989 resultados para H2O
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The structure of silicon surfaces in the orientation range (113)-(5,5,12)-(337)-(112) has been investigated using high resolution LEED and photoemission both on a spherical and on flat samples. We find that Si(5,5,12) [5.3 degrees from (113) and 0.7 degrees from (937)] is the only stable orientation between (113) and (111) and confirm the result of Baski et al. [Science 269, 1556 (1995)] that it has a 2 x 1 superstructure with a very large unit cell of 7.68 x 53.5 Angstrom(2). Adsorption measurements of water on Si(5,5,12) yield a mobile precursor kinetics with two kinds of regions saturating at 0.25 and 0.15 ML which are related to adsorption on different sites. Using these results, a modified structure model is proposed. Surfaces between (113) and (5,5,12) separate into facets of these two orientations; between (5,5,12) and (112), they separate into (5,5,12) and (111) facets. (337) facets in this range may be considered as defective (5,5,12) facets.
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单株树木CO2和H2O交换的研究对森林生态系统碳水循环的深入理解具有重要意义,而目前尚未有使用可靠、操作简便、商品化的成熟观测系统直接应用于单株尺度气体交换观测。 本研究基于国内外常用的美国LI-COR公司生产的Li-6400便携式光合仪,自行设计制作了两套箱式气体交换观测系统:闭路箱式气体交换观测系统和开路箱式气体交换观测系统。对这两套系统进行了调试和评价后,利用这两套系统,以长白山红松针阔叶林主要优势种水曲柳(Fraxinus mandshurica)为试验材料,探讨了单株CO2和H2O交换的日变化特征,并与单叶尺度气体交换结果进行了对比分析。主要结论有: 1)本研究设计制作的闭路和开路箱式气体交换观测系统具有经济实用,适用范围广、改造方便和操作简单等特点。实现了单株树木CO2和H2O气体浓度的同时观测,且能自动采集和存储数据,能够自动监测箱体空气温度、空气相对湿度、光合有效辐射和大气压等环境因子。 2)闭路箱式气体交换观测系统密闭性较好,但在测定过程中箱内气温和相对湿度会升高,其上升速率随着外界气温的升高而增加。基于仪器响应和环境控制等方面的考虑,该系统在应用时实际观测时间为200s,除去20s的混合响应时间,使用180s的数据。该系统环境控制标准为:箱内外温差 <3℃, 箱内外相对湿度差< 10%。 3)开路箱式气体交换观测系统在测定时箱内的环境因子与箱外接近,箱内外的气温和相对湿度差异都很小,与外界气温平均相差1℃以内,相对湿度的最大差异也仅为8.53%。确定开路系统的观测时间为600s,在数据处理过程中需要出气口气体浓度数据进行延迟处理。 4)冠层不同位置叶片的气体交换速率日变化特征为:垂直方向上,由下至上三个层次叶片的平均气体交换速率表现为第三层 >第一层 >第二层;水平方向上,东西南北四个方位叶片的平均净CO2交换速率表现为南向叶>西向叶>北向叶>东向叶,而平均H2O交换速率为西向叶> 南向叶>北向叶>东向叶。不同层次和不同方位叶片的气体交换日变化曲线的走势主要与光合有效辐射PAR和饱和水汽压差VPD的日变化有关,另外还与各叶片氮含量的差异也有关系。 5)闭路和开路箱式气体交换系统对水曲柳单株气体交换速率的日变化观测表明:两套系统内的环境因子基本得到了有效控制,但开路系统优于闭路系统。两套系统测定的单株尺度气体交换速率日变化趋势与各自当天的光合有效辐射变化相同,这与单叶尺度的气体交换表现一致。另外,单株尺度的CO2交换速率与光合有效辐射存在双曲线关系,而该尺度的H2O交换速率与PAR存在线性关系
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本研究以本实验室分离的有机磷农药高效降解菌Pseudomonas sp.WBC-3为材料,通过X-射线晶体学研究确定了甲基对硫磷水解酶(MPH)的三维结构,并在结构基础上探讨了甲基对硫磷水解酶的结构与功能的关系。利用生物信息学手段对Pseudomonas sP.WBC-3中的甲基对硫磷水解酶基因进行分析,推测论H的结构基因的编码序列为398-1393 bp,蛋白大小为331个氨基酸,且具有一个由35个氨基酸组成的信号肤。同时发现,MPH是一个不同于具有相似生物学功能的有机磷水解酶(OPH)的蛋白质,而且在PDB库中尚无与MPH同源性较高的蛋白结构。晶体的生长依赖于高纯度的蛋白质的获得。在本研究中,我们采用阳离子交换树脂和凝胶过滤两步纯化获得了纯度达95%以上的MPH溶液,并采用等离子体质谱仪测定MPH为含锌的金属酶。采用悬滴蒸汽扩散法获得了PI和P43212两种晶型的晶体以及硒标记的MPH晶体。在获得单晶以后,最终利用尸43212晶型的晶体通过多波长反常散射法(MAD)解析了MPH的三维结构。MPH的晶体结构为同源二聚体,具有与OPH类似的二价金属离子组成的活性中心:其中一个单体含有两个锌离子,另一个单体含有一个锌离子和一个锅离子;每个单体的两个金属离子通过AsP 151、His 152、His 302、His 147、His 149、His 234和A印255与蛋白质相连,一个H2O分子桥连于两个金属离子,还有一个H2O分子只与一个金属离子配位。在MPH三维结构知识的基础上,利用分子生物学手段对MPH活性中心附近可能的底物结合氨基酸位点进行了研究。通过定点突变获得了针对Trp179,Phe 196和Phe 119三个位点的六个突变体W179F、W179A、F196W、F196A、FllgW和Fll9A,系统比较了突变体与野生酶的催化动力学特点。结果表明Trp 179,Phel%是MPH活性中心的底物结合部位的关键氨基酸。而Phe 119在与底物结合中的作用不明显。
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A novel method based on wavelength-multiplexed line-of-sight absorption and profile fitting for non-uniform flow field measurement is reported. A wavelength scanning combing laser temperature and current modulation WMS scheme is used to implement the wavelength-multiplexed-profile fitting method. Second harmonic (2f) signal of eight H2O transitions features near 7,170 cm(-1) are measured in one period using a single tunable diode laser. Spatial resolved temperature distribution upon a CH4/air premixed flat flame burner is obtained. The result validates the feasibility of strategy for non-uniform flow field diagnostics by means of WMS-2f TDLAS.
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本文基于可调谐二极管激光器吸收光谱技术(TDLAS),利用7185.597 cm-1、7444.37cm-1+7444.37cm-1(重合吸收线)两条H2O吸收线,采用分时扫描-直接探测策略组建多光路吸收测量系统,在4kHz的测量频率下,定量测量了燃烧室气流的静温、水蒸气浓度和流向速度。利用位移机构,在以C2H4为燃料的超燃直连式试验台中,在单次试验中同时诊断燃烧室内某截面和燃烧室出口的气流参数截面分布。具体工作可分为以下三部分:测量燃烧室出口截面的水蒸气浓度分布和壁面静压判断燃烧效率;测量燃烧室出口截面的静温和速度分布,获得出口气流马赫数截面分布;测量凹腔后部某截面的温度和水蒸气浓度分布,以此判读凹腔附近流场特征。
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手性胺是合成天然产物和手性药物的重要中间体,亚胺和烯胺的不对称催化还原是制备手性胺最直接有效的方式之一。手性有机小分子催化的亚胺不对称还原已取得了可喜的进展,但到目前为止,有机小分子催化的烯胺不对称还原,尤其是环状烯胺的不对称还原还少有报道。 本研究从手性叔丁基亚磺酰胺出发,设计并合成了一系列含有叔丁基亚磺酰基的新型脲类及硫脲类催化剂,并将其用于催化三氯硅烷对烯胺的不对称还原,尤其是1, 4-二氢吡啶酯类环状烯胺的不对称还原。通过对催化反应条件的优化,发现当添加1eq H2O时,反应收率和对映选择性明显提高,获得高达99% 的收率和88% ee,同时也取得了很好的非对映选择性(dr = 8:92)。首次实现了三氯硅烷对1, 4-二氢吡啶酯类环状烯胺的高立体选择性还原。 通过机理方面的研究,我们推测反应过程中可能是:首先,底物1, 4-二氢吡啶酯与催化剂形成氢键而被活化,当加入添加剂后,添加剂与三氯硅烷反应释放出一个质子,然后受活化的1, 4-二氢吡啶酯捕获该质子转变成更活泼的亚胺正离子的中间体。随后,在催化剂上的手性硫氧的活化下,三氯硅烷的负氢加成到受活化的亚胺正离子的中间体上,最后生成比较有利的反式产物1, 4, 5, 6-四氢吡啶乙酯。 Calalytic enantioselective reduction of imines and enamines represents one of the most straightforward and efficient methods for the preparation of chiral amines, which is an important class of intermediates for the synthesis of natural products and chiral drugs. Significant progresses have been made in organocatalytic enantioselective reduction of imines. However, asymmetric reduction of enamines, especially of cyclic enamines catalyzed by small organocatalysts has scarcely been reported. In this study, starting from chiral tert-butanesulfinamide, a series of structurally simple tert-butanesulfinyl urea and thiourea organocatalysts were developed and employed in asymmetric reduction of enamines by triclorosilane, particularly in the reduction of cyclic enamines such as Hantzsch 1, 4-dihydropyridines. During the optimization of reaction condictions, we found that the addition of one equivalent of H2O could significantly improve the yields and enatioselectivities. Under optimal condictions, 99% yield, up to 88% ee, and 8:92 diastereomeric ratio were obtained. Thus, we have for the first time realized the highly stereoselective reduction of Hantzsch 1, 4-dihydropyridines catalyzed by triclorosilane. As for the mechanism, we speculate that the Hantzsch 1, 4-dihydropyridine was firstly engaged with the catalyst through hydrogen bond. The proton released from the reaction of the additive and triclorosilane next added to one of the C=C bond to make an active iminium intermediate, which was then attacked by the nucleophlic hydrogen of HSiCl3 activated by the Lewis basic sulfinyl function of the catalyst to provide superior trans-1, 4, 5, 6-tetrahydropyridine products.
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在糖化学合成中,1,6-脱水吡喃糖不仅是合成具有生物活性低聚糖、糖共体、抗原、抗体以及天然产物等化合物重要原料,而且还是许多具有生物活性的天然产物的结构单元。同时,它还具有[3,2,1]的双环缩醛结构,使其在糖化学合成中具有高的立体选择性和区域选择性,同时减少了C-1 和C-6 位的保护和去保护的优点。此外,环内的缩醛开环后,又可以相应地在C-1 和C-6 位进行官能团转化以及糖苷化反应。 本文报道了一种新的1,6-脱水吡喃糖的合成方法,并设计合成了2-C-支链-1,6-脱水吡喃葡萄糖1-195、1-197、1-198 以及2-C-支链-6-硫代1,6-脱水吡喃葡萄糖1-225。到目前为止,1,6-脱水糖开环并进行糖苷化反应,存在选择性较差、产率低的缺点。我们发现,在乙腈做溶剂的条件下,NiCl5 能高立体选择性高产率地催化化合物1-195、1-197、1-198 开环并与ROH、RSH 发生糖苷化反应。在NiCl5-乙腈条件下,合成了一系列2-C-支链-α-糖苷和2-C-支链-β-硫代糖苷,并对2-C-支链1,6-脱水吡喃葡萄糖的生成机理以及开环机理进行了探讨。 烯糖在糖化学合成中是重要的起始原料,从Fischer 首次合成烯糖至今,一直不断地有新的合成方法出现。但目前文献报道的方法存在所用试剂有毒、价格贵和操作繁琐等缺点。我们对Fischer-Zach 方法进行了改进, 发现Zn-NaH2PO4-H2O 和Zn-PEG600-H2O 体系都能很好地合成烯糖。该方法具有条件温和、绿色环保、操作简单的优点。在Zn-NaH2PO4 溶液或Zn-PEG600 条件下,以溴代糖为原料,高产率地合成一系列的烯糖。 The 1,6-anhydrohexopyranoses are crucial subunits of myriad bioactive nature products, as well as important syntons of carbohydrate chemistry which have been extensively used to prepare the biologically potential oligosaccharides, glycoconjugates, antibiotics, and structurally varied nature products. Their particular [3.2.1] bicyclic skeleton makes them have high regio- and stereo-control in a variety of reactions, and such structure avoids protecting hydroxyl groups at C1 and C6.Additionally, the cleavage of the internal acetal under acidic conditions could be beneficial for further transformations of functional group and glycosylation of the corresponding pyranosyl sugar at the C6 or C1 site. Herein we developed a novel approach to prepare the 1,6-anhydrohexopyranose, and synthesized the 2-C-branched-1,6-anhydrohexopyranose 1-195, 1-197, 1-198 and 2-C-branched-6-thio-1,6-anhydrohexopyranose 1-225. Until now, glycosylation of 1,6-anhydrohexopyranoses has been limited because of the low yields and low stereoselectivity. In this paper, we found that NiCl5-MeCN system could selectively cleave the ring of 1,6-anhydrohexopyranoses with alcohols and thiols at room temperature in high yields. A series of 2-C-branched-α-glycosides and 2-C-branched-β-thioglycosides have been synthesized via NiCl5-catalyzed. Furthermore, we investigated the formation and ring-opening mechanism of 2-C-acetylmethyl-1,6-anhydrohexopyranose. Glycals are significant starting material in carbohydrate chemistry. After the Fischer-Zach method for forming glucal was reported for the first time, the numerous synthetic methods for glycals have been explored. However, there are several drawbacks in the existing methods, such as the usage of very expensive and toxic reagents, intricate operation, and the influence of acid-sensitive and base-sensitive functional group. We improved the Fischer-Zach method and developed a facile, mild and environmentally benign methodology towards the synthesis of the glycals in Zn-NaH2PO4-H2O or Zn-PEG600-H2O system. Our method involves the treatment of glycosyl bromides with Zn in NaH2PO4 aqueous solution or PEG600-H2O at room temperature, affording various glycals in excellent yields.
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本文从新鲜大熊猫粪便和实验室保存的沼气发酵富集物中筛选得到 4 株厌氧纤维素分解菌B5、C3、D3-2、D4-1,利用这4 株菌预处理秸秆,然后将预处理后的秸秆用本实验室保存的厌氧产氢菌来发酵进行生物产氢。同时还比较研究了:○1 用1% H2SO4、25% NH3 · H2O和12% NaOH对秸秆进行化学预处理;○2 用厌氧纤维素分解菌对秸秆进行生物预处理;○3 化学与生物组合预处理对秸秆发酵生物产氢的影响。实验结果表明:12% NaOH和生物组合预处理后的秸秆发酵产氢效果最好,其产氢量为21.04 mL g-1,是未经预处理秸秆的75 倍;最高氢气浓度为57.3%,是未经预处理秸秆的96 倍;其产氢的最适pH 为4.5 ~ 6.0,最佳底物浓度为45 ~ 55 g L-1;其发酵过程中的挥发性脂肪酸(VFAs)以乙酸和丁酸为主。 本实验筛选到的 4 株厌氧纤维素分解菌株中,B5 和D4-1 在降解纤维素的同时还具有直接以纤维素为底物产氢的功能,因此本文分别对菌株B5 和D4-1 以及二者的组合菌株B5+D4-1 直接利用秸秆为基质发酵生物产氢做了初步探索研究。结果发现:组合菌株发酵产氢的效果以及对秸秆纤维素和半纤维素的降解率要比单菌株好。菌株B5+D4-1 发酵,秸秆的产氢量为11.4 mL g-1,分别是B5 和D4-1 单菌株的1.6 倍和3.1 倍;组合菌株B5+D4-1 发酵的最大氢气浓度为31.6%,分别是B5 和D4-1 单菌株的1.3 倍和2.4 倍。在发酵过程中,组合菌株B5+D4-1 对秸秆纤维素和半纤维素的最高降解率分别为35.0%和11.8%,分别是菌株B5 的1.2 倍和1.1 倍,是菌株D4-1的1.5 倍和1.3 倍。菌株B5,D4-1 以及组合菌株B5+D4-1 发酵过程产生的挥发性脂肪酸(VFAs)均以乙酸为主。菌株B5 单独发酵过程中只检测到乙酸和丁酸,菌株D4-1 单独发酵以及组合菌株B5+D4-1 发酵过程检测到有乙醇、乙酸和丁酸。 The fermentative bio-hydrogen production by anaerobic hydrogen bacteria preserved in our laboratory from the straw which had been pretreated by four anaerobic cellulolytic decomposition strains of B5, C3, D3-2, D4-1 which were isolated and screened from giant panda’s excrement and biogas fermentation enrichments conserved in our laboratory was studied. Besides, the impact of chemical(1% H2SO4、25% NH3·H2O and 12% NaOH), biological (cellulolytic strains of B5, C3, D3-2, D4-1) and chemical-biological combination pretreatment on bio-hydrogen production from straw by fermentation was also comparatively studied. The experiments showed that the best results of bio-hydrogen production were obtained from the straw with 12% NaOH-biological combination pretreatment method, its capability of bio-hydrogen production was 21.04 mL g-1, which was 75 times higher than the straw without pretreatment; the maximum concentration of H2 was 57.3%, which was 96 times higher than the straw without pretreatment; its optimum pH range was 4.5 ~ 6.0, and its optimum range of substrate concentration was 45 ~ 55 g L-1; In the process of fermentation, the main composition of VFAs were acetate and butyrate. Among the four strains of B5, C3, D3-2, D4-1, B5 and D4-1 have the function of hydrogen-producing by cellulose used as substrate when it decompose cellulose, so the preliminary exploration and research on fermentative bio-hydrogen production by B5, D4-1 and B5+D4-1 which directly used straw as substrate was carried out. The results showed that the combination strains of B5+D4-1 was strikingly better than either B5 or D4-1 strain in the fermentative hydrogen production. The hydrogen-production capability of B5+D4-1 was 11.4 mL g-1 which was respectively 1.6 times and 3.1times higher than B5 and D4-1; the maximum hydrogen concentration of B5+D4-1 was 31.6% which was respectively 1.3 times and 2.4 times higher than B5 and D4-1. In the process of fermentation, the maximum degradation rate of cellulose and hemicellulose in straw was respectively 35.0% and 11.8% by B5+D4-1, which was 1.2 times and 1.1 times higher than B5, and was 1.5 times and 1.3 times higher than D4-1 respectively. The Volatile Fattty Acids(VFAs) generated in the process of fermentation with strains of B5, D4-1 and B5+D4-1 were all mainly acetate. Acetate and butyrate were detected in the process of fermentation with B5, ethonal, acetate and butyrate were detected in the process of fermentation with D4-1 and B5+D4-1.
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利用含时密度泛函理论和局域密度近似方法,计算了H2O分子在速度为12.5a0/fs的重离子C+和C2+作用下产生的各种电荷态的H2O分子离子的几率、平均逃逸电子数和偶极矩的变化随时间的演化。计算结果表明,在重离子势最大时,电偶极矩的变化最大,重离子的电荷态越高,得到高电荷态H2O分子的几率越大;重离子远离分子时,电偶极矩的变化趋于平缓。
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粒子在强含时外场作用下运动的非微扰量子力学描述是理论物理当前一个重要的研究领域。本论文借鉴已有的含时密度泛函理论的应用经验和方法,在FHI98MD基础上,发展了一个描述复杂体系电子动力学的时间相关局域密度近似模型,并利用该模型完成了以下研究工作。研究了小Nan团簇的光吸收谱,计算结果较好地再现了实验谱。结果表明n=2~4的Na团簇具有二维平面结构;n=6的Na团簇开始出现三维结构。在冻结离子近似下,研究了H2和N2在强激光作用下的电离和高次谐波的产生,结果表明电离几率随着分子取向角的增大而减小,高次谐波的截止频率随着分子取向角的增大而向高能方向移动,平台区高阶谐波的强度随分子取向角的增大而减小,趋势与实验结果一致。同时研究了Na2在单双色激光场中的电离和谐波的产生,发现Na2的谐波与其它原子分子不同,没有出现大范围的平台区;双色激光使偶数阶谐振子产生,电离几率有所增加。将电子自由度和离子自由度耦合,研究了激光作用下Na2+的电离和解离行为,结果与对态的分析是吻合的,表明该模型描述电离和解离的有效性。详细研究了Na2、Na4以及H2O在重离子作用下的离化,结果表明电离几率与入射离子电荷态和速度以及团簇尺寸有关。该研究是建立重离子与生物分子相互作用微观模型的基础
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In this review, a few examples of state-to-state dynamics studies of both unimolecular and bimolecular reactions using the H-atom Rydberg tagging TOF technique were presented. From the H2O photodissociation at 157 nm, a direction dissociation example is provided, while photodissociation of H2O at 121.6 has provided an excellent dynamical case of complicated, yet direct dissociation process through conical intersections. The studies of the O(D-1) + H-2 --> OH+H reaction has also been reviewed here. A prototype example of state-to-state dynamics of pure insertion chemical reaction is provided. Effect of the reagent rotational excitation and the isotope effect on the dynamics of this reaction have also been investigated. The detailed mechanism for abstraction channel in this reaction has also been closely studied. The experimental investigations of the simplest chemical reaction, the H-3 system, have also been described here. Through extensive collaborations between theory and experiment, the mechanism for forward scattering product at high collision energies for the H+HD reaction was clarified, which is attributed to a slow down mechanism on the top of a quantized barrier transition state. Oscillations in the product quantum state resolved different cross sections have also been observed in the H+D-2 reaction, and were attributed to the interference of adiabatic transition state pathways from detailed theoretical analysis. The results reviewed here clearly show the significant advances we have made in the studies of the state-to-state molecular reaction dynamics.
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A 2-kW-class chemical oxygen-iodine laser (COIL) using nitrogen buffer gas has been developed and tested since industrial applications of COIL devices will require the use of nitrogen as the buffer gas. The laser, with a gain length of 11.7 cm, is energized by a square pipe-array jet-type singlet oxygen generator (SPJSOG) and employs a nozzle bank with a designed Mach number of 2.5. The SPJSOG has advantages over the traditional plate-type JSOG in that it has less requirements on basic hydrogen peroxide (BHP) pump, and more important, it has much better operational stability. The SPJSOG without a cold trap and a gas-liquid separator could provide reliable operations for a total gas flow rate up to 450 mmol/s and with a low liquid driving pressure of around 0.7 atm or even lower. The nozzle bank was specially designed for a COIL using nitrogen as the buffer gas. The cavity was designed for a Mach number of 2.5, in order to provide a gas speed and static temperature in the cavity similar to that for a traditional COIL with helium buffer gas and a Mach 2 nozzle. An output power of 2.6 kW was obtained for a chlorine flow rate of 140 mmol/s, corresponding to a chemical efficiency of 20.4%. When the chlorine flow rate was reduced to 115 mmol/s, a higher chemical efficiency of 22.7% was attained. Measurements showed that the SPJSOG during normal operation could provide a singlet oxygen yield Y greater than or equal to 55%, a chlorine utilization U greater than or equal to 85%, and a relative water vapor concentration w = [H2O]/([O-2] + [Cl-2]) less than or equal to 0.1.
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以固相萃取为预处理手段,用高效液相色谱-串联四极杆质谱联用技术,针对澳大利亚南威尔士州畜牧业废水中的丙酸睾酮等13种类固醇化合物含量建立了分析方法.采用大气压化学电离源,在正离子模式下,对色谱条件和质谱条件进行优化,其中,丙酸睾酮等7种化合物以质子化的准分子离子峰[M+H]+、另6种化合物以产生了脱去水的离子峰[M+H-H2O]+为母离子进行二级质谱扫描,以最大丰度确定定量离子对.结果表明:该方法所建立的13种化合物的9点标准曲线的线性相关范围为1~1000ng·ml-1,在该范围内,相关系数均>0.9990;各化合物的平均回收率在83.75%~111.50%,相对标准差2.02%~14.21%;除美雌醇和雌三醇的灵敏度相对较低,检测限高于15ng·ml-1外,其余物质的检测限均低于5ng·ml-1;实际样品测定时,不同处理流程中各化合物的浓度均能得到较好体现,该方法能满足检测要求.
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Multiphoton ionization of the hydrogen,bonded pyrrole-water clusters (C4H5N)(n)(H2O)(m) is studied with a reflectron-time of flight mass spectrometer at 355 mn. With increasing partial concentration of pyrrole in a gas mixture source, a series of poly-pyrrole-water binary-mixed cluster ions can be observed, including unprotonated cluster ions [(C4H5N)(x)(H2O)(y)](+), protonated cluster ions [(C4H5N)(x)(H2O)(y)](+) and dehydrogenated cluster ions [(C4H4N)(C4H5N)(x)(H2O)(y)](+). Ab initio calculations of their structures, bond strengths, charge distributions and reaction energies are carried out. Stable structures of these clusters are obtained from the calculations. A probable formation mechanism of the cluster ions [(C4H5N)(x)(H2O)(y)](+), [(C4H5N)(x)(H2O)(y)]H+ and [(C4H4N)(C4H5N)(x) (H2O)(y)](+) is supposed to be the ionization of clusters followed by dissociation.
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Multiphoton ionization of binary mixed clusters (C5H5N)(x)-(H2O)(y) at 532, 355 and 266 nm laser wavelengths has been investigated using TOF mass spectrometer. The experiments showed that almost all the products were protonated ions, At 532 and 355 nm, the products were mainly protonated pyridine clusters (C5H5N)(n)-H+, while at 266 nm, mixed binary cluster ions (C5H5N)(m)- (H2O)(n)-H+ appeared. It was found that the abundance of the [(C5H5N)(3)-H2O-H](+) ions was abnormally high. The calculation indicated that the ion [(C5H5N)(3)-H2O-H](+) is Of a kind of magic number structures with C-3v symmetry. A stepwise reaction mechanism is suggested that photoionization is followed by dissociation. (C) 2001 Elsevier Science B.V. All rights reserved.