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Injecteur-discrimination .



  1. #1
    24.9

    Injecteur-discrimination .


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    Bonjour,
    Pouvez vous, s'il vous plait, m'expliquer pourquoi il y a discrimination dans le cas des injecteurs en mode split ? Merci.

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  3. #2
    raymond_la_science

    Re : Injecteur-discrimination .

    Bonjour 24.9
    Des explications avec schémas, en anglais malheureusement, ici: http://www.shsu.edu/~chemistry/primers/pdf/GC.pdf
    cordialement
    rls

  4. #3
    24.9

    Smile Re : Injecteur-discrimination .

    Citation Envoyé par raymond_la_science Voir le message
    Bonjour 24.9
    Des explications avec schémas, en anglais malheureusement, ici: http://www.shsu.edu/~chemistry/primers/pdf/GC.pdf
    cordialement
    rls
    Merci beaucoup pour votre réponse .
    J'ai lu les explications, elles ne contiennent pas la réponse à ma question .

  5. #4
    tail

    Re : Injecteur-discrimination .

    Bonsoir
    dans les petit livret offert autrefois (1990) par HP
    GC inlet An Introduction

    il y a un autre livret interessant en Gc
    High resolution gas chromatography freeman de 1981 qui etait offert
    mais peut être encore disponible sur demande ou en vente?

    a la page 43 et 44 du premier il y a les renseignements suivants
    comme je suis mauvais en anglais je te les livre bruts

    troubleshooting

    split inlets are spared from most band-broadening phenomena, since narrow peaks are generated as part of the splitting process. Therefore, any peak broadening or tailing observed with split injection is usually due to improper column installation, low split
    flow, or low inlet temperature. If you suspect that the inlet temperature may be too low, increase it by 50 °C and compare the results to the lower temperature analysis. Repeat
    if results are positive until no further improvement is seen.

    A majority of the problems encountered with split inlets are related to discrimination and decomposition. Both analytical accuracy and reproducibility decrease with the increase in discrimination and decomposition. Split inlets suffer from both needle discrimination and inlet discrimination.

    Needle Discrimination
    Loss of high-boiling solutes or a dectease in areas of late eluters relative to early eluters are symptoms of needle discrimination.
    N eedle discrimination can be reduced by using fast autoinjectors, by minimizing inlet temperature, by injecting larger volumes, and/or by using a solvent with higher boiling point.
    Inlet Discrimination
    The different mechanisms that can cause split inlet discrimination are:
    1. Different diffusion speeds of the sample components from point of injection to column inlet.
    2. Incomplete evaporation of sorne sample components.
    Inlet discrimination of high boilers can be reduced by increasing inlet temperature, by injecting less sample (the reverse of the actions taken to counteract needle discrimination), by switching liner type, or by lowering the split ratio (thereby increasing residenCE time in the inlet).
    Inlet discrimination with low boilers occurs less frequently than discrimination with high boilers and can be more difficult to isolate. Loss of low boilers is influenced by liner design, flashback, sample loss via inlet leaks, and the pressure pulse following injection. Lower inlet temperature, lower injection volume, and a change to higherboiling solvent may help reduce the problem.
    Sample Decomposition
    Sample decomposition is indicated by lost or misshapen peaks, and/or by the generation of new ones. Decomposition is exacerbated by high inlet temperature, long residence time of the sample in the inlet (low split flow, large sample sizes), and activity in the inlet (high surface-area liners, active/unsilanized packings).

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