of a “green and clean” pressurised hot water extraction (PHWE) approach performed in continuous flow mode is explored. Experimental data for extraction and degradation kinetics of selected compounds were utilised to develop a continuous flow extraction (CFE) method targeting thermolabile polyphenols in red onions, with detection by high-performance liquid chromatography (HPLC)–diode array detection (DAD)–mass spectrometry (MS). Water containing ethanol and formic acid was used as extraction solvent. Method performance was focused on extraction yield with minimal analyte degradation. By adjusting the flow rate of the extraction solvent, degradation effects were minimised, and complete extraction could be achieved within 60 min. The CFE extraction yields of the polyphenols investigated were 80–90 % of the theoretically calculated quantitative yields and were significantly higher than the yields obtained by conventional methanol extraction and static batch extraction (70–79 and 58–67 % of the theoretical yields, respectively). The precision of the developed method was lower than 8 % expressed as relative standard deviation.

Constrained-pairing mean-field theory. V. Triplet pairing formalism

Describing strong (also known as static) correlation caused by degenerate or nearly degenerate orbitals near the Fermi level remains a theoretical challenge, particularly in molecular systems. Constrained-pairing mean-field theory has been quite successful, capturing the effects of static correlation in bond formation and breaking in closed-shell molecular systems by using singlet electron entanglement to model static correlation at mean-field computational cost. This work extends the previous formalism to include triplet pairing. Additionally, a spin orbital extension of the "odd-electron" formalism is presented as a method for understanding electron entanglement in molecules.     

Synthesis and pyrolysis of perfluoroazo-2-propane

An improved method has been used to synthesize perfluoroazo-2-propane. Pyrolysis over the temperature range 450–514 K in a static system has been shown to be a homogeneous, first-order process. No pressure dependence was observed in the presence of excess inert gas (SF₆). The only products were nitrogen and perfluoro-2,3-dimethylbutane. The rate constant (k) for the decomposition process is given by: These results lead to a straightforward mechanism for the decomposition process The results are compared with those for other azo compounds. © 1994 John Wiley & Sons, Inc.