Alkylpolysiloxane glass capillary columns combining high temperature stability of the stationary liquid and deactivation of the surface

Summary A new method of making alkylpolysiloxane (OV 1, OV 101, OV 17, Dexsil 400, SE 52, SE 54) columns with high stability at temperatures above 300°C of both the stationary liquid itself (low bleeding) and of the surface deactivation (no tailing of polar solutes with extended use at temperatures beyond 250°C) is described. The best results were achieved on dealkalinized alkali glass but also on borosilicate surfaces which have been additionally HF treated before coating in both cases. The procedure can also be applied to leached alkali and borosilicate surfaces successfully. The best deactivations of the glass surface are attained in a two step procedure: firstly by treatment with gaseous HF/N₂ mixture and secondly by simple heating of the coated and closed column at temperatures between 350° and 450°C for several hours. The tailing behaviour of such columns for polar solutes is considerably improved by this procedure as shown by test chromatograms. The procedure can also be applied to leached alkali and borosilicate surfaces successfully.Extract also presented at the 8th National Meeting on Analytical Chemistry of the Swedish Chemical Society, Lund, June 1979 and at the 10th International Symposium on Chromatography and Electrophoresis, Venice, Italy, June 1979.     

Glass capillary gas chromatography of highly polar solutes like diols,acids and amines deactivation of fused silica and pretreated alkali glass support surfaces

Summary The method of support surface deactivation by PSD (alkylpolysiloxane degradation) at temperature between 300 and 450°C previously described was used to deactivate both fused silica and alkali glass surfaces of capillary columns. The latter surfaces had to be pretreated before deactivation with aqueous HCl leaching or by the dealkalisation method using flowing HCl gas at 450°C and subsequent rinsing with water for alkali removal. Excellent alkylpolysiloxane columns with regard to tailing and irreversible adsorption of highly polar solutes have been obtained on both fused silica and the pretreated alkali glass. Fused silica does not require pretreatment before deactivation by the PSD-method, however. Good polyethyleneglycol (Carbowax 20 M) columns can also be obtained by coating the two types of surfaces when no deactivation is necessary. Deactivation by the PSD method cannot be applied in this case because polar stationary liquids do not adhere to alkylpolysiloxane deactivated surfaces. Sample capacity problems arising when separating highly polar solutes with non-polar stationary phases have also been investigated.     

Separation of 28 to 114°C hydrocarbons with glass capillary columns

Techniques have been developed for the rapid separation (about 20 minutes) of the 39 compounds in crude petroleums, or petroleum distillates, which boil between 28 and 114°C. A 300 meter glass column (0.25 mm i.d.) which is etched, coated with a mixture of normal hexadecane and Kel-F10157 is utilized to perform this separation at room temperature. The separations obtained with this non–polar liquid mixture and the «inert» glass surface are much more rapid than those previously obtained with stainless steel capillary columns.     

Determination of surface hydroxyl concentration on glass and fused silica capillary columns

Summary The concentration of surface hydroxyl groups on three types of capillary columns was determined by exchanging the hydroxyl protons with tritium. The tritium was quantified by combustion to tritiated water followed by scintillation counting. The number of hydroxyl groups on a leached and presumably hydroxylated Pyrex glass capillary column was found to be about 2.8 groups per square nanometer. This value was slightly less than the 4.6 groups per square nanometer that is generally accepted for a fully hydroxylated porous silica. Dehydroxylation of the same glass by heating at 600°C left only 0.4 groups per square nanometer while an untreated fused silica had only 0.2 groups per square nanometer.Dedicated to Dr. Leslie S. Ettre for his 60th birthday.     

Characterization of glass,quartz, and fused silica capillary column surfaces from contact-angle measurements

Summary This paper describes the systematic characterization of glass and the newly introduced fused silica and quartz capillary columns from surface wettability measurements. Common gas chromatographic stationary phases were used in capillary-rise measurements at temperatures up to 300°C. By construction of Zisman plots and using the Cassie equation, the relative surface concentrations of wettable and non-wettable groups were determined. By application of the Fowkes equation, the dispersion force component of the surface energy was investigated. The influence of various surface treatments such as leaching, silylation, and polymeric film formation are discussed. Wettability measurements were also used to evaluate the thermostability of various treated surfaces and to compare the surface properties of glass, quartz, and fused silica. The wettability of the surfaces with selected stationary phases as a function of temperature is also discussed.     

Inhibition of Pb-Leaching from Lead Crystal Glass by Coating with Films Prepared by the Sol-Gel Method

The chemical durability of lead glass tumblers (24% PbO) in a 4% (v/v) acetic acid solution before and after coating with sol-gel derived SiO2 films was assessed to determine the extent of reduction in Pb-leaching that can be achieved. It was found that by coating the internal surface of the glass tumblers with 1 ml of 10% TEOS solutions at 100°C and densifying the coating formed at 500°C for 1 h, it was possible to reduce Pb-leaching to about one quarter of that of the uncoated glass.     

Microstructural and Dielectric Characterization of Sol-Gel Derived Silicon Oxycarbide Glass Sheets

Thin (50—1000 m) silicon oxycarbide glass sheets were synthesized by the pyrolysis of gel sheets obtained from a methyl-modified silica sol containing colloidal silica under inert atmosphere between 900 and 1450°C. The microstructure of these glass sheets was investigated with the help of high resolution scanning and transmission electron microscopy (HR-SEM and HR-TEM), X-ray diffraction and Raman spectroscopy and their dielectric properties were determined. The surface morphology as observed with HR-SEM did not exhibit a notable temperature dependence. HR-TEM studies showed that the glass sheets sintered up to 1200°C are amorphous, whereas those sintered at 1450°C contain uniformly dispersed crystallites of SiC and graphite. X-ray diffraction studies were found in agreement with the HR-TEM results. Raman spectroscopy showed that free carbon is present as an amorphous phase till a temperature of 1000°C, whereas at temperatures 1200°C, the presence of graphitic carbon was observed. Silicon oxycarbide glass sheets heat treated at temperatures up to 1200°C, showed a dielectric constant between 4.1 ± 0.11 and 4.6 ± 0.15 in the frequency range from 75 kHz to 5 MHz, with corresponding losses between 0.0008 and 0.1100. Such silicon oxycarbide glass sheets sintered at 1200°C could find an application as substrates for electronic packaging.     

Glass capillary gas chromatography of chlorinated methyl acetates,propanoates and butanoates on Carbowax 20M and SE-30 columns

Summary The gas chromatography of all chlorinated methyl acetates, methyl propanoates and methyl mono- and dichlorobutanoates has been studied on Carbowax 20M and SE-30 glass capillary columns under various running conditions. The order of elution on a non-polar column was largely determined by the boiling point of esters, whereas on a polar column it was much influenced by the structure of compounds. Complete separation of the combined mixture of all 27 compounds could not be achieved, however, methyl 3,3-dichlorobutanoate was the only ester overlapped on both columns in spite of the various column temperatures used. The best separation of the mixture was on Carbowax 20M with a temperature program from 50°C at 8°C/min, isothermal running conditions leading either to poor separation of volatile components or long analysis time and broad peaks of higher chlorinated esters. The relative retention times for compounds at the various column temperatures are given and the retention order on a polar and on a non-polar column discussed.     

Some investigations into the coating of glass open-tube columns

Summary The etching of soda glass by hydrogen chloride has been studied by determining the weight of sodium chloride per unit area on single and double statically-etched glass. The influence of three coating solvents on the critical surface tension of etched and unetched glass has been determined by measuring the contact angles of a wide range of stationary phases. The dynamic coating procedure has been critically examined and certain aspects which lead to the production of improved columns are explored.     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

Comparison of dynamically coated SE-54, SP-2250 and carbowax 20M wall-coated open tubular (WCOT) glass capillary columns,prepared after surface pretreatment with Superox™-4 or with BaCO3

A new surface pretreatment for the preparation of wall-coated open tubular (WCOT) glass capillary columns has been evaluated. This technique involves the application of a non-extractable layer of Superox?-4, a 4,000,000 MW polyethylene glycol, to the glass surface as a pretreatment and deactivation agent. Unlike other polyethylene glycols, Superox-4 is stable at high temperatures (> 300°C) in the absence of oxygen, coats smoothly onto a bare glass surface and resists droplet formation. WCOT columns (SE-54, Carbowax 20M, and SP-2250) prepared using this technique are compared to columns prepared using a modified Grob [2,3] BaCO₃ procedure. The Superox-4 pretreated columns were equal or superior in quality to the BaCO₃ pretreated columns, based on the appearance of an activity standard and the effective theoretical plates (N_eff) per meter. Chromatograms showing practical application of the WCOT columns prepared using both methods is given.     

High Temperature Behavior of a Gel-Derived SiOC Glass: Elasticity and Viscosity

The high temperature behavior of a sol-gel derived silicon oxycarbide glass containing 12 at.% carbon has been characterized by means of creep and in-situ ultrasonic echography measurements. Temperature induced changes include structural relaxation and densification from 1000 to 1200°C, and crystallization to form a fine and homogeneous -SiC/glass-matrix nanocomposite with 2.5 nm large crystals above 1200°C. Young's modulus measurements clearly reveal a consolidation of the material upon annealing below 1200°C. Crystallization is almost complete after few hours at 1300°C and results in a significant increase in Young's modulus. The viscosity of the oxycarbide glass is much higher than that of fused silica, with two orders of magnitude difference at 1200°C, and the glass transition temperature ranges from 1320 to 1370°C.     

Sol-Gel Preparation of Fast Proton-Conducting P2O5-SiO2 Glasses

We have investigated the proton conductivities of the sol-gel-derived P₂O₅-SiO₂ glass at –50 to 120°C. The obtained glass is porous, where the surface area, pore volume and pore diameter are 740 m²/g, 0.5 cm³/g and <5 nm, respectively. The freezing temperature of water molecules adsorbed in the pores was –20°C, which is much lower than that of free liquid water due to the quantum size effect of the water confined in the pores. The electrical conductivities followed the Arrhenius equation in the temperatures between –20 and 120°C. Below –20°C, the adsorbed-water molecules were frozen, resulting in a rapid decrease of the proton conductivity. Considering the high conductivity, chemical and thermal stability, this oxide glass membranes have potential for the fuel cell membrane.     

Simultaneous determination of C1−C8 n-alkyl acetates and corresponding mono-, di- and trichloroacetates on glass capillary columns with programmed temperature rise

Summary Gas chromatography of mixtures of aliphaticn-alkyl acetates (CH₃–COOR), chloroacetates (CHCl₂–COOR), dichloroacetates (CHCl₂–COOR) and trichloroacetates (CCl₃–COOR), where the alcohol chain length (R) varied between 1 and 8, has been studied on SE-30, Carbowax 20M and OV-351 glass capillary columns with programmed temperatures from 50°C at 2, 4, 6, 8 and 10°C/min. Compounds in the homologous series are eluted in the direct order from methyl ton-octyl acetate. The isomeric chloro esters are eluted on SE-30 according to their boiling points in the order: mono-, di- and trichloro isomer, whereas on polar columns di- and trichloro esters are eluted in the reverse order. The complete separation of all 32 individual components from the mixture could not be reached by any single column, the best separation occurred on SE-30. The mixture can, however, be separated by using columns with polar and non-polar stationary phases. The relative retention times for the compounds are given and the retention order discussed.     

High-efficiency hydrophilic interaction chromatography by coupling 25 cm × 4.6 mm ID × 5 μm silica columns and operation at 80 °C

Recently, hydrophilic interaction chromatography (HILIC) has emerged as a valuable orthogonal tool to reversed-phase liquid chromatography (RP-LC) as it allows for resolution of highly polar ionisable compounds. The relationships between separation efficiency, column length and speed of analysis for 4.6 mm ID × 5 μm silica particle columns in HILIC are demonstrated using kinetic plots. The kinetic plots constructed for conventional pressure systems operating at 350 bar and at 30 °C and 80 °C are confirmed using experimental data for different column lengths. Efficiencies of more than 130,000 theoretical plates could be achieved by connecting up to six columns of 25 cm. As expected, a significant gain in analysis speed without loss of efficiency could be obtained by operating at 80 °C compared to 30 °C. The advantages of using long columns in HILIC in combination with elevated column temperature for the pharmaceutical industry are illustrated using test mixtures comprised of commercially available ionisable compounds (including some containing functional groups with potential genotoxic typical structural alerts) as well as real polar ionisable pharmaceuticals.     

Latex film formation studied with the atomic force microscope: Influence of aging and annealing

The surface structure of latex dispersion films was examined with an atomic force microscope. All measurements were done in air on latex films having a minimum film formation temperature of 12°C and a glass transition temperature of 18°C. One aim of this study was to follow structural changes during film formation. Three minutes after spreading the film, its surface layer dried. Afterwards, the structure of the film did not change anymore. Only after 4 months could structural changes be observed: Though individual latex particles could be identified, the particles partly melted into one another.After annealing films at 50° or 60°C for 4 h, the latex particles partly melted into one another, but individual particles could still be identified. When annealing at or above 80°C, no individual latex particles were visible anymore. With increasing temperature the film roughness decreased from 3 nm without annealing to 0.8 nm at 100°C annealing temperature. In addition, islands of 2–4 nm thickness appeared on the film surface. These islands could be scraped off the film by increasing the force between tip and sample, indicating that they are composed of surfactant which was squeezed out of the film.     

Flame retardant activity of SiO2-coated regenerated cellulose fibres

An alternative route to lower the flammability of viscose fibres is presented. Instead of adding a flame retardant to the viscose dope chemically, we have grown a layer of silica (SiO₂) on the surface of a regenerated cellulose fibre via a sol-gel process. One set of samples was used as-received, while the other was pre-treated in an 18% NaOH solution, giving a rough, etched surface to the fibre. The different surface morphology of both fibre types triggered a different growth of silica layers. On an untreated fibre, silica formed a 300-400 nm thick surface layer containing a high density of cracks and holes. Conversely, on a NaOH pre-treated fibre, the silica layer intruded into fibre interior, adhered more tightly to the fibre structure and formed an almost defect-free, thin (100 nm) layer on the outer fibre surface. This type of silica layer increased the temperature at which the fibre started to decompose by 20 °C. It also hindered significantly the flow of oxygen to the generated volatiles during the thermal decomposition, and increased the temperature of glowing combustion of the residual char; the temperature of the corresponding exothermic peaks increased by ca. 20 °C and 40 °C. In contrast, the thermal effects of silica coatings that grew on an untreated fibre were much smaller.     

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.     

Hybrid plasma bonding for void-free strong bonded interface of silicon/glass at 200 °C

A novel hybrid plasma bonding (HPB) that combines sequential plasma activation (reactive ion etching followed by microwave radicals) with anodic bonding has been developed to achieve void-free and strong silicon/glass bonding at low temperature. The interfacial voids were observed at the silicon/glass interface both in the anodic bonding and in the plasma activated anodic bonding, but the voids were completely disappeared in the HPB method at 200 °C. The bonding strength of the silicon/glass in the HPB was as high as 30 MPa at 200 °C, which was higher than that in the individual treatment of anodic and plasma activated bonding methods. The improved characteristic behavior of the interface in the HPB is attributed to the higher hydrophilicity and smooth surfaces of silicon and glass after sequential plasma activation. These highly reactive and clean surfaces enhance the mobility of alkaline cations from the glass surface across the interface toward the bulk of glass in the HPB. This transportation resulted in a ∼353 nm thick alkaline depletion layer in the glass and enlarged the amorphous SiO₂ across the interface. The void-free strong bonding is attributed to the clean hydrophilic surfaces and the amorphous SiO₂ layer across the interface.     

A SEM/EDXA study on the chemical attack of aqueous NaOH/KOH solutions on the surface of the metal-metalloid glass (Fe, Cr)80 (P, C, Si)20 and Fe75Cr5P8C10Si2, respectively

After a treatment of the metal-metalloid glassy alloy (Fe, Cr)₈₀ (P, C, Si)₂₀ and Fe₇₅Cr₅P₈C₁₀Si₂, respectively, by aqueous alkaline solutions of 1.0M NaOH + 1.0M KOH and 2.5M NaOH + 2.5M KOH, respectively, a SEM/EDXA study of the glass surface was performed.The results of the accelerated ageing procedure demonstrate that the glass treated with the 1.0M NaOH + 1.0M KOH solution at room temperature (20 °C) is characterized by a surface state like that of the initial material.For the glass treatment with the 2.5M NaOH + 2.5M KOH solution at 20 °C the surface layer shows a different morphology and is thicker. It can be supposed that the reinforcing property is reduced.The glass treatment at 80 °C with the aqueous solutions 1.0M and 2.5M (NaOH + KOH), respectively, leads to surface layers of different morphology and such a layer is about 5 m thick. The strength of solid residue of such a treated glass is very low.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday