Preparation,evaluation, and comparison of wide bore (320 μm) and narrow bore (50 μm) cyanosilicone-coated capillary columns for gas chromatography

The preparation of wide bore (320 μm) and narrow bore (50 μm) fused silica capillary columns is described for immobilized cyanopropyl substituted silicones containing 60 and 88% substitution. The effect of high temperature deactivation with cyanopropylcyclosiloxanes was studied with a special test mixture. Curing was achieved with dicumyl peroxide or azo-tert-butane. The columns were evaluated and compared in terms of efficiency, activity, polarity, and temperature stability. Different coating methods were compared for the narrow bore columns. The activity of the 60% cyanopropyl columns that had been immobilized with dicumyl peroxide was significantly larger than for azo-tert-butane immobilized columns. The polarity of polar columns appeared to depend greatly on column temperature and is completely different for wide and narrow bore columns.     

Static coating of capillary columns by means of liquefied gases

The technique of spontaneous coating of capillary columns employing liquefied butane and ethylene chloride as solvents of the stationary phase is described. These solvents and their mixtures are suitable for apolar and medium-polar stationary phases. The dependence of coating time on coating temperature and on the composition of the mixture of solvents was observed. It was found that the coating efficiency decreases with increasing coating speed.     

High resolution glass capillary columns for the gas chromatographic analysis of alditol acetates of neutral and amino sugars

The development of improved high resolulation glass capillary columns for separating the alditol acetates of neutral and amino sugars is described. Different capillary column treatments were evaluated for their activity toward amino sugar derivatives and for their effect on the efficiency of the completed column. The simple two-step procedure of leaching with aqueous hydrochloric acid and dynamic coating with SP-2330 was found to produce efficient and inert columns.     

Free release static coating of glass capillary columns; rapid coating at lower temperatures and elevated pressures

The coating speed upon static coating of glass capillary columans was evaluated in terms of inner diameter and length of the column, viscosity and pressure of solvent vapor, etc. From the equation obtained it can be shown that a smaller diameter of a microbore column restricts solvent vapor transfer to the orifice of the column drastically. To compensate for this restriction, a higher pressure at the meniscus is needed. As an alternative to using a higher coating temperature, application of more volatile solvents such as n-butane and isobutane is proposed. Several glass capillary columns (130 μm i.d.) were coated with SE-54 dissolved inpentane-acetone mixed with n-butane or isobutane and the column performances were evaluated. Selection of these solvents permitted free release static coating of ca. 100 μm columns at lower or even ambient temperatures and they were equally suitable as commonly applied solvents (e.g. pentane) to coat highly efficient columns.     

Whisker surfaces in (GC)2

Growing whiskers on the inner wall of glass capillary columns is an easy roughening technique which allows efficient coating of the columns with any stationary phase. The advantages and disadvantages of whisker surfaces are discussed. Several examples are presented to illustrate the possibilities of whisker-wall coated open tubular (WWCOT) columns.     

The preparation of thick-film glass capillary columns

A detailed method for the routine preparation of glass capillary columns is presented. The method consists of coating a glass tube with quartz powder prior to pulling the tube into a capillary. The inner surface of the capillary consists of an even distribution of quartz particles fused to the walls. This surface has been found readily deactivated by standard procedures and ideal for the preparation of thick-film glass capillary columns. The method has been thoroughly tested in two independent laboratories to ensure that the procedures described are reproducible.     

Deactivation of small diameter fused silica capillary columns with organosilicon hydrides

Small diameter fused silica capillary columns (50–75 μm i.d.) were deactivated at relatively low temperatures (250–300°C) with a mixture of polymethylhydrosiloxanes and several lowmolecular-weight organosilicon hydrides. Reproducible surface deactivations of highest quality were achieved with the polymethylhydrosiloxane (PMHS) reagent. Deactivations performed with PMHS via dynamic coating with neat or diluted reagent were evaluated by gas chromatography. Deactivations achieved with organosiloxane mono-, tri-, and tetrahydrides were also evaluated and compared. Low-molecular-weight organosilicon hydride deactivations were less time consuming and required lower head pressures for filling and coating columns with the reagent. Critical surface tensions of capillary surfaces modified with PMHS and the low-molecular-weight organosilicon hydrides gave support to the dehydrocondensation reaction between silica surface silanols and silyhydride bonds of the reagents. Slopes from Zisman plots indicated that coverage of the surface ranged from highest for the polymer (PMHS) to lowest for the monomers (TMS and PMDS). Efficiency measurements showed the influence that surface modification had on the uniformity and stability of the coated capillary columns. Well-deactivated capillary columns permitted the chromatography of polar solutes using supercritical carbon dioxide as mobile phase.     

High temperature silylation of glass capillary columns

This paper describes the results of a study on the deactivation of the surface of glass capillary columns by high temperature silylation (HTS). The different steps, leaching, washing, dehydration and HTS were optimized. A practical procedure yielding a high percentage of very good columns is given. The influence of leaching and HTS on the temperature stability and coating efficiency of capillary columns coated with OV-1 was studied. The inertness of the glass surface after HTS is demonstrated by several examples.     

Selective retention of explosives and related compounds on gas-chromatographic capillary columns coated with lanthanide(III) β-diketonate polymers

The purpose of this research was to investigate coating capillary columns with lanthanide(III) β-diketonate polymers to provide gas-chromatographic columns with selectivity toward explosives and related compounds. Capillary columns were statically coated with a mixture of a lanthanide(III) β-diketonate polymer, which utilized p-di(4,4,5,5,6,6,6-heptafluoro-1,3-hexanedionyl)benzene (dihed) as a ligand, and SE-30. A novel coating technique was developed that used a methanol-containing azeotrope to provide solubility for both polymers while maintaining a low boiling point compatible with static coating. As based on temperature-programmed retention indices, the experimental columns displayed selective retention of nitroaromatic, nitroalkane, and nitrate ester test probes relative to an appropriate SE-30 control column. Selective retention was more pronounced for strongest Lewis base analyte contained in the test mixture (i.e., cyclohexanone). Relative analyte retention on the La(dihed), Tb(dihed), and Eu(dihed) columns are discussed relative to Lewis acidity and solubility of the polymer in the azeotropic coating solution.     

A problem in etching Pyrex glass capillary columns

Recent attempts to reproduce a literature method for etching of Pyrex glass capillary columns with ?etching ether”? resulted in reduction of the columns to dust through a violent explosion. Although modifications of the method produced etched columns, we found that less than satisfactory results were achieved. Introduction of etching ether by simply coating the column with a thin film of the ether produced an evenly etched column with well defined whiskers. Several observations made during the etching process will also be discussed.     

Inner wall coating of micro-LC columns. Wall effects in LC

An elastic inner wall coating in the fused silica capillaries used for Micro-LC (LC on packed fused silica capillary columns) stabilizes the packed bed and thus increases column efficiency and life expectancy. Probably the particles of packing material are partly forced into the elastic polymer layer which thus holds the packing in position. Bonded polymers of very different chemical polarity can be used with equally good results. Variation of the coating layer thickness shows that there is an optimum value around 0.3 μm. A discussion of various wall effects in LC columns is presented. The i.d. of the columns is a most important parameter in this respect.     

Free release static coating of glass capillary columns; Static coating at elevated pressure — Theoretical considerations and practice

Summary Static coating of glass capillary columns has hitherto solely been carried out by evaporation of the stationary phase solvents under vacuum conditions. However, since a solvent vapour pressure higher than the external pressure is the only requirement for the vapour to flow out of the column, evacuation should not be necessary. Several important factors in the static coating procedure, such as mass (solvent vapour) — and heat transfer, heat of vaporisation of the solvent and viscosity of the stationary phase solution at elevated temperature and outlet pressure are discussed, principally to rationalise an improved static coating procedure. The alternative, so-called free-release static coating procedure, was evaluated practically by coating several columns with OV-101 and SE-30. Coating speed was found to be rapid and relatively constant whereas coating efficiency was between 80 and 100%.     

Parameters affecting the quality of glass capillary columns prepared by the mercury plug dynamic coating method

Summary The paper presents examinations concerning the ways obtaining glass capillary columns. The mercury plug dynamic coating method used for coating capillary columns was investigated in order to establish haw the efficiency of the columns prepared can be related to the physical properties of stationary phase and the velocity of the coating solution through the capillary tube. It was found that there is an optimum range of the viscosity and velocity of the coating solution within which the highest column efficiency can be obtained. Moreover, the mechanism of the mercury plug dynamic coating method in which the thickness of the obtained film depends on interfacial tension between the mercury and the coating solution was confirmed.     

Advances in the preparation and evaluation of GC capillary columns

The preparation of (glass) capillary columns of high quality is still not without difficulties. Six problems in this context are highlighted. Column material choice(l), glass wall modification(2) and coating(3) are considered to have reached a satisfactory level. Deactivation(4) is still in a state of flux. Quantitation(5) is the least satisfactory aspect of capillary GC. Scope expansion(6) will be helped by the introduction of new phases of high thermal stability and by the adoption of solutions exclusively applicable to capillary GC. Evaluation of (glass) capillary GC columns is a rapidly developing field. Hopefully the number and complexity of test or polarity mixtures will not expand much further and it will be possible to make a clear and generally acceptable choice. The preparation and evaluation of ever-improving capillary columns is important to an ever-widening group of chromatographers. Our opinion on selected topics in this already vast field is summarized in the following overview.     

Preparation and evaluation of polar stabilized phase open tubular (SPOT) columns

Summary A method is described for the routine preparation of high resolution stabilized phase open tubular (SPOT) columns. A finely dispersed siliceous material (Cab-O-Sil) is treated with benzyltriphenylphosphoniumchloride and dynamically coated onto the inside wall of glass capillary columns. Additional dynamics coating with a polar stationary phase yields thermostable columns of high efficiency. The columns show favourable adsorption properties and good long term stability. The mechanical stability of the stationary phase film is explained in terms of the rheological behaviour of concentrated disperisons. The designation PLOT columns appers inapplicable, and these columns will be referred to as SPOT columns. A theoretical model, describing band spreading in SPOT columns, is proposed and compared with the experimental results. Some applications in routine use and in ultra trace analysis are presented.     

Stability of surfactant coated columns for ion chromatography

Ionic surfactant coatings are a popular means to convert reversed-phase columns into ion-exchange phases with adjustable ion-exchange capacity and selectivity. However, the perceived lack of stability of surfactant coatings has hindered their use for routine separations. Coating conditions (acetonitrile content, ionic strength, surfactant concentration and temperature) were varied to determine their effect on coating stability. Under all coating conditions, cetyltrimethylammonium (CTAB) coated columns exhibited an initial decrease in ion retention. However, after the initial 1 L flush, both retention times and efficiency remained stable for >or=3000 column volumes. Greatest column stability and control of column capacity are achieved if the surfactant in the coating solution is below its critical micelle concentration.     

Repartition effect of aromatic polyaniline coatings on the separation of bioactive peptides in capillary electrophoresis

The capillary walls of fused-silica capillary electrophoresis (CE) columns were modified with a thin film of polyaniline (PANI), providing open-tubular columns with a stable coating containing aromatic groups and amine functionalities. Fast and efficient separations were observed for small bioactive peptides under acidic conditions on PANI-coated columns. The mechanism of separation is based on hydrophobic interactions between the analytes and the polymeric matrix. Good reproducibility was observed from run-to-run. Due to the simple derivatization procedure, method flexibility, the uniformity of the coating and its stability, conjugated polymers could find practical application in capillary zone electrophoresis (CZE) separations.     

Open-tubular gas chromatography using capillary coated with octadecylamine-capped gold nanoparticles

The octadecylamine-capped gold nanoparticles (ODA-Au-NPs) were prepared and directly used to coat the capillary wall. The hydrophobic coating acted as the stationary phase for open-tubular gas chromatography (OTGC). The ODA-Au-NPs can be adsorbed tightly onto the inner surface of fused silica capillary column via electrostatic interaction and enhanced interaction of van der Waals between gold nanoparticles and the capillary wall. Thus, the modification of the inner surface of capillary column by ODA-Au-NPs can be achieved simply by flushing the capillary with a solution of ODA-Au-NPs and the resulted ODA-Au-NPs coating is very stable. No perceptible degradation in the ODA-Au-NPs-based separation was observed after ∼1900 sample runs. This type of columns also provided excellent chromatographic performances: high number of theoretical plates, outstanding run-to-run and column-to-column reproducibility, and high selectivity for a wide range of test mixtures. An efficiency of 2474 theoretical plates per meter for chlorobenzene was obtained on an ODA-Au-NPs-modified 1.6 m × 100 μm i.d. fused silica capillary column.     

Rayleigh instability of stationary phase films in capillary column chromatography

The film of stationary phase on the wall of a capillary column and that of the phase solution during both static and dynamic coating is subject to Rayleigh instability, which is quite independent of so-called wettability. A theory is developed which shows that the logarithmic growth rate of Rayleigh instabilities is proportional to the surface tension and to the third power of the film thickness, and inversely to the viscosity and to the fourth power of the capillary diameter. Determination of the variation of the viscosities of stationary phase solutions with concentration in coating solvents, and the variation of the viscosities of neat stationary phases with temperature, both revealed that heating and/or diluting changed the viscosities of phases with π-electron-containing, groups much more than for polydimethylsiloxanes. Rayleigh instability is therefore more important during coating of phenyl-containing phases such as OV-17, and later during column operation. The efficiencies of capillary columns of different diameters coated with a number of phases under different conditions of temperature and coating rate, and then operated at different temperatures were in good agreement with the predictions of the theory.     

超动态法快速制备毛细管色谱柱的研究

用超动态法快速制出了几种非极性毛细管柱,柱效、涂渍效率分别为3000～4500理论塔板/m和65～85%。研究了超动态法中涂渍压力、涂渍液浓度与容量因子的关系;考察了制柱重复性和液膜厚度均匀性;给出了涂渍一般口径和试涂大口径厚液膜毛细管柱的部分结果。