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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 17 (1983), S. 481-485 
    ISSN: 1612-1112
    Keywords: Polarity ; Stationary phases ; Temperature dependence ; GC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary It is not commonly appreciated that retention indices are temperature dependent. It is even less common to express this fact in more practical terms by saying that polarity is temperature dependent. Although the meaning of both statements is identical, we believe the second to be particularly relevant, since the majority of practical gas chromatographers tends to handle polarity as an invariable characteristic of a stationary phase. The variability of polarity with temperature is the major source of inadequate reproducibility of exact finger-printing, this particularly when gc/ms traces have to be compared to those obtained by pure gc. On the other hand, the temperature dependence provides a practical means to optimize the polarity of a given column for a given analysis. Film thickness is an essential parameter in this context because of its influence on column temperature and, therefore, on column polarity.
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  • 2
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Sample preparation ; Closed loop stripping analysis ; Charcoal adsorbent filter ; Overcoming contamination ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary columns ; Static coating ; Vacuum sources ; Coating solvent ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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  • 4
    ISSN: 0935-6304
    Keywords: Gas chromatography, capillary ; Column preparation ; Immobilization of stationary phases ; Procedure for polar phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Whereas the immobilization of apolar silicone phases is essentially understood and mastered, the corresponding treatment of even moderately polar phases remains problematical. Upon attack by peroxide radicals, these phases respond by forming active transformation products rather than by bonding to the support surface or to neighboring molecules. OV-1701 is at present the most polar stationary phase which can reasonably be immobilized. An essential feature of the practical procedure is the prevention of film breakage after coating the inert support surface and before immobilization. Two ways of overcoming this problem are presented.
    Additional Material: 2 Ill.
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  • 5
    ISSN: 0935-6304
    Keywords: Gas chromatography, capillary ; Column preparation ; Immobilization of stationary phases ; Influence of vinyl groups ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article presents a preliminary description of the influence exerted by vinyl groups on the process and on the result of immobilization. Vinyl groups may occur in the stationary phase (e. g. in SE-54) or may be bound to the support surface by persilylation with divinyltetramethyldisilazane. In the first case they promote the crosslinking process in the stationary phase. In the second case bonding to the solid surface is intensified. We have observed that vinyl groups in both situations contribute with comparable efficiency to the final non-extractability of the stationary phase. A further, yet entirely independent influence of surface-bonded vinyl groups concerns the acidity of the column. Whereas regular persilylation produces slightly acidic columns, a substantial shift to basic column behavior is observed after persilylation with a vinyl-containing reagent. The potential future importance of both kinds of influence is discussed.
    Additional Material: 1 Ill.
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  • 6
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; Introducing phenyl groups by persilylation ; Dependence of wettability on density of phenyl groups ; Practical instructions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
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  • 7
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; Static coating ; Filling with mechanical closure ; Description of an easy and safe technique ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The static technique is commonly accepted as the most universal and scientific method of coating. At the same time, however, it is said to be experimentally demanding. Great efforts have therefore been made to render the method easier and safer, resulting in a wealth of recommendations confusing non-experts. Over a period of two years we have practically applied most of the reported procedures with the aim of studying their practical convenience. We do not doubt that most procedures are comparably suitable in the hands of expert users, i. e. once the initiation efforts have been forgotten, or are otherwise of little interest. We have attempted to describe a method which is specifically suited for easy and quick introduction to beginners. The method is based on mechanical column closure. The principles of the method are discussed, and a comprehensive description of its practical application is given.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; Advantages of very thick coatings ; Separation efficiency correlated with film thickness ; Preparation of columns with very thick coatings ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: It has become common practice with capillary columns to call film thicknesses of 0.1 - 0.3 μm regular or standard, whereas 0.3 - 1.0 μm is considered to denote thick films. Consequently, films with thickness beyond 1μm (we have explored the range up to 8.0 μm) may be termed very thick. Increasing film thickness, at least to about 5 μm, brings important additionl advantages primarily in terms of loading capacity. Columns with very thick coatings may replace the traditional SCOT columns thanks to at least equivalent loading capacity combined with higher separation efficiency, and better stability characteristics. Additional advantages are increased retention, essential for the analysis of very volatile substances, and increased elution temperature, providing a basis for direct water injection.We observe that TZ (the separation number) drops to roughly 50% when the film thickness is increased by a factor of 300 from 0.025 to 8.0 μm, provided TZ is measured with a standard flow of hydrogen. The reduction is only 30% when the thick-film colums are run with individual optimization with nitrogen as a carrier gas. In contrast to standard columns, very thickly coated columns show slightly increased separation efficiency with nitrogen at drastically reduced flow rate. The HETP increases very slightly in the indicated range of flim thickness. This contradicts widespread theoretical expectations, which probably account for the fact that very thick coatings have so far been neglected. Since the preparation of very thick coatings involves some deviations from the standard procedure, complete and detailed instructions are given.
    Additional Material: 5 Ill.
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  • 9
    ISSN: 0935-6304
    Keywords: Gas chromatography, capillary ; Persilylated, apolar columns ; Immobilized coatings ; Determination of column bleeding ; Re-silylation of fresh and used columns ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The bleeding of apolar high temperature columns may well be the critical factor limiting their applicability for GC/MS-coupling, and for high temperature analyses. Therefore, a bleeding determination procedure has been designed as a basis for a systematic approach to the production of low-bleed columns. Re-silylation is a traditional method of reducing column bleeding. Increased efficiency of re-silylation becomes feasible with immoblized coatings. Experience gained so far shows that resilylation of immoblized coatings may indeed result in the expected strongly reduced bleed rates and in improved overall column quality. Re-silylation may also contribute to column washing by enhancing the solubility of adsorbed contaminants.
    Additional Material: 3 Ill.
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  • 10
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; Immobilization of moderately polar phases ; Combination of surface bonding and crosslinking ; Vinyl groups in the support surface ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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