Determination of Cu and Ni in plants by microdialysis sampling: Comparison of dialyzable metal fractions with total metal content

Microdialysis sampling is presented as an in situ sampling and sample clean-up technique with the potential to be used for determination of metals in plant suspension. Suspensions prepared from ultra pure water and flowers of a Blepharis aspera plant species obtained from a Cu and Ni mineralized site were sampled for Cu and Ni by microdialysis sampling after incorporating an optimal 0.05% (w/v) composition of humic acid in the perfusion liquid. Acid digestion of the plant samples was employed for quantification of Cu and Ni by flame atomic absorption spectrometry. All microdialysis sampling experiments were carried out at room temperature under quiescent conditions using a concentric type of microdialysis probe and electrothermal atomic absorption spectrometry was employed for metal quantification. The versatility of microdialysis as an in situ sampling and sample clean-up technique was demonstrated by the ability to sample Cu and Ni from the complex matrices of plant suspensions. Linear relations between the concentrations of Cu and Ni determined after microdialysis sampling and acid digestion were established and the constant concentration ratios of the metals were found to be 0.0138 and 0.0440 respectively for Cu and Ni thus demonstrating the potential that microdialysis sampling has in prediction of metal concentrations in plant suspension after direct relation with the acid digestion method.     

Comparison of sonic spray lonization with atmospheric pressure chemical lonization as an interface of liquid chromatography-mass spectrometry for the analysis of some local anesthetics

Summary Sonic spray ionization (SSI) was compared with atmospheric pressure chemical ionization (APCI) as an interface for liquid chromatography (LC)-mass spectrometry (MS) for the analysis of some local anesthetics. Peaks at [M+H]⁺ constituted the base peaks for all compounds by both SSI and APCI, except for prilocaine. The sensitivities by SSI for tetracaine, benzoxinate, dibucaine, bupivacaine and mepivacaine were 4–16 times higher than those by APCI; those by SSI for procaine and lidocaine were equivalent to those by APCI. Only for prilocaine was the sensitivity by SSI two times lower than that by APCI. In view of the higher sensitivities obtained for many local anesthetics by SSI, we established a detailed procedure for the assay of these drugs in human plasma and urine by LC-MS with SSI in combination with a diol-bonded silica gel HPLC column that enabled direct injection of crude biological samples without complicated pretreatment. The recoveries, sensitivities, accuracies and precisions were found satisfactory to quantitate them at their therapeutic levels.     

精确固定节面量子Monte：Carlo差值法

本文提出了精确固定节面量子Monte Carlo差值法，这个新算法能够在精确固定节面量子Monte Carlo方法的基础上直接计算两个体系之间的能量差，且使计算结果的统计误差达到10-2 kJ/mol 数量级，获得电子相关能90%以上。我们把这个新算法应用于分子势能面的研究中，使用一个“刚性移动”模型，利用Jacobi变换使分子两个几何构型的能量计算具有很好的正相关性，因而能得到准确的能量差值，于是精确的分子势能面就可以得到。这个新算法已经被使用到BH分子基态势能曲线和H₃分子势能面的研究。这个算法还可应用于分子光谱、化学反应能量变化值等领域的研究。     

LJUNGSKILE: a program for assessing uncertainties in speciation calculations

Speciation calculations are often the base upon which further and more important conclusions are drawn, e.g., solubilities and sorption estimates used for retention of hazardous materials. Since speciation calculations are based on experimentally determined stability constants of the relevant chemical reactions, the measurement and experimental uncertainty in these constants will affect the reliability of the simulation output. The present knowledge of the thermodynamic data relevant for predicting the behaviour of a complex chemical system is quite heterogeneous. In order to predict the impact of these uncertainties on the reliability of a simulation output requires sophisticated modelling codes. In this paper, we will present a computer program, LJUNGSKILE, which utilises the thermodynamic equilibrium code PHREEQC to statistically calculate uncertainties in speciation based on uncertainties in stability constants. A short example is included.     

STM-theory: Image potential, chemistry and surface relaxation

A critical review of the different methods used nowadays for calculating tunneling currents and STM-images is presented with a special emphasis on the role played by the interface image potential and the interaction between the tip and the sample at short distances. After presenting the most commonly used approaches to this problem, we discuss in full detail how the image potential modifies critically the interface tip–sample barrier and how neglecting this effect underestimates the tunneling currents by several orders of magnitude. Although interface non-local image potential effects are difficult to introduce in a plane-wave Density Functional approach, we show how a Green’s function Density Functional formalism based on a local-orbital basis set allows us to introduce those image effects with a good accuracy. The effect of the interaction between the tip and the sample is illustrated for an Al-tip approaching an Al surface; and the role of the electronegative atoms adsorbed on the tip is discussed considering the O/Pd(1 1 1) interface and the effect of having an O-atom adsorbed on the tip apex. Finally, by analyzing the Si(1 1 2)–Ga interface we also show how the Green’s function Density Functional approach based on a local orbital basis can also be reliably used to analyze surface steochiometries.     

悬浮液进样原子吸收光谱分析中样品的粒径效应

研究了悬浮液进样 FAAS和悬浮液进样 GFAAS中样品粒径效应。实验表明 ,悬浮液颗粒粒径 <30 μm能满足石墨炉原子化测定需要 ,而火焰原子化要求在粒径≤ 5 μm的前提下 ,再根据待测元素的性质选择合适的火焰类型 ,方能达到较满意的测定效果。     

预置粒子对均匀胶体粒子形成的影响

研究预置粒子对于均匀胶体粒子形成的影响,对深入了解均匀粒子的形成机理以及开拓覆盖技术的应用具有重要意义.所谓预置粒子就是在经升温陈化能够生成均匀胶体粒子的溶液中,于陈化前加入的具有一定形态(组成、形状和大小),一定浓度的胶体粒子,新形成的沉淀物因预置粒子的表面性质、形态和浓度的不同而变化.据文献报导,新沉淀的形成过程有:①新粒子的形成与预置粒子的存在无关,新沉淀物独立成核并成长为独立的稳定     

Gas-phase combination reactions of SF4 and SF5 with F in plasmas of SF6

Reactions of both SF₄ and SF₅ with F have been studied at 295 K in a gas-flow reactor sampled by a mass spectrometer. The rate coefficient for the combination reaction of F with SF₄ to produce SF₅ was found to increase from (0.9 to 3.0)×10^–12 cm³ s^–1 when the helium bath gas number density was increased from (2 to 26)×10¹⁶ cm^–3. The values obtained here are three orders of magnitude higher than a recent estimate of the high-pressure value based on the modelling of photochemical studies. The experimental results have been compared with RRKM and master equation calculations in which a simplified Gorin model has been used to determine the structure of the transition state. These calculations show that reasonable agreement can be obtained between the experimental data and the calculation if a small (2 KJ/mol) activation energy is assumed. The rate coefficient for the reaction between SF₅ and F to produce SF₆ was found to be independent of helium bath gas number density within the range given above. The value obtained for the rate coefficient was 9×10^–12 cm³ s^–1 with an uncertainty of a factor of 2. This value is close to that of 1×10^–11 cm³ s^–1 computed from the simplified Gorin model and to the value of 1.7×10^–11 cm³ s^–1 deduced from modelling of photochemical experiments.     

Comparison of the evaporation processes of classical spectrography and optical spectrometry tandem technique for the determination of the relevant environmental elements

The evaporation as a part of the spectrochemical excitation process is a complicated procedure during which different thermo-chemical reactions connected mainly to the formation of carbides are overshot. This one is accelerated namely at the 4000 K on the top of the carrier electrode. The carbide creation markedly affects the evaporation process of single elements of the given matrix and modifies this process. In spite of this it is evident that the intensity of the DC arc has a significant impact on the evaporation of all elements. The evaporation capability of two optical methods, the classical non-controlled direct current (DC) arc spectrography and the PC controlled DC arc optical emission spectrometry, have been compared for the determination of some environmental important elements (Al, Cr, Ni, and V). The experiments were carried out using grating spectrograph PGS-2 and simultaneous multi-channel LECO 750 spectrometer which is connected to a separated evaporation cell and adjusted to the Marinković plasma source. Standardized evaporation curves were designed and the half-time (t_50%) values and the total (t_100%) evaporation time values were calculated. The basic statistical evaluation was done and the main figures of the merit were calculated.     

The UCB/MPE cassegrain submillimeter heterodyne spectrometer

The UCB/MPE Submillimeter Heterodyne Spectrometer is a system for ascronomical spectroscopy in the high-frequency atmospheric windows from 500 to 1000 GHz. It contains a molecular laser local oscillator, a cooled Schottky open structure mixer, a quasi-optical coupling system, and an acousto-optical spectrometer. The compact receiver mounts at the Cassegrain focus of large infrared astronomical telescopes. The receiver noise temperature on the telescope is approximately 3500 K (DSB) during observations of the CO J=76 line at 806.652 GHz. The spectrometer's frequency resolution and instantaneous bandwidth (<2 MHz resolution across 1.1 GHz) are well suited for observations of molecular emission lines from a variety of astronomical sources.