Determination of the minimum allowable operating temperature of stationary phases in capillary columns by inverse gas chromatography

A method was developed to determine the minimum allowable operating temperature (MiAOT) of wall coated open tubular capillary columns. Two polyethylene glycol and fourteen polysiloxanes phases with different side groups (methyl, phenyl, cyanopropyl, trifluoropropyl, n-octyl) and backbone stiffening units (tetramethyl-p-silphenylene, tetramethyl-p,p'-sildiphenylene ether, carborane) were investigated by inverse gas chromatography. A sigmoidal profile of temperature versus column efficiency was found for almost all phases, as the column efficiency increased with temperature. The MiAOT was defined as that temperature where the column efficiency is half of its original value at elevated temperatures. It was found that the MiAOT of a stationary phase is approx. 60 K higher than its glass transition temperature.     

一种非晶硅膜改性弹性玻璃毛细管交联中等极性固定相色谱柱的制备

研究了非晶硅膜改性的弹性玻璃毛细管交联ＯＶ－１７０１中等极性固定相色谱柱。在适当温度下，采用过氧化二异丙苯（ＤＣＵＰ）游离基引发交联ＯＶ－１７０１固定液，成功地制备了交联ＯＶ－１７０１柱，该柱具有柱效高、惰性好、耐溶剂、抗腐蚀和耐高温等性能，是一种新型高性能的中等极性交联柱。     

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.     

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.     

The preparation of non-extractable methylphenylpolysiloxane stationary phases for capillary column gas chromatography

Summary The synthesis of methylphenylpolysiloxane polymers and their use in the preparation of crosslinked, non-extractable stationary phases for fused-silica capillary columns are described. By preparing more viscous phenyl-containing polymers than are commercially available, stationary phase films of these polymers could be efficiently coated on fused-silica capillary columns and stabilized by a free radical crosslinking mechanism using peroxides. Four methylphenylpolysiloxane polymers containing different phenyl concentrations were prepared. These included three polymers containing 50% phenyl and one polymer containing 70% phenyl. Two of the 50% phenyl polymers had one phenyl and one methyl group attached to each silicon atom. One of these also had 1% vinyl incorporated. The third 50% phenyl polymer was synthesized in such a way that one half of the silicon atoms had two phenyl groups attached while the rest contained dimethyl groups. The 70% phenyl polymer also had 4% vinyl incorporated. Due to the intrinsic thermal stability of these phenyl phases and the enhanced film stability achieved by crosslinking, the 70% phenyl phase could be utilized up to 400 °C. Using the methods described in this paper, highly efficient and thermally stable fused silica capillary columns coated with crosslinked methylphenylpolysiloxane stationary phases can be successfully prepared.     

Chromatographic properties of tetramethyl-p-silphenylene-dimethyl,diphenylsiloxane copolymers as stationary phases for gas-liquid chromatography

Seven tetramethyl-p-silphenylene-dimethyl, diphenylsiloxane copolymers were coated on fused-silica capillary columns to evaluate their properties as stationary phases in gas-liquid chromatography. The capillary columns were tested concerning their selectivity, separation efficiency, column bleed, inertness, elution temperatures, and working range. The following characteristic properties of the silphenylene unit were found: (i) the impact of the silphenylene group on the chromatographic selectivity is similar to that of two dimethylsiloxy groups and half of a diphenylsiloxy group; (ii) silphenylene-siloxane copolymers offer reduced column bleed and increased maximum allowable operating temperature in comparison to polysiloxanes, since the backbone stiffing phenylene group enhances thermal stability; (iii) the elution temperatures of analytes are increased by 15-30 degrees C on silphenylene-siloxane copolymers compared to polysiloxanes; (iv) the silphenylene unit increases the glass transition temperature of the polymers resulting in elevated minimum allowable operating temperatures.     

Preparation of thermally stable phenylpolysiloxane fused silica capillary columns. Optimization and evaluation of the deactivation by capillary GC and solid state 29Si NMR

The deactivation of fused silica capillary columns with a laboratory-made poly-diphenylvinylmethylhydrosiloxane copolymer has been investigated. The deactivation obtained at different temperatures and reaction times is characterized with a dual column capillary GC system [1]. In parallel, the effect of the silylation temperatures and reaction times on the nature, the structure, and the chemical properties of the deactivation layer has also been studied by solid-state ²⁹Si NMR spoctroscopy. A fumed silica, Cab-O-Sil M5, was used as a model substrate for these spectroscopic studies. The deactivated fused silica capillaries show an excellent thermal stability (up to 400°C), a high resistance to solvolysis, and a minimal interaction to various critical test components. A good wettability of the fused silica capillary columns deactivated with this reagent was confirmed by successful subsequent coating with polysiloxanes with different phenyl contents.     

Siloxane/silarylene copolymers as stationary phases for capillary gas chromatography. Part II: Phenylsubstituted polymers

A commercially available silanol terminated silicone stationary phase, OV-61-OH (33% phenyl), and two phenyl-substituted siloxane/silarylene copolymers, Sila 3 (27% phenyl) and 4 (35% phenyl), have been evaluated for use as stationary phases in fused silica capillary columns for gas chromatography. Ulterations in column adsorptive activity, separation efficiency, stationary phase film thickness and selectivity after column conditioning for 50 h at 370°C have been studied. A high thermal stability was experienced with the stationary phases tested here. For OV-61-OH, the best thermal stability was obtained when coated on untreated fused silica, which illustrates the importance of grafting reactions here. The heat treatment resulted in some deactivation of adsorptive sites in the column. A higher degree of column deactivation was achieved when surface silylation was performed prior to coating. High thermal stability was achieved with Sila 3 when coated on such surfaces. Sila 3 would thus be preferred in cases when high thermal stability in combination with high dsorptive inertness is desired. Sila 4 showed low column bleeding at 370 °C, but prolonged heating at this temperature resulted in the broadening of n-alkane peaks when eluted at 90 °C. This indicates that excessive crosslinking has taken place during the heat treatment and the minimum allowable column operation temperature is thereby increased to ca. 120 °C. The separation of aza-arenes and of triglycerides are shown as applications.     

High temperature gas chromatography: The development of new aluminum clad flexible fused silica glass capillary columns coated with thermostable nonpolar phases: Part 1

With the simultaneous development of blank aluminum clad flexible fused silica glass capillary tubing capable of withstanding temperatures up to 500°C, coincident with a series of special high temperature methyl polysiloxane polymers, it was possible to produce for the first time, long lived fused silica capillary columns containing thin films of thermostable stationary phases which could be maintained isothermally at 400425°C and temperature programmed to 425–440°C. The “bleed rate” here for a well conditioned column was 5 picoamperes or less. Under these circumstances, alkanes with carbon numbers in the C-90 to C-100 area were rapidly and efficiently eluted from these columns. By extrapolation here, one can easily detect certain compounds with boiling points in the 750°C range. Since this type of capillary column was found to possess certain favorable properties, it was thought that it will soon replace the packed column and will probably be more popular than the borosilicate capillary column for many high temperature applications. Moreover, evidence has now accumulated which leads us to further believe that the majority of analyses of “high molecular weight” compounds performed by Supercritical Fluid Chromatography (SFC), utilizing very narrow bore fused silica capillary columns at several hundred atmospheres, can be much more simply, much more rapidly, much more economically, and much more efficiently accomplished by gas chromatography utilizing this new generation of high temperature capillary columns.     

An investigation of glasses for capillary chromatography

An investigation was conducted of various glasses, other than soda lime or borosilicate, for use in glass capillary gas chromatography. The work has uncovered some unique chromatographic qualities in the use of potash soda lead and fused silica glasses as materials for making glass capillary columns. The fused silica proved to be an ideal material for capillary column construction, being inherently more inert than glass containing metal oxides. It has been shown that through the use of thin wall capillary tubing of high flexibility many of the mechanical problems associated with glass capillary columns, such as fragility and column straightening, can be avoided.     

Gas chromatographic – mass spectrometric analysis of compounds generated upon thermal degradation of some stationary phases in gas chromatography – Part II

The applicability of capillary columns for gas chromatography is often limited by stationary phase degradation at elevated temperatures. In order to achieve a better understanding of column thermostability, column bleed products have been analyzed qualitatively by gas chromatography-mass spectrometry (GC-MS). Three silicone stationary phases were studied: SE-52, SE-54, and OV-1701. Each of these was immobilized in the columns. The proportion of cyclics containing diphenyl in column bleed from SE-52 reflected to a large extent the composition of the polymer, while for SE-54 the proportion of such cyclics was unexpectedly high. The polar moiety of OV-1701, the cyanopropyl(phenyl)siloxy unit, was found to exert a highly destabilizing effect on the polymer, and the thermal degradation products consisted mainly of cyclosiloxanes containing this unit.     

High resolution capillary gas chromatography and gas chromatography–mass spectrometry of protein and non-protein amino acids,amino alcohols,and hydroxycarboxylic acids as their tert-butyldimethylsilyl derivatives

A simple, single-step derivatization technique is presented for capillary GC-FID and GC-MS separation and identification of common protein and non-protein constituents of natural peptides as their tert-butyldimethylsilyl (TBDMS) derivatives. The tert-butyldimethyl-silylation of more than sixty compounds was accomplished with high yields and a single peak observed for each component. The TBDMS derivatives of both the protein and non-protein substances, moreover, exhibit excellent separation on apolar capillary columns and can be resolved completely using a polydimethylsiloxane or 5 % phenyl polydimethylsiloxane column and, complementarily, a 50 % phenyl polydimethylsiloxane column. Retention data and molar responses of the TBDMS derivatives on the polydimethylsiloxane column are compiled. Direct coupling of the 5 % phenyl polydimethylsiloxane column to an ion trap mass spectrometer enabled fast separation and identification of the investigated components, at nanomole to picomole levels, on the basis of retention and mass spectral data. The general usefulness of the method is demonstrated by research into new biologically active peptides isolated from entomopathogenic fungi.     

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.     

Capillary gas chromatography of some metal acetylacetonates

Summary The retention and resolution of simple mixture of Al(III), Cr(III), Co(III), and Fe(III) acetylacetonates were investigated on capillary columns coated with methyl and methyl phenyl silicones (OV-1 or OV-17) used as the stationary phase, at different column temperatures and carrier gas flow rates. Successful elution and good resolution were obtained only for the Al(III) and Cr(III) complexes, both under isothermal and programmed-temperature conditions; better resolution was observed on the column coated with OV 17.     

Practical limitations of capillary gas chromatography

Glass capillary gas chromatography is a high resolution separation method which allows the qualitative and quantitative analysis of even complex mixtures, which may contain many components–also isomeric–in a wide range of volatilities, polarities and concentrations. The principal limitation of gas chromatographic application is given by an insufficient volatility of the species to be separated. Elevated temperatures have to be applied if the application range is to be extended and to achieve steep peak profiles, i.e. low detection limits at high resolution. The use of elevated temperatures is limited, of course, by the temperature stability of both the solvent (stationary liquid and support) and the solutes. The problems of trace analysis for low volatility compounds at high resolution and its limitational parameters regarding sampling, separation and detection are discussed. The applicability of glass capillary columns in this field is influenced by the following parameters: tailing behaviour; irreversible adsorption of polar and decomposition of unstable solutes; thermal stability of stationary liquid (including the support deactivation); separation efficiency and sample capacity (film thickness). Multidimensional gas chromatography using capillary columns coupled either with a packed or another capilllary column for preseparations may be applied with advantage in the analysis of complex mixtures.     

Practical aspects of Pt/Ir effluent splitters for multidetector GC and pneumatic solute switching

Practical details are given to produce low dead volume Pt/Ir to glass connections and a variety of components for effluent splitting and pneumatic solute switching. It is shown that the column effluents from a glass capillary column can be split in any desired ratio and maintained constant, regardless of column flow rate. Bandbroadening in the splitter remains negligible even for very low flow rates. A complex pneumatic system to be used for heartcutting with two glass capillary columns is shown.     

Detection of Claisen Rearrangement Occurring in Allyl Phenyl Ether by in situ GC/MS

Itiswellknownthattheallylc0mP0undsexhibitavariety0finterestingrearrangementreacti0ns.Intheliquidphase,temPerature-inducedClaisenrearrangement,cyclizationreactionsandacid-induced0rthoClaisenrearrangementsofallylphenyletherhavebeenstUdiedextensively.'-'However,theClaisenrearrangementinthegasphasewasrepoftedonlyrecelltly,includingtheprotonatedallylphenyletherandN-allylanilineunderpositivecheITilcalionizationcondition4",thedeprotonatedallylphenylacetateanddeprotonatedallylphenyletherundernegati…     

Increased thermostability of non-polar wall-coated open tubular columns

A method of deactivating the inner surface of glass capillary columns is described, which can be used at 350°C without detoriation. A non-polar liquid phase was prepared from a commercially available liquid phase which, when coated on a glass surface, can withstand temperatures of 325°C for isothermal analysis and 350°C for temperature-programmed analysis. After deactivation, the column was coated using the static coating method. Then it was conditioned, tested and kept for 48 hours at 35O°C before being used for the analysis of a mixture of chlorinated pesticides.     

溶胶吸附法制备β—环糊精聚合物玻璃毛细管柱

将自制的非水溶性环糊精聚合物成溶胶,将该溶胶充满柱放置一段时间,固定相微粒均匀地吸附在柱壁上,制备了高效率的玻璃毛细管柱。测试了所制备柱的性能并对某些化合物进行了分离。