Single-laboratory validated method for determination of nordihydroguaiaretic acid in chaparral-containing dietary supplements

Nordihydroguaiaretic acid (NDGA) occurs naturally in chaparral (Larrea tridentate Coville), a plant which commonly grows in the Southwest United States and has been used for medicinal purposes by Native Americans indigenous to that region. In addition to its traditional use as a tea, manufacturers of dietary supplements have marketed chaparral-containing products in a variety of formulations. Because of the hepatotoxicity of NDGA, and its occurrence in regulated products, we have developed a method for the determination of NDGA in dietary supplements and have tested this method in several dietary supplement formulations. Products were extracted with 80% methanol, filtered, and analyzed by high-performance liquid chromatography. NDGA was detected and determined with both a diode array detector and negative-ion electrospray. Fragmentation in the triple-quadrupole mass spectrometer was obtained by collisional activation of the [M-H](-) ion. Collisional activation produced sufficient fragmentation to provide unambiguous identification. Lack of a stable isotope labeled internal standard has led us to compare quantitations based on UV detection with quantitations based on tandem mass spectrometry (MS/MS). Presence of NDGA was confirmed in several dietary supplement products. Quantitative results from the 2 detection methods were comparable for most products. The limit of quantitation using MS/MS was lower and fewer interferences were observed, although UV detection provided better linearity.     

158 A Ge V p-Pb Pb-Pb碰撞中的单奇异和多奇异粒子产生

用描写相对论性核 核碰撞的LUCIAE模型及相应的MonteCarlo事例产生器分析了WA97最近发表的 1 5 8AGeVp Pb和Pb Pb碰撞中单奇异粒子 (Λ ,Λ)和多奇异粒子 (Ξ-,Ξ-,Ω-,Ω-)的多重数和横质量分布 .由于LUCIAE模型包含了弦碎裂微观过程中奇异夸克压低因子随碰撞体系的能量、中心度和质量的增大而增大 ,以及由它导致的相对论性核 核碰撞宏观过程中奇异粒子产额随上述三因素之增而增的物理机制 ;LUCIAE模型计算结果能较好描写WA97实验所揭示的相对论性核 核碰撞中奇异粒子产额随中心度之增而增和奇异粒子增强随奇异夸克数之增而增的实验事实 ,以及单奇异和多奇异粒子的横质量分布 .     

Saturation Effects and the Colored Pump Noise in a Dye Laser

We investigate the statistical properties of two single-mode dye-laser models-the colored-loss-noise model and the colored-gain-noise model. Analytic expressions of the probability,the mean and the variance of the steady-state laser intensity are obtained through the unified expansion theory [Phys. Rev. A43 (1991) 700]. By comparison we find that when the cavity decay rate for the electric field is large and the pump parameter a₀ is small, the differences of the results of the two laser models are small. Otherwise, the differences are large. And the correlation time of the noise has very obvious influence on the results of the two models.     

Combining targeted and nontargeted data analysis for liquid chromatography/high‐resolution mass spectrometric analyses

Increasing importation of food and the diversity of potential contaminants have necessitated more analytical testing of these foods. Historically, mass spectrometric methods for testing foods were confined to monitoring selected ions (SIM or MRM), achieving sensitivity by focusing on targeted ion signals. A limiting factor in this approach is that any contaminants not included on the target list are not typically identified and retrospective data mining is limited. A potential solution is to utilize high‐resolution MS to acquire accurate mass full‐scan data. Based on the instrumental resolution, these data can be correlated to the actual mass of a contaminant, which would allow for identification of both target compounds and compounds that are not on a target list (nontargets). The focus of this research was to develop software algorithms to provide rapid and accurate data processing of LC/MS data to identify both targeted and nontargeted analytes. Software from a commercial vendor was developed to process LC/MS data and the results were compared to an alternate, vendor‐supplied solution. The commercial software performed well and demonstrated the potential for a fully automated processing solution.     

网络上两类物资联合最大流问题的极流特征

当网络上(诸如交通网络、通讯网络)有多种不同物资或信息同时分别从相应的发点输送到相应的收点,要求每条线路上各类物资或信息的输送量总和不超过线路的容量时,寻求所有物资的最大输送量的问题,就是所谓网络多种物资的最大流问题,这个问题在生产实际和理论上都有着重要的意义,1963年T.C.Hu提出了求两类物资联合最大流的标号方法,但是为了保证有限步达到最大流,要求边的容量是偶数。 本文是文献[3]的继续,用图论的语言描述了两类物资最大流问题极流的特征,并对标号方法作了一点修改,使得有限步得到最大流,或者在某一步得到极流后,保证以后的迭代是从极流到极流.这样因极流的个数是有限的,并且最大流总可以在极流上达到,从而保证了有限步内得到所要求的最大流,无须对边的容量作任何限制, 本文所提的算法是使图形特征很强的标号算法和线性规划的极点迭代结合起来,这就使得有可能把这种方法,推广到更大的一类问题中,例如,研究容量的改变对最大流量的影响。     

Mechanism for dehalogenation reactions in fast atom bombardment mass spectrometry

The mechanism of a dehalogenation reaction that occurs during fast atom bombardment (FAB) mass spectrometry was examined using halogenated nucleosides as model compounds. For aglycone-halogenated nucleosides, an inverse linear relationship exists between the extent of FAB dehalogenation and the calculated electron affinity of an individual nucleoside. The degree of dehalogenation for a given nucleoside also varies inversely with the calculated electron affinity of most FAB matrices. The observed dehalogenation reaction can be completely inhibited when matrices with positive electron affinities, such as 3-nitrobenzyl alcohol and 2-hydroxyethyl disulfide, are used. High-performance liquid chromatographic analysis of the bulk glycerol matrix following exposure to the FAB beam indicates measurable amounts of dehalogenated product, suggesting that this reaction occurs in the condensed phase prior to gas-phase ion formation. A dehalogenation mechanism involving thermal electron capture and subsequent negative charge stabilization is consistent with these observations.     

分子束研究GaAs和InP与氯的激光化学反应动态学

本文采用CW超声分子束和时间分辨质谱技术,研究了在紫外和可见(355nm和560nm)脉冲激光辐照下GaAs(100)和InP(100)表面与氯的激光化学反应动态学。由质谱和飞行时间谱测得反应的主要产物为GaCl_x和InCl_x(x=1,2),研究了激光波长和能量密度对产物飞行时间谱的影响,首次发现提高入射Cl₂分子的平动能对上述激光诱导气-固相反应有明显的增强作用。     

Experimental factors affecting the quality and reproducibility of MALDI TOF mass spectra obtained from whole bacteria cells

Numerous experimental factors are shown to significantly influence the spectra obtained when bacteria are analyzed by MALDI TOF/MS. Detailed investigation of the instrument parameters and sample preparation are all shown to influence the spectra. Of these, the preanalysis sample preparation steps incorporate the most important elements influencing the quality and reproducibility of the spectra. Some of the most important sample preparation factors include the method employed for sterilization, the type of matrix, the matrix solvent and concentration of cells in the matrix, as well as the type and concentration of acid added to the matrix. The effects of these parameters, as well as other aspects of sample preparation and the effects of several instrumental parameters on spectra are presented. Optimization and control of all experimental variables leads to a stable protocol for analysis of bacteria. The protocol employs a Nd:Yag laser and describes both sample handling and instrument conditions which consistently yield reproducible MALDI TOF mass spectra with greater than 25 peaks from both gram-positive and gram-negative bacteria.     

A Study of Synthesis, Immobilization and Catalytic Capability of Metalloporphyrin

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