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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 18 (1984), S. 197-201 
    ISSN: 1612-1112
    Keywords: Capillary GC ; Co-injection ; Solvent effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Co-injection techniques (introducing additional pure solvent with the sample) were tested to eliminate peak distortion due to partial solvent trapping. Co-injections of solvent identical with the sample solvent were not successful, because first only partial solvent trapping of the strong type could be eliminated and second, there was no practicable method of placing a band of pure solvent ahead of the sample in the column inlet. Successful co-injections have to accept mixing of the sample with the pure solvent. Either the solvent trapping is improved by co-injection of a solvent which enhances solution of the critical solutes in the sample layer, or it creates a phase soaking effect in the stationary phase and reconcentrates broadened bands beyond the flooded inlet. The added solvent must have the appropriate polarity and some of it must remain in the column inlet at least until the sample solvent has completely evaporated.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 2 (1979), S. 15-21 
    ISSN: 0935-6304
    Keywords: Gas Chromatography ; Capillary ; Injection errors by sample discrimination ; Specific sorption within the syringe needle ; Pull back sample insert needle, warm up, inject than ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The discrimination of the high boiling components of a C9 to C44 alkane test mixture in a vaporizing injector (analysed with stream splitting on a capillary column) is mainly due to a selective elution of the sample out of the syringe needle. Different methods of handling the syringe needle are tested. The discrimination is quantitated and correlated with the material left in the needle. The poorest method of injection was found to retain the sample in the needle when the latter is introduced into the vaporizer. The sample should be pulled back into the barrel of the syringe and the needle allowed to warm up in the injector before the sample is transferred into it. The solvent flush technique may be preferred for components sensitive to the hot metal surface of the needle.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 3 (1980), S. 286-290 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary ; Discrimination due to FID ; Effect of carrier gas flow changes on detector sensitivity ; Hydrogen as carrier gas ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The sensitivity of an FID may change when the carrier gas flow rate changes during a chromatographic run. Sample parts which are eluted at reduced FID sensitivity produce a reduced peak area, hence are discriminated as compared to other components. Sensitivity changes were studied for hydrogen as carrier gas. For the detector tested, differences in the carrier gas flow rates of 1 ml/min shifted the FID sensitivity by 1 to 5% (depending on the fuel gas supply). Thus the stability of the sensitivity is no longer ensured as soon as the carrier gas flow rate is changed manually or by an automatic programmer during an analysis. Sensitivity drifts may also occur during temperature programmed runs with a pressure regulated carrier gas supply since the gas flow through the capillary drops with increasing temperature. Such shifts in the response became noticeable as soon as relatively high carrier gas flow rates combined with long range temperature programmes were used. The typical patterns of such discriminations are shown, closing with a discussion on the possibilities for minimizing such undesired effects.
    Additional Material: 5 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 9 (1986), S. 405-407 
    ISSN: 0935-6304
    Keywords: Capillary GC ; Solvent effects ; Solvent trapping ; Phase soaking ; Large sample volumes ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 11 (1988), S. 388-394 
    ISSN: 0935-6304
    Keywords: Solvent effects ; Co-solvent effects ; Concurrent solvent evaporation ; Large sample volumes ; Coupled HPLC-GC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The concept and some first results of a method are described for evaporating large volumes of solvent in a relatively short pre-column (retention gap) in such a way that solvent trapping retains volatile components in the inlet up to completion of solvent evaporation. The method was developed for transferring large volumes (easily exceeding 1 ml) of HPLC eluent to GC when using on-line coupled HPLC-GC, but is equally suited for injecting large sample volumes (at least some 50 μl) and could be particularly useful for introducing aqueous solutions.Concurrent solvent evaporation allows introduction of very large volumes of liquid into GC. However, peaks eluted up to some 40-80° above the column temperature during introduction of the liquid are strongly broadened due to the absence of solvent trapping. On the other hand, previous retention gap techniques involving solvent trapping were not suited for transferring very large volumes of liquid into GC. Using a relatively high boiling co-solvent added to the sample or the HPLC eluent, advantages of concurrent solvent evaporation can be combined with solute reconcentration by solvent effects, allowing elution of sharp peaks starting at the column temperature during introduction of the sample.
    Additional Material: 6 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 9 (1986), S. 95-101 
    ISSN: 0935-6304
    Keywords: Coupled HPLC-capillary GC ; Concurrent solvent evaporation ; Retention gap ; Solvent effects ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A technique is proposed which allows introduction of very large volumes of liquid (10 ml were tested) into capillary columns equipped with short (1-2 m long) retention gaps. It is based on concurrent solvent evaporation, i.e. evaporation of the solvent during introduction of the sample. The technique presupposes high carrier gas flow rates (at least during sample introduction) and column temperatures near the solvent boiling point. The major limitation of the method is the occurrence of peak broadening for solutes eluted up to 30°, in some cases up to 100°, above the injection temperature. This is due to the absence of solvent trapping and a reduced efficiency of phase soaking. Therefore, use of volatile solvents is often advantageous. Application of the concurrent solvent evaporation technique allows introduction of liquids which do not wet the retention gap surface. However, the method is still not very attractive for analysis of aqueous or water-containing solutions (reversed phase HPLC).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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