An on‐line sample pretreatment technique for the HPLC analysis of plant samples

A continuous‐flow, on‐line sample pretreatment technique using a silica gel microsyringe extractor has been developed. All steps including extraction, separation, clean‐up, and concentration occur in the microsyringe. The overall sample pretreatment process takes <10 min per sample. Different polarity chemicals in the plant sample are successively extracted and separated, and analyzed in parallel using HPLC–UV and HPLC–UV–MS/MS. Polycyclic aromatic hydrocarbons, alkylphenols, and plant hormones were determined as model compounds for nonpolar, intermediate polarity, and polar fractions, respectively. All the parameters that influence the extraction and separation efficiency of the microsyringe extractor have been optimized and evaluated. Under the optimized conditions, recoveries of target compounds ranged from 78.4 to 101.9%, the RSD was <12.8% and the square of the correlation coefficient was >0.99. Complex plant samples of Sambucus Mandshurica Kitag have been tested using this method. Fluorene, phenanthrene, pyrene, and plant hormones were detected in all the samples, and concentrations ranged from 24.2–34.9, 43.8–67.1, 25.9–29.2, and 14.5～110.8 ng/g, respectively.     

沉积物中壬基苯酚类雌性激素化合物的加速溶剂提取方法研究

为了同时提取和检测沉积物中的雌性激素化合物对壬基苯酚(NP)、对壬基苯酚一乙氧醚(NP1EO)和对壬基苯酚二乙氧醚(NP2EO),对加速溶剂提取体系的各种条件和对壬基苯酚类化合物的硅烷基化反应条件等进行了优化。在丙酮和丙酮-二氯甲烷混合液(丙酮含量≥60%)介质中,这些化合物的硅烷基化反应很快达到反应终点。加速溶剂提取体系的最佳提取条件是120℃、8.4MPa、两次循环提取;最佳提取溶剂是二氯甲烷。与索氏提取和酸化悬浮液液提取比较,明显提高了提取率、重现性和准确性。平均添标回收率在89.3%~95.7%之间,相对标准偏差为2.3%~13.4%。本方法对壬基苯酚、对壬基苯酚一乙氧醚和对壬基苯酚二乙氧醚化合物的检出限分别为10、30、35ng/gdw(干重)。     

MALDI-TOF-MS analysis of small molecules using modified mesoporous material SBA-15 as assisted matrix

Mesoporous silica, SBA-15 was successfully functionalized with quinoline moiety, and was applied as a matrix in the MALDI-TOF-MS analysis of small molecules. The modified SBA-15 material [SBA-15-8-(3-(triethoxysilyl)propoxy) quinoline, SBA-15-8QSi] was obtained by using calcined SBA-15 and 8-hydroxy quinoline. The structure of the functionalized mesoporous material was systemically characterized by TEM, the N₂ adsorption-desorption isotherm technique and FT-IR spectra. Compared with DHB and SBA-15, SBA-15-8QSi demonstrated several advantages in the analysis of small molecules with MALDI-TOF-MS, such as less background interference ions, high homogeneity, and better reproducibility. Based on these results, the various analytical parameters were optimized. The ideal operating conditions were (1) methanol used as the dissolving solvent; (2) sample first dropping method; (3) a ratio between the analyte and the matrix of 3.5:10. Under these optimization conditions, a low detection limit (8 pmol for L-Arginine-HCl) and high reproducibility (≤29%) were obtained. This technique was successfully applied to the analysis of various types of small molecules, such as saccharides, amino acids, metabolites, and natural honey.     

关于国家自然科学基金资助摩擦学基础研究的分析与讨论

本文首先对国家自然科学基金在１９８６－１９９１年间资助摩擦学基础研究的情况进行了简洁的分析，接着就其资助办法作了介绍，最后着重对如何利用科学基金促进摩擦学的发展问题作了讨论，指出应当把坚持应用摩擦学学科发展战略的研究成果、鼓励和支持创新性研究、积极支持交叉学科研究和注意扶植新的学科生长点、加强摩擦学研究与实际应用相结合和促进优秀青年摩擦学研究人才的迅速成长等作为国家自然科学基金资助摩擦学基础研究的     

Gas purge microsyringe extraction for quantitative direct gas chromatographic-mass spectrometric analysis of volatile and semivolatile chemicals

Sample pretreatment before chromatographic analysis is the most time consuming and error prone part of analytical procedures, yet it is a key factor in the final success of the analysis. A quantitative and fast liquid phase microextraction technique termed as gas purge microsyringe extraction (GP-MSE) has been developed for simultaneous direct gas chromatography-mass spectrometry (GC-MS) analysis of volatile and semivolatile chemicals without cleanup process. Use of a gas flowing system, temperature control and a conventional microsyringe greatly increased the surface area of the liquid phase micro solvent, and led to quantitative recoveries of both volatile and semivolatile chemicals within short extraction time of only 2 min. Recoveries of polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and alkylphenols (APs) determined were 85-107%, and reproducibility was between 2.8% and 8.5%. In particular, the technique shows high sensitivity for semivolatile chemicals which is difficult to achieve in other sample pretreatment techniques such as headspace-liquid phase microextraction. The variables affecting extraction efficiency such as gas flow rate, extraction time, extracting solvent type, temperature of sample and extracting solvent were investigated. Finally, the technique was evaluated to determine PAHs, APs and OCPs from plant and soil samples. The experimental results demonstrated that the technique is economic, sensitive to both volatile and semivolatile chemicals, is fast, simple to operate, and allows quantitative extraction. On-site monitoring of volatile and semivolatile chemicals is now possible using this technique due to the simplification and speed of sample treatment.     

A BLOW-UP RESULT FOR A CLASS DOUBLY NONLINEAR PARABOLIC EQUATIONS WITH VARIABLE-EXPONENT NONLINEARITIES

This paper deals with the following doubly nonlinear parabolic equations(u + |u|~(r(x)-2)u)t-div(|?u|~(m(x)-2)?u) = |u|~(p(x)-2)u, where the exponents of nonlinearity r(x), m(x) and p(x) are given functions. Under some appropriate assumptions on the exponents of nonlinearity, and with certain initial data, a blow-up result is established with positive initial energy.     

Application of pressurized fluid extraction technique in the gas chromatography-mass spectrometry determination of sterols from marine sediment samples

In order to determine steroid compounds in GC/MS an analytical method using pressurized fluid extraction (PFE) was developed. While extracting in-house reference material (coastal sediment) typical recovery in PFE ranged from 80 to 120% (+/-2.5-14.5) and the average extraction yield in PFE in comparison to conventional soxhlet extraction was 115%. In particular, the PFE showed higher extraction efficiency for C29 and dien sterols. Optimizing parameters such as temperature and pressure is critical in achieving this efficiency. Sterols in the sediment were derivatized with silyl reagent BSTFA in acetone for the final determination. A short column florisil cleanup offered the best separation of the GC/MS sensitive derivatives from co-contaminants. Thirty-three coastal sediment samples were analyzed using PFE and Soxhlet extraction methods. The results on extraction efficiency, silyl derivatization kinetics and purification efficiency demonstrated that PFE is far superior in extracting sterols from sediment samples. It is simple, fast, efficient and amenable for automation.     

Studies on the Binary Coalescence Model

The jumping coalescence phenomenon between two separate water drops under microgravitation was observed for the first time. Two suspended water drops separated by quite a distance (0.558 mm) coalesce in a certain time (158 s) without any extra forces. The coalescence driving force within the water drops should be responsible for the jumping coalescence phenomenon. Copyright 2001 Academic Press.     

A Study of the Measurement of Surface and Interfacial Tension by the Maximum Liquid Drop Volume Method

The maximum liquid drop volume (v(max)) is measured by using a back-suction micrometer syringe piston technique. Different very viscous liquids are measured by (v(max)) and (v(f)) methods to observe the effect of viscosity on tension measurement. No apparent viscosity effect was observed in surface tension data obtained by using Harkins-Brown factors and the theoretical correction factors in the viscosity range 5.9-100,900 mP. Copyright 2001 Academic Press.