The influence of the syringe needle on the precision and accuracy of vaporizing GC injections

The discrimination of the high boiling components of a C9 to C44 alkane test mixture in a vaporizing injector (analysed with stream splitting on a capillary column) is mainly due to a selective elution of the sample out of the syringe needle. Different methods of handling the syringe needle are tested. The discrimination is quantitated and correlated with the material left in the needle. The poorest method of injection was found to retain the sample in the needle when the latter is introduced into the vaporizer. The sample should be pulled back into the barrel of the syringe and the needle allowed to warm up in the injector before the sample is transferred into it. The solvent flush technique may be preferred for components sensitive to the hot metal surface of the needle.     

陶工尘肺辅助性诊断的方法研究——测定发中微量元素 建立判别方程

测定了陶工Ｉ期尘肺患者的头发中Ｚｎ、Ｃｕ、Ｓｅ、Ｎｉ、Ｆｅ、Ｍｎ、Ｍｇ７种金属元素，用陶工可疑患者作对照，建立Ｆｉｓｈｅｒ判别方程，对陶工尘肺进行判别。自身回代正确率９４．４４％，前瞻性回代达８３．３３％，各其流行病学指标计算均属良好。     

Chiral discrimination in hydrogen‐bonded complexes of hydrogen peroxide with methyl hydroperoxide: Theoretical study

For the first time, the discrimination of different chiral forms of 1:1 complexes with hydrogen peroxide and methyl hydroperoxide have been investigated using density functional theory (DFT) and Møller–Plesset type 2 (MP2) methods at varied basis set levels from 6‐31+G(d,p) to 6‐31++G(2d,2p). Three pairs of chiral enantiomers were considered. The optimized geometric parameters, interaction energies, and chirodiastatic energies for various isomers at different levels are estimated. To take into account the water solvation effect, the polarized continuum model (PCM) method has been used to evaluate the ΔG_solv. The gas phase results show that the heterochiral six‐membered ring complex (structure I) and homochiral five‐membered ring complexes (structures IV and V) are preferred configurations for the three pairs of chiral enantiomers. The solvation effect on six‐membered ring complexes (structures I and II) shows nonsignificant changes in the configurations preferred, but on five‐membered ring complexes, the homo‐/heterochiral preference is found to be inverse in the polar solvent. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

The comparative spreading behavior of enantiomeric and racemic tyrosine amphiphiles

Several derivatives of tyrosine or its methyl ester have been synthesized in which the para hydroxyl group on the aromatic side chain has been converted to a long chain alkyl ether or urethane. The surface behavior of these compounds is discussed. Enantiomeric discrimination, the ability of a chiral molecule to distinguish between mirror-image stereoisomers, has been investigated for the urethane derivates by comparing the surface pressure-area isotherms of the enantiomer with that of the racemic compound. Enantiomeric discrimination was demonstrated for the methyl ester analog, but was not conclusively observed for the zwitterionic compounds. Possible structural requirements for enantiomeric discrimination in a chiral molecule are discussed.     

Multi‐Channel Surface Acoustic Wave Sensors Based on Principal Component Analysis (PCA) and Linear Discriminate Analysis (LDA) for Organic Vapors

A multi‐channel surface acoustic wave (SAW) detection system which is employed to detect various organic molecules in a static system was prepared using 315 MHz one‐port quartz resonators and a home‐made computer interface for signal acquisition and data process. The oscillating frequency of the quartz crystal decreases on adsorption of organic molecules on the coating materials. The principal component analysis (PCA) method with SAS software was applied to select the appropriate coating materials onto the SAW crystals for organic vapors, e.g. hexane, 1‐hexene, 1‐hexyne, 1‐propanol, propionaldehyde, propionic acid, and 1‐propylamine. A dataset for a multi‐channel sensor with 19 SAW crystals for 7 analyses was collected after comparing the correlation between the 19 coating materials and the first six principal component (PC) factor. Furthermore, linear discriminate analysis (LDA) with SPSS software and a profile discrimination map were also applied and discussed for the discrimination of these organic vapors. These organic molecules could be clearly distinguished by the six‐channel SAW static sensor. The effect of concentration for various organic vapors was investigated and discussed.     

Chiral discrimination of quinine and quinidine based on notable room temperature phosphorescence lifetime differences with γ-cyclodextrin as chiral selector

Upon addition of small amount of bromocyclohexane (BrCH), quinine (QN) and quinidine (QD) display strong room temperature phosphorescence (RTP) in γ-cyclodextrin (γ-CD) solution without deoxygenation. The associated phosphorescence decay curves can be best fitted to biexponential patterns and quite different RTP lifetimes are obtained for QN (86.9 and 12.5 ms) and QD (12.1 and 4.17 ms), indicating a distinct chiral discrimination of γ-CD toward this pair of pseudo-enantiomers. The corresponding association constants evaluated for QN/γ-CD/BrCH and QD/γ-CD/BrCH are 3.47 × 10⁵ and 4.67 × 10⁴ L mol⁻¹, respectively. It can be inferred that their different ability to form complexes with the chiral γ-CD is accounted for the notable difference in RTP lifetimes between QN and QD.     

Chiral discrimination in biliverdin (S)-amino acids,II: Structural variations of the amino acid functional groups

The Biliverdin-(S)-amino acid derivatives2–21 have been synthesized, and are subject to a thorough c. d. and u. v.-vis. electronic absorption analysis in the bilatriene chromophoric region. It is shown that the extent of chiral discrimination of the bilatriene helices is particularly sensitive towards structural variations of the amino acids bound to the propionic side chains. Thus, a pronounced decrease of chiral induction occurs if hydrogen bonding between one of the two essential coordination sites of the amino acid entity and the bilatriene backbone is disturbed. Accordingly, derivatives of (S)-amino acidt-butyl esters (3,5,7,16 and17) andN-substituted (S)-amino acids (8–10, 20 and21) generally display weak c. d. spectra. If additional polar groups are present in bis(amino acid) derivatives mutual interferences of the adjacent side chains must be taken into account. The attenuations of -values observed for the bis(serine) and bis(aspartic acid) compounds14 and15 thus are mainly due to intramolecular interchain interactions. The results provide evidence in support of the proposed mechanism of chiral discrimination in biliverdin amino acids.Dedicated to Prof. Dr.Kurt L. Komarek on the occasion of his 60th birthday.     

Improved quantitative capillary GC by the use of CO2 as secondary coolant in cold on-column injection

A comparison is made between air and carbon dioxide as secondary cooling gases in cold on-column injection into capillary columns. Because CO₂ is a more effective coolant than air, the injection zone can be kept at a colder temperature, thus preventing loss of sample vapor through the open injector even as the initial oven temperatures because greater than the boiling point of the solvent. Sample loss at these elevated temperatures is shown as a reduction in peak area as functions of column temperature during injection and different injection zone temperatures. The maximum allowable oven temperature during injection is significantly higher when CO₂ is used as secondary coolant rather than air.     

关于类质同晶与同质多晶判断的札记

当个主要依据X光等衍射方法测定晶体结构以判断类质同晶和同质多晶现象。在形式化学式相同或相似的前提下，关键在于正确判断晶体的空间群。本文通过实例枚举类质同晶和同质多晶这一常见现象以及由于空间群指定失误等原因导致有关判断的不同结论。     

Chiral discrimination of phenoxypropionic acid herbicides on teicoplanin phase: Effect of mobile phase modifier

Summary The chiral recgonition mechanism for a series of phenoxypropionic acid herbicides was investigated in reversed phase liquid chromatography (RPLC) on a teicoplanin stationary phase over a wide range of column temperatures. Thermodynamic constants, of the transfer of an enantiomer from the mobile to the teicoplanin stationary phases were determined. The van't Hoff plots for all solutes had a break at a critical temperature T^* showing a variation in the enantiomer retention mechanism due to a change in the conformational state of the teicoplanin, structure. Additionally, enthalpy-entropy compensation confirmed both the change in enantiomer interaction mechanism observed for regions T<T^* and T>T^* and the independence of this mechanism from (i) herbicide molecular structure,s i.e. the position of the chloro group on the phenol ring and (ii) the carbon absolute configuration. Moreover, the increasing enantioselectivity with increasing methanol fraction in the mobile phase was attributed to restriction of the solute association in the teicoplain, stationary phase, leading to favorable stereoselective interactions. This behavior was used to optimize chromatographic conditions for separation of herbicide enantiomers on teicoplanin.