用塔板理论证明正常峰为拖尾峰

以往,我们在色谱教学中也曾强调标准的色谱峰应服从正态分布,现在觉得这一做法欠妥。虽然根据塔板理论作适当近似处理,可以推得标准的色谱峰应当服从正态分布,但同样根据塔板理论,不作任何近似处理,也可证明标准的色谱峰其实是一个前陡后缓的不对称图形(即:拖尾峰)。文献虽曾指出     

非平衡塔板理论的几个问题

本文用非平衡方法对塔板理论进行了重新处理,导出了描述塔板过程的统一方程（平衡或非平衡）如下：（注：符号ｐｆ（ｒ,ｎ）表示交换ｎ次后第ｒ号塔板流动相中的物质分数;符号ｑｆ（ｒ,ｎ）表示交换ｎ次后第ｒ号塔板固定相中的物质分数）经计算机数值计算,得到如下初步结果：（１）色谱峰是不对称峰,其形状与流速有关。流速增大,不对称性将增大。流速的改变,也会引起峰形的其它改变。（２）色谱峰的峰宽与流速有关。流速增大,峰宽（以塔板数为量纲）将增大。（３）色谱峰的峰高与流速有关。流速增大,峰高将减小。     

应用电子计算机求解色谱过程动力学方程

提出采用计算机求取色谱过程动力学方程解的方法。在此基础上考察了在Ｌａｎｇｍｕｉｒ吸附等温线情况下色谱柱效率、色谱峰的偏态、峰态与分酸系数、流动相线速、进样量之间的关系,从而明确指出,动力学过程是使色谱峰峰形拖尾的一个原因,但不是主要原因。实践中观察到的峰非对称性现象主要是分配系数非线性所致。     

电中性溶质在反相毛细管电色谱柱上峰展宽的研究

根据溶质在色谱柱中迁移的基本特征及柱分离过程弛豫理论的一般输运方程,在平衡色谱和不单独考虑逆向流的简化情况下,得到了能够说明多种因素对半峰宽影响的流出曲线的二阶中心矩表达式。通过反相毛细管电色谱实验,讨论了电压、柱长及保留因子等因素与峰展宽之间的关系,也探讨了溶质在色谱柱内峰展宽的规律。结果表明:半峰宽随柱长的增加和保留因子的增大而线性增加,随电压的增加而呈非线性减小。     

线性非理想条件下液相色谱柱末端峰形规律

色谱流出曲线的二阶中心矩μ２和三阶中心矩μ３以及描述峰形非对称程度的偏态系数∑ｋ＝μ３／μ１．５２是反映色谱峰形的重要参数。从液相色谱过程动力学方程出发，运用电子计算机证明了在线性非理想条件下高效液相色谱体系中不同保留值组分在柱末端峰形的分布基本一致的结论。     

线性非理想条件下液相色谱柱末端峰形规律

 色谱流出曲线的二阶中心矩μ２和三阶中心矩μ３以及描述峰形非对称程度的偏态系数∑ｋ＝μ３／μ１．５２是反映色谱峰形的重要参数。从液相色谱过程动力学方程出发，运用电子计算机证明了在线性非理想条件下高效液相色谱体系中不同保留值组分在柱末端峰形的分布基本一致的结论。     

使色谱峰产生拖尾的一个因素--柱出口效应

使用塔板理论证明存在一种使正常色谱峰产生拖尾的因素－柱出口效应。证明符合线性分配的样品组分虽然在色谱内存在3种不同浓度的分布形态,但在流出色谱后却都因柱出口效应的影响而转变成拖尾峰。在不加任何近似处理的情况下,使用塔板理论直接对不同塔板数、容量因子的色谱峰不对称性进行了计算;计算结果同样支持了柱出口效应的存在。     

塔板理论流出线的统计特征

直接从原始塔板理论的级数形式色谱流出曲线表达式出发,得到了流出曲线一级原点矩及二、三级中心矩的数学表达式,并依此讨论了色谱峰的形状特征及各种因素对峰形的影响规律。本文结果直接证实原始塔板理论曲线为不对称分布,描述峰型不对称性的偏态系数与塔片数及容量因子有关,且随容量因子的增大逐渐变小。当塔片数很大时,容量因子不很小的组分流出曲线有相似的对称性。     

化学计量学用于决明子色谱指纹图谱峰纯度的鉴别

应用化学计量学方法鉴别色谱指纹图谱的峰纯度。对背景进行扣除后,用对照组分光谱构建正交投影矩阵对目标色谱峰的光谱进行投影,以目标色谱峰投影后的残余光谱与投影前的原始光谱的夹角余弦为判据鉴别目标色谱峰的峰纯度：用该方法对决明子药材色谱指纹图谱的峰纯度进行识别,鉴别出大黄素、大黄酚和大黄素甲醚三个纯色谱峰。此方法用于色谱指纹图谱峰纯度的鉴别,结果可靠。     

氨氯地平圆二色谱的理论解析

采用量子化学密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)在B3LYP/6-311++G**水平上对氨氯地平分子的圆二色谱进行理论研究。计算结果表明:振动圆二色谱(VCD)的803、1113、1190、1238、1348、1509、1514、1736、2972、3022和3091 cm-1处存在吸收峰,产生以上吸收峰的振动均涉及到分子手性中心或者所处的基团与分子手性中心形成相关。研究还发现,甲醇溶液使电子圆二色谱(ECD)的吸收峰红移;甲醇溶液中,S-氨氯地平的ECD谱在207、366 nm处存在正性康登效应,223 nm处存在负性康登效应;以上吸收峰均来源于π-π*电子跃迁。这些结论对于深入理解氨氯地平的手征光学性质具有一定的指导意义。     

ChemInform Abstract: Icosahedron Oligomerization and Condensation in Intermetallic Compounds. Bonding and Electronic Requirements

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Crystallization of markoffian copolymers

An equilibrium theory is proposed for crystallization of (A, B) binary copolymers whose comonomeric unit sequences are statistically described by conditional pair probabilities P_AA, P_AB, P_BA, and P_BB. These are linked to the product of the reactivity ratios by r = r_Ar_B = (P_AAP_BB)/(P_ABP_BA). Three cases are considered here, (i) B units are rejected from the crystals, (ii) cocrystallization of A and B comonomeric units is possible in the full range of compositions within a single crystal structure (copolymer isomorphism), (iii) cocrystallization takes place either in a poly(A)-type or in a poly(B)-type structure, depending on composition (copolymer isodimorphism). For case (i) crystallization the theory demonstrates, according to expectation, that alternating copolymers (r = 0) produce the largest melting point depression, whereas in case (ii) they give rise to the smallest composition difference between the crystals and the liquid. The theory developed here further illustrates that for binary copolymers which are isodimorphic (case iii), a phase diagram is obtained similar to that for a classical binary system of small molecules.     

ChemInform Abstract: Ab initio Study of the Structure and Stability of L2AO3 and MAO3 Carbonates,Silicates, Nitrates,Phosphates, Borates,and Aluminates (L: Li and Na; M: Ba and Mg; and A: C,Si, N+, P+, B-, and Al-).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Study of simulation method of time evolution of atomic and molecular systems by quantum electrodynamics

We discuss a method to follow step‐by‐step time evolution of atomic and molecular systems based on quantum electrodynamics. Our strategy includes expanding the electron field operator by localized wavepackets to define creation and annihilation operators and following the time evolution using the equations of motion of the field operator in the Heisenberg picture. We first derive a time evolution equation for the excitation operator, the product of two creation or annihilation operators, which is necessary for constructing operators of physical quantities such as the electronic charge density operator. We, then, describe our approximation methods to obtain time differential equations of the electronic density matrix, which is defined as the expectation value of the excitation operator. By solving the equations numerically, we show “electron‐positron oscillations,” the fluctuations originated from virtual electron‐positron pair creations and annihilations, appear in the charge density of a hydrogen atom and molecule. We also show that the period of the electron‐positron oscillations becomes shorter by including the self‐energy process, in which the electron emits a photon and then absorbs it again, and it can be interpreted as the increase in the electron mass due to the self‐energy. © 2014 Wiley Periodicals, Inc.     

Theory of generalized variables in electrochemical kinetics: Simulation of the slow discharge theory equations

It is shown that theory of similarity and analysis of dimensionalities (theory of generalized variables) is applicable for a kinetic analysis of a simple electrochemical reaction described by equations of the slow discharge theory. The corresponding dimensionless complexes are derived and quantitative interrelation between them is analyzed.Translated from Elektrokhimiya, Vol. 41, No. 1, 2005, pp. 116–120.Original Russian Text Copyright © 2005 by Protsenko, Danilov.     

Comments on group theoretical analysis of NQR spectra of crystals

The use of generating function methods for the number of NQR lines of crystals exhibiting distortion is outlined. The intensity ratios of NQR lines can be obtained using a double coset method.     

ChemInform Abstract: Relationships Among Ionic Lattice Energies,Molecular (Formula Unit) Volumes,and Thermochemical Radii

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.