气相色谱-串联质谱法测定茶叶中88种农药残留量

采用气相色谱-串联质谱(GC-MS/MS)分析技术,建立了高灵敏度检测茶叶中88种农药残留量的方法。目标化合物经加速溶剂萃取(ASE), Carb/NH2净化小柱净化,乙腈-甲苯(3:1, v/v)洗脱,采用GC-MS/MS测定。对方法的准确性、精密度、线性范围、最低检出限(LOD)和定量限(LOQ)进行了测试。其中87.5%的农药在低水平(6.4 μg/kg)的加标回收率为70%～100%; 87.5%的农药的相对标准偏差(RSD)小于15%。每个化合物均采用灵敏度最高的离子对进行定量,并采用空白茶叶基质配制标准工作液。LOQ以10倍信噪比(S/N=10)计算,86.4%农药的LOQ值低于10 μg/kg。该方法灵敏度高、准确、可靠,适用于绿茶、乌龙茶、红茶以及普洱茶中多种农药残留量的检测。     

光度法快速测定铜合金中微量铝

在pH 4-6的六次甲基四胺介质中,显色剂偶氮氯膦I与铝形成稳定的蓝紫色络合物.讨论了吸收光谱、酸度、试剂用量、干扰离子等因素对实验的影响,确定了反应的最佳条件.铝含量在0-25μg/(50 mL )范围内符合比耳定律,铝络合物在600 nm处有最大吸收,表观摩尔吸光系数为3.9×104L/(mol·cm).用EDTA...     

Liquid chromatography/mass spectrometry-based metabolic profiling to elucidate chemical differences of tobacco leaves between Zimbabwe and China

An approach was developed for extracting and analyzing the chemical components of tobacco leaves based on solvent extraction and rapid & resolution liquid chromatography/quadrupole time-of-flight mass spectrometry analysis. Two solvents with different polarities were used to extract hydrophilic components and hydrophobic components, respectively, the combined analytical data can provide a "global" view of metabolites. Based on the evaluation of parallel samples, it was found that this approach provided good repeatability, accurate and reliable profiling data, and is suitable for the metabolomics study of tobacco leaves. In order to find the chemical component differences of tobacco leaves, 56 samples from Zimbabwe and China were analyzed using the developed method. The metabolite data were processed by multivariate statistic technique; an obvious group classification between Zimbabwe and China was observed, 14 significantly changed compounds were found, and 9 of them were identified.     

Gas chromatography-mass spectrometric method for metabolic profiling of tobacco leaves

A gas chromatography-mass spectrometric method was developed for profiling of tobacco leaves. The differentiation among tobacco leaves planted in two different regions was investigated. Prior to analysis, the extraction solvent formulation was optimized and a combination of water, methanol and acetonitrile with a volume ratio of 3:1:1 was found to be optimal. The reproducibility of the method was satisfactory. Kendall tau-b rank correlation coefficients were equal to 1 (p<0.05) for 82% of the resolved peaks (up to 95% of the overall peak areas), indicating the good response correlation. Forty-four compounds including 9 saccharides, 9 alcohols, 9 amino acids, 16 organic acids and phosphoric acid were identified based on standard compounds. The method was successfully applied for profiling of tobacco leaves from Zimbabwe and Yunnan of China. Our result revealed that levels of saccharides and their derivatives including xylose, ribose, fructose, glucose, turanose, xylitol and glyceric acid were more abundant while sucrose, glucitol and D-gluconic acid were less abundant in tobacco leaves from Yunnan as compared to those from Zimbabwe. Amino acids such as L-alanine, L-tyrosine and L-threonine were found to be richer in Zimbabwe tobacco than in Yunnan tobacco.     

On the block GMRES method with deflated restarting

In this paper, we consider the block-GMRES method with deflated restarting for solving nonsymmetric linear systems with multiple right-hand sides. We modify slightly the restarted block-GMRES method with deflation of eigenvalues proposed by Morgan to obtain a new one. It is shown that the modified method is mathematically equivalent to the Morgan’s original method. However, the error analysis shows the modified version minimizes the numerical errors during a restart and therefore is better suited if the linear systems have to be solved with high precision. Numerical experiments report the effectiveness of the modified method.     

Determination of cusp forms by central values of Rankin–Selberg <Emphasis Type="BoldItalic">L</Emphasis>-functions<Superscript>*</Superscript>

Let f be a fixed holomorphic Hecke eigen cusp form of weight k for \( SL\left( {2,{\mathbb Z}} \right) \), and let \( {\mathcal U} = \left\{ {{u_j}:j \geqslant 1} \right\} \) be an orthonormal basis of Hecke–Maass cusp forms for \( SL\left( {2,{\mathbb Z}} \right) \). We prove an asymptotic formula for the twisted first moment of the Rankin–Selberg L-functions \( L\left( {s,f \otimes {u_j}} \right) \) at \( s = \frac{1}{2} \) as u _j runs over \( {\mathcal U} \). It follows that f is uniquely determined by the central values of the family of Rankin–Selberg L-functions \( \left\{ {L\left( {s,f \otimes {u_j}} \right):{u_j} \in {\mathcal U}} \right\} \).     

Structures and stabilities of the donor–acceptor complexes HXPY (X=Al,B; Y=H,F, OH)

The optimized geometries, complexation energies, etc. of HXPY (X?=?Al, B; Y?=?H, F, OH) donor–acceptor complexes have been investigated at the B3LYP/6-311+G(d,p), MP2/6-311+G(d,p) and/or CCSD(T)/6-311+G(d,p) levels. The results show that HBPY (Y?=?H, F, OH) is more stable than the corresponding HAlPY (Y?=?H, F, OH), F (or OH) substitution on phosphorus results in decreasing complex stability, and the stronger the electron-attracting nature of the substitution atom, the more stable the complex. Moreover, the thermodynamic and kinetic properties of the formation reaction of these donor–acceptor complexes were also examined within the temperature range 200–800?K using the general statistical thermodynamics and Eyring transition state theory with Wigner correction. It is concluded that the formation of HBPY is thermodynamically favoured over that of the corresponding HAlPY, especially at low temperature, and is kinetically favoured over that of the relevant HAlPY (Y?=?H, F, OH), especially at high temperature.     

Study on Adsorption States by Surface-Enhanced Raman Spectroscopy

Abstract

SERS has been used as a state-resolving probe to study the adsorption states. in the case of pyridine (Py) adsorbed on the Ag electrode surface, the equilibrium and transition between two adsorbed states, i.e., the perpendicular mode adsorbed through the nitrogen lone-pair electrons and the flat mode through the π electrons of the aromatic ring, were studied. It was found that in the low pyridine concentration or the initial stage of adsorption, the flat mode was favored. While the concentration became higher and the adsorption tended to equilibrium, the adsorbed molecules would transit to the perpendicular mode. The similar phenomenon was also observed when changing the applied electric potential and the pH value of the solution. In the case of the adsorption of Methylene Blue (MB) on the HNO₃-etched silver surface, the influence of Cl^? ions on the adsorption states of MB was investigated. It showed that MB molecules adsorbed on the silver surface tended to transform from the “lying-down” state to the “end-on” state while adding Cl^? ions.     

A CLASS OF RANDOM NUMBER GENERATORS BASED ON WEYL SEQUENCE

The generation of good pseudo-random numbers is the base of many important fields in scientific computing, such as randomized algorithms and numerical solution of stochastic differential equations. In this paper, a class of random number generators （RNGs） based on Weyl sequence is proposed. The uniformity of those RNGs is proved theoretically. Statistical and numerical computations show the efficiency of the methods.     

GF（4）上RM展式系数转换的高效算法

在二值和多值逻辑研究中,最常用的两种函数表达式是基于格代数的SOP表达式和基于Galois域的Reed-Muller展式(RM展式)。由RM展式实现的电路由于具有故障诊断容易和线性运算功能,因而在可靠性设计、编码理论和数字通信中得到了广泛的应用。然而,RM展式系数向量不象SOP表达式那样与函数值向量有直接对应关系,因此RM展式系数向