灰色理论在液相色谱保留值研究中的应用

本文应用灰色理论中的ＧＭ（１，１）模型，对液相色谱中的Ф和ｋ＇的关系进行了研究，其结果达到用Ｓｃｈｏｅｎｍａｋｅｒｓ公式和卢佩章公式预测及计算ｋ＇的水平。结果指出：灰色理论完全适用于对色谱保留问题的研究，其方法也这无全能满足实际工作中的应用。     

液相色谱手性柱的温度效应

使用脲衍生型手性色谱柱作正相色谱,在不同温度下拆分３,５－二硝基苯甲酰氨基酸丁酯对映体。结果表明,柱温在－６℃至４０℃间变化时,ｌｎｋ＇与１／Ｔ以及ｌｎα与１／Ｔ皆呈直线关系。随着柱温的下降,相对保留值α上升,但部分化合物的Ｒｓ－Ｔ曲线在低温时出现转折。     

反相液相色谱中温度对蛋白分子构象变化的新表征

液相色谱中溶质计量置换保留模型的Ｚ值可用来对反相高效液相色谱中热变蛋白的分子构象进行表片。发现在异丙醇－甲酸４４％（Ｖ／Ｖ）－水体系为流动相对完全变性蛋白的Ｚ值随温度升高而降低。且Ｚ值与绝对温度例数（１／Ｔ）成正比，因此蛋白分子构象变化可用Ｚ对１／Ｔ作图所得两条直线的斜率差值来表征，差值愈大，蛋白分子构象变化愈甚。该两直线的交点即为蛋白分子构象的突变温度。与通常采用的１ｇＫ＇对１／Ｔ的作图相比，用     

应用扩展的重叠分辨率法优化液相色谱条件分离二茂铁类化合物

本文对优化液相色谱分离条件的重叠分辨率法进行了改进与扩展：首先利用全范围的二元线性梯度淋洗进行溶剂强度的优化，再通过重叠分辨率法进行了溶剂选择性的优化，并且建立了计算机系统，使此方法程序化。利用此方法建立了分离Ｎ－二茂铁甲酰基－Ｎ＇－芳基硫脲类衍生物的最佳流动相体系。     

高效液相色谱选择性优化的基本方法和策略

〕本文综述了高效液相色谱法方法发展中选择性优化的基本方法和策略,介绍了影响色谱选择性优化的三个主要方面：即色谱参数的选择、优化指标和实验设计及优化方法,并评述了今后色谱选择性优化的发展趋势。     

逆流色谱分离中选择性试剂的应用研究进展

逆流色谱中添加选择性试剂可有效提高分离度,常用选择性试剂主要有金属离子、多糖衍生物、阴离子表面活性剂、离子对、手性试剂、p H-区带逆流色谱中酸碱试剂等6类。该文综述了国内外选择性试剂在逆流色谱分离中的应用研究进展,介绍了其基本原理,阐述了不同选择性试剂的适用范围,并展望了选择性试剂发展的新趋势。     

双苯甲酰胺冠醚固定相的合成及毛细管柱气相色谱性能…

合成了一种新型的双苯甲酰胺冠醚固定相：（１Ｓ，２Ｓ）－１－（对苯甲酰胺基）苯基－２－苯甲酰胺基－１６－冠－５，其结构经红外光 谱、核磁共振、质谱及元素分析数据证实这种固定相的柱交、热稳定性、极性及选择性等色谱特性。该类固定相对极性位置异构分离效果良好。由于冠醚上引入苯甲酰胺取代基，因而对苯胺类及不经衍生化 碱性化合物能特殊选择性地分离。     

福州小花茉莉全花期中花源质量稳定性的研究Ⅱ．净油和头香化学成分分析

为了观察福州茉莉花源质量的稳定性,曾时其精油成分作过连续三年的成分研究￣［１］。本文继续对净油和头香成分作进一步探讨。本实验室用溶剂提取和用冷乙醇分离花蜡来获得净油．用低温吸附和溶剂洗脱获得头香样品。采用石英毛细管气相色谱（ＣＧＣ）和色谱－质谱（ＣＧＣ－ＭＳ）对成分进行剖析。实验结果对福州茉莉花源质量随气候变化的规律￣［１］作了进一步地确认。     

五种批号国产硅油固定液的性能评价

气相色谱的核心部分是色谱柱。对于某一混合物的分离,至少应从柱效率和柱的选择性两方面来考虑。例如,在柱效率上,虽然给出了锐敏的色谱峰,但如果该柱对混合物各成分的选择性不好,则仍然不能实现分离。而色谱柱的分离性能主要是取决于     

关于液相色谱保留值公式的补充

本文介绍了液相色谱保留值公式研究的历史,根据色谱保留值公式的统一形式运用液相吸附公式得到ｌｎｋ＇＝Ａ＋Ｂｌｎ（Ｃ＿（Ｂ＿１）／θ＿（Ｂ＿１））＋ＣＣ＿（Ｂ＿１）。当强溶剂浓度Ｃ＿（Ｂ＿１）不至太低时有ｌｎｋ＇≈Ａ＋ＢｌｎＣ＿（Ｂ＿１）＋ＣＣ＿（Ｂ＿１）：作者证明了当强溶剂浓度Ｃ＿（Ｂ＿１）→０时,ｋ＇→常数,从而纠正了长期存在于色谱热力学理论中Ｃ＿（Ｂ＿１）→０,ｋ＇→∞的谬误。     

Reversed-phase retention thermodynamics of pure-water mobile phases at ambient and elevated temperature

The use of pure water at superheated temperatures, between 100 and 200 degrees C, as a mobile phase for reversed-phase separations is explored. The thermodynamics of the retention process at low temperature (15-55 degrees C) are compared to the thermodynamics at elevated temperature (125-175 degrees C). Significant differences in the enthalpy of the retention process are observed between the two temperature ranges. This is possibly due to changes in the hydrogen-bond network of the pure-water mobile phase, which would change the solvation, and therefore retention, of non-polar solutes. The change in thermodynamic values between the two temperature regions invalidates extrapolation of retention as a function of temperature between the two temperature regions for the prediction of room-temperature pure-water retention factors. The thermodynamic changes observed as the temperature is increased are similar to those seen when mobile phase composition is changed (by adding organic modifier) at constant temperature.     

Effect of temperature and flow-rate on analysis of basic compounds in high-performance liquid chromatography using a reversed-phase column

The peak shape and retention of some basic probes together with a neutral reference compound were investigated as a function of temperature and flow-rate using a reversed-phase HPLC column at both pH 3.0 and pH 7.0. The retention of bases often showed an anomalous increase with temperature; retention mechanisms are complex as shown by studies of the effect of buffer cation concentration on retention. Considerable improvements in column efficiency for bases may result from operation at elevated temperature. Improvements did not seem attributable either to incidental changes in the retention factor, or (in this particular study where low sample masses were utilised) to the influence of sample load. The optimum flow-rate for highest efficiency is generally lower for basic compounds than neutrals, and due to the steepness of the Van Deemter curves obtained, high flow-rates appear to be particularly detrimental in the chromatography of basic compounds.     

Effect of Column Temperature on the Retention of Inorganic Anions and Organic Acids in Non-Suppressed Anion-Exchange IC

An investigation has been conducted into the effect of column temperature on the retention of inorganic anions and organic acids in non-suppressed ion chromatography on an anion-exchange column. Potassium biphthalate and p-hydroxybenzoic acid–tris–boric acid were used as mobile phases. The column temperature was from 25 to 50 °C. Endothermic and exothermic retention of inorganic anions were both observed when potassium biphthalate was used as mobile phase. When p-hydroxybenzoic acid–tris–boric acid was used as mobile phase, however, endothermic behavior only was observed. Moreover, for the two mobile phases, variation of the retention time of the system peaks with changing temperature was reversed. For retention of the organic acids, only endothermic behavior was observed with the two mobile phases. Variation of retention time was greater when p-hydroxybenzoic acid–tris–boric acid was used as mobile phase than when potassium biphthalate was used. These results indicated the exchange reaction in anion-exchange chromatography could be either endothermic or exothermic, depending on the solute and mobile phase ions involved. Different relative changes of retention time were observed for individual inorganic anions and organic acids with increasing column temperature. In general, variation of retention time with increasing temperature was greater for strongly retained inorganic anions and organic acids than for weakly retained species. Van’t Hoff plots for inorganic anions, organic acids, and system peaks were linear. Selectivity variation of the retention of inorganic anions and organic acids was achieved by changing the temperature. In achieving optimum separation of inorganic anions and organic acids, temperature was a valuable tool. To reduce the retention times of the ions and avoid interference from system peaks in non-suppressed anion-exchange ion chromatography with the two mobile phases, a low column temperature, for example, 35 °C, was best.     

Investigation of the low temperature effect in normal phase micro high performance liquid chromatography

The low temperature effect has been investigated on a set of three different silica-gel micro columns with FC-78 as eluent. An open tubular micro glass capillary, a packed micro glass capillary, and a packed micro teflon column were examined. Temperature dependences of separation factors and theoretical plate numbers were determined. It appears that a decrease in column temperature improves chromatographic selectivity while column efficiency decreases. The compensation temperatures were determined for these systems. The results suggest that the retention mechanism operative in the low temperature range is almost the same as that in the normal temperature range. However, the mechanism differs from that of reversed phase systems.     

Joint use of cyclodextrin additives in chiral discrimination by reversed-phase high-performance liquid chromatography: temperature effects

The temperature dependence of chiral separations was investigated in combined system of reversed-phase (RP) liquid chromatography using two chiral additives: single or β native cyclodextrins and their permethylated derivatives. The model tested compounds of pharmaceutical interest were: methylphenobarbital, mephenytoin, morsuximide and camphor. Taking the localization of a complexation process as a criterion – the combined system with two selectors has been rationalized as occurring in three stages. The influence of temperature (in narrow range of 20°C) on retention and enantioselectivity was studied in; System I (complexation occurs in the mobile phase), in System II (complexation on the stationary phase) and in System III (complexation in both phases together). In System III (as for System I) it has been found that the model compounds could be classified into three groups based on their retention dependence on temperature: retention decrease with temperature decrease, retention increase with temperature decrease or no influence of temperature on retention. For all the compounds investigated, decrease in temperature increases the selectivity. Standard enthalpy (ΔH⁰) and entropy (ΔS⁰) changes of solute transfer between the mobile and the stationary phase and standard enthalpy (ΔH⁰_CD) and entropy (ΔS⁰_CD) changes of complex formation were also calculated. In Systems I and III, if the complexation in the mobile phase is favored process compared with interaction with the stationary phases (RP or covered by permethylated cyclodextrin), the shortest retention time and the best selectivity is observed at low temperature.     

Temperature programmed retention indices: Calculation from isothermal data. Part 1: Theory

Direct conversion of isothermal to temperature programmed indices is not possible. In this work it is shown that linear temperature programmed retention indices can only be calculated from isothermal retention data if the temperature dependence of both the distribution coefficients and the column dead time are taken into account. Procedures are described which allow calculation of retention temperatures and from these, accurate programmed retention indices. Within certain limits the initial oven temperature and programming rate can be chosen freely. The prerequisite for this calculation is the availability of reliable isothermal retention data (retention times, retention factors, relative retention times, or retention indices) at two different temperatures for one column. The use of compiled isothermal retention indices at two different temperatures for the calculation of retention temperatures and thus temperature programmed indices is demonstrated. For the column for which programmed retention indices have to be determined, the isothermal retention times of the n-alkanes and the column dead time as a function of temperature have to be known in addition to the compiled data for a given stationary phase. Once the programmed retention indices have been calculated for a given column the concept allows the calculation of temperature programmed indices for columns with different specifications. The characteristics which can be varied are: column length, column inner diameter, phase-ratio, initial oven temperature, and programming rate.     

Lowering the molecular mass limit of thermal field-flow fractionation for polymer separations

Thermal field-flow fractionation (ThFFF) is capable of separating a wide molecular mass range of polymers by their molecular mass (Mr) and chemical composition. However, retention and resolution decrease significantly for polymers with Mr<20 kDa. Various approaches for increasing the retention of low Mr (<15 kDa) polymers were investigated. Our results showed that temperature conditions and single-component solvents had a limited effect on polymer retention and that certain binary solvent mixtures caused a dramatic increase in retention. The binary solvents approach has enabled the use of a ThFFF system and temperature conditions to separate 2.6 kDa PS from 4.4 kDa PS, thereby extending the applicability of ThFFF to lower molecular masses. The effect of binary solvent mixtures on polymer retention is correlated with the mixture viscosity.     

Utilization of Rohrschneider's concept and Tekler equation in linear temperature programmed GC. Precalculation of retention data

Summary An extension of Rohrschneider's concept to the field of the linear temperature programmed gas liquid chromatography, is proposed, which is based on Antoine's equation for the temperature dependence of the reduction index of Takács et al. and Tekler. The new method presented in this paper, applied to retention data of two stationary phases of low polarity, PS-255 and OV-105, gives a new possibility of precalculating retention data.     

Temperature effect on HPLC retention of PCBs on porous graphitic carbon

Summary The effect of column temperature on solute retention was investigated for 10 PCBs with different degrees of planarity (degree of ortho position substitution). The variation of retention values (lnk) with temperature was measured using two solvents, n-hexane and dichloromethane, as mobile phase: retention decreases as temperature increases. The relationship between lnk values and temperature (1/T) exhibits a good linearity. The ΔH ⁰ values calculated are in the −2 to −5 kcal mole^{− 1} range: they are very similar for compounds with the same degree of ortho-substitution and are significantly higher for non-ortho substituted congeners. High temperature significantly improves separation efficiency (plate number significantly increases): this effect is the dominant factor controlling chromatographic resolution, which improves with increasing temperature. Operating at 40 °C, an efficient separation of planar PCBs was obtained with low solvent consumption.     

Temperature effects on solute retention for hydride-based stationary phases

The effect of solute retention is investigated for two hydride-based stationary phases: bidentate C18 and cholesterol. Several small molecules and peptides are used as solutes. In the reversed-phase mode, most compounds have the expected temperature behavior, i.e. decreasing retention with increasing temperature. Two analogs of the drug lisinopril do exhibit the opposite behavior on the cholesterol column; increasing retention with increasing temperature. In the aqueous normal phase (ANP) mode, more compounds, particularly certain peptides, have this unusual retention behavior with respect to temperature. These preliminary studies indicate that as ANP retention becomes stronger, there is a greater possibility of observing increasing retention with increasing temperature.