Retention time in series-coupled columns: An experimental investigation of the non-thermodynamic effects

A previously established model of a system of series-coupled columns is implemented for the experimental investigation of non-thermodynamic contributions to the retention time in systems of two series-coupled columns. The results show excellent agreement between theory and experiment and also stresses the importance of non-thermodynamic contributions to retention times.     

The effect of temperature and pressure on the retention time in series-coupled gas-chromatographic columns

The promising technique of controlling chromatographic selectivity by the adjustment of individual column temperatures in systems of series-coupled columns is investigated by means of a general model incorporating the effects of temperature and mobile phase compressibility. Expressions are derived for the linear flow velocity, the effective partition coefficient and the retention time for a system of n columns assuming an ideal mobile phase gas, under conditions of constant overall pressure drop and neglect of the temperature dependence of the mobile phase viscosity. The results indicate the importance of thermodynamic parameters, relative to parameters influencing the linear flow velocity, in determining the effect of temperature on the chromatographic retention time. Numerical results are illustrated graphically for two-column systems which are discussed in greater detail. Switching of columns is also discussed and it is shown that even if thermodynamic contributions remain unchanged, non-thermodynamic contributions have a notice-able effect.     

A study of the effects of temperature and pressure on the retention time in series-coupled columns under conditions of constant mass flow rate

The technique of controlling chromatographic selectivity by the adjustment of column temperatures in systems of series-coupled columns is investigated by means of a general model incorporating the effects of temperature and mobile phase compressibility. In a previous article the performance of series-coupled columns was investigated under conditions of constant overall pressure drop. The present paper, on the other hand, considers systems in which a constant mass flow rate is maintained at all temperatures. The expressions derived for the effective partition coefficient and the retention time are compared with those of the previous paper. The numerical results for two-column systems exhibit the same major trends as those for constant pressure drop. It is shown that the effective partition coefficient is slightly dependent on the mass flow rate.     

Chromatographic separation of simulants of nerve and blister agents by combining one‐ and two‐channel columns with different stationary phases

A two‐channel gas chromatography column and a single‐channel column were made by deep reactive‐ion etching technology. The two short columns were coated with different stationary phases, and then linked without a modulator. This is to aim at increasing the sample capacity and achieving a higher separation efficiency in complex environments. The results show that the capacity of the connected column is approximately 4 and 1.5 times larger than that of the single‐ and two‐channel columns, respectively. The linked column was utilized to separate a six‐component mixture, composed of three simulants of nerve and blister agents and three interfering vapors. The results demonstrate that the combined column has a remarkably higher separation efficiency than the individual columns, and an acceptable resolution is achieved although the total length of the linked column is only 1.5 m.     

The effect of the temperature dependence of mobile phase viscosity on the retention time in series-coupled gas chromatographic columns

A previously established model of a system of series-coupled columns, incorporating the effects of temperature and mobile phase compressibility, is generalized to take the temperature dependence of the mobile phase viscosity coefficient into account. Expressions are reported for the linear flow velocity, the effective partition coefficient, and the retention time for both the case of constant mass flow rate and that of constant overall pressure drop. Numerical results indicate that the temperature dependence of the viscosity coefficient affects the retention time and pressure drop while the effective mass distribution coefficient remains essentially unchanged.     

Retention index values of hydrocarbons on open-tubular columns coated with methylsilicone liquid phases

Summary The influence of temperature and liquid phase film thickness of open-tubular (capillary) columns on the retention index values of hydrocarbons on methylsilicone liquid phases is discussed. Data obtained on methylsilicones and squalane are compared. Retention index values of 43 hydrocarbons between 40 and 70 °C on OV-101 liquid phase are listed.     

Retention times of fifty one chlorobiphenyl congeners on seven narrow bore capillary columns coated with different stationary phases

Retention times of fifty one important chlorobiphenyl congeners have been determined on seven narrow bore GC columns coated with different stationary phases. The retention times of the chlorobiphenyls relative to tetrachloronaphthalene were plotted for different column combinations; the plots generated can be used to choose an optimum column combination for the multidimensional gas chromatographic separation of the chlorobiphenyls.     

一种内嵌三嗪环酰胺极性基团新型固定相的制备及其在碱性化合物分离中的应用

以γ-氨丙基三乙氧基硅烷为偶联剂,三聚氯氰为反应物,采用固液表面连续反应法,依次与乙二胺、十二酰氯进行亲核取代反应,制备了一种嵌入三嗪环酰胺极性基团的新型反相色谱固定相,并采用元素分析法进行了表征。用制备的固定相装填色谱柱,以商品化C18色谱柱作为参考,对比考察了碱性化合物的分离情况。结果表明,极性三嗪环酰胺基团被成功地键合到硅胶表面,连续制备3次所得固定相的C、N、H含量的最大相对偏差均小于5%,说明制备工艺重现性良好;用制备的固定相装填的色谱柱分离5种苯胺类、4种吡啶类碱性化合物的选择性好,峰形对称。该结果为进一步推进该新型固定相的商品化提供了参考数据。     

Analysis of normal and modified nucleosides in urine samples by high‐performance liquid chromatography with different stationary phases

The main aim of the present work was to study the retention behavior and quantification of nine nucleosides with the use of octadecyl, alkylamide, cholesterol and alkyl‐phosphate stationary phases. The influence of organic solvent and buffer concentration on the separation of these compounds was under investigation. The retention factor had the highest values for the octadecyl and cholesterol packing materials. Complete separation of all the studied nucleosides was achieved in case of cholesterol stationary phase. The optimized separation method was applied for the quantification of nucleosides in the urine samples. Calibration plots showed good linearity (R² > 0.999) and the limits of detection were in a range of 0.3–0.5 µg/mL, while the limits of quantitation were >0.9 µg/mL. Accuracy was in the range of 5–11%. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation of inert glass capillary columns coated with UCON 50 HB-5100. An attempt to rediscover industrially produced α, ω-polyethylene/polypropyleneglycol ethers as stationary phases in capillary gas chromatography

Using UCON 50 HB-5100, one of the most successful stationary phases in capillary gas chromatography during the past decade, as an example, we wish to redirect attention to the excellent properties of the polyethylene/polypropyleneglycol ether copolymer coatings. Based on experience gained in work with OH-terminated polysiloxanes, a method is described for preparing inert and relatively temperature stable chemically bonded and crosslinked coatings in a single working step. Methyltrimethoxysilane was used as coupling agent, and trifluoroacetic acid was introduced as an acidic catalyst. The reaction mechanisms involved as well as the influence of additional crosslinking on the column behavior are discussed, particularly with respect of the inertness of the coatings.